What is: history of, and reason behind, '(HP + torque)/2' ?

[cwbaader]

Understood, Joe, and I have already picked one...SCCA ITA. \\

 

Now, not to shoot too many holes in your theory, but you have forgotten a major factor. My megatorque motor revs to 5600rpm...done. Most other motors in the class are 6500-7000rpm motors. Now, figure the horsepower APPLIED AT THE WHEELS VIA GEAR RATIO. The high torque motor is still at a disadvantage. We have a method to class cars...it worked well until the change. Horsepower is a function of torque and rpm...that is the only way to correctly classify cars. Seems every other organization knows this. CB

[944-Spec#94]

It seems to me if you want to ditch torque in the calcuations you then need to change from using peak hp to using average hp over the last 2000 to 3000 RPM to redline. In this way you can not just account for peak hp, but proper assess a car with a very wide power band as one compared to a narrow peaky one.

[cwbaader]

Joe, you haven't been paying attention. Reread the last 10 or so posts.

 

Note, horsepower is an engineering term. It is the relationship to work vs. time. Torque is the work and as so, is included in the horsepower calculation. CB

[rabbit_diesel]

It seems to me if you want to ditch torque in the calcuations you then need to change from using peak hp to using average hp over the last 2000 to 3000 RPM to redline. In this way you can not just account for peak hp, but proper assess a car with a very wide power band as one compared to a narrow peaky one.

 

In my opinion, Joe has the right idea.

And some variation of that is what I think we should implement. And carefully done, I think the new classing rule would keep most cars classed right where they are, however it would tend move the 'outliers' in each class to another more appropriate class (if the disparity is great enough).

 

Will

[Sterling Doc]

Joe, you haven't been paying attention. Reread the last 10 or so posts.

 

Note, horsepower is an engineering term. It is the relationship to work vs. time. Torque is the work and as so, is included in the horsepower calculation. CB

 

...and so one measurement, at one RPM, tells the whole story? The area under the HP curve that the engine operates in under racing conditions is what is important, and the torque reading is relavent to that.

 

FYI, Joe is an aerospace engineer. You can spare him the lecture on the denition of HP .

[Eric W.]

Joe, you haven't been paying attention. Reread the last 10 or so posts.

 

Note, horsepower is an engineering term. It is the relationship to work vs. time. Torque is the work and as so, is included in the horsepower calculation. CB

 

FYI, Joe is an aerospace engineer. You can spare him the lecture on the denition of HP .

 

That's aviation HP. It's different than car hp

[cwbaader]

And I am a mechanical engineer.

 

Yes, the hp at one rpm does tell the whole story because it is interwoven with torque...they are inseparable...so two different engines can be compared fairly. CB

[rabbit_diesel]

I am sure that many readers know by heart the formula for calculating horsepower from torque and rpm. For those which do not, here it is:

 

HP = (T * RPM) / 5252

 

(Note: The figure 5252 is not exact, it is an approximation that is correct to 4 digits. Torque is in ftlb, or lbft, whichever one wants to call it.)

 

If instead, the HP and RPM are the values known, the torque can be calculated by rearranging the formula:

 

T = (HP * 5252) / RPM

 

Will

[944-Spec#94]

Joe, you haven't been paying attention. Reread the last 10 or so posts.

 

Note, horsepower is an engineering term. It is the relationship to work vs. time. Torque is the work and as so, is included in the horsepower calculation. CB

 

 

I have been paying attention. - Eric I am a mechnical engineer by training and work in aerospace.

 

The reality is hp is the only number that means anything. 1000ft-lbs of torque at 5 rpm is useless.

 

However in race cars peak hp is also rather pointless. The reason is what you really want is the area under the curve. More area under the curve = better acceleration.

 

Now most piston engines have similar hp vs RPM polt. The reason is the torque the motor makes (ie torque curve) is relativly similar over the normal RPM band these motors run. However some motors like a 2.0L Honda S2000 motor make big hp, but still only makes 2.0L torque levels. That motor makes 240 hp, but so does a 3.0L E36 M3 motor. The E36 motor has much more torque.

Now why is this torque important? The ONLY reason it is important is it helps define how wide the power band is. Motors that make more torque tend to have wider powerbands. This means they may only make 240 hp peak, but 2000 less than peak I bet the E36 makes alot more power than the S2000. Sure good gearing makes up for some of it, but not all.

 

So the idea is if you know peak power and peak torque you can determine if the motor is high reving peaky motor (as is the case with most motors with high hp & low torque) or a low revving motor with a fat power band (as is the case with bigger torque numbers).

 

 

Here one case in point. 944 NA motors. 2.5L vs 2.7L. Both have 158 to 162 peak hp rated from the factory and 150 flbs and 165 ftlbs. So seems like 4 hp is no big deal. Well the difference is that the 2.7L makes alot more torque. So much so that in the rev band from 4000 rpm to 6000 rpm the 2.7L makes up to 10 hp more right up to about 5800 rpm where the gap closes down. So that 10 hp of mid range make a big difference. So classing both on power alone means go for the 2.7L. However class both with hp and torque and wider power band of the 2.7L comes into play. On track performance from 944 cup shows it takes about 150-200 lbs of ballast to make these cars equal.

