Differential gear ratio? [Archive]

rotarygod

01-16-2009, 02:10 PM

You have some good info in there but to put your theory to the test try putting your 8 in 5th gear(direct drivewhich is 4th gear in most cars) or a 1:1 torque multiplication from a dead stop and see where you go. It is true that hp is what will keep you going but without torque you are not getting anywhere quickly. Your horsepower is constant through you gears not your torque. And yes engines are built bigger to handle torque not hp do to longevity of the engine but when building a track car I am not concerned with engine life and driveability I am concerned with winning.

Plug in any gear ratio you want into those equations. It always works. I used a 1:1 ratio merely for simplicity sake. I don't care if it's a 7.654:1 ratio. It'll still work.

The whole point of a transmission is not to "increase torque". The whole point is to get your engine into an rpm range where it makes the most horsepower. If I tried to start the RX-8 from a dead stop in 5th gear, the engine would be turning so slowly that first of all it probably wouldn't even run as that's below idle speed and second it's not making enough HORSEPOWER at that engine rpm to get us moving! If we had engines that made roughly the same amount of horsepower across their entire rpm range, we'd direct drive them, hence my liking of electric motors. Their torque falls off with rpm but that's not important to performance anyways as torque does no work!

You may be concerned with winning but if it comes to a track car, you'd better be concerned about longevity as you can't win if you can't finish. You sure as hell aren't winning any arguments either. If I need to be more detailed, let me know but I thought simple math equations were pretty explanatory.

StealthTL

01-16-2009, 02:14 PM

Epic.

One day he don't know the rear end from the final drive, the next he's arguing with RG on the topic......

S

rotarygod

01-16-2009, 02:35 PM

You know what, I'm going to just go ahead and plug in that crazy 7.654:1 gear ratio from above just to prove my point. Remember in my linked post I said that the theoretical engine makes 200 hp at 8000 rpm and that regardless of gearing, it's always going to make that at the wheels assuming no losses of course. Since he wants me to use 6th gear instead of a 1:1 5th gear, instead I figured I'd go all out and make up this crazy 7.654:1 gearing instead. You'll see that the end result will be 200 HP to the wheels. Please pay attention to wheel rotational speed as that's what we are trying to make this power at by utilizing gearing.

As a flashback:

HP X 5252 / RPM = TQ
TQ / 5252 x RPM = HP

I stated the variables of:
200 HP @ 8000 engine RPM. Plugging that in, that equals 131.3 ft. lbs. of torque at 8000 rpm. Let's do some math!

131.3 ft lbs X 7.654 gearing X 4.44 rear end ratio = 4462.07 ft lbs.
What wheel speed is this at though? Remember torque is nothing without speed and speed adds movement over time to get what we call HORSEPOWER! Let's see...

8000 engine rpm / 7.654 gear / 4.44 rear end ratio = 235.4 wheel rpm! Tada! Now we can plug in speed over time to our torque number. Remember these all receive a new name called horsepower and that's what we care about.

4462.07 ft lbs / 5252 rpm x 235.4 wheel rpm = 200 HP to the wheels!!!

Holy crap it works! It's getting HORSEPOWER to the ground that gets and keeps us moving!!!

If not having torque means you aren't getting anywhere very quickly, Formula 1 cars must be damned slow race cars since their 850 hp only makes roughly 260 ft lbs of torque. A Dodge Cummins diesel must get from place to place much faster with all that extra torque! If you still don't believe me, let Paul Yaw explain it. His article title is appropriate:

http://www.yawpower.com/tqvshp.html

tubingchamp

01-16-2009, 03:28 PM

:) Always a good read, RG.

Your knowledge pwns the newb know-it alls...

Pwns me too, but I'm not going to argue against it :)

rotary.enthusiast

01-16-2009, 03:59 PM

If I tried to start the RX-8 from a dead stop in 5th gear, the engine would be turning so slowly that first of all it probably wouldn't even run as that's below idle speed and second it's not making enough HORSEPOWER at that engine rpm to get us moving!

Oh boy, the old torque vs. horsepower thing again. I know you think I'm wrong, but I'll say it again anyway: it's the amount of torque at the wheels that you're generating at any given instant in time that dictates how quickly you will accelerate at that instant in time. Adding super steep gearing does make you accelerate more quickly, but for a smaller amount of time (because you fall outside of the engine's acceptable operating RPM more quickly). Add the cost of extra shift times in there, and you quickly see why steep gears are not the answer.

Horsepower has jack to do with it. Horsepower is a measure of work over a period of time. All it tells you is how fast you can make something move, not how fast you can make it accelerate. To illustrate this point, think about a somewhat extreme and silly hypothetical: Car A makes 100 ft-lbs of torque at 5252 RPM and none anywhere else, and has a constant velocity transmission to keep it at that RPM. Car B makes 100 ft-lbs of torque from 1000 RPM to 5252 RPM with an appropriately geared 6 speed transmission. Both cars make 100 peak horsepower, and car B will be operating at a much lower horsepower than car A most of the time. Which will hit top speed faster?

rotarygod

01-16-2009, 04:17 PM

I think I'll just further than absurdity through math!

Let's just throw out some more numbers for example's sake. Let's say the avrage shift point is at 5K rpm driving on the street. Let's say the rpms fall to an average of 3K rpm during the shift. That would center us at 4K rpm for street driving so that's the power number I'm going to use.

Let's say our engine makes 75 hp at 4K rpm (98.48 ft lbs tq.) and this is the average (hp) in the rpm range when accelerating. Since it's this horsepower that accelerates us and keeps us moving, we want this to be over a wide range of wheel speeds. However we can't stay in this small engine rpm range by only keeping it in one gear. So we need to shift gears to hold the engine there. Let's throw out some gear ratios:

1st: 4.02:1
2nd: 2.46:1
3rd: 1.77:1
4th: 1.33:1
5th: 1.08:1
6th: .84:1
Rear end ratio: 4.44:1

We know horsepower and we know rpm. Now we need to see what wheel rpm this will center us at. To make things short I'm going to just plug the numbers into the above formulas on my own without showing them here. Here are the results. Remember this is wheel rpm at this engine rpm and hence this horsepower level:

1st: 224 wheel rpm
2nd: 366 wheel rpm
3rd: 509 wheel rpm
4th: 677 wheel rpm
5th: 834 wheel rpm
6th: 1072 wheel rpm

As you can see in order to hold that powerband but move faster, we have to shift up in gears. You can clearly see what is being accomplished with the transmission. As the gear ratio decreases, speed increases. Power stays the same because it's power that moves us. As speed increases, torque decreases. What if I wanted to know how much torque was getting to the ground with each gear shift? Let's show those numbers.

Torque at the wheels at the same rpm through the same gears is:

1st: 1757.75 ft lbs
2nd: 1075.64 ft lbs
3rd: 773.93 ft lbs
4th: 581.54 ft lbs
5th: 472.23 ft lbs
6th: 367.29 ft lbs

As you can see as speed goes up and gear ratios go down, so does torque. Now I know someone may look at this chart and say I just proved that torque is what gets you moving. Nope. Sorry. The faster we go, the more effort it takes to hold us there and the more and more it takes to keep accelerating us. Where is the effort going to come from, horsepower or torque? Horsepower is staying the same but torque is decreasing with speed. How can torque really be doing anything if we can accelerate while it's going down? That means it can't be doing anything! At some point at this horsepower level our car will stop accelerating as it will require this much power to hold it there and would need more to go faster. It doesn't matter if you've got 200 ft lbs of torque at the ground or 2000. Neither will get you moving any better than the other.

rotarygod

01-16-2009, 04:43 PM

I know you think I'm wrong...
What I think is irrelevant. I just happen to agree with what is.

