rotarygod

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

iTrader: (1)

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

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

iTrader: (3)

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

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

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

What I think is irrelevant. I just happen to agree with what is.

See response #1

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?

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!


I'll agree with that!

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

iTrader: (1)

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

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

DarkLord7854

*cries on the inside a bit*

rotarygod

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 than car A either has some SERIOUS drivetrain loss or weighs a hell of alot more!!!

Kane

iTrader: (1)

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

rotarygod

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

iTrader: (1)

Gravity is for punk b*tches!!!!

rotary.enthusiast

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

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

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. 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

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

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.

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

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...

RX8-Frontier

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

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

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

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

Kane

iTrader: (1)

Ever?

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

rotary.enthusiast

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