HP / Torque discussion 928 vs M3 (need a S4 graph at 285rwhp)
11-13-2006, 01:56 PM
#1
Rennlist Member
Thread Starter
HP / Torque discussion 928 vs M3 (need a S4 graph at 285rwhp)
I got into a discussion with Randy Pobst and the team owner that he was testing for regarding the always misunderstood, flywheel toruqe vs HP subject.
Of course, Randy,, the competitor that he is, had to mention that i had a porsche V8 with all that torque and thats why i passed him at the start! Of course, the team manager of the 2002 BMW E46 M3, devopled to Grand Am Cup GS specs ( 315 to 340rwhp is common and costs of the car are near $80 to 100k) continued to chime in about having only 250ft-lbs of torque and the 928 having 300ft-lbs+. Forget the fact that I got a jump and draft from the 550hp evo at the start and never was able to close on Randy again on a straight after he passed me as he had better turn in and near the same acceleration while i was having major handling issues with that GT3 wing)
Of course, the first thing i came back with was, HP determines rear wheel toruqe at any speed. (regardless of engine torque) acceleration is proportional to power at any speed. (remember the 'ole, acceleration =power/(mass x velocity) identity?)
so, we all agreed that if the 928 had a broader hp curve, this would be an advantage, and this clearly can be true. HOWEVER, see the curve comparisons for a 928 and a M3 with near the same peak HP of 285.
(note: it would be nice to have a better cleaner 928S4 curve at this level if anyone has one.)
Anyway, here are the two curves of a stock M3 rated at 333flywheel hp and a stock '87 928 S4 rated at 315hp. both have no mods.
Mark
Of course, Randy,, the competitor that he is, had to mention that i had a porsche V8 with all that torque and thats why i passed him at the start! Of course, the team manager of the 2002 BMW E46 M3, devopled to Grand Am Cup GS specs ( 315 to 340rwhp is common and costs of the car are near $80 to 100k) continued to chime in about having only 250ft-lbs of torque and the 928 having 300ft-lbs+. Forget the fact that I got a jump and draft from the 550hp evo at the start and never was able to close on Randy again on a straight after he passed me as he had better turn in and near the same acceleration while i was having major handling issues with that GT3 wing)
Of course, the first thing i came back with was, HP determines rear wheel toruqe at any speed. (regardless of engine torque) acceleration is proportional to power at any speed. (remember the 'ole, acceleration =power/(mass x velocity) identity?)
so, we all agreed that if the 928 had a broader hp curve, this would be an advantage, and this clearly can be true. HOWEVER, see the curve comparisons for a 928 and a M3 with near the same peak HP of 285.
(note: it would be nice to have a better cleaner 928S4 curve at this level if anyone has one.)
Anyway, here are the two curves of a stock M3 rated at 333flywheel hp and a stock '87 928 S4 rated at 315hp. both have no mods.
Mark
Last edited by mark kibort; 07-15-2009 at 06:17 PM.
11-13-2006, 02:22 PM
#2
Race Director
MK
Looking at the graph......at the shift point (lowest RPM)....the 928 engine is making about 50ftlb more torque than the BMW....granted the HP is the same and thats all that matters
Looking at the graph......at the shift point (lowest RPM)....the 928 engine is making about 50ftlb more torque than the BMW....granted the HP is the same and thats all that matters
11-13-2006, 02:50 PM
#3
What do you think could improve your "turn in" Since you mentioned that as a handicap?