Horsepower has jack to do with it.
See response #1

Horsepower is a measure of work over a period of time.
Yay, something correct! Torque however is not a measure that involves time and if there is no time there is no work. If there is no work there is no movement and if you aren't moving torque isn't doing much! If you are moving you are doing work and since movement involves time and this just so happens to be a requirement of horsepower, guess which one is doing which?

All it tells you is how fast you can make something move, not how fast you can make it accelerate.
In order to accelerate, you must move! If it can tell us how fast something can move, it can tell us how fast it can accelerate!

To illustrate this point, think about a somewhat extreme and silly hypothetical:
I'll agree with that!

Car A makes 100 ft-lbs of torque at 5252 RPM and none anywhere else, and has a constant velocity transmission to keep it at that RPM. Car B makes 100 ft-lbs of torque from 1000 RPM to 5252 RPM with an appropriately geared 6 speed transmission. Both cars make 100 peak horsepower, and car B will be operating at a much lower horsepower than car A most of the time. Which will hit top speed faster?

Thank you for proving my point!!! I've just highlighted it. If car A makes 100 ft lbs of torque at 5252 rpm, it is also making 100 hp at that same rpm. If you are holding that engine rpm over the entire acceleration range, you are averaging 100hp. Car B at 1000 rpm is only making 19hp! At 2000 rpm it's making 38 hp. At 3000 it's making 57 hp. At 4000 it's making 76 hp. At 5000 it's making 95 hp. Car A makes 100 average horsepower and car B makes lets say 59 average horsepower. Notice that average torque for each is IDENTICAL for their powerbands? How can this be? If torque has anything to do with movement, acceleration, velocity, etc, both cars would HAVE to be capable of the same rate of acceleration but they aren't!

I feel like I've walked into a room full of drunk people discussing the meaning of life.

heyarnold69

01-16-2009, 04:43 PM

math makes me cry!

I saw an rx8 gear today .... 3.97
any thaughts a company "black jack racing" is selling them

claims the difference off of first is slower but it increases both mpg and top speed?

thaughts? why?

rotary.enthusiast

01-16-2009, 04:57 PM

Thank you for proving my point!!! I've just highlighted it. If car A makes 100 ft lbs of torque at 5252 rpm, it is also making 100 hp at that same rpm. If you are holding that engine rpm over the entire acceleration range, you are averaging 100hp. Car B at 1000 rpm is only making 19hp! At 2000 rpm it's making 38 hp. At 3000 it's making 57 hp. At 4000 it's making 76 hp. At 5000 it's making 95 hp. Car A makes 100 average horsepower and car B makes lets say 59 average horsepower. Notice that average torque for each is IDENTICAL for their powerbands? How can this be? If torque has anything to do with movement, acceleration, velocity, etc, both cars would HAVE to be capable of the same rate of acceleration but they aren't!

I feel like I've walked into a room full of drunk people discussing the meaning of life.

Just to clarify for everybody, you're saying car A will accelerate faster in this example?

DarkLord7854

01-16-2009, 05:01 PM

So you want to do a slower start? The 09 RX-8 has a 4.777.

*cries on the inside a bit*

rotarygod

01-16-2009, 05:02 PM

Kane

01-16-2009, 05:06 PM

Funny I am having the same fight on another website.... LOL

rotarygod

01-16-2009, 05:11 PM

I don't know how it's a fight. It's like arguing against the laws of physics. Actually that's exactly what it is!

Kane

01-16-2009, 05:12 PM

Gravity is for punk b*tches!!!!

rotary.enthusiast

01-16-2009, 05:13 PM

If car A is making 100 average horsepower over it's usable rpm range and car B is only making 59 or so average horsepower over it's usable rpm range, car A will absolutely be faster. Don't make me laugh and claim otherwise. If this isn't true tharn car A either has some SERIOUS drivetrain loss or weighs a hell of alot more!!!

Ignore drivetrain loss and shifting times... this is just an example.

And yes, car B will accelerate faster. Think about it. Car A is continuously decreasing its effective gear ratio as it accelerates (to maintain the magic RPM number), which means it is continuously reducing the force generated at the wheels. Car B will produce a constant amount of force at the wheels through each of it's six gears (decreasing for each upshift obviously).

Forces are what cause things to accelerate at the end of the day. You say a force by itself doesn't imply that any work will be done, and you're right... if the net force ends up being 0. So long as the force applied by the wheels is greater than all opposing forces (wind, drivetrain loss, whatever), then that force WILL cause the car to accelerate at a rate proportional to the force itself.

rotarygod

01-16-2009, 05:14 PM

Oh my god I just got dumber reading that! The words under your name are apparently an admission.

If that's true then who the hell cares about having more power than the next guy? Fast cars must not be the ones with the most power. They must be the ones with the most creative transmissions! Congrats. You have officially created a new level below zero on the logic meter!

RX8-Frontier

01-16-2009, 05:16 PM

Car A has 4.44 gears, 200 hp, and 131.3 ft-lbs of torque at 8,000 rpms.

Car B has 4.77 gears, 200 hp, and 131.1 ft-lbs of torque at 8,000 rpms.

Both transmissions are 1:1.

RG, you did the math in another thread proving that regardless of the rear end ratio, the same hp at the engine is the same hp at the wheels, however the torque numbers are different.

Car A would have 582.97 ft-lbs to the rear wheels.
Car B would have 626.30 ft-lbs to the rear wheels.

Why does Car B accelerate quicker? It can't be horsepower, because at any given RPM, the horsepower of both cars A and B will be identicle at the engine, and at the tire.

Something causes Car B's RPMs to increase faster, though. But it can't be horsepower, because horsepower is a calculated product of and Torque and Time.

Here's the thing.

Horsepower is a calculated product of measured values: Torque and time. It does not cause torque to happen. It does not cause time to happen. So why do we care about it? Because it is a calculated number to give engineers (originally) a comparative number (and curve) to be able to quickly check on the performance of an engine. Just torque alone doesn't tell you anything; ya' gotta' know the rpms and the time in order for you to be able to predict what the engine will be able to do, aka, how much work it'll be able to do over time, which is, incidentlly, what Horsepower actually is.

But unfortunately, too many people have fallen into the trap that Horsepower is what makes a vehicle move. Sorry, but no. TORQUE is actually what makes it move. HORSEPOWER is just a number that can be used to compare DIFFERENT engines with each other instead of having to include TORQUE, TIME, and RPM in conversation/comparisons.

From an engineering standpoint, horsepower is a calculation that was invented in order to compare apples to apples. Comparing torque values of one engine to another directly is impossible; but it's found through physics that comparing the torque over time, aka, the rate of WORK two engines can do is a number that can be compared. (RG, if you think about, you reaffirmed that in your post here (http://www.rx8club.com/showpost.php?p=2820409&postcount=32). You can't directly compare torque from Engine A to Engine B. You can directly compare horsepower. And the one with more horsepower wins...but only because it's a function of torque and time, NOT because it's the cause of anything.

So RG is right, and he's wrong. If you're going to compare two engines to each other, you compare HORSEPOWER. If you're wanting to make 1 engine go FASTER than it could before, you increase the TORQUE. Horsepower of that same engine will be increased, too, by nature.

This is why it is physically impossible to reduce torque but increase horsepower at any instantaneous point in time. And likewise, it's physically impossible to decrease horsepower and increase torque at any instantaneous point in time.

Horespower is NOT a physical anything. It's a calculated value of the rate that WORK can be done. The physical things in the equations are TORQUE and TIME.

Paul Yaw is 100% correct when he said, "the laws of physics are non-negotiable." Yep. They sure are. Darn shame he got lost in his explanation of things....

To simplify and reiterate... Torque is a physical property; a measurement of the strength (FORCE) of an engine. It is NOT able to be compared directly between two engines in any meaningful conversation, as the TIME it takes and the RPMS it can produce are important.

