I can see the need to keep your engine revving within a certain rpm for a piston engine, hence the need for a 6 speed (or 5 speed) manual tranny.

What real use is there going to be with having a 6 speed hooked up to the Renesis? Won't 3 or 4 speeds be all you really need?

well, good question, but two reasons really... first (the one that Mazda or any manufacturer will feed you) is that there is still significant gain in fuel economy and performance when going from a 5 speed to a 6 speed, allowing greater gearing advantages, and smaller steps inbetween each gear to exploit the highest portions of the power band (this actually does help)... but the real reason is marketing... if buying purely on what's written about the car, who really wants a 5 speed RX-8 when there's a 6 speed RX-8 for about the same money?? more is better in the public eye, and it's difficult to market an "inferior" transmission with less speeds... people don't realize that a 5 speed could be made significantly smaller, lighter, cheaper, and more mechanically stout than any given 6 speed: for those reasons Mazda went with just a Porsche-derived 5 speed for the Le Mans winning 787B in 1991... almost no "respectable" race car has used anything less than 6 speeds for a while now...

The way trannies are going, im looking forward to my 22-speed 911 in the year 2030 :D

The "more is better mentality was disscused here (http://www.rx8forum.com/showthread.php?s=&threadid=2138) about 18 inch vs. 17 inch wheels. The main reason was because there was a demand for them and they looked cooler. It is a decent read. Check it out.

For many lower horsepower cars, 6 speeds will be useless because the wheel torque of one gear will overlap with the wheel torque of the next if the gears are spaced too closely.

6 speed transmissions allow closer spacing of the lower gears for better acceleration and a taller ratio in top gear for better fuel economy.

The only way the RX-8 could make it to production was if concerns about rotary emissions and fuel economy were addressed. The 6 speed is not just for the "more is better" idea. The only way the RX-8 could exist is with at least one version of the 6-speed transmission.

Brian

This car has a wide "torque band", not a wide power band. Cars with wide power band have a big torque peak at low rpms. The 6 speed allows you to keep the engine rpms near the power peak.

I'm with Wakeech on this one. It seems trendy to have a 6 speed these days. People will explain the performance gains to be had with a properly spaced 6 speed transmission (vs. 5 speed tranny) but just the words " six speed transmission" are like instant buzz words to most americans. My take on it? *yawn* it's about time...

Darril

The Renesis has a narrow powerband.
It only make power when all three ports are online and cooking. 6250 revs the 3rd port opens up, and the renesis only really shines from 7250 to 8750

http://www.rx8forum.com/showthread.php?s=&threadid=2026

isnt it supposed to be like 90% torque from 3500 up? or something
________
INFANTS DEPAKOTE (http://www.classactionsettlements.org/lawsuit/depakote/)

sure it may produce 90% torque at 3500 rpm, but lets say at 45mph, and you're in 4th gear at 3500 rpm you are getting less torque at the wheels than if you were in 2nd gear at 8000 rpm because of gearing, sure the torque coming out of the engine is pretty similar you lose a lot more of that torque at the wheels when in 4th gear, than in 2nd gear.

btw those numbers are just a rough estimate for example

this is one of those cases, where horsepower, which is the energy output of the engine is a more applicable figure, as opposed to the torque the renesis puts out

-nate

Originally posted by MikeW
The Renesis has a narrow powerband.
It only make power when all three ports are online and cooking. 6250 revs the 3rd port opens up, and the renesis only really shines from 7250 to 8750

http://www.rx8forum.com/showthread.php?s=&threadid=2026

Hi MikeW,

Another classic from MikeW. I didn't think you could outdo your statement that cars like the fd3s were only made to go straight (and not to turn) because of it's torsen LSD. :D

It would be interesting to know... What is your definition of a narrow powerband and what is your definition of a wide powerband? Examples?

Brian

Originally posted by Buger


It would be interesting to know... What is your definition of a narrow powerband and what is your definition of a wide powerband? Examples?

Brian

Anytime the peak torque is near the peak horsepower, the car has a narrow powerband. My RX-8 will have a narrow powerband because it doesn't have a turbo or a large displacement engine. A 6 speed transmission will allow the skilled driver to select a gear that puts the engine near peak horsepower. Horsepower RULES!

