Revisiting Torque

[Knestis]

The ITAC continues to noodle over how to equitably consider what we all seem to think of as "torque" in our specification math, and I have a question: Without getting bogged down in math, can I sample your first principles on the issue...?

Some questions for consideration...

** When you say "a Mustang has a lot of torque" or "Hondas don't have any torque," what do you mean? Drill into your own language and try to be as explicit as possible about what you are thinking when you say that.

** How would you compare these four cars, in terms of their "torque" relative to one another, AND how would you expect them to compete against one another (there no "right" answers, so far as I know)...

Car 1 - 150 hp, 150 lb-ft of torque

Car 2 - 110 hp, 190 lb-ft of torque

Car 3 - 190 hp, 110 lb-ft of torque

Car 4 - 170 hp, 170 lb-ft of torque

** If they were all otherwise the same, which of those cars would you choose to race against the others? Why?

** (The first hard one) - How is it that you think "torque" makes a difference in competitiveness? If we all have different conceptions of the mechanism by which it matters, we'll probably never get anything like a consensus answer re: how to manage this variable - or variables.

** (The second hard one) - The ITAC can really only control a very few factors, in terms of specifications we can set, the key one of course being weight. How do the factors that we MIGHT control bear on torque, to your way of thinking? Is it safe to say for example that more weight mitigates against a "torque" advantage?

** Finally (and this is kind of an easy one, since it's about philosophies) - Do you even think we should try to accommodate torque in the processes we use? One philosophy says, "We don't try to control a lot of the variables that make a difference to competitiveness, and since we don't have a very good grasp on torque, we should ignore it." Another would suggest that "mathematical models are good enough that a digital car on a digital track can reasonably approximate the real thing, so we should try to take any and all variables that we can into consideration, to make the cars as equal as possible." Where are you on these issues?

THANKS!

K

PS to ITAC members. I'd be interested to hear from the membership before we dive into the conversation ourselves.

[Ed Funk]

I'd choose car # 4, because it's numbers are almost the same as my "C" car!:rolleyes:
Seriously, it has the best of both worlds, should come out of the corners hard and wind tighter than the low hp high torque example.

Question 1, sure take torque into consideration, but it's going to make the "napkin" math more "interesting". Add weight, but then take it off for bad brakes? Where does it stop?

Maybe it wasn't politically correct back in the beginning when we raced at our manufacturers "curb" weight, but it did let those that could read specs pick the right car. The old "we'll give you a place to race, but your car may not be competitive" has been replaced by "no car left behind".

Just my opinion, yours may be wrong!:D

[chuck baader]

I would prefer a similar hp/tq because the curves will be flatter making a wider power band and easier to drive fast. However, you left the most important variable out of the equation....RPM. Torque only works at the wheels. Applied torque is what moves the car. The 190/110 example, if it turns 9k, will easily out run the 170/170 that turns 7k beacuse it can run a much shorter gear.

I don't think tq is a consideration above what is currently given based on the parity of the top running cars in SEDIV. (clevat: that would be a most biased comment although I am researching the rpm route rather than torque.) Of more concern to me is the ability to generate grip, and the fully independent cars seem to have a better handle on that than the strut cars. As more of the fully independent cars are classified/built, consideration should be given to the older strut cars. Jes Sayn Chuck

[Andy Bettencourt]

Don't we need to know the applicable minimum weights before we can make a decision?

[Knestis]

Assume that the minimum weights are the same for the purposes of this discussion. Since we're talking about figuring out how to consider torque (or if we should), don't presume that given whatever the final process might be, the result would be that they are different.

We have WAY too many of these conversations that get all tangled up because we're all talking about different things. All I want to understand from this is how people understand this torque thing, and generally how (or if) we should tackle it.

K

[pfcs]

Looking at torque w/o rpm is senseless.
Engines that develop torque at much lower rpm than their peak horsepower peak are potent because they neccessarily develop good torque across a relatively large (rpm) band. This implies good airflow design and somewhat agressive cam timing or variable cam timing. The allowed IT prep and their pre-existing advantages will make them competetive.
Engines that develop torque at low speeds and rpm at conservative speeds, (often more torque than hp), imply airflow restricted engines. Often they are on the large end of the displacement spectrum for their #of cyls. Their response to IT tunes will depend on how much that restriction responds to IT prep. If the airflow restriction is due to conservative cam timing/lift and/or restricitve cylinder head design, then they likely won't respond as well to IT prep-and they will be toads.
V8s that have well seperated torque and hp peaks-look out! phil

[rsportvolvo]

Kirk,

Have you considered running the cars through a simulator? Bosch LapSim has a free version that you can do this on.

http://www.bosch-motorsport.de/content/language2/html/3589.htm#a_D9200D2E6B014D0792809A16EA4A4C14

This is a good way to compare the cars.

I assume for this comparison all other aspects of the car stays the same, i.e. same car with different engines. In that case the gearing options are eliminated.

I think it's track dependent and more specifically turn dependent. I prefer an engine with more torque if there are elevation changes (VIR). On a flat (Roebling Road) track I'd settle for less torque.

[ddewhurst]

K, I applaud your thought process relative to being a ITAC member. :023: As stated all else being EQUAL including were road racing, torque gets you there & HP keeps you there. Overall car number 4 please.:eclipsee_steering:

With all that ^ aside is this IT class slipping towards, well you know where................

