Revisiting Torque

[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.

[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.

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.



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...sepower-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.