Because of those dependent variables, engineers figured out a way to compare two engines based on the amount of WORK an engine can do over a period of time. THIS IS WHAT HORSEPOWER IS!!! Again, horsepower is a calculated value of the rate at which an engine can do WORK. It can be used to compare two different engines to compare which one can do WORK faster. It does not, however, cause any movement in the vehicle, as it is NOT a physical property.

Horsepower can NOT be increased without either an increase in TORQUE, or an increase in RPMS in an engine. Period. It is a dependent, calculated value to compare engines. If you want a car to go faster, you INCREASE the TORQUE by either increasing the amount the engine puts out, or the gear ratio (torque multipliers) between the engine and the wheels, because that's almost always cheaper than increasing the RPMS the engine can sustain before KABOOM!! Horsepower will INCREASE if either of these items are increased, because it is a function of them.

rotarygod

01-16-2009, 05:21 PM

Car A has 4.44 gears, 200 hp, and 131.3 ft-lbs of torque at 8,000 rpms.

Car B has 4.77 gears, 200 hp, and 131.1 ft-lbs of torque at 8,000 rpms.

Both transmissions are 1:1.

What's the wheel speed of each car?
Car A: 1801 rpm
Car B: 1677 rpm

Car A is moving faster! ;)

FYI: Figure out the wheel circumference and plug in those rpms? Look at the mph! We know this isn't possible though.

Car B would accelerate faster because it would be up to it's average powerband at the wheels quicker than car A. It's that simple.

RX8-Frontier

01-16-2009, 05:29 PM

Man... Are you trying to argue with RG?.... Kind of pointless, just read his threads and learn.

When it comes to a rotary engine and it's workings, hell no!

But in this instance, when it's just physics, and he's *almost* there, but not quite, in his understanding of it, then yep.

What's the wheel speed of each car?
Car A: 1801 rpm
Car B: 1677 rpm

Car A is moving faster!

FYI: Figure out the wheel circumference and plug in those rpms? Look at the mph!

Yep. Speed is a CALCULATED value, again...

(Psst... Pretend both Car A and Car B's engines have flat torque curves at the engine, and Car B will STILL accelerate faster... Why? 'Cause it's putting more TORQUE to the ground...)

It's a "chicken and egg" situation... Except in this case, there's only 1 value that an engine actually can produce, and that's torque. An engine doesn't "make" horsepower, as horsepower is NOT a physical property. It's a calculated value to compare the rate at which something can do WORK.

You can increase its ability to do work quickly, but how do you do that? Well, that'd be an increase in horsepower. But, seeing as horsepower is a CALCULATED value that can't be measured directly since it's NOT a physical property, you increase the horsepower by increasing the TORQUE. Torque is the independent variable. Horsepower is the dependent.

gawd this takes me way back to dynamics class... AAAGGGGHHH!!!!!!

rotarygod

01-16-2009, 05:31 PM

RX8-Frontier

01-16-2009, 05:35 PM

I honesty give up. I've given absolute proof and people just either can't or are completely mentally incapable of any degree of comprehension. Then again I used to always notice in school that the "special" kids were always the happiest. Hmmm...

Interestingly enough, the "special" kids at my school, the ones capable of comprehending the difference between a physical, independent property and a calculated, dependent property, were the "special" ones that passed...

The ones that never figured that out switched majors.

04RX8man

01-16-2009, 07:15 PM

JUST FOOD FOR THOUGHT!

The Purpose of a transmission:
A four stroke engine does not produce equal torque at all times. it has lower torque when starting from a stop. That is why on a MT you must slip the clutch to begin movement. When the engine is operated in low gear, the engine's crankshaft/eccentric shaft turns approx. 3 times to one turn of the trans output shaft. this is call a 3:1 ratio.

Without the extra leverage that this GEAR REDUCTION provides the engine would stall or lug during takeoff. compare this to riding a 10 speed bicycle. When you shift into a low gear, the pedal crank revolves much faster and you climb the hill easier. In a low gear a small gear drives a larger. The gears provide leverage like that of a light person lifting a heavy person on a teeter-totter.

USING GEARS TO INCREASE TORQUE:

To measure torque, the force applied is multiplied by the distance from the centerlind of rotation. twenty pounds of force applied to the end of a 1-foot rod produce 20 ft/lbs of torque. Ten pounds of force applied to a 2-foot rod also produce 20 ft/lbs of torque. when the driving gear is smaller than the driven gear it's output speed decreases and the output torque INCREASES. The distance from the center of a gear to it's outside edge is the radius. the radius is where the torque of that gear is measured.

rotary.enthusiast

01-16-2009, 07:39 PM

I honesty give up. I've given absolute proof and people just either can't or are completely mentally incapable of any degree of comprehension. Then again I used to always notice in school that the "special" kids were always the happiest. Hmmm...

Ignorance is bliss, I'll give you that.

So I sat down and actually did the math in my own example, and it turns out I've lived up to my title :uh:

You are correct. I am an idiot. It somehow made sense in my head when I typed it all out.

Please ignore all posts by me :rolleyes:

Kane

01-16-2009, 07:42 PM

Please ignore all posts by me :rolleyes:

Ever? :spank:

Sorry - just bored. Gotta respect a good discussion when no one gets their panties in too much of a bunch...

rotary.enthusiast

01-16-2009, 07:44 PM

Ever? :spank:

It probably wouldn't be a bad idea in all honesty. I tend to type before I think :banghead:

Brettus

01-16-2009, 07:53 PM

you already have all the answers in this thread - fit the 4.77 if you want more fasterrer .
Or get serious and go FI .

oops - i didn't read page 2 before i posted . me FTL

04RX8man

01-16-2009, 07:58 PM

of course being turely faster FI will do that not a 4.777 rear end

rotarygod

01-16-2009, 09:17 PM

To those who I was arguing with, sorry if I came off as insulting. It's actually just frustration and not any anomisity.

The key word that was mentioned was "leverage". If we look at a lever, it's really nothing more than a simple transmission. You can't just arbitrarily increase torque. There's a tradeoff somewhere. If power stays the same and torque increases, speed goes down. If speed goes up and power stays the same, torque goes down. If power goes up and torque stays the same, speed goes up. It goes on and on... When we "increase torque" through a transmission, we are slowing everything down to gain the leverage. That's the tradeoff. That's why distance and time are so important and relevant. If we had 1 hp, we could move almost anything of any size through gearing or enough leverage. How quickly we can do it however is another thing altogether. The farther back from the fulcrum you move on a simple lever, the farther you have to move to move the object a certain distance. Notice in a low gear that you aren't going very fast for the same reason but you've got great leverage. It's horsepower that is doing the work as without horsepower all the leverage in the world is useless.

“Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.” - Archimedes

solito

01-16-2009, 09:29 PM

Gravity is for punk b*tches!!!!

:lol:

subatomicparticle

01-16-2009, 11:10 PM

subatomicparticle

01-16-2009, 11:29 PM

rotarygod

01-16-2009, 11:46 PM

A transmission is a torque multiplier. I never said it wasn't. It multiplies torque by changing speed. Actually the math verifies torque increases through a transmission. Horsepower doesn't and this is what it verifies. Please read it better and actually plug in some numbers. Skimming through it wasn't very effective.

rotarygod

01-16-2009, 11:55 PM

Just because he says it doesn't make it true that is one of the stupidist things I have ever heard that torque has nothing to do with moving the car are you kidding me, obviously the guy has no idea how a trans works or a car for that matter just because he calls himself rotarygod doesn't mean anything I read his threads and as I said there is some useful info in there but still than why does a car have torque and why is an srt-4 with less hp and more torque a lot faster than an 8 with more hp and less torque?

I don't really care what you think about me personally so say whatever you want but please do some research before you spout off nonsense to a person you are trying (and failing) to call out. Here I'll school you right now.