[Knestis]

... With all that ^ aside is this IT class slipping towards, well you know where................

Actually, I don't...

We already consider "torque" when cars are specified - and have for ages, formally or otherwise.

We're just trying to work through some "should we and if so, how?" questions.

K

[tnord]

if all the weights are the same, and we take RPM out of the equation.....

car #1 isn't even in the running.
car #2 is quickly dismissed because that sounds like something that will only do well at very specific tracks....if anywhere
car #3 is only slightly favorable to car #2. but everytime i ask myself "why?" i end up with an answer that is directly related to RPM.
car #4 is the obvious choice to me. it's the only one that you KNOW will have a solid powerplant for racing.

to me there is no consistent way that torque "matters." climbing up the hill at Road America it matters a lot. but a fast, flowing track with high speed corners it matters very little. i think it matters less in lighter cars than it does in heavy cars (which kind of answers the third question). the more rubber you can put to the pavement via advantage in drive-wheel suspension layout, wheel size, and drive layout, the bigger of an advantage it is.

i don't think there is a consistent, repeatable way to treat ALL cars in the ITCS equally for torque. peak HP can be used because it's always measured within the usable RPM range. this is not true for torque. i don't know if i think it should be 100% ignored, as some cars are so far "out there" one way or another that they warrant some sort of consideration, but the means in which that is done doesn't seem to be the goal here.

[Eagle7]

I've never owned a muscle car, and only ever raced a rotary, so I probably know squat, but... I'm pretty sure that the only thing that matters is the size and shape of the HP curve in the RPM band of interest - in simple terms "the area under the curve". On my rotary, the torque keeps climbing all the way up to 6200 RPM, so the HP curve is very steep. Drop your RPMs and you lose much of your HP - the peak is good, but the area under the curve sucks. On engines where torque exceeds HP the torque curve is falling with RPM, leading to a more flat HP curve. This maximizes the area under the HP curve. So if you class based on peak HP, the flat HP curve engine has an advantage.

BTW, if someone has some dyno plots confirming or refuting my premise I'd love to see them.

[Andy Bettencourt]

Some have said that because final drives are free, torque is a factor we should not try and manage because you can make up for less torque with shorter gearing and take advantage of torque with taller gearing. It's about building around your platform.

So the question for me is simple: does the open final drive rule mitigate these strengths and weaknesses enough to not want to monkey with it?

[dickita15]

Andy, while the final drive helps I really think the low torque cars are hurt more by lousy tranny ratios. I was looking at the gear spacing on the newly classed mustangs and comparing them to my Rx7 and thinking it is a good thing the stang has high torque and probably a wide power band.
Final drive would make up for a lack of torque if we had 6 speed hewlans.

[Tak]

The way to look at torque properly is to graph wheel torque vs miles per hour for all gears, then take the area under the combined curve from say 25mph to 125mph...(appropriate race speeds for car and tracks)
This is how one chooses the correct gear shift points, tire sizes, and final drive ratio. Once you have a torque curve, it is realatively easy to do in Excel. Even easier if you have the data output from a Dyno. Anything else is just guessing!

[Knestis]

I kicked this off without benefit of any real world context but there ARE some things to be considered.

Such as, we are stuck with limited data so are trying to find some proxy or estimate for actual measures of "useful torque," that would require the kinds of data Tak describes. We know that "anything else is just guessing" but don't have any choice but to do so.

Ultimately, the questions are DO WE guess and, if so, HOW...? **

K

** By "guess" I mean "informed guess," not POOMA. We're trying to get away from the latter. EDIT - and we're talking about informed guesses to establish repeatable practices/processes for all cars, rather than informed guesses in isolation for each car we look at.

[GKR_17]

First off, for all who have forgotten, horsepower is just torque multiplied by RPM (with a linear factor to make the units work). A single torque number has very little value. As several others have pointed out, the area under the power curve is actually what matters. In general, a higher torque motor will have a flatter power curve, but that is far from the whole story. Higher reving motors get the same power to the ground from less torque. The transmission ratios are just as important as the power curve.

The important factor here is how much power does the engine have after shifting gears? Any math that doesn't account for the power curve and the transmission ratios is never going to get the job done. Since it is unrealistic to get the power curve for every car, I think it should be ignored. Sure that's not perfect, but using one torque number is no better than what we have now, and is more complicated. I would rather have the rules more stable so we know what to expect year after year - something that makes IT far better than prod, most of us would agree right?

I was glad to see the V-8's added to ITR, but I think the torque adder was excessive.

[dickita15]

So the information that is available to the ITAC is: peak hp at a specific rpm, peak torque at a specific rpm and tranny ratios. Can any constructive formula be made with this data?

[JeffYoung]

To me only peak hp at a specific rpm means anything.

I've personally reached the conclusion, barring a stroke of lightning, that we can't do anything formulaic with torque.

[Tak]

A crude rule of thumb has always been to run the engine between the torque peak and the HP peak.
Since you have HP peak @ rpm, you have the torque at that rpm (torque = HP*5250/rpm).
I suspect a linear interpoloation between the two points on the torque curve will be reasonable.
You have the gear ratios, pick a popular tire size, and reasonable final drive (e.g. 4.10 for a torqy motor, 4.60 for a medium torque motor, 5.10 for a low torque high revving motor). I think that is enough information to draw the torque vs mph curve for all the gears.
That is better than guessing in my opinion.
The more I think about it, I like it.
Use excel to calculate the wheel torque value for each mph from 25 to 125. Summing the torque value at each mph is simple way to get the area under the curve. A conditional function (if/then) will be needed to pick the higher of the two numbers when curves overlap. Another conditional could linearly extend the torque curve past the HP peak when curves do not overlap.
Such a model might even help balance gearing differences between cars...