11-13-2006, 03:53 PM
#4
Rennlist Member
Thread Starter
i think on that day, Randy was totally bashing my used tire program. saying that new tires are worth about 1 second and who knows how bad my tires were due to them being from 2003. (and he was using brand new hoosiers S06s which he said are worth yet another second) He got a kick out of the fact that I was actually running on his rear tires when he ran the Audi RS6 in 2003!! (my other set was michael galati's!)
the main problem is that im getting more downforce with the new wing than i barganed for. so, i took a ton of wing setting out of it, and have been doing testing. still, its much more downforce than the little stock GTS wing was. that 160lbs at near 100mph is like lifting the front of the car up with 50lbs. if i had perfect turn it before, which i never had it perfect, its easy to see how this has caused a handing issue. heck, im not complaining about a 1:39.0 and lots of 1:39.1-2-3s and 4s, but it wasnt fun to drive with this issue. part of the good was the rear firmly planted to get on the gas early, and that was fun, but the downside was an uncontrollable push, that even the throttle couldnt correct.
The fix is a splitter and less wing settings, as well as the venting of the hood and removal of a lift generator under the front of the car.(tilted air dam)
MK
the main problem is that im getting more downforce with the new wing than i barganed for. so, i took a ton of wing setting out of it, and have been doing testing. still, its much more downforce than the little stock GTS wing was. that 160lbs at near 100mph is like lifting the front of the car up with 50lbs. if i had perfect turn it before, which i never had it perfect, its easy to see how this has caused a handing issue. heck, im not complaining about a 1:39.0 and lots of 1:39.1-2-3s and 4s, but it wasnt fun to drive with this issue. part of the good was the rear firmly planted to get on the gas early, and that was fun, but the downside was an uncontrollable push, that even the throttle couldnt correct.
The fix is a splitter and less wing settings, as well as the venting of the hood and removal of a lift generator under the front of the car.(tilted air dam)
MK
Originally Posted by BrendanC
What do you think could improve your "turn in" Since you mentioned that as a handicap?
11-13-2006, 03:56 PM
#5
Rennlist Member
Thread Starter
So yes, you get this and this is the ROOT of the confusion. 50ft-lbs of torque more at the low shift point, doesnt correlate into more torque at the rear wheels at any same speed. HP does. so, at that shift speed, both cars with the same HP will accelerate the same because they have the same torque through the gear boxes. whats cool about this comparison, is that the gear boxes are pretty close to the same as the 928 as far as spacing, so this is a great comparison to make the point of HP matters, flywheel torque is absolutely comparitively meaningless.
Mk
Mk
Originally Posted by IcemanG17
MK
Looking at the graph......at the shift point (lowest RPM)....the 928 engine is making about 50ftlb more torque than the BMW....granted the HP is the same and thats all that matters
Looking at the graph......at the shift point (lowest RPM)....the 928 engine is making about 50ftlb more torque than the BMW....granted the HP is the same and thats all that matters
11-13-2006, 04:31 PM
#6
Originally Posted by mark kibort
but it wasnt fun to drive with this issue. part of the good was the rear firmly planted to get on the gas early, and that was fun, but the downside was an uncontrollable push, that even the throttle couldnt correct.
The fix is a splitter and less wing settings, as well as the venting of the hood and removal of a lift generator under the front of the car.(tilted air dam)
MK
The fix is a splitter and less wing settings, as well as the venting of the hood and removal of a lift generator under the front of the car.(tilted air dam)
MK
11-13-2006, 05:09 PM
#7
Three Wheelin'
Originally Posted by mark kibort
I got into a discussion with Randy Pobst and the team owner that he was testing for regarding the always misunderstood, flywheel toruqe vs HP subject.
Of course, Randy,, the competitor that he is, had to mention that i had a porsche V8 with all that torque and thats why i passed him at the start! Of course, the team manager of the 2002 BMW E46 M3, devopled to Grand Am Cup GS specs ( 315 to 340rwhp is common and costs of the car are near $80 to 100k) continued to chime in about having only 250ft-lbs of torque and the 928 having 300ft-lbs+. Forget the fact that I got a jump and draft from the 550hp evo at the start and never was able to close on Randy again on a straight after he passed me as he had better turn in and near the same acceleration while i was having major handling issues with that GT3 wing)
Of course, the first thing i came back with was, HP determines rear wheel toruqe at any speed. (regardless of engine torque) acceleration is proportional to power at any speed. (remember the 'ole, acceleration =power/(mass x velocity) identity?)
so, we all agreed that if the 928 had a broader hp curve, this would be an advantage, and this clearly can be true. HOWEVER, see the curve comparisons for a 928 and a M3 with near the same peak HP of 285.