Why is an SRT-4 faster even though it has less horsepower? Are you referring to peak horsepower? Go look up AVERAGE power levels. It's got 223 hp which is realistically what the RX-8 has so peak isn't really higher anyways. I assume you are talking about the Neon SRT-4 and not the 300 hp Caliber SRT-4. The Neon SRT-4 weighs over 200 lbs less than the RX-8. Since it's got boost, it's got far more average horsepower in the usable rpm range which means that although peak numbers may suggest otherwise, that car should be faster due to a better average power to weight ratio. Incidentally the Neon SRT-4 is a bit quicker than the higher horsepower Caliber SRT-4. It's not due to torque. The Caliber weighs more and has a worse power to weight ratio.

Any other questions Einstein?

zoom44

01-17-2009, 12:00 AM

Funny I am having the same fight on another website.... LOL

cheater- whats wrong with us? we're not enough for you, you got another one on the side?

paulmasoner

01-17-2009, 12:21 AM

Then again I used to always notice in school that the "special" kids were always the happiest. Hmmm...

"Chocolate milk? This is the best day of my life!"

http://media.ebaumsworld.com/picture/Wrath1013/retards.jpg

no direct offense to anyone in this discussion of course

Kane

01-17-2009, 12:29 AM

cheater- whats wrong with us? we're not enough for you, you got another one on the side?

We're just friends!!!! Gah I can't take the pressure - RX8Club is smoothering me!!! Sometimes I just have to go out and be on my own! :doughpoke

subatomicparticle

01-17-2009, 01:51 AM

Believe me I did read it and the funny thing is I told my trans teacher at uti what you said and he didn't believe me when I told him, and then he laughed hysterically.And I have done the math and I do it everyday and I don't think you quite understand what those numbers mean. I was talking about the neon and obviously 100 ft. lbs have nothing to do with it. And you said that the trans is a torque multiplier now and that no horsepower is multiplied in the trans then how come when your in 5th gear in an 8 which is a 1:1 gear ratio (also known as direct drive because the trans is not multiplying torque) the horsepower stays the same through all gears as you said before you don't go anywhere. it has nothing to do with horsepower it is because there is not enough torque to move the wheels.I believe we covered this before and in regards to your race car theory the reason those cars are high hp and not much torque is because they don't weigh much it doesn't take much force to get th is moving and then the rest is top end or hp. And the last time I checked the 8 is not quite that light. And the real answer is you need both you need enough torque to get you going and you need hp to keep you going.

olddragger

01-17-2009, 12:26 PM

subatomicparticle

01-17-2009, 06:22 PM

SUb--- in all that you are saying you are forgetting "speed"
an old racing saying: hp=to how fast you hit the wall, torque is how far you take the wall with you.
Think speed ok---like this
example --- for this accept that the weight and all the gearing is the same, same rpm shift points--
one car has 400hp and 250lbs tq, and a 8Krpm rev cut the other has 300 hp and 300lbs torque and also a 8k rev cut . Which one will get to its maxium speed first? The 400 hp car will.
Now gear the car with the higher torque to maximize its performance and gear the highest hp car to fit its max performance which way do you think you have to go and why?
maybe this will help you understand what RG is trying to say.
olddragger
right i understand that, but the point is to find a good balance of both he is saying that you don't need torque at all it is all hp. As far as your hitting the wall analogy that is absolutely true which like I said before torque is what gets the weight of the car moving once you get up to a good engine speed the hp takes over but you need torque to get you going. When you are taking the wall with you that is pulling power how easily you can move the weight.

rotarygod

01-17-2009, 06:29 PM

Believe me I did read it and the funny thing is I told my trans teacher at uti what you said and he didn't believe me when I told him, and then he laughed hysterically.

Either you have a moron for a teacher or you told him what you think I've been saying rather than what I have been saying. I supect it's the latter as I hope your teacher isn't in fact a moron. However if your teacher doesn't agree with me (it's not really agreeing with me as I didn't make this stuff up) then I have no choice than to not recommend UTI as a viable school. Sorry. Get your teacher on here and I'll clarify it with him so he can go back and teach it to you. If he still doesn't understand, see my previous sentence.

And I have done the math and I do it everyday and I don't think you quite understand what those numbers mean.

Clearly the reverse is true here as I understand just fine. Again, sorry. Just remember which of us is a student currently trying to learn this stuff and which one of us actually works in an engineering department in the real world and has a career making money from designing up to 2200hp equipment because of this knowledge. If you make a mistake, it's a mark on a piece of paper. If I make one, it's potentially millions of dollars.

I was talking about the neon and obviously 100 ft. lbs have nothing to do with it.

Not sure what you're getting at here as your entire argument has been solely focused on torque and now you're saying it has nothing to do with it.

And you said that the trans is a torque multiplier now and that no horsepower is multiplied in the trans then how come when your in 5th gear in an 8 which is a 1:1 gear ratio (also known as direct drive because the trans is not multiplying torque) the horsepower stays the same through all gears as you said before you don't go anywhere.

The transmission doesn't multiply horsepower. It can't. You always have the amount of horsepower coming out of a transmission as you do going in. Obviously I'm ignoring drivetrain loss but you get the drift. In a 1:1 gear where it is just a direct drive scenario, you are saying that the trans is not multiplying torque. That's correct. It has everything to do with ratio. You have the same ratio out as in. I don't see what the problem is. That gear, that one ratio wouldn't be a torque multiplier. The rear end still does though.

it has nothing to do with horsepower it is because there is not enough torque to move the wheels.

This isn't even a rational thought as torque can't move anything. Only horsepower can. In your thinking, don't confuse the words "force" and "work". They are different.

I believe we covered this before and in regards to your race car theory the reason those cars are high hp and not much torque is because they don't weigh much it doesn't take much force to get th is moving and then the rest is top end or hp.

Again, not really much in the way of rational thought here. The reason many race cars make good top end horsepower and little low end torque has to do with the engine setup. Intake and exhaust port/valve timing along with runner sizes, lengths, and a host of other things determine where an engine makes it's best power. As you are focused on torque, bigger engines make more torque than smaller ones. But why? It all goes back to leverage. You have more displacement to absorb the shock of combustion and transfer it to the drivetrain. A smaller engine at the same rpm doesn't have this leverage. How do we get around that. We need to get the same amount of leverage per the same amount of time. You keep ignoring time. How do we get this? We have to spin the smaller engine faster. If we have a 350 cu in piston engine and are spinning it at 2000 rpm, it's displacing 350,000 cu in of area in 1 minute. Remember that a piston engine sees full displacement in 2 revolutions. Now lets say we have a 190 cu in Honda piston engine at 2000 rpm. It's only displacing 190,000 cu in in that same minute. How do we make each see the same amount of displacement in the same 1 minute time period? We speed the smaller engine up. It need to be travelling 1.82 times faster which means instead of 2000 rpms, it needs to be moving at 3640 rpms to see the same amount of air. Of course this is simplifying things greatly and I'm not taking into account VE of each engine.

Now we can see that no matter what rpm we are at, our engine of whatever size will always have the same amount of leverage on the air since this is a function of displacement. Remember torque should really be thought of as leverage. Obviously if a "torque curve" isn't flat, it's due to changes in VE. If VE were a constant, torque would be completely flat regardless of rpm. Since this leverage (torque) isn't doing any work, as it has this displacement even if the engine isn't moving, the only way to make it do any work is to add motion. However adding motion means adding time which you constantly want to ignore. The faster we spin an engine, the more we are using this leverage on the crank. Fortunately once we apply this new variable of time and distance into our stationary engine, the output now becomes known as horsepower. As long as VE doesn't fall off, the faster we spin the engine, the more horsepower we can make. Once we get to a point where VE falls off, there's no point in going any higher.