Tak

[dickita15]

To me only peak hp at a specific rpm means anything.

I've personally reached the conclusion, barring a stroke of lightning, that we can't do anything formulaic with torque.

Jeff I understand you do not think this is workable but I applaud Kirk’s effort to explore in this conversation whether it is possible both technically and with political consensus to account for torque in a les subjective manner. It is very possible that in the end your position that this is too hard will be proven right but we will not know unless we fully vet the options.

[dickita15]

A crude rule of thumb has always been to run the engine between the torque peak and the HP peak.
Since you have HP peak @ rpm, you have the torque at that rpm (torque = HP*5250/rpm).
I suspect a linear interpoloation between the two points on the torque curve will be reasonable.
You have the gear ratios, pick a popular tire size, and reasonable final drive (e.g. 4.10 for a torqy motor, 4.60 for a medium torque motor, 5.10 for a low torque high revving motor). I think that is enough information to draw the torque vs mph curve for all the gears.
That is better than guessing in my opinion.
The more I think about it, I like it.
Use excel to calculate the wheel torque value for each mph from 25 to 125. Summing the torque value at each mph is simple way to get the area under the curve. A conditional function (if/then) will be needed to pick the higher of the two numbers when curves overlap. Another conditional could linearly extend the torque curve past the HP peak when curves do not overlap.
Such a model might even help balance gearing differences between cars...

Tak

Tak, that is the way I think it works as well but I admit limited real world knowledge.

[Knestis]

I've been playing with something that tries to get to that same place but yet another challenge looms. We'd have to figure out what weights to associate with the resulting "torque number." Knowing something is only half the battle: The ITAC has to turn that into a factor it can specify that will adjust for the differences we're trying to control for - weight.

I've gotten dinged by some who've seen it because we have to make assumptions to set how the torque input variable influences the weight adder/subtractor. I KNOW that's necessary, and am willing to trade a couple of assumptions right up front that we then stick with, for a new set of assumptions with every car classified.

Any ideas on this piece of the puzzle, from a theoretical perspective?

K

[Gary L]

A crude rule of thumb has always been to run the engine between the torque peak and the HP peak.
Since you have HP peak @ rpm, you have the torque at that rpm (torque = HP*5250/rpm).

Hold on a minute. We do not have the HP peak @ rpm, nor the torque at that rpm, for the engines actually being raced... we have the data for stock engines. I submit there is enough difference between the two (using headers, ECU tuning, etc.), to make this just another WAG. Without the as-raced data for every engine out there, we've simply replaced a guess with another, slightly more sophisticated, guess.

I tend to agree with those who think the way to handle this is to look more closely at gearbox ratios, specifically the split percentages between the reasonably useable gears. At least that's something for which we have hard data, and unlike HP/torque numbers, it's not a moving target.

[ddewhurst]

****We'd have to figure out what weights to associate with the resulting "torque number." Knowing something is only half the battle:

Any ideas on this piece of the puzzle, from a theoretical perspective?***

Use the model our production car big brothers use.:unsure::lol::happy204:

[Andy Bettencourt]

Without the as-raced data for every engine out there, we've simply replaced a guess with another, slightly more sophisticated, guess.



This is the main question. If you think 'sophisticated' is also 'a little more accurate', then it deserves consideration. If not, then no.

3 choices in my mind. Eliminate torque from the equaion all together, keep using subjective chunks or create a formula that removes subjectivity and applies weight in small amounts OR chunks once thresh-holds have been met.

[Knestis]

This is the main question. If you think 'sophisticated' is also 'a little more accurate', then it deserves consideration. If not, then no.

3 choices in my mind. Eliminate torque from the equaion all together, keep using subjective chunks or create a formula that removes subjectivity and applies weight in small amounts OR chunks once thresh-holds have been met.

That's actually four choices but it gets to the nut of the question...

Opponents to formulaic solutions (3 and 4) are correct that we'd still have to apply some assumptions up front - no doubt.

As is often the case, Andy's done a good job of getting past the pedantic crap. :happy204:

K

[JeffYoung]

Yes, I think that is something we can agree on -- those do appear to be the 4 choices we have.

David, while I hesitate to ask, what do the prod guys use to deal with torque?

[Andy Bettencourt]

Yes, I think that is something we can agree on -- those do appear to be the 4 choices we have.

David, while I hesitate to ask, what do the prod guys use to deal with torque?

Data acquisition from HPT! :)

[dickita15]

If reasonable assumptions can be made I would prefer they be made up front. This allows consistency and repeatability and may I say it, eventually total transparency.

[ddewhurst]

***David, while I hesitate to ask, what do the prod guys use to deal with torque?***

Jeff, I don't have a clue. I would guess that if one of the ITAC were to talk with Jesse Prather who is either PAC or CRB??? he would offer their latest version of what they use. It may be good for the IT class or may not be good for the it class.

It is acknowledged on the Prod site the positives the ITAC has been doing. Maybe they still throw the darts towards their long time rumored formula.

