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Dyno reclass?


ken o

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If torque is the same between two engines at 100rpm and 10,000rpm it doesn't make a bit of difference how fast whatever is strapped to those engines will go. The engine spinning at 10,000rpm will make a crap ton more horsepower but it won't be any faster. It goes against our caveman like instincts that the faster and louder we rev something the faster it should go.

 

By this description, A V6 Mustang that makes 300tq at 2500rpm should be just as fast as a F1 car (circa 2013) making 300ish TQ but 800hp at 18,000rpm.

 

I think you are trying to simplify it a little too far.

 

It really is that simple! The Mustang would be somewhat slower than the F1 car though as it is ~2500lbs heavier and lacking a few thousand pounds of downforce...

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When you distill the torque / horsepower argument down to it's roots, and look hard at it, I agree that WHP could be used as a sole metric. The real problem, as I had mentioned in a different thread, is that right now NASA is only looking at peak WHP.

 

In essence NASA is comparing the total performance of every engine competing in TT, PT, and ST all based on one single point of data. When you think about it, the concept is absurd. I may as well say every human being's athletic performance can be accurately judged by looking at only their age. It holds the same degree of overall description of their physical abilities.

 

The reason people keep asking for torque, is that it represents looking at the power output of an engine at a second data point, and brings more parity into the comparison of the performance of different engine types. If the current method did actually work as well as the rules makers wished, we probably would not need quite as many line item modifiers and table adjustments to the current power to weight formulas to make them work.

 

Instead of torque, NASA could just as easily use two WHP data points. Possibly one at peak WHP, and one at 50% (or some other similar data point) of engine redline. If NASA were to either average or add those two figures, then the improved quality of it's method of comparing engine performance would probably lead to more balanced classes, and fewer needed adjustments to the power to weight formulas to maintain close competition.

 

I honestly think this would be a good step for NASA to try out with an up and coming class. If the idea worked, then NASA gains a tool to help balance problems in the current power to weight classes. If the idea does not, then it was just something they can show they tried and discarded. In either case, it could be used to put the "torque" argument to rest permanently.

 

Of course then the bench-grinding of the rule set would probably move on to frontal area, drag and surface area...

 

Actually, let me restate my position a bit. If NASA were to use a decent two data point system for comparing engine performance, I have a mothballed race car project that I'd bring back to life. I would be willing to stop work on next year's chump car, and go back finishing my ST project with plans to go racing with NASA. That's a real wallet vote for a two data point system.

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I don't see what the big deal is. Pretty straightforward if you ask me. I'll use my car as an example.

 

I knew I wanted to be TTE.

I knew I had +16 in non-power mods (shocks/springs/sways/subframe brace[for 25.4mm rear sway]/gears/LSD).

I knew I wanted a +10 compound 205 tire (+3 aggregate; +19 total).

I knew my engine swap made 140whp in the winter and 138 in the summer (8+ runs in each weather over a 2 year span).

I asked for 142 max whp and TTE base reclass. My weight is what it is. Where I fall in regards to PTW is what it is.

I just have to slap on some stickers and go beat the other guy. The end.

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It really is that simple! The Mustang would be somewhat slower than the F1 car though as it is ~2500lbs heavier and lacking a few thousand pounds of downforce...

Allan, you are incorrect in your statements. "But...but...but"....NO! They are false. Sorry, I'm not trying to be rude, but they are wrong.

If you want to argue that torque is what moves a car, then you have to be talking about torque at the drive wheels. The torque you see on a dyno plot is torque at the engine, despite being measure at the wheel on a chassis dyno. Torque is not a conserved property, the transmission multiplies it. Power, however, is conserved. Power is what determines the acceleration capability of a car. I really, really don't want to go into more detail as I'm not in the mood.

 

 

To a separate point, having a constant hp curve does help, but not as much as one would think. How much depends on the shape of the curve you started with, and on how close your gear ratios are. For example, if you ran a CVT transmission, then having constant power wouldn't help at all. If your car drops 4000 rpm between 3rd and 4th gear, it'll likely help a lot. I have spent much time modeling, tuning, and driving a constant power race car. I've had a band of 3000rpm of constant hp at one point. You're looking at 'maybe' half a second a lap for most E cars, and that's a stretch. Anyway, the point of this is that if you're loosing by 2 seconds, don't look at your competitors 'mad torque' dyno plot, and say it isn't fair and that's why he's winning. It's not the reason.