(note: it would be nice to have a better cleaner 928S4 curve at this level if anyone has one.)
Anyway, here are the two curves of a stock M3 rated at 333flywheel hp and a stock '87 928 S4 rated at 315hp. both have no mods.
Mark
Of course, Randy,, the competitor that he is, had to mention that i had a porsche V8 with all that torque and thats why i passed him at the start! Of course, the team manager of the 2002 BMW E46 M3, devopled to Grand Am Cup GS specs ( 315 to 340rwhp is common and costs of the car are near $80 to 100k) continued to chime in about having only 250ft-lbs of torque and the 928 having 300ft-lbs+. Forget the fact that I got a jump and draft from the 550hp evo at the start and never was able to close on Randy again on a straight after he passed me as he had better turn in and near the same acceleration while i was having major handling issues with that GT3 wing)
Of course, the first thing i came back with was, HP determines rear wheel toruqe at any speed. (regardless of engine torque) acceleration is proportional to power at any speed. (remember the 'ole, acceleration =power/(mass x velocity) identity?)
so, we all agreed that if the 928 had a broader hp curve, this would be an advantage, and this clearly can be true. HOWEVER, see the curve comparisons for a 928 and a M3 with near the same peak HP of 285.
(note: it would be nice to have a better cleaner 928S4 curve at this level if anyone has one.)
Anyway, here are the two curves of a stock M3 rated at 333flywheel hp and a stock '87 928 S4 rated at 315hp. both have no mods.
Mark
Here is a dyno run from an '87 S4 5spd. I can't remember what car it was. Might have been mine.
https://rennlist.com/forums/attachme...d=152055&stc=1
'87S4 5spd FullExhaust.jpg
Last edited by Louie928; 03-18-2008 at 01:11 PM.
Trending Topics
11-13-2006, 05:23 PM
#8
Rennlist Member
Thread Starter
usually they do this to get better flow for cooling , and to fit a radiator in a short area in the nose. i dont know the pressure drop across a radiator, but i bet its big. im sure there are some gains from the vent air going through the radiator to be vented up through the hood vs it going under the car, but i dont know the actaul gain. You could look at the flow of the fans as the indicator of the total air through the radiator at moderate speeds. maybe both electric fans make near 5-10lbs of thrust and at some point that matches the air flow through the car's radiator. so, you could assume that 5-10llbs could be the max downforce you could get at the nose in our cars. however, the air that cant penetrate the radiator, (which is certainly a lot) helps to build the pressure zone in front of the nose, which is then routed around the car via the splitter as this is the primary contributer to downforce in the front of race cars.
I think there are a ton of factors here, im just wondering if the cutting of a hole in the hood is worth it, or if i should just work on making a better splitter.
Mk
I think there are a ton of factors here, im just wondering if the cutting of a hole in the hood is worth it, or if i should just work on making a better splitter.
Mk
Originally Posted by BrendanC
What changes to vent the hood are you going to try? Where do you put the splitter? What about tilting the Radiator forward and moving the bottom foot back so you can pick up lower air and have it rushout the top of the hood before the engine?
11-13-2006, 06:56 PM
#9
What about a flat bottom
11-13-2006, 07:36 PM
#10
Nordschleife Master
I'm honored that a man of Mr. Pobst's stature shares my position.
Too bad the graphs are clipped off so I can't see all the numbers.
Don't forget: once you're in a gear the acceleration rate follows the torque. If it's a flat line you'll accelerate smoothly. If the torque tails down so will the acceleration.
Too bad the graphs are clipped off so I can't see all the numbers.
Don't forget: once you're in a gear the acceleration rate follows the torque. If it's a flat line you'll accelerate smoothly. If the torque tails down so will the acceleration.