[ekim952522000]

If reasonable assumptions can be made I would prefer they be made up front. This allows consistency and repeatability and may I say it, eventually total transparency.

I agree

[Tak]

Many years ago, I got to play with some fairly sophisticated lap simulation software. We broke car performance into 3 categories: weight, power, and grip.
Grip was, by far, the most important factor in a fast lap time. carrying an extra mph or 2 onto each straight is a huge advantage...a 5% increase in grip translated to more than a 5% increase in lap time.
Power was the second most imortant, but less than linear. A 5% increase in power decreased lap times by 1-2% if memory serves.
Weight was the least important factor. a 5% change in weight affected lap times by <1 %.
Anecdotally we have seen this several times in professional racing. Remember the Audi's in Trans Am? Great grip (4wd IRS cars competing against solid axle cars). It took something like 400lbs and inlet restrictors to even up the competition. Look at F1 this year. Brawn has more downforce (more grip) than the others. Renault got more power over the winter, but that hasn't translated to pace...
Sooo, what's the point of this story? Weight adjustments are the least effective way to level the playing field; and the initial class placement of a car is THE most important thing the comp board can do. To that end I applaud the effort to evaluate the power curve, but acknowledge that the assumption of how much power is gained during race prep is a big assumption. Also note that the assumptions around handling gains are even more important than power assumptions or models. But tha't a different thread...
In the end, I think the comp board should look at power curve--and I think they should spend more energy considering handling gains.

Tak

[chuck baader]

Tak, the quote below is from my first post on this thread. I agree with you 100%. Chuck


"I don't think tq is a consideration above what is currently given based on the parity of the top running cars in SEDIV. (clevat: that would be a most biased comment although I am researching the rpm route rather than torque.) Of more concern to me is the ability to generate grip, and the fully independent cars seem to have a better handle on that than the strut cars. As more of the fully independent cars are classified/built, consideration should be given to the older strut cars. Jes Sayn Chuck"

[TomL]

Kirk, thank you for posting this question. I continue to be baffled by the importance a lot of people seem to give to the torque number. The rate of acceleration of a vehicle at any given speed is strictly a function of the available horsepower at that speed. So, in the absence of any other information, any choice other car other than number 3 (the 190 hp version) is going to lose.

I realize that the breadth of the power band is also important and if the 170 hp car in your example (#4) had a very broad power band and the 190 hpcar had a narrow band, #4 might be better. But if all we have is the peak power and peak torque numbers, then I have to go with the higher horsepower.

There seems to be a belief that high torque numbers = broad power band, but I haven't seen any data that supports that on a consistent basis. For example, looking at Ron Earp's two cars in his related post, the power band for the low torque (160 lbft) car #2 is just as broad as for the 197 lbft car #1. While some commenters thought the high torque car would have great acceleration, I'm sure the two would be nearly identical (similar power and power band width, similar weight). What a lot of people seem to forget is that if one car has 160 hp and low torque while another has 160 hp and high torque, the latter is going to produce its torque at lower RPMs. And when you give the low torque car the shorter final drive that its higher rev range requires, the "low torque" car will have just as much torque available at the wheels (again assuming identical power band - and transmission gearing) as the "high torque" car. In fact, if you do the math, you get back to my original point - all that matters is horsepower. Just remember the old adage - "You can multiply torque. You can't multiply horsepower."

Bottom line for me - there is absolutely no basis for making any adjustments based on torque. (And I drive an RX7, so this is hardly self interest!) I guess you could make adjustments based on power band width, but I doubt the information is readily available for most cars. And it would be a "power band width" adjuster, not a "torque" adjuster anyway.

[GKR_17]

The rate of acceleration of a vehicle at any given speed is strictly a function of the available horsepower at that speed.

Absolutely correct. And a better transmission keeps the motor nearer to the sweet spot in the power curve.

[wrcRS]

Absolutely correct. And a better transmission keeps the motor nearer to the sweet spot in the power curve.

I too, whole heartedly agree with the two posts above.

If there was a popcorn eating smiley I would use it right now.

[Dyno]

There seems to be a belief that high torque numbers = broad power band, but I haven't seen any data that supports that on a consistent basis.


Remember the old fuel-injected CanAm cars? The intake "trumpets" were two or three different lengths. This was done to spread the torque peak over a wider operating range. The peak would have been higher (but narrower) if all runners were the same length.

http://www.ritzsite.demon.nl/Sportscars/Pics/Lola_T163_1969_side.jpg

Gawd, those were beautiful cars.

Physics says that best results come from the greatest area under the horsepower curve. Sometimes this can be best accomplished by broadening the torque peak even if the max torque value comes down a little.

Over-the-road diesel truck engines have very high torque levels (around 1500 ft-lbs) but very narrow speed ranges (max rpm of about 2000 rpm). This is why they require 13-speed gearboxes. If trucks were limited to fewer gears, like our cars are, the engine designers would create broad speed range engines to match -- likely with lower peak torque values.

[TomL]

I don't disagree that, for a given engine, the power band is usually narrower as the horsepower goes up (and the torque band is narrower but the peak higher). But my point was that, given the wide variety of cars in IT (lousy-breathing and/or low-revving old designs vs. modern 4- valves, carb vs. FI, varying displacements, etc.) I haven't seen much evidence that you can make that assumption for any given pair of of ITA cars, say. I'm willing to be proven wrong, but I haven't seen it.