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It really is that simple! The Mustang would be somewhat slower than the F1 car though as it is ~2500lbs heavier and lacking a few thousand pounds of downforce...

Allan, you are incorrect in your statements. "But...but...but"....NO! They are false. Sorry, I'm not trying to be rude, but they are wrong.

If you want to argue that torque is what moves a car, then you have to be talking about torque at the drive wheels. The torque you see on a dyno plot is torque at the engine, despite being measure at the wheel on a chassis dyno. Torque is not a conserved property, the transmission multiplies it. Power, however, is conserved. Power is what determines the acceleration capability of a car. I really, really don't want to go into more detail as I'm not in the mood.

 

 

To a separate point, having a constant hp curve does help, but not as much as one would think. How much depends on the shape of the curve you started with, and on how close your gear ratios are. For example, if you ran a CVT transmission, then having constant power wouldn't help at all. If your car drops 4000 rpm between 3rd and 4th gear, it'll likely help a lot. I have spent much time modeling, tuning, and driving a constant power race car. I've had a band of 3000rpm of constant hp at one point. You're looking at 'maybe' half a second a lap for most E cars, and that's a stretch. Anyway, the point of this is that if you're loosing by 2 seconds, don't look at your competitors 'mad torque' dyno plot, and say it isn't fair and that's why he's winning. It's not the reason.

 

You are perfectly entitled to your opinion but we're going to have to agree to disagree. If you need to give me a dissertation regarding conserved properties, trans ratios, torque at crank, wheels or wherever to prove your point but I could explain mine with a horse pulling a weight up a well or a pedal bike (these simple formulas and principles extend beyond cars right?) then we're going to have to chalk it up to the phenomenon of asking 10 engineers a question and getting 10 different answers.

 

But I'll make it simple for you. Take your model and build yourself a car with a constant power curve (linearly decreasing torque) and one with constant torque (with same peak torque as your constant power car) over the RPM range used for the gearing and limit the RPM so that hp doesn't go above your constant power model (so you can't argue the constant torque car makes more horsepower) and let me know which one is faster.

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It really is that simple! The Mustang would be somewhat slower than the F1 car though as it is ~2500lbs heavier and lacking a few thousand pounds of downforce...

Allan, you are incorrect in your statements. "But...but...but"....NO! They are false. Sorry, I'm not trying to be rude, but they are wrong.

If you want to argue that torque is what moves a car, then you have to be talking about torque at the drive wheels. The torque you see on a dyno plot is torque at the engine, despite being measure at the wheel on a chassis dyno. Torque is not a conserved property, the transmission multiplies it. Power, however, is conserved. Power is what determines the acceleration capability of a car. I really, really don't want to go into more detail as I'm not in the mood.

 

 

To a separate point, having a constant hp curve does help, but not as much as one would think. How much depends on the shape of the curve you started with, and on how close your gear ratios are. For example, if you ran a CVT transmission, then having constant power wouldn't help at all. If your car drops 4000 rpm between 3rd and 4th gear, it'll likely help a lot. I have spent much time modeling, tuning, and driving a constant power race car. I've had a band of 3000rpm of constant hp at one point. You're looking at 'maybe' half a second a lap for most E cars, and that's a stretch. Anyway, the point of this is that if you're loosing by 2 seconds, don't look at your competitors 'mad torque' dyno plot, and say it isn't fair and that's why he's winning. It's not the reason.

 

You are perfectly entitled to your opinion but we're going to have to agree to disagree. If you need to give me a dissertation regarding conserved properties, trans ratios, torque at crank, wheels or wherever to prove your point but I could explain mine with a horse pulling a weight up a well or a pedal bike (these simple formulas and principles extend beyond cars right?) then we're going to have to chalk it up to the phenomenon of asking 10 engineers a question and getting 10 different answers.

 

But I'll make it simple for you. Take your model and build yourself a car with a constant power curve (linearly decreasing torque) and one with constant torque (with same peak torque as your constant power car) over the RPM range used for the gearing and limit the RPM so that hp doesn't go above your constant power model (so you can't argue the constant torque car makes more horsepower) and let me know which one is faster.

eq1 Power = Force*Speed (unit analysis ex, Newton*meter/s. Nm/s = watt, a unit of power)

eq2 Force = Mass*Acceleration (newtons 2nd law)

Substituting eq1 into eq2, we have: Power = Mass*Acceleration*Speed

Solving for Acceleration, Acceleration = Power/(Mass*Speed)

 

Acceleration = P/(m*V)

Notice how torque isn't one of the parameters in the equation?

