Another torque versus horsepower question for a track car
01-01-2008, 12:31 AM
#62
Rennlist Member
That was good. Thanks.
However, i never said power was the same as energy.
I said HP-second, kW-hr , etc was a unit measure of work, (or energy) not of power.
A kw or HP is a unit measure of power.
So, what is the thought or concept that is more straight forward to understand than HP-seconds to maximize acceleration based on the identiy showing that
acceleration is proportional to power at any same vehicle speed?
The main problem that most have with the torque vs HP discusssion , is that there is confusion with the torque of the engine vs the torque generated at the rear wheels, or better said, thurst forces acting on the car at the rear tires!
At any same HP level, any two cars will have the same accelerative forces acting on them, regardless if we have 850ft-lbs of peak engine torque on a low reving diesel or 425 ft-lbs on a high reving gas engine both with 650hp. (again, as long as the HP curves are the same shape, and if they are not, then the one car has close ratio gears to keep the HP-seconds applied equal over any vehicle speed range!)
I think we are saying the same thing. the only think i would add to you first post is that even though it is torque that is the force , or "Thrust force" that will accelerate you and the car, its found at the rear tires, acting on the road, after the gear box. Power determines the level of that torque or linear force. This way of thinking allows folks to not get confused with the hoopla of engine torque values, and "flat torque curves, etc.
mk
However, i never said power was the same as energy.
I said HP-second, kW-hr , etc was a unit measure of work, (or energy) not of power.
A kw or HP is a unit measure of power.
So, what is the thought or concept that is more straight forward to understand than HP-seconds to maximize acceleration based on the identiy showing that
acceleration is proportional to power at any same vehicle speed?
The main problem that most have with the torque vs HP discusssion , is that there is confusion with the torque of the engine vs the torque generated at the rear wheels, or better said, thurst forces acting on the car at the rear tires!
At any same HP level, any two cars will have the same accelerative forces acting on them, regardless if we have 850ft-lbs of peak engine torque on a low reving diesel or 425 ft-lbs on a high reving gas engine both with 650hp. (again, as long as the HP curves are the same shape, and if they are not, then the one car has close ratio gears to keep the HP-seconds applied equal over any vehicle speed range!)
I think we are saying the same thing. the only think i would add to you first post is that even though it is torque that is the force , or "Thrust force" that will accelerate you and the car, its found at the rear tires, acting on the road, after the gear box. Power determines the level of that torque or linear force. This way of thinking allows folks to not get confused with the hoopla of engine torque values, and "flat torque curves, etc.
mk
One more try, probably won't do any good but what the hey, I've got nothing better to do right now
So to sum up power is not the same as energy
energy and torque are in some fundemental way the same thing, just looked at differently
In any event what I said was that the concept of torque that I outlined in responce to the first Marks question, fundementally agrees w/ Mark's concept of hp-sec. But I think that my thoughts are more straight forward and easier to understand, but that's just my opinion, your of course may differ.
So to sum up power is not the same as energy
energy and torque are in some fundemental way the same thing, just looked at differently
In any event what I said was that the concept of torque that I outlined in responce to the first Marks question, fundementally agrees w/ Mark's concept of hp-sec. But I think that my thoughts are more straight forward and easier to understand, but that's just my opinion, your of course may differ.
Last edited by mark kibort; 01-01-2008 at 02:11 PM.
01-01-2008, 02:41 AM
#63
Rennlist Member
Join Date: Aug 2004
Location: Land of the Old People
Posts: 2,097
Likes: 0
Received 5 Likes
on
2 Posts
Interesting. Then why are racing gears so close together? When I look at the various trannies for the 993, the Cup ones and RS gears are alot closer together then the stock North American trannies (G50/20). That tells me I am going to be rowing through the gears much more with the racing gears than the stock ones.
Exactly. I just put a shorter box in my car and yes, I'm shifting a lot more BUT, I'm never out of the powerband SO the car feels like it has more torque. Throttle steering in the corner was treacherous for the first few laps until I got used to the increased power. In looking at the data from the race, I gained 1 second in time, 5 mph (huge) at the end of the front straight (probably the second that I picked up) at Moroso and my fuel efficiency dropped by almost 10%....
01-01-2008, 02:05 PM
#64
Rennlist Member
Did you put a shorter box in, or one with a closer set of ratios?