Originally posted by Buger
It would be interesting to know... What is your definition of a narrow powerband and what is your definition of a wide powerband? Examples?

Originally posted by Randy
Anytime the peak torque is near the peak horsepower, the car has a narrow powerband. My RX-8 will have a narrow powerband because it doesn't have a turbo or a large displacement engine.

Hi Randy,

My question was originally meant for MikeW but since you tried answering it...

You mention that a narrow powerband is "Anytime the peak torque is near the peak horsepower". What would you consider "near"? How would you numerically quantify "near"?

I was hoping for some examples of cars with a wide powerband. Would the Chevy Corvette Z06 be an example of a car with a wide powerband?

Thanks in advance, Brian :)

Originally posted by Buger




Hi Randy,

My question was originally meant for MikeW but since you tried answering it...

You mention that a narrow powerband is "Anytime the peak torque is near the peak horsepower". What would you consider "near"? How would you numerically quantify "near"?

I was hoping for some examples of cars with a wide powerband. Would the Chevy Corvette Z06 be an example of a car with a wide powerband?

Thanks in advance, Brian :)

One example is a C4 L98 Corvette. Max torque about 300, max HP of 250. Here is a link to some dynos:
http://www.corvette.co.za/DynoDay2.htm

Originally posted by Randy


Anytime the peak torque is near the peak horsepower, the car has a narrow powerband. My RX-8 will have a narrow powerband because it doesn't have a turbo or a large displacement engine. A 6 speed transmission will allow the skilled driver to select a gear that puts the engine near peak horsepower. Horsepower RULES!

I'm no expert, but the Renesis peaks on torque at 5500 rpm and hp at 8500 rpm. Those are 3000 rpm apart. That doesn't seem "near" to me. That's not to mention the flat torque curve of this engine. There really isn't a huge difference between peak torque and the rest of the curve with the Renesis. I think Randy is assuming that if the peaks are near then they are both at high rpm. In that case you would only be getting power at high rpm indicating a narrow power band.

EDIT:

It just occured to me that Randy might be talking about "near" in number. I assumed that he meant "near" the same rpm. If that is the case then I am not sure how the two being "near" proves anything. I would think that a low torque and high hp would show that the engine has to go to high rpm to make power. A high torque number and low hp would seem to indicate and engine that either has a low redline or torque that falls off at a low rpm. The only conclusion I can make on an engine where the hp and torque peaks are near in number is that the peaks are both close to 5252 where hp always equals torque. I don't see where that is a bad thing though.

Can anybody clear this up?
:confused:

Originally posted by Randy
Anytime the peak torque is near the peak horsepower, the car has a narrow powerband. My RX-8 will have a narrow powerband because it doesn't have a turbo or a large displacement engine.

Originally posted by Buger
You mention that a narrow powerband is "Anytime the peak torque is near the peak horsepower". What would you consider "near"? How would you numerically quantify "near"?

...Would the Chevy Corvette Z06 be an example of a car with a wide powerband?

Originally posted by Randy
One example is a C4 L98 Corvette. Max torque about 300, max HP of 250. Here is a link to some dynos:
http://www.corvette.co.za/DynoDay2.htm

Hi again Randy,

I was hoping that you would define how you quantify "near" and tell us whether you thought the Corvette Z06 had a wide powerband.

You did mention the C4 L98 Corvette as an example of a wide powerband. The stock car has it's peak torque @ 3200 and peak hp @ 4300.

Brian

Originally posted by Fëakhelek
EDIT:

It just occured to me that Randy might be talking about "near" in number. I assumed that he meant "near" the same rpm. If that is the case then I am not sure how the two being "near" proves anything. I would think that a low torque and high hp would show that the engine has to go to high rpm to make power. A high torque number and low hp would seem to indicate and engine that either has a low redline or torque that falls off at a low rpm. The only conclusion I can make on an engine where the hp and torque peaks are near in number is that the peaks are both close to 5252 where hp always equals torque. I don't see where that is a bad thing though.

Can anybody clear this up?
:confused:

Hi Fëakhelek,

I am hoping that Randy will try to clarify exactly what he meant. ;)

Most people get a little confused because they use torque and peak torque and hp and peak hp interchangeably. The peak torque and peak hp figures do not explicitly tell you anything about the shape of the torque curve below the 2 peaks.