11-13-2006, 07:58 PM
#11
Rennlist Member
Thread Starter
glen,
pobst doesnt get it either. dont worry, he is not alone. maybe its one of the reasons that a 20 year old car with no tunning, used tires and too much wing can keep up with a top pro, motons, 340ish rwhp and brand new hoosiers!
what numbers are you looking for? if you want torque numbers, unfortunately, the torque units on the S4 (i just noticed)is in metric (notice that torque and hp dont intersect at 5250) in that case, just use the plot that louie just provided.
Now, i know we dont have to go over this again, but acceleration follows torque in each gear, but remember, it follows the torque at the rear wheels at any speed. its tied to engine torque, but if you look at the range of operation, if the HP curves are the same shape, the torque curves will be too. generally in race cars, the point at which you operate a race car to keep max acceleration , is on the falling side of the torque curve anyway. on the bmw its 5500 to 7800rpm and on the S4 its 4200 to 6000rpm. the engine torque values are tremendously different, (ie BMW has 200ft-lbs of torque while the 928 has 265ft-lbs of torque at the same 95% of max rpm) what this means is that becasue the gearing is off by 30%, the lower torque at any speed is multplied more, so at the same speed, the resultant torque to accelerate the car is near identical (see 1,200ft-lbs of rear wheel torque at 100mph based on either 200ft-lbs x 5.9:1 for the BMW or 265ft-lbs x 4.5:1 for the porsche = 1,200ft-lbs of torque at either car's rear wheels accelerating them both at the SAME rate at that same speed!
basic newtonian identity again.
acceleration=Power/(mass x velocity) this means acceleration is proportional to power at any vehicle speed.
It also means pobst is making up excuses for why i passed him and led a lap against a faster car. i was drafting at 100mph, he wasnt, i got a jump on the flag, he didnt. later, he passed me and was .5 to 1 second faster a lap. but then again, why???? I should show you an even more dramatic example of these concepts. the race in early october, i ran against a speed World challenge HONDA Civic. we were neck and nect for the entire race. bumper to bumper, i had no advantage anywhere! in fact, the only place i found advantages was underbraking as even though he is a laguna local, he was leaving time on the table, i could clearly see it. otherwise gear for gear we were dead nuts on!! ever see a 4 banger Civic HP /torque curve? i bet i had 2x the torque at the engine! HP to weight ratio was identical and that was why we accelerated the same!
MK
EIDT: Here are the revised curves using a S4 graph with english units for torque and the entire graph for your review Glen.
I challenge you to find one spot at any speed that a BMW or porsche 928 would have any advantage in acceleration, even though the porsche has 100ft-lbs more engine torque!! thats the point of all this!
pobst doesnt get it either. dont worry, he is not alone. maybe its one of the reasons that a 20 year old car with no tunning, used tires and too much wing can keep up with a top pro, motons, 340ish rwhp and brand new hoosiers!
what numbers are you looking for? if you want torque numbers, unfortunately, the torque units on the S4 (i just noticed)is in metric (notice that torque and hp dont intersect at 5250) in that case, just use the plot that louie just provided.
Now, i know we dont have to go over this again, but acceleration follows torque in each gear, but remember, it follows the torque at the rear wheels at any speed. its tied to engine torque, but if you look at the range of operation, if the HP curves are the same shape, the torque curves will be too. generally in race cars, the point at which you operate a race car to keep max acceleration , is on the falling side of the torque curve anyway. on the bmw its 5500 to 7800rpm and on the S4 its 4200 to 6000rpm. the engine torque values are tremendously different, (ie BMW has 200ft-lbs of torque while the 928 has 265ft-lbs of torque at the same 95% of max rpm) what this means is that becasue the gearing is off by 30%, the lower torque at any speed is multplied more, so at the same speed, the resultant torque to accelerate the car is near identical (see 1,200ft-lbs of rear wheel torque at 100mph based on either 200ft-lbs x 5.9:1 for the BMW or 265ft-lbs x 4.5:1 for the porsche = 1,200ft-lbs of torque at either car's rear wheels accelerating them both at the SAME rate at that same speed!
basic newtonian identity again.
acceleration=Power/(mass x velocity) this means acceleration is proportional to power at any vehicle speed.
