HP vs Torque Discussion (No Jokes, No bantering. Just facts and reality)
02-15-2009, 03:17 PM
#331
Whoops, the BMW is down 10% on power in this situation. Not good. In a perfect world, on paper or a whiteboard, these two cars may seem to be equal. However, in the real world where nobody hits their shift point perfectly every single time, where things happen that upset your rhythm, the car with the broader and flatter torque curve (and resulting flatter HP curve) will be more forgiving and will benefit the less-than-perfect driver(just about everyone).
Another way to minimize the flaws from the optimal HP-curve is to have a gearbox that masks mistakes like this and let you stay in the power range even if you shift too early. So swapping the 27% to another figure can let you stay in the power range, even when up shift too early.
Most people who DE or club race, don't change their gears very often or at all. So in the end, it depends also on the gearbox the car came with. (I doubt the Chevy and the BMW even have the same gear ratio increase, do they?)
P.S (Flat torque = constant slope of HP curve, but I think you either meant something else or it was a typo.)
02-15-2009, 03:26 PM
#333
Rennlist Member
Also I was building in some assumptions that take gearing out of the discussion, which I gathered was germane.
My example of being outside of the ideal RPM range was intended to show an example of how things change when you leave the perfect world of the whiteboard and enter the real world where "it depends".
02-15-2009, 03:35 PM
#334
Rennlist Member
Thread Starter
Lets just agree that the shape of the HP curve is what we need to look at. Putting a flatness requiment on the torque curve, or whatever, just confuses the situation. You want a HP curve that maximizes HP over the operational range. Preferably flat. this means torque is actually going down. (declining torque) most all engines have a declining torque curve in the usable range.
the I6 vs V8 is a great example of two different types of HP and torque curves. Look which works out best and why.
mk
the I6 vs V8 is a great example of two different types of HP and torque curves. Look which works out best and why.
mk
That's what I meant, yes -- the two properties "flatness" and "slope" are unrelated until you add a modifier like "constant slope" which is what I meant by "flatter". Note that the BMW chart varies in slope -- e.g. less "flat".
Also I was building in some assumptions that take gearing out of the discussion, which I gathered was germane.
My example of being outside of the ideal RPM range was intended to show an example of how things change when you leave the perfect world of the whiteboard and enter the real world where "it depends".
Also I was building in some assumptions that take gearing out of the discussion, which I gathered was germane.
My example of being outside of the ideal RPM range was intended to show an example of how things change when you leave the perfect world of the whiteboard and enter the real world where "it depends".
02-15-2009, 03:40 PM
#335
Rennlist Member
Thread Starter
Sorry Dave!
Yes, a broader hp curve will be beneficial. no question there. BUT, the point of this entire discussion is that a numerically higher torque value will not ALWAYS indicate this. Proved by a comparison of the I6 vs V8 comparison on page 17.
Im only pointing out that it is not the rule. there are exceptions based on the shape of the HP curves that point to a lower torque engine being better on a road course, where the HP of both is the same.
Ive said this before, often the higher engine torque value indicates a broader HP curve, but not always and that is the point.
mk
Yes, a broader hp curve will be beneficial. no question there. BUT, the point of this entire discussion is that a numerically higher torque value will not ALWAYS indicate this. Proved by a comparison of the I6 vs V8 comparison on page 17.
Im only pointing out that it is not the rule. there are exceptions based on the shape of the HP curves that point to a lower torque engine being better on a road course, where the HP of both is the same.
Ive said this before, often the higher engine torque value indicates a broader HP curve, but not always and that is the point.
mk
First off, I'm still not Brian. 
See the bold above -- you are contradicting yourself. The latter part of your statement that I quoted above simply helps drive home the point that I was making, that a broader powerband can be beneficial. Whether by mistake or intent, you occasionally drive outside the "ideal" RPM range and the broad powerband benefits you in these cases.
See the bold above -- you are contradicting yourself. The latter part of your statement that I quoted above simply helps drive home the point that I was making, that a broader powerband can be beneficial. Whether by mistake or intent, you occasionally drive outside the "ideal" RPM range and the broad powerband benefits you in these cases.
02-15-2009, 03:53 PM
#336
That's what I meant, yes -- the two properties "flatness" and "slope" are unrelated until you add a modifier like "constant slope" which is what I meant by "flatter". Note that the BMW chart varies in slope -- e.g. less "flat".
Also I was building in some assumptions that take gearing out of the discussion, which I gathered was germane.
My example of being outside of the ideal RPM range was intended to show an example of how things change when you leave the perfect world of the whiteboard and enter the real world where "it depends".
Also I was building in some assumptions that take gearing out of the discussion, which I gathered was germane.