Mazda currently says that the renesis' peak torque occurs @ 5500 rpms and the peak hp occurs @ 8500 rpm. For anybody that hasn't already seen the renesis torque curve, this gives 2 points on the curve but doesn't give any information on what the torque curve looks like before 5500. Knowing nothing else, it is possible that the torque at 2000 rpms could be 158 ft-lbs (approx 60 hp) because 158 < 159. Of course this isn't the case (renesis makes approx 50 hp @ 2000 rpms) but this shows that the "nearness" of the peak figures is not a definition of a wide powerband (some people like to call it a "torqueband").

Brian

Here's my perspective on this issue:

The FD (93-95 U.S. RX-7) has a 5 speed. On this car, 4th gear tops out at about 140 MPH. 5th gear tops out at about 200 MPH (though of course you don't have the power to redline in 5th). There are some tracks where you can go 140+ on the straights. 5th is too tall, so unless you have a bunch more straight away, you just stay in 4th to the corner. With 6 speeds, you could have 5 gears for accelerating and one highway gear to cruise in. That would be nice; 6 speeds sounds good to me.

With the powerband as it is (note: I don't want to argue about what I mean by that), a six speed in the RX-8 is a good idea to keep the revs up.

-Max

An objective definition of powerband used to be the revs between peak torque and peak horsepower. But that is old way, and it neglects the power over the horsepower peak.

I would say that the powerband is the rev range that the engine makes 75% or better of maximum horsepower. So 75% of 247=185.25, and that occurs between (roughly) 6250 and in excess of 10,000 revs. The 3rd port opens @ 6250, and the variable resonance switches @ 7250, and the variable air filtration opens also at 7250

The BMW (euro) M3 makes 338 hp@7900, 269 ft-lbs @4900, So 75% occurs (just before) 5000 revs.

The Corvette Z06, makes 405 hp@6K, 400 ft-lbs@4800, horsepower@ 4800 is 365.5 =90%

Hey I NEVER said: the fd3s were only made to go straight (and not to turn) because of it's torsen LSD
stop putting words into my mouth.

Back to the original post, there is a need for a 6 speed transmission. While the torque curve may be flat, the power curve is not. Saying this you ask, what is the difference between torque and power?

In simplest terms, torque is a measure to pull the car. Horsepower is ability accellerate the car. Torque is the measure of work. Horsepower is the measure of work per given time. Reading a torque value by itself will not tell you how fast a car will accellerate.

A flat torque curve will be adequate for you to spin your tires at any speed simply by mashing the throttle, but that does not neccearrily mean you will accelerate at a high rate. Horsepower is what lets you accellerate.

Let's take a look at a diesel big rig engine. many of those engines are only 150-200 horsepower or so. Well, you say, my RX-8 has more horsepower but can the RX-8 pull a 20,000 lb trailer? Hell no. The difference is that a big rig is 200 hp, but the torque is 2000 ft-lb where your RX-8 is maybe.. 158 ft-lb. See how slow big rigs accellerate, they are low horsepower. Torque is the ability to pull, not the ability to accelerate.

Now let's look at the Honda J series engine found in the S2000. The engine makes almost no torque at low rpm but there is loads of power above 8000 rpm. It's probably making 200+ hp from 7500-10000 rpm redline. Well, to keep the car accellerating, you need the the engine to be keep in the high horsepower band. By having closely spaced gears, everytime you shift, you will still stay withing the narrow power band and you will keep on accelerating.

The intent of having the 6 speed is to keep the car within the narrow high powerband to keep the car accellerating.

whatever... i just cause ppl more confusion.

Originally posted by ironqqq
The intent of having the 6 speed is to keep the car within the narrow high powerband to keep the car accellerating.


yup.