If it is the closer ratio gear box, like found in the cup cars, you will be shifting more, but the gains are in keeping the engine in the power band. if you go to a lower ratio, which you can do in combination with a closer gear box, this can optimize the rpm levels to maximize HP utilization for a given track and a car with a given HP. You change the track, the hp levels, etc, and it can also work against you. In most circumstances, the gains are very slight. I can remember when Mark Anderson and his monster 500hp 928 went from a high numerical rear end to the low one. his times at his favorite track remained unchanged, although i remember him telling me he was much busier shifting gears!
(same at Laguna seca)
At a track like Road america, his number of shifts didnt change, but the lower gears allowed him to take advantage of more HP by runnig the engine to near redline on most all of the straights. Since you spend most of the time there, thats a thing that can have the greatest positive effects on lap times.
MK
If it is the closer ratio gear box, like found in the cup cars, you will be shifting more, but the gains are in keeping the engine in the power band. if you go to a lower ratio, which you can do in combination with a closer gear box, this can optimize the rpm levels to maximize HP utilization for a given track and a car with a given HP. You change the track, the hp levels, etc, and it can also work against you. In most circumstances, the gains are very slight. I can remember when Mark Anderson and his monster 500hp 928 went from a high numerical rear end to the low one. his times at his favorite track remained unchanged, although i remember him telling me he was much busier shifting gears!
(same at Laguna seca)At a track like Road america, his number of shifts didnt change, but the lower gears allowed him to take advantage of more HP by runnig the engine to near redline on most all of the straights. Since you spend most of the time there, thats a thing that can have the greatest positive effects on lap times.
MK
Exactly. I just put a shorter box in my car and yes, I'm shifting a lot more BUT, I'm never out of the powerband SO the car feels like it has more torque. Throttle steering in the corner was treacherous for the first few laps until I got used to the increased power. In looking at the data from the race, I gained 1 second in time, 5 mph (huge) at the end of the front straight (probably the second that I picked up) at Moroso and my fuel efficiency dropped by almost 10%....
01-01-2008, 02:58 PM
#65
Rennlist Member
I will still wager that, on some tracks, tq is more important/valuable than hp. Very tight, technical tracks with short straights will reward good tq in the lower and mid range, as well as the time saved by doing fewer shifts as a result of tq, whereas longer, more open & sweeping tracks with long straights will reward hp & will not dish out a penalty for shifting more to keep the motor in its hp sweetspot.
01-01-2008, 03:25 PM
#66
Rennlist Member
This is the misconception I am talking about. Are you talking about torque at the rear axles, or engine torque? Again, a great example of this is the many races against the 9000rpm S2000s with the same HP as me, as well as the BMWs found somewhere in between. (more like a cup car HP/torque curve)
If you are racing, you NEVER use the engine in the "lower" rpm range. For example, if you have a 6600rpm redline car, and .75 gear spacing, you will shift at redline, and end up at near 4500rpm. you will always be in this range. If you are not, then like i said, you need to learn how to always keep you engine in this range. If you are coming off a curve, say at a very tight track like Sears Point (Infinion), you will be in a gear that allows for this RPM. At the HP level you are at at that rpm, a resultant TORQUE at the rear wheels will be produced. anyone with the same HP at that same speed will have the same TORQUE at the rear wheels, REGARDLESS of engine torque values.
what i think you are talking about is more about the shape of the HP curve. a peaky HP curve, for the same peak HP value, will have less HP at the lower rpms. If you have a peaky HP engine, you should have it matched with a closer ratio gear box, so that you and your " torquey" engine competitor will be on a level playing field. Otherwise, as you talk about, you could have less power coming out of the turn (and subsequently, less rear wheel torque). NOW, this is in no way limited to coming out of a turn. It is the same at EVERY SINGLE SHIFT POINT. So, there is no advantage to have a peaky HP curve over a flat HP curve powered racer, unless that peak is greater than you competitor!