My example of being outside of the ideal RPM range was intended to show an example of how things change when you leave the perfect world of the whiteboard and enter the real world where "it depends".
Understand what you mean with "take gearing out of the discussion". To do that we'd have to have optimal gear elevation and not same gear elevation. Since same elevation would benefit one engine more than the other.
But as you said, real world and whiteboard are not really the same. Driver errors and parts not optimized for track; are part of most peoples lives. I can mention another 20 parameters that would just cause more headache here. The whole thing reminds a lot with suspension optimization which brings up the same issue. (Quickest in Theory vs. Driver friendly).
02-15-2009, 03:59 PM
#337
Rennlist Member
Thread Starter
Good points!
https://rennlist.com/forums/6282005-post246.html
If you look at these two HP curves, you can see that even without any gearing optimization , a greater torque engine CAN have less performance over an operational range, AND if you were in the wrong gear too
(even 500 or 1000rpm in the wrong gear!)
Obviously, if we have a narrower Hp band, closer gear ratios make up this difference, but doesnt completely protect the racer from being in the wrong gear. If you are looking for more safety margin in your racing platform, its a different story and sometimes, and probably more often than not, be in favor of the Higher numerical engine torque value . However, and the point of all this is, its NOT the rule. You need to look at the HP curves.
https://rennlist.com/forums/6282005-post246.html
If you look at these two HP curves, you can see that even without any gearing optimization , a greater torque engine CAN have less performance over an operational range, AND if you were in the wrong gear too
(even 500 or 1000rpm in the wrong gear!)Obviously, if we have a narrower Hp band, closer gear ratios make up this difference, but doesnt completely protect the racer from being in the wrong gear. If you are looking for more safety margin in your racing platform, its a different story and sometimes, and probably more often than not, be in favor of the Higher numerical engine torque value . However, and the point of all this is, its NOT the rule. You need to look at the HP curves.
IC.
Understand what you mean with "take gearing out of the discussion". To do that we'd have to have optimal gear elevation and not same gear elevation. Since same elevation would benefit one engine more than the other.
But as you said, real world and whiteboard are not really the same. Driver errors and parts not optimized for track; are part of most peoples lives. I can mention another 20 parameters that would just cause more headache here. The whole thing reminds a lot with suspension optimization which brings up the same issue. (Quickest in Theory vs. Driver friendly).
Understand what you mean with "take gearing out of the discussion". To do that we'd have to have optimal gear elevation and not same gear elevation. Since same elevation would benefit one engine more than the other.
But as you said, real world and whiteboard are not really the same. Driver errors and parts not optimized for track; are part of most peoples lives. I can mention another 20 parameters that would just cause more headache here. The whole thing reminds a lot with suspension optimization which brings up the same issue. (Quickest in Theory vs. Driver friendly).
02-15-2009, 04:14 PM
#338
Mark,
I think you and Dave are probably awfully close in what you both advocate. (Perhaps some details are not the same, but in general). But if this is going to really be near a 100% conclusion it's very dependent that everyone speaks the same lingo. Without pointing out anyone, there are a lot of misconceptions, misused words and some clowns in this quite long thread now that would give any race engineer a headache. It would probably do many good to read the Blue Book (Bosch Automotive Handbook) as mandatory before even posting in these topics.
I think you and Dave are probably awfully close in what you both advocate. (Perhaps some details are not the same, but in general). But if this is going to really be near a 100% conclusion it's very dependent that everyone speaks the same lingo. Without pointing out anyone, there are a lot of misconceptions, misused words and some clowns in this quite long thread now that would give any race engineer a headache. It would probably do many good to read the Blue Book (Bosch Automotive Handbook) as mandatory before even posting in these topics.
02-15-2009, 04:35 PM
#339
Rennlist Member
Having drawn those conclusions it is mildly interesting to go back and look at the torque curve, but it doesn't tell you enough. Note that nobody ever talks about "Torque-to-weight ratio".
02-15-2009, 11:17 PM
#340
Formula One Spin Doctor
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02-15-2009, 11:33 PM
#341
Rennlist Member
Thread Starter
"Torque to weight ratio. " exactly!!
I think a lot of folks get really twisted when talkng about shapes of torque curves. Ideally you reallly want a declining torque curve, for a given HP level.
If its flat, HP is rising so your HP over an operational range will be rising (probably going to be an arc). If its rising, its rising even more, but still an arc. If its falling the HP curve is flat yielding the most amount of acceleration forces found at the rear wheels.
again, shapes of torque curves, values of torque curves are very limited. unless they are matched with rpms they are absolutely meaningless. I could just hear the torquee's on the Brumos team with porsche engine vs the V8 powered lexus complaining about concessions due to their lack of torque. they would get laughed out of any apeal meeting! Unless the redlines were the same there wouldnt be a reason for arguement based on torque values alone!
mk
I think a lot of folks get really twisted when talkng about shapes of torque curves. Ideally you reallly want a declining torque curve, for a given HP level.