Originally posted by ironqqq
See how slow big rigs accellerate, they are low horsepower. Torque is the ability to pull, not the ability to accelerate.[/B]

nope. big rigs accelerate slowly becuase they're really, really heavy. torque is a measure of the force the engine is producing. force is the only thing that can accelerate a mass: power (energy) doesn't do this, but you can do some messy converting to find acceleration if you know the time over which there is a change in energy... bah!! i'm making less and less sense all the time.

the reason we use power to measure performance of an engine is because it brings the speed the engine is going into the torque equation... like on an electric motor, it "makes" only as much power as you put into it at all rpm, so in theory it has maximum torque at zero rpm (which would be infinite... torque, that is). the higher you rev it, the slower it will accelerate the mass, becuase its torque is deminishing as rpms rise if power stays constant (which would only make sense to use max power at the lowest rpms).

in application to IC engines, we can use power to account for gearing advantages 'cause the traditional empirical way for converting ft*lbs into hp is POWER * RPM / 5252... simple equation, and kinda sorta accounts for rpm...
to really get a fix on it, what you'd ideal want is some fucky unit where you've just got the torque * rpm, which would have some screwy name or something, and that would give a way, way better indication of how "well" that engine would accelerate a vehicle as you could easily factor in gearing and stuff like that.
(Rich used to explain this way way better, but he's not been around for a while...)

Originally posted by ironqqq
The difference is that a big rig is 200 hp, but the torque is 2000 ft-lb.

Something just seems really screwy to me with these numbers. To make 2000 lb-ft of torque and only make 200 HP, the engine would have to be spinning at 525 RPM. That sounds unrealistically low to me. Admittedly, I don't know much about big rig engines, so could you tell me what is their operating RPM range?

Originally posted by ironqqq
In simplest terms, torque is a measure to pull the car. Horsepower is ability accellerate the car. Torque is the measure of work. Horsepower is the measure of work per given time. Reading a torque value by itself will not tell you how fast a car will accellerate.

You're not quite there on the physics, but you do have a better grasp of what's going on than a lot of people do. At least you realize that how fast a car goes is more subtle than reading the peak torque figure.

"Pulling" the car and "accelerating" the car are the same thing. Torque is not a measure of work as you state, but is a measure of rotational force. If you want to measure the acceleration of a car, the torque value is exactly what you need to calculate it.

Force and acceleration are related by F=ma (remember Sir Isaac Newton :) ) If you want to know how fast the car will accelerate, you need to know the torque at the wheels, the diameter of the wheels (so you can convert rotational force into linear force) and the mass of the vehicle. That's it. Horsepower is nowhere in the equation.

But horsepower is important. Notice I said torque at the wheels and not at the engine? That's because there is gear reduction between the engine and the wheels. The effect of the gear reduction is to multiply the torque but reduce the rotational speed. While torque at the engine may only be 150 lb-ft, torque at the wheels will be as high as 2500 lb-ft due to the gear reduction. But it is possible to have too much gear reduction since it also reduces rotational speed. You could be geared so short that you are making ridiculous amounts of torque at the wheels, but the wheels are spinning so slowly that you are not going anywhere. Because of this, you can see that it is advantageous to have an engine which revs higher...if it revs higher, you can get away with more gear reduction, increasing your torque at the wheels. In a sense, you could say that revs are worth torque. This is where horsepower fits into the picture.

Horsepower is the relationship between torque and revs. HP = T *RPM / 5252. If you've ever noticed that engine dyno curves always have HP = Torque at 5252 RPMs, this is the reason. Although HP doesn't directly accelerate the vehicle, it is very useful in comparing two dissimilar engines. Take a high revving engine that makes 250 HP at 8500 RPM, and another low revving engine that makes 250 HP at 4000 RPM, and you'll find that they'll provide roughly equal acceleration given the cars they are in are properly geared, are of the same mass, and the shape of their power curves are similar. The horsepower takes into account the revs so you don't have to worry about how the torque multiplies through the gear box.

Anyway, that's how it works. I hope that helps shed a little light on what accelerates a car and how torque and hp fit into the picture.

RIGHT!! :D what he said.

Originally posted by RedRotaryRocket


Something just seems really screwy to me with these numbers. To make 2000 lb-ft of torque and only make 200 HP, the engine would have to be spinning at 525 RPM. That sounds unrealistically low to me. Admittedly, I don't know much about big rig engines, so could you tell me what is their operating RPM range?

well, he's talkin' about the big ass turbo deisels, which have redlines at 3k rpm, which is why you see them switch gears like a million times, with all those plumes of black smoke billowing as they mash the throttle after switchin' cogs. the first ones barely move it, so it can have some amount of momentum, and they just keep workin' their way through the box up to the gears that are massively overdriven for cruising on the freeways.