[JoshS]

Full disclosure: I'm an ITAC member, and I think I made a mistake.

I believed conventional wisdom. I believed that torque monster cars had some sort of big advantage on the track. I thought high-revving 4-cylinders with weak torque had a disadvantage. I didn't fully understand the math behind it, but I believed all of the conventional wisdom, and my gut. I've been doing this a long time.

So about a month ago, I decided it was high time that I figured out WHY the big torque cars had that advantage. And I wanted to try to quantify the effect, and I wanted to try to find a way to predict the effect based on info that the ITAC has at hand.

But when I went through the analysis, I disproved my theory. And then I did what any good internet geek does: I blogged about it.
http://www.godoggoracing.org/2009/05/07/horsepower-torque

Basically, I concluded that the shape of the HP curve near its peak is what's important, and that there's no good correlation between the torque monster cars and a good shape. In fact, I concluded the opposite, that the high-revving so-called gutless cars have a better shape than the big V8s.

Ironically, the next day, Tom Lyttle posted here that torque isn't important and then a bunch of people agreed with him. Where were you guys a couple of months ago? :-) Well, abyway, now I agree too. I don't think that the IT process should use any weight adders at all for torque, positive or negative.

Please read the blog entry and weigh in.

[Z3_GoCar]

To take Tom's point further, I don't think you can a-priori predict how any particular motor will respond to an IT build in terms of HP, but torque gain or loss is an even bigger SWAG.

[TomL]

Josh -

This torque misunderstanding has bugged me for a long time. I had been thinking that, over the winter dead time, I would start a flame war by publishing a rant about this whole topic (You need to keep everybody excited when you can't race!) If it would have helped you, I'm sorry I didn't get around to it.:D

Your analysis using the only two numbers available - HP at peak and torque (and indirectly HP) at peak sort of confirms my point (wish I'd thought of that!) I would quibble with a couple of things. You say that the transmission ratio gaps are about the same for all cars, so that the number of shifts is about the same for everyone. But then you turn around and say that the high reving (shorter-geared) car increases its revs faster and thus has to shift more. Obviously, it can't be both. The first statement is the correct one. The reason the second statement is erroneous points to the main shortcoming in you analysis. The short-geared/high reving car increases engine speed faster, but not car speed. If one car shifts at 6000 with a 3.40 final drive and another shifts at 9000rpm car using a 5.10 final drive, they'll be shifting at exactly the same car speed (trans gears and tires diameter being equal).

Similarly, when you look at the power band, you need to consider the effective rev range not as a specific number of rpm (3000 in your example), but as a percentage of your maximum rpm. In other words, because of the differences in revs at which cars operate, the high reving car needs to have a broader hp range, at least as expressed in rpm. As in the example above, if your 9000 rpm car needs a 3000 rpm rev band, the 6000 rpm car needs only a 2000 rev band because of the longer gearing.

Since your analysis is based on absolute rpm instead of a percentage of the peak, it makes the low reving cars look a little worst than they actually are. A further and related problem is that the low reving cars tend to have a greater rpm variation between hp peak and torque peak, so your slope (hp/ 500rpm) is based on a broader range of absolute rpm than for the high reving cars. And if you again account for rpm as a percentage of peak this problem is exacerbated. Bottom line - the way your analysis is done makes the low rev cars look considerably worse than they actually are. If you could account for both these factors, I suspect you'd find that the power bands are fairly similar for all the cars.

That gets me back again to my original point - horsepower is what counts. I've heard all those torque mottos before. Just remember mine - "You can multiply torque. You can't multiply horsepower." (Not that it's original with me - I think it's Paul van Valkenburgh).

[JoshS]

A further and related problem is that the low reving cars tend to have a greater rpm variation between hp peak and torque peak, so your slope (hp/ 500rpm) is based on a broader range of absolute rpm than for the high reving cars.

Thanks Tom! Glad we agree on the conclusion, even if I missed a couple of points. I need to really digest the rest of what you said, but let me just quickly address this point: it's not true, at least not for the sample of cars I chose for my analysis. Here are the rev difference between the peaks for those cars:

Integra Type R: 700
SN95 Mustang: 800
Celica GT-S: 800
S2000: 800
Fox Mustang: 1000
Camaro 305: 1200
Prelude VTEC: 1500
300ZX: 1600
Z3 2.8: 2000
968: 2100
Mustang V6: 2500
RX-8: 3000

So we have both high-and-low revving cars at the top of the list (ITR & Mustang), and high- and low-revving cars at the bottom (Mustang V6, RX-8).

No clear correlation.

[JoshS]

Similarly, when you look at the power band, you need to consider the effective rev range not as a specific number of rpm (3000 in your example), but as a percentage of your maximum rpm. In other words, because of the differences in revs at which cars operate, the high reving car needs to have a broader hp range, at least as expressed in rpm. As in the example above, if your 9000 rpm car needs a 3000 rpm rev band, the 6000 rpm car needs only a 2000 rev band because of the longer gearing.

Good point. I replaced "500" with the revs at the HP peak, and things do get a lot more equal. I'm actually glad about that, since my previous analysis had actually inverted my expected results. Now it's really just showing that it makes no difference at all.

When I get a moment I'll update my dissertation with that point.