Race car engines rev high because they are getting the most horsepower out of their engines. Pure and simple. They tune everything here because their VE is highest up here which means a sacrifice of low end horsepower or as you keep wanting to refer to it as, torque.

And the last time I checked the 8 is not quite that light. And the real answer is you need both you need enough torque to get you going and you need hp to keep you going.

I see no reason why you are bringing weight into it as that involves a HORSEPOWER to weight ratio and not a torque to weight ratio. Incidentally, have you ever wondered why you never see a tq/wt ratio listed? Its because it doesn't tell you anything! Your last sentence again is an irrational thought. Sorry.

I have no idea why I keep apologizing to you when I'm not the one who's wrong. Hmmm....

rotarygod

01-17-2009, 06:30 PM

right i understand that, but the point is to find a good balance of both he is saying that you don't need torque at all it is all hp. As far as your hitting the wall analogy that is absolutely true which like I said before torque is what gets the weight of the car moving once you get up to a good engine speed the hp takes over but you need torque to get you going. When you are taking the wall with you that is pulling power how easily you can move the weight.

Now you're getting confused with momentum. Torque actually wouldn't pull you through a wall anyways as torque can't do anything on it's own.

rotary.enthusiast

01-17-2009, 07:51 PM

What RG has been saying and what I've been too stupid to understand is that the optimal torque to the ground can always be had via mechanical advantage at the engine's HP peak. Running through the math of the CVT example I gave made that blindingly obvious, and I don't know how I could have been quite so stupid. What he says is 100% correct: you want to reach your peak horsepower as quickly as possible, and remain there if you can, regardless of the amount of torque the engine is producing. Why? Because it will maximize via the transmission the amount of torque made at the wheels.

What I took issue with initially is that I thought RG was saying that if there was no transmission at all, just a 1:1 direct shaft to the engine that acceleration would be greatest at the horsepower peak, not the torque peak. That's not (I don't think) what he has been saying.

I remain both humbled and embarrassed :dunce:

swoope

01-18-2009, 02:16 AM

rotarygod

01-18-2009, 11:44 PM

What I took issue with initially is that I thought RG was saying that if there was no transmission at all, just a 1:1 direct shaft to the engine that acceleration would be greatest at the horsepower peak, not the torque peak. That's not (I don't think) what he has been saying.

Gear ratio is irrelevant in this regards, 1:1 or otherwise. Your car would accelerate fastest around the horsepower peak. The torque peak is also irrelevant. Cars are geared specifically to place the engine rpms centered around peak horsepower and not peak torque. Your car doesn't accelerate fastest around the torque peak. You engine is running at it's highest VE at the torque peak though. If your torque peak were very close to your horsepower peak, then it might seem that your car accelerates fastest here as a result but it's still only based on horsepower.

I'll use my 2nd gen RX-7 as a prime example. It's torque peak is centered at 3500 rpm. It's horsepower peak is 6500 rpm. No one in their right mind would race that car with a shift point based on an average powerband centered at the torque peak. That car is fastest over 5000 rpm with a shift point of a bit over 7000 rpm. This is because that's where the car makes it's most average horsepower and horsepower is what moves cars. All cars work the same way.

At the end of the day, the only thing that moves your car down the road, acclerates it to speed, or keeps it moving, is horsepower.

Brettus

01-19-2009, 12:57 AM

bravo to RG :worship:

rotary.enthusiast

01-19-2009, 01:36 AM

Gear ratio is irrelevant in this regards, 1:1 or otherwise. Your car would accelerate fastest around the horsepower peak. The torque peak is also irrelevant. Cars are geared specifically to place the engine rpms centered around peak horsepower and not peak torque. Your car doesn't accelerate fastest around the torque peak. You engine is running at it's highest VE at the torque peak though. If your torque peak were very close to your horsepower peak, then it might seem that your car accelerates fastest here as a result but it's still only based on horsepower.

I'll use my 2nd gen RX-7 as a prime example. It's torque peak is centered at 3500 rpm. It's horsepower peak is 6500 rpm. No one in their right mind would race that car with a shift point based on an average powerband centered at the torque peak. That car is fastest over 5000 rpm with a shift point of a bit over 7000 rpm. This is because that's where the car makes it's most average horsepower and horsepower is what moves cars. All cars work the same way.

At the end of the day, the only thing that moves your car down the road, acclerates it to speed, or keeps it moving, is horsepower.

I'm still a little gun-shy after the last beat-down I received in this thread, but here goes:

At any given speed, if you could be at the engine's HP peak, then you would be accelerating at the maximum rate, and therefor you would always design a transmission to attempt to stay in this high HP range as much as possible. That I agree with.

However, in any single gear I would contend that you are accelerating faster at the engine's torque peak. Get in your 2nd gen sometime and accelerate in 1st gear. Does your rate of acceleration really seem to increase after the torque peak as you approach redline? All physics aside, I can say that isn't my own experience.

ASH8

01-19-2009, 01:50 AM

Check the YT link (in your country) about horsepower and why you need more to go faster..why the BV needs another 730HP to go another 100MPH.

And yes I know many of you have seen it.

http://au.youtube.com/watch?v=LO0PgyPWE3o

Great Vid and a truly superb piece of Automotive engineering.

kersh4w

01-19-2009, 02:21 AM

you guys should check your maths:
http://www.youtube.com/watch?v=drE5cHe6c3s&feature=related

paulmasoner

01-19-2009, 02:30 AM

damn you!! u had to stop the video and do the spider/shoe bus stop thing...

/angry

RX8-Frontier

01-19-2009, 09:02 AM

RG: No worries. You didn't offend. Just thought it was odd on page 2 when all the sudden you got flustered & resorted to typical internet "last resort" speak. That doesn't seem like you, and that's what promted my last post in this thread.

Honestly, we are very close to "the same page" on this, in that we both understand that horsepower, and the area under the curve, is the most important thing to talk about when talking about the rate of acceleration in a car. That's pretty obvious when 'ya understand that that's exactly what the function of the "acceleration" calculation is for...to give a numerical value to torque applied over time to find out how much work an engine can do in a period of time.

The only thing I'm stating is, torque IS important, because to increase the HORSEPOWER of an engine, you've only got 2 options: Increase the TORQUE, or increase the RPM. You can't increase horsepower, directly, because the physical things you can change are torque & rpm. And the reason to change them is to INCREASE the rate at which work can be done, aka, HORSEPOWER (to those that still don't quite get it....)

Anybody that tried to compare torque values straight up between two engines doesn't understand what torque is. I'll definately agree w/ 'ya on that one, too. When comparing, or even generally talking about an engine, horsepower is the only value that matters, because it is the TERM used to talk about how FAST work can be done by an engine. Plain and simple.

Basically, for the "every day" person, horsepower is the only thing that really matters; both peak and area under the curve. For the engineer working on increasing the horsepower, they have to focus on 2 things: increase torque, or increase RPM. They can't increase horsepower directly, because it's not a physical characteristic.

And that's where I think we disagree, if I'm reading your posts right. But, seeing as how you "work "in an engineering department in the real world and has a career making money from designing up to 2200hp equipment," then you already know all this and are just talking to "every day" people on here in terms that actually matter to them.

(Just for the e-penis comparison, I'm a Civil Engineer, but was forced to take a lot of Mechanical classes (dynamics, thermo, hydraulics, etc.) for ABET. I don't know a lot of the factory production side, but I know the math involved.)

subatomicparticle

01-20-2009, 10:25 PM

zoom44

01-20-2009, 11:05 PM

You know.. You are all a bit daft!