(only 99 more to go to a grand!! :D)

Originally posted by wakeech
well, he's talkin' about the big ass turbo deisels, which have redlines at 3k rpm, which is why you see them switch gears like a million times, with all those plumes of black smoke billowing as they mash the throttle after switchin' cogs. the first ones barely move it, so it can have some amount of momentum, and they just keep workin' their way through the box up to the gears that are massively overdriven for cruising on the freeways.

Three grand huh? Then the numbers don't make sense to me. Unless the power curve is really screwy, they either have to make a lot less torque than 2000 lb-ft, or a lot more HP than 200. I guess it's time for me to do a little google search :D

Ok, I found some info. The lowest power big rig engine I could find makes 315 HP and 1000 lb-ft of torque with a max engine speed of 2100 RPM. There are some engine models that make closer to 2000 lb-ft of torque, but their horsepower ratings are much higher...in the 500 to 600 HP range.

To keep this somewhat on topic...wouldn't it be nice to have 500 to 600 HP in an RX-8? :D

Or how about:

I wonder if anyone has ever made a wankel engine for commercial big rigs? :D

6 speed transmissions allow closer spacing of the lower gears for better acceleration and a taller ratio in top gear for better fuel economy.

Mazda did not gear the RX-8 for maximium acceleration. They spaced the gears so that top speed is in 5th and 6th is just taller for better fuel economy. The approx speeds @ redline for each of the gears are below:
1st gear ... 42
2nd gear ... 69
3rd gear ... 96
4th gear ... 132
5th gear ... 157 but drag limited at approx 155?
6th gear ... 186 but drag limited at approx 150?

If you compare this with some other 6-speed performance cars, you can see that they are geared much shorter so that they can have better 0--60 acceleration #s. Usually 2nd gear ratios are designed so that redline is very close to 60 mph for best acceleration.

350z
1st gear ... 38
2nd gear ... 63
3rd gear ... 90

G35
1st gear ... 37
2nd gear ... 60
3rd gear ... 85

Even older RX-7s with 5-speeds were geared so that redline in 2nd gear was around 60 mph for faster magazine times.

2nd gen RX-7
1st gear ... 35
2nd gear ... 61
3rd gear ... 89

3rd gen
1st gear ... 35
2nd gear ... 61
3rd gear ... 88

The only way the RX-8 could make it to production was if concerns about rotary emissions and fuel economy were addressed. The 6 speed is not just for the "more is better" idea. The only way the RX-8 could exist is with at least one version of the 6-speed transmission so that the fuel economy figures can disprove the notion that rotaries are grossly inefficient.

and for MikeW,

Originally posted by MikeW
The Renesis has a narrow powerband.

Originally posted by Buger
It would be interesting to know... What is your definition of a narrow powerband and what is your definition of a wide powerband? Examples?

Originally posted by MikeW
An objective definition of powerband used to be the revs between peak torque and peak horsepower. But that is old way, and it neglects the power over the horsepower peak.

I would say that the powerband is the rev range that the engine makes 75% or better of maximum horsepower. So 75% of 247=185.25, and that occurs between (roughly) 6250 and in excess of 10,000 revs. The 3rd port opens @ 6250, and the variable resonance switches @ 7250, and the variable air filtration opens also at 7250

The BMW (euro) M3 makes 338 hp@7900, 269 ft-lbs @4900, So 75% occurs (just before) 5000 revs.

The Corvette Z06, makes 405 hp@6K, 400 ft-lbs@4800, horsepower@ 4800 is 365.5 =90%

Do you actually believe what you write? :D Let's go with your definition of the powerband and numbers.

You say that the RX-8 has 75% of peak power from (roughly) 6250 - 10000 rpms. Taking your numbers, this is 3750 rpms at 75% or greater peak power.

Of course the relevent question is how many rpms of their powerband do the BMW M3 and the Corvette Z06 have from 75% of peak power? The wideness of the powerband is what we were discussing yes? It appears that you got started on the right track than got confused again and tried relating % of peak hp under 5000 rpms for some odd reason? What does 5000 have to do with anything?

Of course you did pick two very good candidates that are known for having a very wide powerband. I can explain why their powerband is so wide in another discussion but it is off-topic for this thread about 6-speed transmissions. The simple fact is that the RX-8 does not have a narrow powerband.