[GKR_17]

Where were you guys a couple of months ago? :-) .
Uh... I did... several times. Here just one: July 30, 2008
Maybe I should stop posting this because no one seems to listen...

A single torque value is not a good indication of the potential of an engine. The power transmitted to the ground at that instantaneous engine speed is what makes the car go. Horsepower is basically torque multiplied by RPM. Many of the cars with low torque are also turning higher revs, so they're still putting good power to the pavement.

What is really important is the full dyno plot combined with the transmission ratios,

[pfcs]

pfcs (http://www.improvedtouring.com/forums/member.php?u=9090) Online!
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My physics courses were not yesterday, I don't have all the formula's memorized but the basics of what I am telling you are true. Fact not opinion... please do some research before you try to tell me I am wrong again.
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I took physics a long time ago, but force=mass x accelleration (F=MA) still applies.
Or A= F/M. The greater the force, the greater the acceleration. In any gear, the force is maximized at the torque peak of the engine. If you shift up, the gearing multiplies the torque out of the trans, but the engine torque is lower, and the derived torque out of the transmission is less than the torque at the same output rpm (vehicle velocity). You can make it clear by thinking what happens to rear wheel torque when you shift to a lower gear-look at the torque curve and do the math: you're running a fixed ratio with a variable torque as you move along the torque curve, where will the torque at the wheels be max? At the engine torque peak. I know it's somewhat counter-intuitive, but it's the hard truth and simple physics. This does not mean we want to lug the engine, just that when you're at peak torque in any gear, the vehicle will have it's max accelleration at that velocity-if you're revving a gear past the point where the next gear would bring you to the torque peak, you're leaving accelleration on the table.
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phil hunt

Above from 2007

TomL (http://www.improvedtouring.com/forums/member.php?u=9345) Offline
Junior Member
Join Date: Jul 2004
Location: Decatur , GA, USA
Posts: 20


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Kirk, thank you for posting this question. I continue to be baffled by the importance a lot of people seem to give to the torque number. The rate of acceleration of a vehicle at any given speed is strictly a function of the available horsepower at that speed. So, in the absence of any other information, any choice other car other than number 3 (the 190 hp version) is going to lose.

Tom-its strictly a function of available (crankshaft) torque at that rpm. Period. However, horsepower is a better indicator of performance. This discussion is attempting to discern the possibility that looking at the shape of (area under the curve) the torque curve is germane to predicting the relative competetiveness of a given vehicle.

[TomL]

You're right, Josh. As soon as I posted the comment about HP/torque peak RPM variation being higher in lower rev engines, I looked back and realized that it wasn't much of a correlation at all. I think I got focused in on the S2000 and V6 Mustang and didn't do a proper analysis. Sorry.

However, I'm glad to see my point still bears out when RPM weighted. BTW, when I looked at the RX8s 3000 rpm variation, I back-calculated the the torque at 8500 and found that even at 8500, it still had 149 lbft, only 10 less than at 5500. What a broad torque band!! Ought to dominate ITR! :D (Steve Eckrich, forgive me.)

One other thought. In my discussion about high reving cars needing a wider power band, I was assuming everyone had about the same trans ratios. After looking further, I realized that in reality that's not always the case. If a particular car has noticeably closer ratios, then the needed rev band is also much smaller. As GKR noted earlier, that keeps you closer to the peak hp. In some cases (e.g., the S2000), the ratios are so much closer that the high rev car probably doesn't need to have a wider power band in absolute rpm than another low rev car with more typical trans ratios.

Phil Hunt -

I agree with most of what you said. But I'm not sure I followed all of your discussion. And I think you're still missing my point. I'll try again tomorrow when I feel like doing a couple charts to explain what I'm saying.

Knestis' original question related to using the torque number as a factor in setting IT weights, not anything about torque curve (and rightly so, since the torque curve info is generally not available.) One of my main points was that the torque number doesn't really tell you anything about the car's performance that you don't already know from the HP.

So I can better understand where you're coming from, are you saying that 160hp, 200 lbft car is going to accelerate faster than a 160hp, 140 lbft car? And if so, could you explain a little more why you think that's the case?

[JoshS]

Uh... I did... several times. Here just one: July 30, 2008
Sorry man, maybe I just wasn't ready to listen yet!

[Bill Miller]

Kirk,

I applaud what you're doing here, but honestly, you lost me when you said a 150/150 car would weigh the same as a 170/170 car.

I'm pretty much in agreement w/ Phil, and have advocated for a long time, that the area under the power curve is much more indicative of performance than some peak value.

[rx7chris]

Torque makes all the difference in the world. HP is just a figure derived from a torque reading. For example, gonna use motorcycles cause i can speak from experience. Say Bike 1 makes 52lbs of torque and 120HP Bike 2 makes 47lbs of torque and 130hp. Bike 1 and 2 are otherwise equal. Both bikes come out of a turn at the exact same time, Bike 1 will win the race to the next turn given that it's not at such a distance that the added hp of bike 2 allows it to catch up. Say if this turn is the bus-stop at daytona. By the time both bikes reach start finish they should be about equal again. If the turn was the carousel at sebring bike 1 would have a definitive lead by the time they reach the short-course start finish. Each side has it's pro's and con's and you can have a different advantage depending on track lay-out.

Torque can also be massaged with dyno time as well.

Don't try to measure it, you'll go insane with 300+ cars at an event.