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eq1 Power = Force*Speed (unit analysis ex, Newton*meter/s. Nm/s = watt, a unit of power)

eq2 Force = Mass*Acceleration (newtons 2nd law)

Substituting eq1 into eq2, we have: Power = Mass*Acceleration*Speed

Solving for Acceleration, Acceleration = Power/(Mass*Speed)

 

Acceleration = P/(m*V)

Notice how torque isn't one of the parameters in the equation?

 

Its right there in your first equation.

 

Torque = Nm

RPM = 1/s

 

Power = Nm/s = Torque*RPMs

 

We're aligned on the basics. As I mentioned in an earlier post...torque is the foundation for power with a linear relationship (Luke I am your father). Give in to the torque side!

 

On second thought I keep getting beat by a pesky S2000...maybe I just need one of those.

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T=r*F. Now it's part of the equation.

 

Yup T_wheel = r_tire*F_tire, and F_tire is proportional to acceleration (f=ma)

 

The key is that it's wheel torque though, not engine torque. Consider the following example:

 

2 identical mass vehicles, both traveling at 60mph, with a tire diameter of 24".

Car A is at 2000rpm, putting out 500 ft-lbf

Car B is at 8000rpm, putting out 150 ft-lbf (S2000 hehe)

 

In order for the cars to be at those engine speeds and at 60mph:

Car A has an overall gearing ratio of 2.38

Car B has an overall gearing ratio of 9.52

 

So, wheel torque is engine torque multiplied by overall gear ratio:

Car A has 1190 ft-lbf at the rear wheel

Car B has 1428 ft-lbf at the rear wheel

 

Which one do you think would accelerate faster?

 

I could also have calculated those wheel torques easier using power:

Car A engine power = 2000*500/5252 = 190.4 hp

Wheel speed = 840 rpm at 60mph

Car A wheel torque = 190.4hp*5252/840rpm = 1190 ft-lbf

 

The moral of the example is that the value of the engine torque has no bearing on acceleration, rather the value of the engine power dictates acceleration. When someone says "a torqier motor will accelerate faster" what they really mean is that "they accelerate faster because the engine makes a fatter power band". Higher average power.

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I'm getting into this one late, and probably not technical enough here to follow.

 

But if you're saying 'torque' has anything to do with acceleration on a racetrack, I can tell you I proved this theory wrong long ago.

 

HP & Gearing overcome Tq. regardless. It's why S2000's, Miata's and many other cars do so well in racing.

 

TQ can win in an Auto-X, and TQ can make a car easier to drive on a Road Course, but HP & Gearing will always win the race. (assuming all else being equal)

 

Dave

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T=r*F. Now it's part of the equation.

 

Yup T_wheel = r_tire*F_tire, and F_tire is proportional to acceleration (f=ma)

 

The key is that it's wheel torque though, not engine torque. Consider the following example:

 

2 identical mass vehicles, both traveling at 60mph, with a tire diameter of 24".

Car A is at 2000rpm, putting out 500 ft-lbf

Car B is at 8000rpm, putting out 150 ft-lbf (S2000 hehe)

 

In order for the cars to be at those engine speeds and at 60mph:

Car A has an overall gearing ratio of 2.38

Car B has an overall gearing ratio of 9.52

 

So, wheel torque is engine torque multiplied by overall gear ratio:

Car A has 1190 ft-lbf at the rear wheel

Car B has 1428 ft-lbf at the rear wheel

 

Which one do you think would accelerate faster?

 

I could also have calculated those wheel torques easier using power:

Car A engine power = 2000*500/5252 = 190.4 hp

Wheel speed = 840 rpm at 60mph

Car A wheel torque = 190.4hp*5252/840rpm = 1190 ft-lbf

 

The moral of the example is that the value of the engine torque has no bearing on acceleration, rather the value of the engine power dictates acceleration. When someone says "a torqier motor will accelerate faster" what they really mean is that "they accelerate faster because the engine makes a fatter power band". Higher average power.

 

If I understand you correctly you are saying that between two otherwise identical cars that have two different engines, one with 500ftlb at low RPM and one with 150ftlb at high RPM, the 150ftlb car will be faster? You can do whatever you want with the gearing but I don't think we saw or will ever see a Z06 with an S2K motor swap winning in GTLM.