[cwbaader]

I agree with what you are saying on the "P" cars. Fortunately, we all don't race them...we race a wide variety of cars and each of us optimizes our particular set up. Area under the curve is fine, except it does not account for final gear ratio. Old adage..."you can build torque with gear ratio, but not horsepower", and that is how dis similar cars are classified...by horsepower!! CB

[944-Spec#94]

I agree with what you are saying on the "P" cars. Fortunately, we all don't race them...we race a wide variety of cars and each of us optimizes our particular set up. Area under the curve is fine, except it does not account for final gear ratio. Old adage..."you can build torque with gear ratio, but not horsepower", and that is how dis similar cars are classified...by horsepower!! CB

 

 

By definition GTS only care about engine performance, weight and tires (slick or DOT). Everything else is open. So gears are free. There is no intent to capture gearing in the GTS rule set. Like I said peak hp is not the best way to describe engine performance. Peak hp and Peak torque do a better job. However the best job is the actual curve itself. Simply put factoring in peak torque it an attempt to factor in cars with narrow power bands and those with wide ones. It does not make and differece who makes the motor. The Porsche example was just one were the hp levels are very similar, but the effect of a wider power band cannot be denied.

 

Now if you want to get into how much power hits the ground you can, but that is not really in the scope of the GTS rules. PT & ST rules take into account which wheels are being driven as well as host of other factors.

[cwbaader]

I assume you will write the program to determine area under the curve and come up with a new rule to implement an area/weight classification. Good suggestion, however, in reality almost impossible to implement. Until then, HP is still a better method. Chuck

[JSirota]

I assume you will write the program to determine area under the curve and come up with a new rule to implement an area/weight classification. Good suggestion, however, in reality almost impossible to implement. Until then, HP is still a better method. Chuck

 

If you start to use area under the curve (which seems totally possible in a class that requires dyno testing before racing), then the arguments will start to shift around what width (rev range) makes sense to use for the calculations. Can't wait to watch it.

 

BTW, I am personally convinced that there is no strong correlation between high torque peaks and flat hp curves. I challenge anyone who thinks that there is (and I've seen this asserted several times in this thread alone, never mind elsewhere on the internet) to prove it to me.

[rabbit_diesel]

... Simply put factoring in peak torque it an attempt to factor in cars with narrow power bands and those with wide ones. ...

Including the peak torque in the classing formula, can result in valid assessments so long as all the engines being compared make their most useful power in essentially the same RPM range.

 

The problem comes in when comparing an engine that makes its most useful power from 4000 to 7000 RPM, against an engine that makes its most useful power from 3000 to 5000 RPM. The current GTS rules apply an unreasonable handicap.

 

For example:

 

Engine #1: 200 HP @ 7000 RPM, will have a torque at 7000 RPM of 150 lbft; and a healthy engine might have a peak torque of about 195 lbft at about 4200 RPM.

 

Engine #2: 200 HP @ 5000 RPM, will have a torque at 5000 RPM of 210 lbft; and an equally healthy engine might have a peak torque of about 270 lbft at about 3000 RPM.

 

Notice that the area under the torque curves is quite similar for these two engines, about 1% larger for engine #1. Alternatively, notice that the average horsepower is quite similar, less than 1% larger for engine #1. (Assuming a 'power band width' from peak-torque to peak-horsepower.) (Also notice that the ratio of 'power band width in RPM' to 'RPM at peak HP', is identical in the two cases.)

 

Two cars weighing 3250 lb and on slicks, and the same in every way except for the engine and the rearend ratio, would compete rather closely.

 

The current GTS rules would place the car with engine #1 near the top of GTS-2. The car with engine #2 would be well up in the next class, one would have to add 570 pounds of ballast to get it back down to the same place in GTS-2.

 

It is not reasonable that out of two similar cars, one car be assigned a large handicap.

 

Will

[944-Spec#94]

I never said GTS was perfect. I was just trying to explain the intent behind using torque as part of the equation. I feel it is in most cases better then peak hp alone, but it does have limitations.

 

 

Frankly I find tht GTS rule set too wide open for my tastes. Then again that is why I run in a spec class. What I do feel is that some GTS drivers need to realize the class is WIDE OPEN. So pretty much anything goes. It is very much run what you brung and hope you brung enough. So I just seems off if you complain about NOT being competitive. The rule ares just not like that.

[Damon in STL]

I've been reading this thread and all I keep thinking is "How long can you keep beating a dead horse?"

 

I had three choices when deciding where and who to race with....NASA, SCCA, BMW Club Racing. I chose one group and it makes my car have a distinct disadvantage with the other clubs. This was my choice and I do not feel that I'm entitled to have any rules changed to make my car more competitive in the other classes/clubs.

 

Pick a class/club to run with, build your car to that class/club, and move on. It's really pretty simple.

 

Damon in STL