Originally posted by MikeW
Hey I NEVER said: the fd3s were only made to go straight (and not to turn) because of it's torsen LSD
stop putting words into my mouth.

Originally posted by MikeW
Torque sensitive differentials do not make any sense for vehicle that want to turn. (not go straight)

The last RX-7 has a torsens with TBRs of 2.6:1 to 3.0:1. They were made to turn and not to just "go straight".

Brian

Originally posted by RedRotaryRocket


Something just seems really screwy to me with these numbers. To make 2000 lb-ft of torque and only make 200 HP, the engine would have to be spinning at 525 RPM. That sounds unrealistically low to me. Admittedly, I don't know much about big rig engines, so could you tell me what is their operating RPM range?


I made those numbers up. The numbers were to prove a point. Diesel engines are very low revving and low hp but veryhigh on torque. I should have pointed out that I made those number up. if you wish, I can dig up data I took about 2 years when I did a dyno pull from a Catapillar engine. The point is diesel truck are basically, very high torque and very low hp. It was to illustrate disparity between hp and torque and to show why they accell so slowly, because they have such a low hp output. I apologize if I made up numbers and did not clarify.



You're not quite there on the physics, but you do have a better grasp of what's going on than a lot of people do. At least you realize that how fast a car goes is more subtle than reading the peak torque figure.

"Pulling" the car and "accelerating" the car are the same thing. Torque is not a measure of work as you state, but is a measure of rotational force. If you want to measure the acceleration of a car, the torque value is exactly what you need to calculate it.

Force and acceleration are related by F=ma (remember Sir Isaac Newton :) ) If you want to know how fast the car will accelerate, you need to know the torque at the wheels, the diameter of the wheels (so you can convert rotational force into linear force) and the mass of the vehicle. That's it. Horsepower is nowhere in the equation.



This is where you are wrong my friend.

I will attempt to explain why torque determines how you "pull a car" with why torque has no bearing on accelleration. I will also show why HP determines how fast you can accellerate.

I believe you have misinterpreted the basic definitions of torque. you may have mis-interpreted the effects of F=ma term.


Torque

By definition torque is "force applied at a distance", what is called a moment or couple. This is defined by the equation

T = r * F,

where r is the distance F is the force applied. Well, tehn you might say, F = ma, can be applied. Sure.. it can.

T = r * m * a

well, then shouldn't it be moving? yes and no. Let's say you are trying to turn a rusted bolt with a wrench. You are applying a force to the wrench causing resulting in a moment(bolt) at the bolt. You are applying a force and by newtons law your wrench should be turning, but it is not.

Let me give another example, A diver stands on the edges of a diving board. The diver is basically a weight,

T = r * m * a = r * m * g

where g is the accelleration due to gravity. Is the diver moving? No. Is there a torque being applied to the diver board? Yes.

No where does torque imply finite movement. Torque does applied at a cars wheels can push/pull the car, but does not determine how fast the car will move or whether or not the car will accellerate. Let's say your whells can apply 100 ft-lbf of torque at the road/tire interface but the car is pushed up against a solid brick wall. Does the car accellerate? No. Is there torque applied? yes.

Look at the units for Torque, T = ft-lbf

A foot pound only implies a force applied at a given distance. No movement is implied.


Work

This will show the difference between torque and work. Torque and work have the same units most often in automotive terms we use ft-lbf (lbf means "pound force", in engineering there is a clear distinction of "pound force" and "pound mass, lbm"... for all purposes, pound force is adequate for this discussion and usage. In the regular world, we blatantly use the term pound, making no distinction between the two. In 99% of cases, the distinction is a non-issue.

Work is derived again from the F=ma equation, but the key characteristic of work is it must have finite movement. meaning, something must move for work to be done.

From my inserted picture you will see that F=ma is used in the derivation of work, but you will see that the "dr" and "ds" terms imply a movement for work to be possible. In this case, accelleration must result in a movement for work to be accomplished.

Again, there is no term that determines the rate at which work is done. in this case let's say we were to displace an engine block 1 feet. There are no terms in the equations I posted to determine whether that displacement occurred in 1 second or over a period of 1 million years.

Again work has the same units, ft-lbf.