There is also no advantage in the concept of "fewer" shifts, unless you are comparing a close ratio gear box set up. As far as keeping a "torquey" motor in a taller gear because you have more torque, is also a bet you will loose if you think it is as fast. A simple downshift of a peakier HP car will yeild MUCH more torque at the rear wheels. remember, with a .7 rpm drop gear box spacing, that will yield a 40% increase in rear wheel torque through a lower gear (even though the rpms will be higher and engine torque will be lower, so call it 30%) . In order for you to win your bet, you better have a torque curve that has 30% more torque at the lower rpm in that same gear, vs your competitor in a lower gear
Again, it all boils down to one simple concept. He who applies the most amount of HP over the lap, will win (all other things being equal, and regardless of engine torque values)
mk
edit: I had to fix the 140% value to 40% and add the part about less engine torque, lowering that value to 30%
If you are racing, you NEVER use the engine in the "lower" rpm range. For example, if you have a 6600rpm redline car, and .75 gear spacing, you will shift at redline, and end up at near 4500rpm. you will always be in this range. If you are not, then like i said, you need to learn how to always keep you engine in this range. If you are coming off a curve, say at a very tight track like Sears Point (Infinion), you will be in a gear that allows for this RPM. At the HP level you are at at that rpm, a resultant TORQUE at the rear wheels will be produced. anyone with the same HP at that same speed will have the same TORQUE at the rear wheels, REGARDLESS of engine torque values.
what i think you are talking about is more about the shape of the HP curve. a peaky HP curve, for the same peak HP value, will have less HP at the lower rpms. If you have a peaky HP engine, you should have it matched with a closer ratio gear box, so that you and your " torquey" engine competitor will be on a level playing field. Otherwise, as you talk about, you could have less power coming out of the turn (and subsequently, less rear wheel torque). NOW, this is in no way limited to coming out of a turn. It is the same at EVERY SINGLE SHIFT POINT. So, there is no advantage to have a peaky HP curve over a flat HP curve powered racer, unless that peak is greater than you competitor!
There is also no advantage in the concept of "fewer" shifts, unless you are comparing a close ratio gear box set up. As far as keeping a "torquey" motor in a taller gear because you have more torque, is also a bet you will loose if you think it is as fast. A simple downshift of a peakier HP car will yeild MUCH more torque at the rear wheels. remember, with a .7 rpm drop gear box spacing, that will yield a 40% increase in rear wheel torque through a lower gear (even though the rpms will be higher and engine torque will be lower, so call it 30%) . In order for you to win your bet, you better have a torque curve that has 30% more torque at the lower rpm in that same gear, vs your competitor in a lower gear
Again, it all boils down to one simple concept. He who applies the most amount of HP over the lap, will win (all other things being equal, and regardless of engine torque values)
mk
edit: I had to fix the 140% value to 40% and add the part about less engine torque, lowering that value to 30%
I will still wager that, on some tracks, tq is more important/valuable than hp. Very tight, technical tracks with short straights will reward good tq in the lower and mid range, as well as the time saved by doing fewer shifts as a result of tq, whereas longer, more open & sweeping tracks with long straights will reward hp & will not dish out a penalty for shifting more to keep the motor in its hp sweetspot.
01-01-2008, 06:21 PM
#67
Rennlist Member
Mark, I disagree. This all depends on the characteristics of the motor. As an example, let's look at 2 BMW's. E36 M3, in US spec, makes great torque from ~3000 rpm, and also makes good HP...but above around 6300 on the way to redline at 7000 to 7200 (depending on chip), it mostly makes noise. So it really does nto make sense to keep the car at redline, and works better to use the torque as much as possible. E46 330i, which I have raced professionally, makes less torque, and has a lower redline, which is a lot better aligned with the power peak. Thus, it makes more sense to keep the RPMs high.
01-01-2008, 06:39 PM
#68
Drifting
Join Date: Jul 2006
Location: ..."RECALCULATING"
Posts: 3,496
Likes: 0
Received 0 Likes
on
0 Posts
Dave, my original post on this issue questioning the concept of "avoiding shifts" was actually based on the idea that I have a gearing that puts me out of the power band going from 1st to 2nd and 2nd to 3rd (a la US 993 stock). Given the choice of a transmission that keeps me in the power band but makes an extra shift and one that does not...I'll take the extra shift everytime..it more than makes up for the split second loss of the shift....
...is there anything wrong with that logic? I realize it is track dependant also...as I could end up putting the new shift points right where I don't want them.