[Andy Bettencourt]

Torque makes all the difference in the world. HP is just a figure derived from a torque reading. For example, gonna use motorcycles cause i can speak from experience. Say Bike 1 makes 52lbs of torque and 120HP Bike 2 makes 47lbs of torque and 130hp. Bike 1 and 2 are otherwise equal. Both bikes come out of a turn at the exact same time, Bike 1 will win the race to the next turn given that it's not at such a distance that the added hp of bike 2 allows it to catch up. Say if this turn is the bus-stop at daytona. By the time both bikes reach start finish they should be about equal again. If the turn was the carousel at sebring bike 1 would have a definitive lead by the time they reach the short-course start finish. Each side has it's pro's and con's and you can have a different advantage depending on track lay-out.

Torque can also be massaged with dyno time as well.

Don't try to measure it, you'll go insane with 300+ cars at an event.

But in IT things aren't otherwise equal. You can run a R&P that helps your problems and exploits your strengths.

[pfcs]

"You're right, Josh. As soon as I posted the comment about HP/torque peak RPM variation being higher in lower rev engines, I looked back and realized that it wasn't much of a correlation at all. I think I got focused in on the S2000 and V6 Mustang and didn't do a proper analysis. Sorry."
It's more illustrative to look at this by % of rpm difference than rpms difference. And the relative numbers (ft/lbs and hp). They reveal a whole lot about the area under the curve and the ballistics of said engine. Engines with more torque than hp will have the hp peak nearer the torque peak and are stones, running out of torque quickly, they generate little hp because hp is a product (in the math sense) of torque and rpm. There's little area under this curve.
Imagine other scenarios and you can imagine the neccessary tq curves and the implications.
AB: "But in IT things aren't otherwise equal. You can run a R&P that helps your problems and exploits your strengths."
And if the %difference between peak tq and hp is less than the %difference between 2 transmission gears you use, you're screwing the pooch-when you're out of torque, you're better drinking beer.

[JoshS]

Engines with more torque than hp will have the hp peak nearer the torque peak and are stones, running out of torque quickly ...

There's lots of conventional wisdom like this, but IT JUST ISN'T TRUE, at least for the fairly random sampling of cars I ran. There seems to be very little correlation between these factors.

[JoshS]

Torque makes all the difference in the world. HP is just a figure derived from a torque reading. For example, gonna use motorcycles cause i can speak from experience. Say Bike 1 makes 52lbs of torque and 120HP Bike 2 makes 47lbs of torque and 130hp. Bike 1 and 2 are otherwise equal. Both bikes come out of a turn at the exact same time, Bike 1 will win the race to the next turn given that it's not at such a distance that the added hp of bike 2 allows it to catch up.

Please prove it with math.

[Knestis]

Kirk,

I applaud what you're doing here, but honestly, you lost me when you said a 150/150 car would weigh the same as a 170/170 car.

I'm pretty much in agreement w/ Phil, and have advocated for a long time, that the area under the power curve is much more indicative of performance than some peak value.

I'm pretty sure that I didn't say that. What I suggested was that both should have the same "torque adjustment." The weight will ALWAYS be based on the power.

K

[lateapex911]

Found it.
Read this:
http://www.yawpower.com/tqvshp.html

[pfcs]

The point I keep trying to make is so easy to miss, and I'll bet people like Bill O'Reilly wouldn't admit they got it if they did!
Horsepower is a FUNCTION of TORQUE and VELOCITY (rpm in a crankshaft). To make a lot of horsepower, you need to have good torque at higher rpm. (Xtorque@4000rpm =Yhp; Xtorque@8000rpm=2Yhp). Understanding their interelatedness, and how their relative amounts and %rpm-spreads describe the area under the curve in question tell a lot about the dynamics of the engine and its likely response to tuning. (an airflow restricted engine [high tq/lowhp/small rpm-spread] is unlikely to respond much to IT tuning unless the restriction is in the exhaust system). Yes, you need a lot of horsepower to go fast but hp is still determined by torque AND-torque is what accellerates the car, even at 10,000rpm, hp simply describes how well it makes that torque at high rpm. Get it? You need to know BOTH to describe the dynamics of an engine. If you only know one parameter, hp is more informative; if you know both (tq@rpm/hp@rpm), you have much clearer info.
On another front-I actually heard Rush Limbaugh suggest that what killed Detroit was trial lawyers. Turn you r radios off please.

[quadzjr]

Kirk,

I'm pretty much in agreement w/ Phil, and have advocated for a long time, that the area under the power curve is much more indicative of performance than some peak value.

I agree as well, that makes 100% sense. however implementing would be a nightmare. Anybody have a factory issued dyno plot for an opel GT?:D

[JoshS]

I agree as well, that makes 100% sense. however implementing would be a nightmare. Anybody have a factory issued dyno plot for an opel GT?:D

Yes, area under the operational part of the curve is the right answer. In other words, a flat power curve near the peak is better than a peaky curve, because we base the vehicle weight on the peak. The closer you can stay to the max HP, the better. And I claim that you can't derive anything about the shape of the HP curve from the any published vehicle specs. That's the ITAC's problem.

[Bill Miller]

I'm pretty sure that I didn't say that. What I suggested was that both should have the same "torque adjustment." The weight will ALWAYS be based on the power.

K



Assume that the minimum weights are the same for the purposes of this discussion. Since we're talking about figuring out how to consider torque (or if we should), don't presume that given whatever the final process might be, the result would be that they are different.