If its flat, HP is rising so your HP over an operational range will be rising (probably going to be an arc). If its rising, its rising even more, but still an arc. If its falling the HP curve is flat yielding the most amount of acceleration forces found at the rear wheels.
again, shapes of torque curves, values of torque curves are very limited. unless they are matched with rpms they are absolutely meaningless. I could just hear the torquee's on the Brumos team with porsche engine vs the V8 powered lexus complaining about concessions due to their lack of torque. they would get laughed out of any apeal meeting! Unless the redlines were the same there wouldnt be a reason for arguement based on torque values alone!
mk
Throughout this discussion, whenever I referenced a chart and described its flatness or slope, I was only referring to the HP curves. I do agree that that's the important thing to draw conclusions from because it is the only value that expresses an engine's ability to accelerate.
Having drawn those conclusions it is mildly interesting to go back and look at the torque curve, but it doesn't tell you enough. Note that nobody ever talks about "Torque-to-weight ratio".
Having drawn those conclusions it is mildly interesting to go back and look at the torque curve, but it doesn't tell you enough. Note that nobody ever talks about "Torque-to-weight ratio".
02-15-2009, 11:36 PM
#342
Rennlist Member
Thread Starter
Dave,
To be fair, will you do the analysis of the V8 vs the I6 in the dyno charts provided. It shows even in a wrong gear the I6 with much less torque, can have more rear wheel torque at ANY vehicle speed even without the aid of a close ratio gear box.
https://rennlist.com/forums/6282005-post246.html
mark
To be fair, will you do the analysis of the V8 vs the I6 in the dyno charts provided. It shows even in a wrong gear the I6 with much less torque, can have more rear wheel torque at ANY vehicle speed even without the aid of a close ratio gear box.
https://rennlist.com/forums/6282005-post246.html
mark
Going back to this post. Assume that both cars are geared such that gearing is irrelevant. What I mean by that is, each car redlines in each gear at the same speed. To simplify, let's say that's 8K for the Beemer and 6K for the Chevy - er - Caddy. Also assume 27% drop between gears.
Based on the above, I would derive the ideal RPM ranges for each as follows:
BMW: 5,840 - 8K RPM
Caddy: 4,380 - 6K RPM
Using the lower HP curves for each, I then find the point on the HP curve where we will be after shifting to the next higher gear:
BMW: 5,840 RPM, 330HP
Caddy: 4,380 RPM, 325 HP
This bears out your theory in a perfectly ideal situation. However, let's say that we hit that taller gear 500 RPM lower in the band, for any number of reasons. For example, held up in traffic or other situation where the gear change is too costly to be worth doing. Forget about sequential whiz-bang video game transmissions for a second, consider H-pattern and manual clutch, which I think most of us have. The cost of downshifting to use 500RPM to redline, then upshifting again may not be worth paying in some situations.
BMW: 5,340 RPM, 290 HP
Caddy: 3,880 RPM, 320 HP
Whoops, the BMW is down 10% on power in this situation. Not good. In a perfect world, on paper or a whiteboard, these two cars may seem to be equal. However, in the real world where nobody hits their shift point perfectly every single time, where things happen that upset your rhythm, the car with the broader and flatter torque curve (and resulting flatter HP curve) will be more forgiving and will benefit the less-than-perfect driver(just about everyone).
I've seen you go both ways in your videos, Mark. I've seen you hit 1st gear leaving turn 11 at Laguna. I've also seen you stay in a higher gear when on paper, you could have hit a lower gear for ~500RPM and chose not to.
Based on the above, I would derive the ideal RPM ranges for each as follows:
BMW: 5,840 - 8K RPM
Caddy: 4,380 - 6K RPM
Using the lower HP curves for each, I then find the point on the HP curve where we will be after shifting to the next higher gear:
BMW: 5,840 RPM, 330HP
Caddy: 4,380 RPM, 325 HP
This bears out your theory in a perfectly ideal situation. However, let's say that we hit that taller gear 500 RPM lower in the band, for any number of reasons. For example, held up in traffic or other situation where the gear change is too costly to be worth doing. Forget about sequential whiz-bang video game transmissions for a second, consider H-pattern and manual clutch, which I think most of us have. The cost of downshifting to use 500RPM to redline, then upshifting again may not be worth paying in some situations.