...is there anything wrong with that logic? I realize it is track dependant also...as I could end up putting the new shift points right where I don't want them.
01-01-2008, 06:47 PM
#69
Rennlist Member
Given the ultra-wide spacing of those stock gears, I guess I'd have to agree with you, but you are right--on some tracks, you'd be adding new shift points where they may be literally impossible to make...necessitating a short shift...negating the advantage. Tough call.
01-01-2008, 07:39 PM
#70
Dave, my original post on this issue questioning the concept of "avoiding shifts" was actually based on the idea that I have a gearing that puts me out of the power band going from 1st to 2nd and 2nd to 3rd (a la US 993 stock). Given the choice of a transmission that keeps me in the power band but makes an extra shift and one that does not...I'll take the extra shift everytime..it more than makes up for the split second loss of the shift....
...is there anything wrong with that logic? I realize it is track dependant also...as I could end up putting the new shift points right where I don't want them.
...is there anything wrong with that logic? I realize it is track dependant also...as I could end up putting the new shift points right where I don't want them.
01-01-2008, 08:47 PM
#71
Rennlist Member
Having raced and driven one, plus understanding the concepts and can mathematicaly show you, i have to say you might want to rethink this.
I had a very good friend that thought the same way as you did with his e36 racer. He picked up a second after we fought about this over a years time, and finally got it. keeping the engine in the meat of the HP peak, allowed for greater acceleration overall. Now i wish i didnt share that information with him. he is now one of my biggest competitors!
the point is, based on both cars you have raced, even the torquier US 3.2 will benefit from redline shift. that noise near redline, is still greater power than the more engine torque in the next gear. So, if you want to challenge this concept, find any vehicle speed where you would have more torque to the rear wheels, while at near redline vs at a taller gear at max torque. It is very rare to have an engine that has more than the .75 rpm drop with .75 power drop (or torque drop) on the HP / torque curve. I had a car that did equal this, but it was a stock US 928 and its HP curve fell off like a rock after 5400rpm. But, at worst it was near equal to shift before redline, but why use the rpms if you dont need to . The BMW 3.2 e-36 motor is not such an engine.
so, does it make sense to drive the engine in you BMW 3.2 US motor to redline? ..........you bet !
I do have a US 3.2 BMW curve available and the gear ratios. what do you want to bet, there is NO gear that would benefit from a short shift?
mk
I had a very good friend that thought the same way as you did with his e36 racer. He picked up a second after we fought about this over a years time, and finally got it. keeping the engine in the meat of the HP peak, allowed for greater acceleration overall. Now i wish i didnt share that information with him. he is now one of my biggest competitors!
the point is, based on both cars you have raced, even the torquier US 3.2 will benefit from redline shift. that noise near redline, is still greater power than the more engine torque in the next gear. So, if you want to challenge this concept, find any vehicle speed where you would have more torque to the rear wheels, while at near redline vs at a taller gear at max torque. It is very rare to have an engine that has more than the .75 rpm drop with .75 power drop (or torque drop) on the HP / torque curve. I had a car that did equal this, but it was a stock US 928 and its HP curve fell off like a rock after 5400rpm. But, at worst it was near equal to shift before redline, but why use the rpms if you dont need to . The BMW 3.2 e-36 motor is not such an engine.
so, does it make sense to drive the engine in you BMW 3.2 US motor to redline? ..........you bet !
I do have a US 3.2 BMW curve available and the gear ratios. what do you want to bet, there is NO gear that would benefit from a short shift?
mk
Mark, I disagree. This all depends on the characteristics of the motor. As an example, let's look at 2 BMW's. E36 M3, in US spec, makes great torque from ~3000 rpm, and also makes good HP...but above around 6300 on the way to redline at 7000 to 7200 (depending on chip), it mostly makes noise. So it really does nto make sense to keep the car at redline, and works better to use the torque as much as possible. E46 330i, which I have raced professionally, makes less torque, and has a lower redline, which is a lot better aligned with the power peak. Thus, it makes more sense to keep the RPMs high.
01-01-2008, 09:51 PM
#73
Rennlist Member
Thread Starter
Wow, I had no idea this topic would be so debatable. Thanks for the great info. I'm not an engineer and am trying to see the forest for the trees, but the problem is that sometimes I mostly see a pile of toothpicks.