Power
This is where power comes in. Power by definition is a "rate change of work". There are derivations to obtain power, but we will forgo that and look at the popular equation

hp = T * RPM / 5252

This is a equation that relates hp to torque, not a equation that defines power or torque. That is very key.

From this equation we see the addition of the RPM term, this effects a "rate" at which torque is be applied. only from this equation do we introduce a rate, a rate of work is done. Here the equation says that the torque is applied at every cycle divided by a factor (5252). It is only when we introduce the RPM has a "rate change" been introduced.

You can apply all the torque you want but if there is no movement, there is no work and this there is no power delivered.

This is why I say that HP determines how fast a car accellerate. This is why I say that torque determines how a car pulls.

Torque alone has not bearing on how fast a car accellerates. Torque applied at a specified rate determines how fast you accellerate.

with the HP = T * RPM / 5252 equation if the RPM wa high enough you coudl accellerate like crazy even with very little torque.

Please don't say my physics isn't there.

Originally posted by ironqqq
Please don't say my physics isn't there.

It appears I have offended you. For that I appologize. My intent was not to berate you, but rather to correct a few points which were not correctly stated. I will submit that I did say your understanding was better than most...that was intended as a compliment.

You have written a nice summary of the concepts of force, work, and power. As I said before, it is clear you have a better understanding than most; however, I will re-assert that force (torque when rotational) is the motivation behind acceleration. To drive home this point, re-consider F=ma. The relationship between force and acceleration is DEFINED right there. There is no need to go through convoluted contortions to derive work or power. There is no need to know extra information like the time or the distance the force was applied.

There can be no acceleration without force. You're examples of a rusty bolt and a car against a wall were not quite complete as they did not take into consideration all the forces. The rusty bolt does not turn because the force you apply is directly opposed by two other forces: 1) friction and on a smaller scale, 2) the force of the electrical bonds you must break to break the rust. The same can be said of the car against the wall: the normal force of the wall on the car is exactly the opposite of the force generated by the wheels (actually, it is the road that imposes a force on the car.) The net force on the car is zero. This is the only reason why it does not accelerate.

I don't think I can make it more clear than that. If you still have your doubts, that's ok...but you'll just have to trust me. :) No flames intended.

The top speeds in gear for the 3rd gen RX-7 that were posted are wrong for 5-speed manual, 4.10-rear end versions (the ones sold in the U.S.). The correct speeds are roughly:

1st 40 MPH
2nd 70 MPH
3rd 105 MPH
4th 140 MPH
5th 200 MPH (drag limited to 160 or so in stock form)

-Max

Still don't see the need to have 6 speeds, other than to improve gas mileage some.

Unless someone can convince me otherwise, because of the extended torque range, I see me using selected gears routinely, such as 1st, 3rd, 4th (or 5th) & 6th.

Using information that I've found in this thread and others, I've calculated that 3,000 rpms in 6th gear is about 60mph.

Is this correct? If it is, that seems awfully short. I'm doing at least 70mph at 3,000 rpms in 5th gear in my '86.

Why would I rev higher in a car with more gears?

Brian

Go to a mazda dealer, and ask to drive an Ls miata with a 5 speed, and an Ls with a 6 speed back to back. the 6 speed seems to accelerate marginaly quicker. Plus it's easier to find just the right gear for each curve. on the 5 speed model, some curves are better suited to second gear, but your bouncing off the rev limiter coming out of the corner, put it in third gear, and you don't have the power to pull through the corner. in the 6 speed 3rd is just right, a little taller than the 2nd gear and not quite as tall as the 3rd gear in the 5sp. Personally I'm sold on 6 speed transmissions

Now when it comes to driving skills on the track, I have none.

But if bdclary is right about 60mph in the 6th gear hitting 3k rpm, then no wonder the mileage is so very low:( . I love to drive fast well cuz I can't stand driving at speed limit (65 mph in so cal). My average mileage is at 30 (70 mph or less) and I usually drive around 75-80 mph. and I know that I hit 3k rpm at about 78 mph (guestimate) driving a crappy 97 civ hatch. The only thing I like about the car is that is has really good mileage. I like to drive and I like to drive far. Man this is going to suck that means on average I'll get 6 less miles per gallon. Oh yeah does any know what fuel grade is recommended for the 8?