BMW: 5,340 RPM, 290 HP
Caddy: 3,880 RPM, 320 HP
Whoops, the BMW is down 10% on power in this situation. Not good. In a perfect world, on paper or a whiteboard, these two cars may seem to be equal. However, in the real world where nobody hits their shift point perfectly every single time, where things happen that upset your rhythm, the car with the broader and flatter torque curve (and resulting flatter HP curve) will be more forgiving and will benefit the less-than-perfect driver(just about everyone).
I've seen you go both ways in your videos, Mark. I've seen you hit 1st gear leaving turn 11 at Laguna. I've also seen you stay in a higher gear when on paper, you could have hit a lower gear for ~500RPM and chose not to.
02-16-2009, 03:07 AM
#343
Rennlist Member
Dave,
To be fair, will you do the analysis of the V8 vs the I6 in the dyno charts provided. It shows even in a wrong gear the I6 with much less torque, can have more rear wheel torque at ANY vehicle speed even without the aid of a close ratio gear box.
https://rennlist.com/forums/6282005-post246.html
mark
To be fair, will you do the analysis of the V8 vs the I6 in the dyno charts provided. It shows even in a wrong gear the I6 with much less torque, can have more rear wheel torque at ANY vehicle speed even without the aid of a close ratio gear box.
https://rennlist.com/forums/6282005-post246.html
mark
As before, assume that both cars are geared such that gearing is irrelevant. Rather than each car redlining in each gear at the same speed, we have to find the optimum shift point, because it's not necessarily redline. Maybe it is, but let's check. I'm arbitrarily going to pick a 6K shift point and see where that lands us. Doing the math, we would drop to 4,380 RPM when shifting -- far down the curve from peak. OK, based on that I think we can go to redline -- 6,200 RPM -- and shifting will drop us to 4,526.
The L6 redlines at 7,600 RPM, shifting to a gear that is the assumed .73 away gives us 5,548 RPM in the next gear.
Based on the above, I would derive the ideal RPM ranges for each as follows:
L6: 5,548 - 7,600 RPM
V8: 4,526 - 6,200 RPM
Using the upper HP curve for the L6, I then find the point on the HP curve where we will be after shifting to the next higher gear:
L6: 5,548 RPM, ~245 HP
V8: 4,526 RPM, ~255 HP
It seems the L6 is dropping off a touch further than the V8. Let's see what happens if we shift 500 or 1,000 RPM early(for whatever reason).
500 RPM Early:
L6: 5,048 RPM, ~230 HP
V8: 4,026 RPM, ~220 HP
1,000 RPM Early:
L6: 4,548 RPM, ~200 HP
V8: 3,526 RPM, ~180 HP
So in this case there is a slight edge to the L6 engine in that it seems to have a somewhat broader powerband.
* When a horsepower curve falls off like this the ideal RPM range may not include redline; the goal is to fit the usable RPM range to the highest possible points on either side of the peak of the horsepower curve.
02-16-2009, 03:16 AM
#344
Rennlist Member
If the torque curve is rising all the way to redline, then the horsepower will be rising all the way to redline. What you said is true if, and only if, over the "ideal" range of usable power, the flatter HP curve contains more "area under the curve", "HP-seconds", or whatever you want to call it.If you shift into a gear, and are making say 300 HP from the time you shift into the gear until the time you shift into the next higher gear, that is not going to perform as well as an engine that is at say 290 HP when you shift into the gear and rises steadily to 350HP at redline.
"It depends".
02-16-2009, 04:49 AM
#345
Rennlist Member
Thread Starter
Its kind of a trick question or comment (although not intended to be one)
In that your last sentence hits it on the head. Remember we have to be considering two equal HP engines.
mk
In that your last sentence hits it on the head. Remember we have to be considering two equal HP engines.
mk
Unless you don't. If the torque curve is rising all the way to redline, then the horsepower will be rising all the way to redline. What you said is true if, and only if, over the "ideal" range of usable power, the flatter HP curve contains more "area under the curve", "HP-seconds", or whatever you want to call it.
If you shift into a gear, and are making say 300 HP from the time you shift into the gear until the time you shift into the next higher gear, that is not going to perform as well as an engine that is at say 290 HP when you shift into the gear and rises steadily to 350HP at redline.
"It depends".
If the torque curve is rising all the way to redline, then the horsepower will be rising all the way to redline. What you said is true if, and only if, over the "ideal" range of usable power, the flatter HP curve contains more "area under the curve", "HP-seconds", or whatever you want to call it.If you shift into a gear, and are making say 300 HP from the time you shift into the gear until the time you shift into the next higher gear, that is not going to perform as well as an engine that is at say 290 HP when you shift into the gear and rises steadily to 350HP at redline.
"It depends".