Maybe I misunderstood what you meant by the above comment.

[Knestis]

Ah, gotcha. That wasn't an argument - it was an exercise to try to suss out how we think about the value of these things we think of as 'power' and 'torque.' Sorry for the confusion.

K

PS - Good to have you back in the fold, Bill...!

[Bill Miller]

Now you know why I was confused.

And thanks to both you and Greg for the 'welcome back', but I probably won't be staying long. If nothing else, reading that entire thread on ITB wheel widths reminded me why I took a hiatus from this place to begin with. Honestly, I just don't have the energy for those kinds of discussions any more. Especially when it's just the same crap from the past 8 or so years just getting re-hashed over and over again. I now totally understand how it burned Darin out. You know the old saying, the more things change, the more they stay the same.

I'll pop in from time to time, just to say Hi, but Jake's got no worries about losing his position atop the post-count mountain. Let's chat off-line.

[lateapex911]

............. but Jake's got no worries about losing his position atop the post-count mountain. Let's chat off-line.

Damn........that's one thing I really don't WANT to win. Hi Bill! c'mon...skip the board, get a car, and get out and race!

[Marcus Miller]

or at least skip the rules & regs forum.

[TomL]

Jake - Thank you for finding the Paul Yaw dissertation. He has basically written the rant on this topic that I had threatened to write and post here. He even included the F1 engine versus diesel truck engine comparison I was going to use. For those of you who haven't read the link on Jake's post, answer this question. If you put into the same 2500 lb car, an F1 engine with 800 HP and 281 lb ft of torque, or a diesel with 305 HP and 550 lbft of torque, which one would accelerate faster? Then check out the answer - it's near the bottom of that article. If you guessed wrong, you need to read the whole article, and even if you were right, you might learn something.

One point for the folks who say that torque is what accelerates the vehicle. Yes, that's right. But at any given car speed, it's torque at the drive wheels, not torque at the crank. And the high HP, low torque engine (i.e., the one with higher revs) can multiply crank torque a lot more (through shorter final drive, gears and/or tires) than the lower HP, high torque engine.

Phil - do you have some dyno charts to demonstrate your argument that high torque/low rpm engines respond less to IT tuning? Because if you do, that would say that we need to give high torque engines a weight decrease! Definitely not conventional wisdom. :)

[Bill Miller]

Damn........that's one thing I really don't WANT to win. Hi Bill! c'mon...skip the board, get a car, and get out and race!

Got a race car, that's the easy (and cheap) part. Need someone to pony up the $$$$$$ so I can go racing.

As far as your post count goes, you've got no one to blame for that but yourself.

[ekim952522000]

Found it.
Read this:
http://www.yawpower.com/tqvshp.html

Best article I have ever read on TQ and HP. :023::023:

[chuck baader]

I would guess that the consensus it that those of us with the 50# torque adder should have that removed post haste. Chuck

[Bob Roth]

My apology if these points have been made, I've been busy for a while.

There is no difference between any of the engines at the conditions you list, but there is a big difference in the racing potential of them.

Look at the Honda VTEC 1.6 which is the 160 hp 110 ft pound torque at 8000 RPM. It is limited by valvetrain to 8500, which is kind of academic because everything in its VTEC "racecam", to intakedesign, to 10.5 to 1 compression to 4-2-1 stock exhaust system means there is little to be done unless you wanta cheat big time. Its already 1 hp per liter which is very good for internal combustion engines. If I can't make it rev more, and displacement is fixed, 150 wheel hp at 8000 rpme is all its going to give. And since its torque curve is flat from VTEC cut in, it also means when it shifts loses 25% rpm to 6000, it loses 25% HP to 112 hp.

Meanwhile look at a non VTEC ITS '93 prelude S with a 2.3 liter 160 hp engine that produces 70 hp /liter at 6700 RPM. Given that its heads and valves are the same as the prelude VTEC and given that this was the base prelude, it has no VTEC "race cam" trick intake filters and exhaust and Honda wants to have a significant derate compared to the 190 hp prelude VTEC, its reasonable that there is some increased RPM range and breathing to be found and that the prelude can be revved for good power to 7500 RPM before really bad power falls off. I would assume a 10% increase at the rating point with constant hp at speed above with a drop at redline.

Lets compare the HP across the 75 to 100% for the respective ranges
75% 80% 85% 90% 95% 100%
1.6 6000 6400 6800 7200 7600 8000
hp 120 128 136 144 152 160

2.3 5625 6000 6375 6750 7125 7500
hp 150 158.4 167.2 176 170 150

Delta 30 30.4 31 32 18 -10

The point is that its extremely difficult to increase high Hp per liter engines because there is nothing left to get for torque, or RPM range. On the other hand a non optimized engine "probably" will respond to the headers, air filters and releasing of artificial rev limits allowed in IT. Soo, a long the point is, its easy, get a large displacement, low HP/liter (0.6 to 0.7) engine which is the high torque one. Assuming that its a 2000sx, BMW or Honda Non VTEC with decent chassis, reliability and brakes, things look good. Note this rule falls apart with cars like gremlins, Monza's, and straight 6 ford mustangs, and other crap cars. As long as you avoid the high torque junk, I think you have a good chance wherever you race.

So, if HP is equal, get the lowest stock torque as it has the highest hp potential and area under the resulting curve.