RX8SaxMan

01-20-2009, 11:57 PM

finally someone is making sense. I may have been a little off on the 8/srt-4 comparison. Let's try a different scenario what rg is telling me is that identical cars in every way except one has 300 hp and 300 ft. lbs will have no advantage over a car with 300 hp and 50 ft. lbs. And in regards to rg's comment about not backing uti because they teach that torque is an important number. Since they are backed by porche, bmw, mercedes, audi, international, ford, cummins, etc. I don't think that they really are going to care.

Most likely the 300 ft. lbs torque car will be faster (in a drag race scenario) and that does not contradict anything RG said. See, the car with 300 torque will reach 300hp @ 5252rpm, whereas the 50 torque car will not reach 300hp until 31,512rpm. Because the powerband is so much narrower on the high torque car, it's average horsepower is higher, and therefore faster. The low torque car is going to spend quite a bit of time in low-hp territory while its revving up to 31.5k rpm. HOWEVER, if you can keep both cars in their optimal RPM ranges, there will not be a difference between them. Hence why Formula 1 cars manage to be so damn fast, despite their low torque, and also why nobody drag races them ;)

Bottom line is, it all has to do with horsepower, not torque....just like RG has been saying.

RX8SaxMan

01-21-2009, 03:48 AM

Just to clarify, I was assuming these theoretical engines had constant torque across the powerband. This obviously isn't realistic, but it makes the point easier to illustrate, since it seems as though some people are having a hard time understanding the dynamics of an engine.

rotarygod

01-21-2009, 12:37 PM

If both cars make the same average horsepower within the same usable rpm range and of course are geared the same, weigh the same, etc, they will accelerate at the exact same rate of speed. You guys need to get over torque. You DO NOT need to know the word torque even exists when it comes to determining rate of acceleration. It is completely irrelevant. However...

You DO need to know torque if you are designing engine blocks, transmissions, drivetrain components, etc as this will help you design around the twisting forces that are trying to tear it all apart. Torque is a completely worthless and irrelevant value when it comes to determining how fast your car can go and how fast it can accelerate to that point but you need to know it when determining how strong stuff needs to be built. Ever wonder why a diesel engine is built so robust compared to gasoline engines of the same horsepower levels? Someone is going to say it's based on compression ratio but that's not it at all. That's a very small part of it but not nearly enough to justify how overbuilt those engines appear to be. Diesels also don't run on detonation so don't go there either. It's all about torque on engine components. The same horsepower at a lower rpm is far more twisting on the engine block and drivetrain and you need to design for this. This is why F1 engines are built out of aluminum and can be so light. They make great power but they don't produce much torque. That's where torque is a need to know number. It's not in determining acceleration. Modern diesel engines such as VW's are slowly being built lighter and lighter and out of "weaker" (for lack of a better word) materials. Why? They make less torque. How? They rev higher than they used to and their powerbands are shifted upwards as a result. There is less torque being exerted on the engine components. Many of these engines are still cast iron but the trend is changing.

Remember an 850 hp F1 engine revving up near 18K rpm makes somewhere around 250 ft lbs of torque. If they had engines that revved to only 8K rpm and made 850 hp, at that rpm, it would make somewhere around 550 ft lbs of torque. If the only difference were the engines, and the transmission gear ratios were different to account for the powerband differences, and everything else stayed the same from a weight standpoint, which car would be faster? Neither! They'd be the same speed. Why? Torque didn't tell you jack! The car with the higher torque is not faster. It can't be. Only horsepower matters from a performance standpoint as only horsepower moves you.

Keep in mind I didn't specifically say UTI was a bad school. I said that one of 2 things was happening with the instructor. One was that he was being told something I wasn't saying which is why he disagreed with me. The other option was that he was being told what I've been saying but is just plain wrong about what he understands. I did make it perfectly clear that I think he is probably just not correctly being told what I'm saying which is why he disagrees. However if in fact he does get the info correct but still doesn't agree with me, only then would I say UTI is crap. I doubt it is and I've just explained what I think has been happening. Clear yet or do I need to draw a picture or perhaps a pie chart of probable outcomes?

subatomicparticle

01-21-2009, 01:06 PM

the f1 scenario your math is correct but the car with more torque would absolutely have a better 1/4 mile time but yes they would have the same top speed and mid and high end acceleration characteristics but you absolutely need torque to get you going. you said yourself that torque is a twisting force kind of like your wheels turn it goes back to the leverage thing you have a horse with a plow (1 horsepower) trying to pull a large rock and is stuck use a large lever (to increase the torque) and it will pull the rock out because when torque is applied to a wheel it is in essence leverage.

subatomicparticle

01-21-2009, 01:09 PM

I like my 4.77 gears better than all the other bolt on mods I have had (except wheels), and I have had them all.

Only thing that bothers me is the mileage and the ratio of 6th with the swap. 80mph on the interstate is pretty close to 5K rpms. :(

Thanks I imagine you went from the 4.44 if you have any other info on how this all worked out for you I would like to hear it.

RX8SaxMan

01-21-2009, 02:44 PM

the f1 scenario your math is correct but the car with more torque would absolutely have a better 1/4 mile time.

Not if the car with less torque had a transmission optimized for its higher powerband. A transmission is essentially a torque multiplier.

rotarygod

01-21-2009, 03:29 PM

the f1 scenario your math is correct but the car with more torque would absolutely have a better 1/4 mile time but yes they would have the same top speed and mid and high end acceleration characteristics but you absolutely need torque to get you going.

The car with more torque wouldn't accelerate any faster as torque does no work. I'm not sure how often I have to keep saying it. Torque does no work. Torque does no work. Torque does no work. Torque does no work. Torque does no work. If it does no work, it can't get you moving or accelerate you. Why? torque does no work! Each car in my example of course would have to be geared around their respective powerband (horsepower). Torque can't just get you moving and then miraculously hand off somehow to horsepower. It doesn't work that way. The same thing that gets you moving off the line is the same thing that accelerates you and that is pure and simple horsepower. Forget you've ever heard the word torque as it's as relevant to vehicle acceleration as a ham sandwhich to keeping an airplane up. ONLY horsepower is relevant.

you said yourself that torque is a twisting force kind of like your wheels turn it goes back to the leverage thing you have a horse with a plow (1 horsepower) trying to pull a large rock and is stuck use a large lever (to increase the torque) and it will pull the rock out because when torque is applied to a wheel it is in essence leverage.

You bet it's a twisting force. However we aren't using it because that twisting force is work. It isn't. It's leverage. We are gaining leverage by changing output vs input speed. You may need leverage to get you moving but it's not the leverage that's moving you. It's the force acting upon that leverage that is. You can have all the leverage (torque) in the world but have no input horsepower acting on it. What would happen? Nothing. Why? Torque does no work! It's leverage. That's it. Go sit on a see saw alone and let me know when you suddenly go up. That fulcrum isn't going to get you moving as it's not doing any work.

You admit torque is leverage and that's good. However torque isn't horsepower and without horsepower nothing is going to move. Torque does NO work! It takes work to get your car moving. Torque allows you to have leverage that will permit work to be done through the input of horsepower but without that horsepower nothing is going to move anywhere. The whole point of a transmission is to get the engine rpms up to the max horsepower range.

RX8-Frontier

01-21-2009, 04:23 PM

Torque does no work! It's leverage. That's it.

No it's not. It's a FORCE applied at a DISTANCE... ("Leverage" is just a distance)

:bootyshak

Torque does NO work! It takes work to get your car moving. Torque allows you to have leverage that will permit work to be done through the input of horsepower but without that horsepower nothing is going to move anywhere.

Technically speaking... horsepower does NO work...

Horsepower is a RATE at which WORK gets done. It's not the actual WORK itself...

(But if you wanted to find out how much WORK got done, you'd use the HORSEPOWER curve for your calcs)

:evil_laug

If 'ya get right down to it... WORK actually is physically done by TORQUE (fuel/air/sparky go boom, applying a force at a distance to make things go spinny...). However, the RATE at which that WORK gets done is HORSEPOWER (a force applied at a distance during a period of time).