It also means pobst is making up excuses for why i passed him and led a lap against a faster car. i was drafting at 100mph, he wasnt, i got a jump on the flag, he didnt. later, he passed me and was .5 to 1 second faster a lap. but then again, why???? I should show you an even more dramatic example of these concepts. the race in early october, i ran against a speed World challenge HONDA Civic. we were neck and nect for the entire race. bumper to bumper, i had no advantage anywhere! in fact, the only place i found advantages was underbraking as even though he is a laguna local, he was leaving time on the table, i could clearly see it. otherwise gear for gear we were dead nuts on!! ever see a 4 banger Civic HP /torque curve? i bet i had 2x the torque at the engine! HP to weight ratio was identical and that was why we accelerated the same!
MK
EIDT: Here are the revised curves using a S4 graph with english units for torque and the entire graph for your review Glen.
I challenge you to find one spot at any speed that a BMW or porsche 928 would have any advantage in acceleration, even though the porsche has 100ft-lbs more engine torque!! thats the point of all this!
Originally Posted by GlenL
I'm honored that a man of Mr. Pobst's stature shares my position.
Too bad the graphs are clipped off so I can't see all the numbers.
Don't forget: once you're in a gear the acceleration rate follows the torque. If it's a flat line you'll accelerate smoothly. If the torque tails down so will the acceleration.
Too bad the graphs are clipped off so I can't see all the numbers.
Don't forget: once you're in a gear the acceleration rate follows the torque. If it's a flat line you'll accelerate smoothly. If the torque tails down so will the acceleration.
Last edited by mark kibort; 07-15-2009 at 06:17 PM.
11-14-2006, 01:00 PM
#12
Rennlist Member
Thread Starter
Glen,
Is there ONE point on the comparison graphs where one car will accelerate at a faster rate than the other? if so, name that speed.
There wont be, because the HP curves are mirror images of each other, (close to the same) even though the TORQUE curves are almost 100ft-lbs off from one another!
This kind of blows a hole on the whole, "the V8 has the grunt down low" thing that all the annoucners in racing seem to talk about as well as Randy and the Evo guys. (and i seems, still you) It also is a great example that summarizes all of the HP vs torque talk.
as far as your last sentence goes, yes in each gear acceleration is proportionate , in that gear to torque. I dont agree with the term, "smoothly" as acceleration could be at a constant rate with a flat torque curve traverse, however, when do we or anyone in racing to maximize acceleration , use the flat spot of a torque curve? second, a flat torque curve doesnt assure constant acceleration, as the forces acting against the car go up with the square (and some proportional ) of speed. But, i get your point there.
MK
Is there ONE point on the comparison graphs where one car will accelerate at a faster rate than the other? if so, name that speed.
There wont be, because the HP curves are mirror images of each other, (close to the same) even though the TORQUE curves are almost 100ft-lbs off from one another!
This kind of blows a hole on the whole, "the V8 has the grunt down low" thing that all the annoucners in racing seem to talk about as well as Randy and the Evo guys. (and i seems, still you) It also is a great example that summarizes all of the HP vs torque talk.
as far as your last sentence goes, yes in each gear acceleration is proportionate , in that gear to torque. I dont agree with the term, "smoothly" as acceleration could be at a constant rate with a flat torque curve traverse, however, when do we or anyone in racing to maximize acceleration , use the flat spot of a torque curve? second, a flat torque curve doesnt assure constant acceleration, as the forces acting against the car go up with the square (and some proportional ) of speed. But, i get your point there.
MK
Originally Posted by GlenL
I'm honored that a man of Mr. Pobst's stature shares my position.