 

Think about the last statement you made. How do you explain the sudden rush of acceleration an old school turbo car gives you when it comes on boost? Look at any dyno plot like the one Rob S posted earlier (at the wheels or crank doesn't matter)...that is not power kicking in, its torque. For LP turbos why does the acceleration rush die off as you get closer to redline? After all the more you rev the more power you make right?...its because the slug of torque that provides acceleration happened in the mid range RPMs and dies off in higher RPMs. How do turbo diesels have faster in gear acceleration times than petrol powered cars with much higher horsepower? How does an electric motor exhibit max acceleration from essentially zero RPMs when its making close to zero horsepower? Have you simulated those engines yet from my earlier post?

 

If you have more formulas to explain away the real world proof of the above then there is not much else I can say other than you should look into the KISS principle. Its the one that engineers struggle with the most.

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People are getting too focused on the function of torque. Hp is what is important but not just peak whp (as currently written in the PT/ST/TT rules). This the key point. Area under the whp curve is also important. An engine that makes 300whp from 4-7Krpm will have a larger area under the whp curve and be faster than an engine with a relatively constant slope up to 300whp at 7Krpm. Also the engine that makes 300whp from 4-7Krpm will have higher peak torque. This is the reason GTS and AI have chosen to include peak torque in the "Power" calculation for classing. It is a method to control area under the whp curve. Differences in FD gearing, trans gearing, tire diameter, engine redline, etc make it difficult to write a specific rule about area under the curve. Wtorque however is measureable and discourages power plateau engine builds/tuning. Some engine types cannot even get to a power plateau hp curve no matter what. Not a perfect solution but it is a method that uses a quantifiable attribute, wtorque.

 

Jason - to your comment about the relevance of a power plateau whp curve on a PT/TTE car. The delta will vary based on the area under the curve. The larger the rpm range that the engine makes the same whp, the larger the area under the whp curve. Therefore the larger the impact on lap times. On a NA PT/TTE engine, this will not be as significant as a turbo or big displacement engine making more power in a higher class. Also, I agree a 0.5sec decrease won't matter if you are getting beat by 2secs in TT but it will make a notable difference over an entire PT race.

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People are getting too focused on the function of torque. Hp is what is important but not just peak whp (as currently written in the PT/ST/TT rules). This the key point. Area under the whp curve is also important. An engine that makes 300whp from 4-7Krpm will have a larger area under the whp curve and be faster than an engine with a relatively constant slope up to 300whp at 7Krpm. Also the engine that makes 300whp from 4-7Krpm will have higher peak torque. This is the reason GTS and AI have chosen to include peak torque in the "Power" calculation for classing. It is a method to control area under the whp curve. Differences in FD gearing, trans gearing, tire diameter, engine redline, etc make it difficult to write a specific rule about area under the curve. Wtorque however is measureable and discourages power plateau engine builds/tuning. Some engine types cannot even get to a power plateau hp curve no matter what. Not a perfect solution but it is a method that uses a quantifiable attribute, wtorque.

 

Jason - to your comment about the relevance of a power plateau whp curve on a PT/TTE car. The delta will vary based on the area under the curve. The larger the rpm range that the engine makes the same whp, the larger the area under the whp curve. Therefore the larger the impact on lap times. On a NA PT/TTE engine, this will not be as significant as a turbo or big displacement engine making more power in a higher class. Also, I agree a 0.5sec decrease won't matter if you are getting beat by 2secs in TT but it will make a notable difference over an entire PT race.

Rob, you had me curious, so I did some simulation:

 

For a 'normal' shaped miata power curve, a miata with a CVT running at the peak power point of the first miata is only a half second quicker at Mid Ohio.

 

Furthermore, I was curious if the delta became larger with faster cars, say a TTB turbo car. I used the dyno plot you posted on the first page of this thread for the simulation at Mid Ohio, slightly modified as per the excel chart below. Lap time improvement for the really torqy power curve is only 0.3 seconds faster! Why only 0.3? Because with the 6-speed transmission in that car, the gear ratios are such that the car spends very little time below 5000rpm. The blue dyno curve doesn't make all that much less power than the red curve above 5000rpm. Thus, very little difference in lap time. Interesting! Basically, who gives a crap how much more torque/power/whatever the engine makes down at 4000rpm, because you're never there....

 

2wp8ebr.png

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Except if you build the motor to make peak power from 4000 to 8000 you can then save a bunch of time by eliminating the need to shift... Did you take that into account in your simulations?