ACCELERATION is the result of WORK being done to the car... So it's pretty simple, really... Do you want to talk about FORCES, or RATES? You have to talk apples and apples, here... So talking RATES means you talk about HORSEPOWER and the RATE OF ACCELERATION.

So if you want to know how FAST WORK will get done, you want to talk about HORSEPOWER. TORQUE won't tell you how quickly the WORK can be done; only how much FORCE is gonna' be added at any second.

RG:

Unfortunately, you're not quite there when talking about what is doing the actual WORK. HORSEPOWER can't do work; it's a RATE at which WORK gets done. TORQUE is the actual force, applied at an actual distance, and if the car is turned on, then it's being done over an actual amount of time. This is the WORK being done by the engine.

BUT, that doesn't tell you how quickly it's being done; for that, you need to talk HORSEPOWER (which you already know, and some others haven't quite gotten there, yet.), which adds the last physical property, revolutions of the engine, into the conversation.

Everybody else, pay attention!

RG is 100% right that HORSEPOWER is what's important in discussing acceleration rates. Torque is NOT a RATE, and therefore is NOT going to give you any information regarding how fast a car accelerates!

rotary.enthusiast

01-21-2009, 04:31 PM

I like your new title RG :lol2:

Some basic physics equations:

F = m*a
W = F*d
P = W/t
v = d/t

Let's get power and acceleration into the same equation shall we?

P = W/t = (F*d) / t = F*v = m*a*v

Solving for a, we get:

a = P / (m*v)

So if we know power, mass, and velocity, we can compute instantaneous acceleration. Assuming we don't have a car that magically changes mass over time, acceleration will be greatest at any given velocity at maximum horsepower.

This just so happens to be when torque at the wheel will be greatest as well. Let's simplify our equation a bit more:

a = P / (m*v) = W / (m*v*t) = W / (m*d) = (F*d) / (m*d) = F / m

Hey look, we're right back at Newton's second law. Looks like all we really need to compute instantaneous acceleration is force and mass. If that's true, then based on what we figured out earlier, the force generated at the wheels will be greatest if we have a transmission that puts us at our horsepower peak at any given speed. Can we all agree that the force applied to the ground is proportional (not equal) to torque generated at the wheel? I'd rather not get into angular accelerations and moments of inertia because I'll probably have an aneurysm :eyetwitch

If I'm still being retarded, somebody please correct me :)

Mazmart

01-21-2009, 04:49 PM

This is so funny. I was literally JUST speaking about the topic of the relationship of torque to hp (5 mins ago) and only this weekend had to explain it to a good car ghuy friend of mine. Torque could be described as 'potential' work whereas hp is work performed.

Paul.

rotarygod

01-21-2009, 04:57 PM

Assuming we don't have a car that magically changes mass over time, acceleration will be greatest at any given velocity at maximum horsepower.

This just so happens to be when torque at the wheel will be greatest as well.

Are you saying that torque at the wheels is greatest where maximum horsepower occurs? That's not correct. Here's why. Let's say our engine does 175 hp (141 ft lbs) at 6500 rpm. That's it's horsepower peak. Let's say it's peak torque is 155 ft lbs (103 hp) at 3500 rpm. The car is definitely going to accelerate it's fastest around the horsepower peak. We know this. If all we want to know is torque at the wheels, time becomes irrelevant. All we need to know is gear ratios, or in other words, torque multiplication. It's always going to be a fixed number x the torque of the engine. That means that in a 1:1 ratio, it's number in, same number out. Let's say we've got a 4.00 rear end. This means that there is 564 ft lbs (141 x 4) at the wheels at our hp peak but 620 ft lbs (155 x 4) at our torque peak. Plug in any gear ratio. It still works the same. That means greatest acceleration is not where the torque peak occurs. Not even at the wheels. Why doesn't the vehicle accelerate fastest at peak torque? ;)

rotarygod

01-21-2009, 05:02 PM

No it's not. It's a FORCE applied at a DISTANCE... ("Leverage" is just a distance)

:bootyshak

Technically speaking... horsepower does NO work...

Horsepower is a RATE at which WORK gets done. It's not the actual WORK itself...

(But if you wanted to find out how much WORK got done, you'd use the HORSEPOWER curve for your calcs)

:evil_laug

If 'ya get right down to it... WORK actually is physically done by TORQUE (fuel/air/sparky go boom, applying a force at a distance to make things go spinny...). However, the RATE at which that WORK gets done is HORSEPOWER (a force applied at a distance during a period of time).

ACCELERATION is the result of WORK being done to the car... So it's pretty simple, really... Do you want to talk about FORCES, or RATES? You have to talk apples and apples, here... So talking RATES means you talk about HORSEPOWER and the RATE OF ACCELERATION.

So if you want to know how FAST WORK will get done, you want to talk about HORSEPOWER. TORQUE won't tell you how quickly the WORK can be done; only how much FORCE is gonna' be added at any second.

RG:

Unfortunately, you're not quite there when talking about what is doing the actual WORK. HORSEPOWER can't do work; it's a RATE at which WORK gets done. TORQUE is the actual force, applied at an actual distance, and if the car is turned on, then it's being done over an actual amount of time. This is the WORK being done by the engine.

BUT, that doesn't tell you how quickly it's being done; for that, you need to talk HORSEPOWER (which you already know, and some others haven't quite gotten there, yet.), which adds the last physical property, revolutions of the engine, into the conversation.

Everybody else, pay attention!

RG is 100% right that HORSEPOWER is what's important in discussing acceleration rates. Torque is NOT a RATE, and therefore is NOT going to give you any information regarding how fast a car accelerates!

That I'll gladly concede to! :)

rotary.enthusiast

01-21-2009, 05:08 PM

Are you saying that torque at the wheels is greatest where maximum horsepower occurs? That's not correct. Here's why. Let's say our engine does 175 hp (141 ft lbs) at 6500 rpm. That's it's horsepower peak. Let's say it's peak torque is 155 ft lbs (103 hp) at 3500 rpm. The car is definitely going to accelerate it's fastest around the horsepower peak. We know this. If all we want to know is torque at the wheels, time becomes irrelevant. All we need to know is gear ratios, or in other words, torque multiplication. It's always going to be a fixed number x the torque of the engine. That means that in a 1:1 ratio, it's number in, same number out. Let's say we've got a 4.00 rear end. This means that there is 564 ft lbs (141 x 4) at the wheels at our hp peak but 620 ft lbs (155 x 4) at our torque peak. Plug in any gear ratio. It still works the same. That means greatest acceleration is not where the torque peak occurs. Not even at the wheels. Why doesn't the vehicle accelerate fastest at peak torque? ;)

No, I'm saying that at any given speed, if you could be at the horsepower peak then the torque at the wheels would be the greatest due to the mechanical advantage the transmission give you. If you're stuck in a single gear ratio, then the torque to the ground will be greatest at the torque peak, and you will indeed accelerate faster there. Horsepower tells you where acceleration will be greatest at a specific velocity. It's all in the equations above. Correct me if I'm wrong, but I don't think I am this time around.

EDIT: the math based on your example:

a = P / (m*v)
n = velocity at 6500 RPM in whatever gear you want

at 3500 RPM: a = 103 / (m*(3500/6500)*n) = 103*6500 / (m*3500*n) = 191 / (m*n)
at 6500 RPM: a = 175 / (m*(6500/6500)*n) = 175 / (m*n)

Acceleration at 3500 RPM in the same gear is greater.

RX8-Frontier

01-21-2009, 05:14 PM

I like your new title RG :lol2:

Assuming we don't have a car that magically changes mass over time, acceleration will be greatest at any given velocity at maximum horsepower.