Too bad the graphs are clipped off so I can't see all the numbers.
Don't forget: once you're in a gear the acceleration rate follows the torque. If it's a flat line you'll accelerate smoothly. If the torque tails down so will the acceleration.
Too bad the graphs are clipped off so I can't see all the numbers.
Don't forget: once you're in a gear the acceleration rate follows the torque. If it's a flat line you'll accelerate smoothly. If the torque tails down so will the acceleration.
11-14-2006, 02:05 PM
#13
Nordschleife Master
I'm now honored that you've responded to my post twice!
Of course you had to see my comment about Mr. Pobst as a fun taunt.
I chose "smoothly" over "at a constant rate" as that's confounding to the technical purists. But you got my point.
The Evo guys are right in that their turbo (or is it turbos?) needs to be spooled up but cubic inches are always ready.
As for the initial conversation, perhaps the gearing of the cars favored you in that start.
Of course you had to see my comment about Mr. Pobst as a fun taunt.
I chose "smoothly" over "at a constant rate" as that's confounding to the technical purists. But you got my point.
The Evo guys are right in that their turbo (or is it turbos?) needs to be spooled up but cubic inches are always ready.
As for the initial conversation, perhaps the gearing of the cars favored you in that start.
11-14-2006, 02:35 PM
#14
Rennlist Member
Thread Starter
Glen, you know your my technology pal! ("cubed, not squared!!"
yes, i see all this as fun, but educational too!
as far as the turbo's go. i havent seen the curve for their car, but similar cars have the turbos pumping out the same hp as andersons car, right at the start. remember they can run up to 7000rpm and have gear spacing like our cars. I think i saw some graphs that had no degredation in the engine speeds used on the track.
lastly, the gears of the M3 are equally spaced to ours and have the same MPH shift points, with some subtle differences.
ours are
1st 55mph
2nd to 80mph
3rd to 115mph
4th to 155mph
bmw is
2nd to 56mph
3rd to 85mph
4th to 115mph
5th to 141mph
so, the gearing is almost identical.
Mk
yes, i see all this as fun, but educational too!
as far as the turbo's go. i havent seen the curve for their car, but similar cars have the turbos pumping out the same hp as andersons car, right at the start. remember they can run up to 7000rpm and have gear spacing like our cars. I think i saw some graphs that had no degredation in the engine speeds used on the track.
lastly, the gears of the M3 are equally spaced to ours and have the same MPH shift points, with some subtle differences.
ours are
1st 55mph
2nd to 80mph
3rd to 115mph
4th to 155mph
bmw is
2nd to 56mph
3rd to 85mph
4th to 115mph
5th to 141mph
so, the gearing is almost identical.
Mk
Originally Posted by GlenL
I'm now honored that you've responded to my post twice!
Of course you had to see my comment about Mr. Pobst as a fun taunt.
I chose "smoothly" over "at a constant rate" as that's confounding to the technical purists. But you got my point.
The Evo guys are right in that their turbo (or is it turbos?) needs to be spooled up but cubic inches are always ready.
As for the initial conversation, perhaps the gearing of the cars favored you in that start.
Of course you had to see my comment about Mr. Pobst as a fun taunt.
I chose "smoothly" over "at a constant rate" as that's confounding to the technical purists. But you got my point.
The Evo guys are right in that their turbo (or is it turbos?) needs to be spooled up but cubic inches are always ready.
As for the initial conversation, perhaps the gearing of the cars favored you in that start.
11-14-2006, 07:19 PM
#15
Rennlist Member
Originally Posted by mark kibort
Glen,
Is there ONE point on the comparison graphs where one car will accelerate at a faster rate than the other? if so, name that speed.
Is there ONE point on the comparison graphs where one car will accelerate at a faster rate than the other? if so, name that speed.
THAT is what low-end grunt means IMHO -- you have a very fat margin of error, and I'd be very surprised if you tried to tell me that this is of no use in the rough & tumble of a race environment.