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Except if you build the motor to make peak power from 4000 to 8000 you can then save a bunch of time by eliminating the need to shift... Did you take that into account in your simulations?

That's essentially how and why I built/geared my transmission the way I did.

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Furthermore, I was curious if the delta became larger with faster cars, say a TTB turbo car. I used the dyno plot you posted on the first page of this thread for the simulation at Mid Ohio, slightly modified as per the excel chart below. Lap time improvement for the really torqy power curve is only 0.3 seconds faster! Why only 0.3? Because with the 6-speed transmission in that car, the gear ratios are such that the car spends very little time below 5000rpm. The blue dyno curve doesn't make all that much less power than the red curve above 5000rpm. Thus, very little difference in lap time. Interesting! Basically, who gives a crap how much more torque/power/whatever the engine makes down at 4000rpm, because you're never there....

 

2wp8ebr.png

 

 

Now run the simulation on the torquey car keeping the revs between 3500 and 5500 rpm (highest average torque). If it makes torque like a diesel you need to drive it like one. It will be even faster.

 

To another posters comment about shifting...shifting takes time away from forward progress and more frequent shifting means a need for more forward gears to make high top speeds possible...and that is the real world crux of engine design to achieve desired hp/tq plots that rev out well beyond max torque values and applying appropriate gearing. This is why analyzing area under the hp/tq curves when tuning an engine is so important and also a major reason why you really don't see turbo diesels (or engines with mad low end torque that don't rev out) in auto racing. But now with dual clutch technology that basically makes shifting a non event and a very high number of forward gears available in transmission sets we are sort of at the tipping point for the everyman (not just LMP1 factory teams) to start campaigning TDIs.

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^^^ Exactly. You would change your shift points and short shift. If controlling area under the curve didn't matter than GTS and AI wouldn't include torque in the "Power" calculation.

 

Everyone needs a restrictor.........problem solved

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There is a bit of gain to be had by skipping the need to shift since you have so many RPM of constant power. I have measured this both analytically and empirically, and it's good for an average of ~0.05 seconds per skipped shift, depending where on the straight the shift would have occurred. In my car, there'd be about about 3 skipped shifts at Mid-Ohio, so take off another 0.15 seconds. Pretty small gains. I actually don't rev my motor out unless I really, really need to. The lap time gain isn't worth the extra wear and tear on the motor.

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Now run the simulation on the torquey car keeping the revs between 3500 and 5500 rpm (highest average torque). If it makes torque like a diesel you need to drive it like one. It will be even faster.

 

To another posters comment about shifting...shifting takes time away from forward progress and more frequent shifting means a need for more forward gears to make high top speeds possible...and that is the real world crux of engine design to achieve desired hp/tq plots that rev out well beyond max torque values and applying appropriate gearing. This is why analyzing area under the hp/tq curves when tuning an engine is so important and also a major reason why you really don't see turbo diesels (or engines with mad low end torque that don't rev out) in auto racing. But now with dual clutch technology that basically makes shifting a non event and a very high number of forward gears available in transmission sets we are sort of at the tipping point for the everyman (not just LMP1 factory teams) to start campaigning TDIs.

Allen, sorry, I'm done catering to you, spending time running simulations that I already know the answer to, which you will ignore the results of anyway. I'm all for debates such as those in the rules thread, were discussion revolves around peoples opinions - those are interesting, and everyone's opinion is worth something. Unfortunately, physics, math, science, and engineering are based on facts. There are few opinions, just how it is. Operating further down in the rpm band where torque is higher, but power lower will result in a slower lap time. Period. I am sorry that I have been unable to teach you this. Feel free to continue believing what you wish.

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Allen, sorry, I'm done catering to you, spending time running simulations that I already know the answer to, which you will ignore the results of anyway. I'm all for debates such as those in the rules thread, were discussion revolves around peoples opinions - those are interesting, and everyone's opinion is worth something. Unfortunately, physics, math, science, and engineering are based on facts. There are few opinions, just how it is. Operating further down in the rpm band where torque is higher, but power lower will result in a slower lap time. Period. I am sorry that I have been unable to teach you this. Feel free to continue believing what you wish.

 

Again...agree to disagree. I was trying to get my point across with real world examples that are easy to relate to and not get bogged down in equations. I have however simulated using many different engine types what you apparently already know the answer to but if you give it a try you may be surprised.

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