This just so happens to be when torque at the wheel will be greatest as well. Let's simplify our equation a bit more:

If I'm still being retarded, somebody please correct me :)

Yes. You're being retarded. :)

Peak torque and Peak Horsepower don't ever coincide at the same point in time, at the same RPM. Maybe you could make a theoretical one that would, but I'm not going to sit and do the math to figure it out.

Basically, torque typically peaks much, much, MUCH sooner than horsepower does in an engine, because if the engine RPMs keep increasing after the peak torque value, then the horsepower still increases.

Just snagging a generic image off the internet shows my point:

http://www.noisybrother.co.uk/Public_Photos/931_Dyno_06-10-2007/XNT_Dyno_HP&Torque_wheels.jpg

The torque started decreasing, but because the RPMS kept increasing, the Horsepower kept increasing, to a point when the RPMS no longer increased fast enough to make up for how much torque was dropping; that that point, horsepower begins to drop, too. But the point is, the peak torque/horsepower come at different times.

rotary.enthusiast

01-21-2009, 05:21 PM

Yes. You're being retarded. :)

Peak torque and Peak Horsepower don't ever coincide at the same point in time, at the same RPM. Maybe you could make a theoretical one that would, but I'm not going to sit and do the math to figure it out.

Basically, torque typically peaks much, much, MUCH sooner than horsepower does in an engine, because if the engine RPMs keep increasing after the peak torque value, then the horsepower still increases.

Just snagging a generic image off the internet shows my point:

The torque started decreasing, but because the RPMS kept increasing, the Horsepower kept increasing, to a point when the RPMS no longer increased fast enough to make up for how much torque was dropping; that that point, horsepower begins to drop, too. But the point is, the peak torque/horsepower come at different times.

Torque at the wheels, not at the fly-wheel. If you're at peak horsepower, then the torque generated at the wheels is greatest for whatever velocity you are traveling.

RX8-Frontier

01-21-2009, 05:40 PM

Torque at the wheels, not at the fly-wheel. If you're at peak horsepower, then the torque generated at the wheels is greatest for whatever velocity you are traveling.

Torque at the wheels is 100% dependent on transmission & differential gear ratios, and wheel size. Those 3 things are picked to attempt to keep the engine in its powerband (powerband is horsepower, not torque... apples to apples, ok?). BUT, that doesn't mean they do a bang-up job of it; it'll never be perfect. Change anyone of those 3 things, and all the sudden the theoretical goes out the window. Even something so small as overinflating/underinflating the tires, or even tire wear over the life of the tire will change it.

RGs math/example a few pages back show that Horsepower to the wheels is the same as Horsepower at the flywheel (assuming no drivetrain losses), regardless of the gear variations.

AND... Since gears are nothing but different size levers, all they will do to the torque curve is scale it by whatever the ratio is. So the torque at the wheels will be numerically higher, but will be the EXACT same curve. So if the maximum torque at the flywheel occurs at 3,000 engine rpm, the maximum torque at the wheels is still at 3,000 engine rpm; it'll just be a numerically higher number. The horsepower, however, will keep on increasing as the RPM increases, so no, even at the wheels, the maximum torque does NOT occur at the same time as maximum horsepower.

Nice try, though. :)

rotary.enthusiast

01-21-2009, 05:48 PM

You're missing the velocity component. Go back up and read my edited post that shows some math using RG's 2nd gen RX8's numbers.

RX8-Frontier

01-21-2009, 06:11 PM

You're missing the velocity component. Go back up and read my edited post that shows some math using RG's 2nd gen RX8's numbers.

velocity of the car doesn't matter. You're mixing velocity of the car with angular velocity of the engine in your formulas.

Make your life easier.

Look at the horsepower/torque curves. Yes, engineers are trying to select the right gear ratios to get a high amount of force to the tires when the engine is in its peak horsepower. BUT, it can't be exact, because no matter what you do, the engine's peak torque doesn't happen at the same time the peak horsepower does. And scaling the torque up or down isn't gonna' change that.

rotary.enthusiast

01-21-2009, 06:22 PM

velocity of the car doesn't matter. You're mixing velocity of the car with angular velocity of the engine in your formulas.

Make your life easier.

Look at the horsepower/torque curves. Yes, engineers are trying to select the right gear ratios to get a high amount of force to the tires when the engine is in its peak horsepower. BUT, it can't be exact, because no matter what you do, the engine's peak torque doesn't happen at the same time the peak horsepower does. And scaling the torque up or down isn't gonna' change that.

I'm going to use RG's number as an example again.

Let's say you're moving along at 30MPH at 3500 RPM (the torque peak of the engine). What if you were going 30MPH at 6500 RPM? The engine makes less torque at 6500 RPM, but you've changed the mechanical advantage by 6500/3500.

Pick any speed... if you have a gear ratio (be it because of transmission gear, diff gear, or wheel size, it doesn't matter) that puts you at the engines HP peak, then the torque delivered to the ground at that point in time is the greatest that it can possibly be for that speed.

RIWWP

01-21-2009, 06:31 PM

velocity of the car doesn't matter. You're mixing velocity of the car with angular velocity of the engine in your formulas.

Make your life easier.

Look at the horsepower/torque curves. Yes, engineers are trying to select the right gear ratios to get a high amount of force to the tires when the engine is in its peak horsepower. BUT, it can't be exact, because no matter what you do, the engine's peak torque doesn't happen at the same time the peak horsepower does. And scaling the torque up or down isn't gonna' change that.

Curious... (i really am, not challenging, just inquiring as to why. You guys are smarter than I am)

Why can't the HP and TQ peak be the same? I've never seen a dyno that show they are, but if we are talking math here, then isn't it mathematically possible for the 'curve' for both of them to be flat enough and steep enough that they are both continually increasing? If so, then each of the lines would have their peak at the same point: 'redline'.

For example, take the graph above. Imagine a redline at 3500rpm. Both torque and horsepower peak at the same time then.

The only thing I can think of that pushes against it relates to the expansion rate of the combustion, it pushes harder the slower the piston/rotor is traveling. (/side point: Also doesnt that mean that there is a max RPM where the rotor/piston is already traveling away from the point of combustion at the speed of expansion of that combustion?)

PS: I am also curious when the realization comes across that god > enthusiast :)

rotary.enthusiast

01-21-2009, 06:40 PM

Why can't the HP and TQ peak be the same?

HP = TQ * RPM / 5252

The only time HP and RPM are equal is at 5252 RPM. If your HP peak is at 5252 RPM, then they would be the same :)

PS: I am also curious when the realization comes across that god > enthusiast :)

Ouch :crying:

RIWWP

01-21-2009, 06:49 PM

HP = TQ * RPM / 5252

The only time HP and RPM are equal is at 5252 RPM. If your HP peak is at 5252 RPM, then they would be the same :)

Ouch :crying:

(Meant that as a friendly joke :) )
I really wish I had a graphing tool on hand. I can see a circumstance where HP and TQ are truely (As you say) equal at 5,252. Prior to that TQ is higher, after HP is higher. But both lines are both on an increasing angle (on the graph) before AND after, the entire way to redline. Nothing says that TQ must be decreasing after 5252 that I have seen. Just that TQ must be lower than HP after 5252.

Kinda like this: (pick your own scale :) ) Obviously no dyno chart looks like that. but the question is, is it possible? Seems to me that it is. Put the redline anywhere you want, it will be peak for both HP and TQ, while still conforming to the /5252 math.

I'm, talking math here, not engines. Real world isn't this smooth, i get that, but then real world engines run on math, so it makes me wonder.

http://i250.photobucket.com/albums/gg244/pengajawin/crudegraph.jpg

rotarygod

01-21-2009, 09:17 PM

^Yes it's possible. It almost never happens though but that doesn't make it impossible.

subatomicparticle

01-21-2009, 10:28 PM