I need your help- HP vs torque discussion
02-14-2009, 06:30 PM
#3
I think you're doing just fine on your own.
02-14-2009, 07:11 PM
#4
Nordschleife Master
Can someone please explain to me why are people debating this torque vs. horsepower issue? Given the rpm, there's a linear relationship between the two. Where's the beef?
475hp/460lb.ft
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02-14-2009, 07:30 PM
#8
Nordschleife Master
I am planning a turbo engine, and generating or reducing torque with boost is not a problem. My plan right now is to run a gear-based boost controller, and shoot for 80% of the peak torque from 3500 to 7000rpm, a power band ratio of 2. In my opinion, powerband of two is going to be wide enough for even a bad driver like myself. With the control unit, I can also shave off all peaks in the torque curve.
By the way, is my understanding correct that a perfectly flat torque curve would be the ideal torque curve, and perfectly linear power curve equivalently so?
To the question:
How much torque can the '87 s4 transmission take? Specifically, how much on the engine side and how much on the drive shaft side? Another way to ask the question is how high traction tires can I run and how much torque can I put thru the transmission at each gear?
The clutch will be Spec 3+ (SP143F), so it should hold a bunch. A bunch beeing 775 lbf-ft. At 7000 rpm, 775 lbf-ft equates to 1033hp, so it's safe to say that the clutch is not going to be the limiting factor. My worry is the transmission.
02-14-2009, 07:34 PM
#9
Nordschleife Master
A clarification: This is regarding '87 s4 5-speed manual transmission.
Here's my torque question to everyone.
I am planning a turbo engine, and generating or reducing torque with boost is not a problem. My plan right now is to run a gear-based boost controller, and shoot for 80% of the peak torque from 3500 to 7000rpm, a power band ratio of 2. In my opinion, powerband of two is going to be wide enough for even a bad driver like myself. With the control unit, I can also shave off all peaks in the torque curve.
By the way, is my understanding correct that a perfectly flat torque curve would be the ideal torque curve, and perfectly linear power curve equivalently so?
To the question:
How much torque can the '87 s4 transmission take? Specifically, how much on the engine side and how much on the drive shaft side? Another way to ask the question is how high traction tires can I run and how much torque can I put thru the transmission at each gear?
The clutch will be Spec 3+ (SP143F), so it should hold a bunch. A bunch beeing 775 lbf-ft. At 7000 rpm, 775 lbf-ft equates to 1033hp, so it's safe to say that the clutch is not going to be the limiting factor. My worry is the transmission.
I am planning a turbo engine, and generating or reducing torque with boost is not a problem. My plan right now is to run a gear-based boost controller, and shoot for 80% of the peak torque from 3500 to 7000rpm, a power band ratio of 2. In my opinion, powerband of two is going to be wide enough for even a bad driver like myself. With the control unit, I can also shave off all peaks in the torque curve.
By the way, is my understanding correct that a perfectly flat torque curve would be the ideal torque curve, and perfectly linear power curve equivalently so?
To the question:
How much torque can the '87 s4 transmission take? Specifically, how much on the engine side and how much on the drive shaft side? Another way to ask the question is how high traction tires can I run and how much torque can I put thru the transmission at each gear?
The clutch will be Spec 3+ (SP143F), so it should hold a bunch. A bunch beeing 775 lbf-ft. At 7000 rpm, 775 lbf-ft equates to 1033hp, so it's safe to say that the clutch is not going to be the limiting factor. My worry is the transmission.
02-14-2009, 07:43 PM
#10
Man of many SIGs
Rennlist Member
Rennlist Member
I want to thank you all for the effort to make this happen! It couldn't have been done without you.
I want to particularly thank Mark for continuing to reach deep into his bag of questions that nobody asked, asking them himself, and then providing his answers without wasting the time it would take to see if anyone wanted to hear it. You are the best!
I want to particularly thank Mark for continuing to reach deep into his bag of questions that nobody asked, asking them himself, and then providing his answers without wasting the time it would take to see if anyone wanted to hear it. You are the best!
02-14-2009, 08:55 PM
#11
Rennlist Member
Thread Starter
How it started
There was a guy named "Dez" that asked, if you have equal HP cars, if one has more engine torque than the other, which is better on a road course. Of course, all the knowitalls, jumped in to proclaim the one with more torque. However, I jumped in (big mistak) and said, "IT depends". There are examples of lower torque engiens that can have an advantage at ANY vehicle speed on any road course. As we have debated much more civilized here, the ole, Acceleration = power /(mass x velocity) concept. (or Power= Force x speed)
Later, someone posted the M5 (500hp stock, but modified to 550hp) and Caddy CTSV 550hp dyno runs. both had near the same hp but the caddy had 120ft-lbs more engine torque. The "Knowitalls" came back with the Caddy would get out of turns better. In this example, the caddy and M5 HP curves were almost identical in shape, showing almost the same HP level at any vehicle speed. this was contrdicted by the knowitalls, onw of which has driven both and thought the Caddy got off turns better and ended up with a self verified 10mph higher speed down a straight at VIR. I tolk him, great, is that proof or were those the two cars that were dyno'ed?? He has never replied to any question and just likes to bust folks chops. (ON a massive ego scale)
Sure, I could have just let it go, by out you know me. pursuit of truth!
So, I posted an interesting dyno run set of a 928 (scots 5 liter v8) vs my buddies M3 3.2 euro motor. As expected to me, the M3 had more HP at any speed that the two cars would compete at, at ANY track, off any curve, etc.
I showed the dyno rus, I showed the gearing charts and picked a speed at the 928s PEAK TORQUE level. The math was simple and shows the 928 lacking in REAR WHEEL MULTIPLIED TORQUE, at that speed and any other.
This was declared nonsense, magic and not real world. EVen though the facts that we have seen both of these cars at the track, and ewn without the lighter weight of the BMW, it has some GET UP off the curves. seeing the dyno runs, its NO surprise why.
This discussion went on for 20 pages and still the leader of the nay sayers, stick by their guns quoting that engine torque is what determines off turn acceleration , or "real world " performance. The only point to Dez, was to point out that " It DEPENDS". shape of HP curve, all other things being equal is the determinant factor for rear wheel torque, and to the pavement forces!
Anyway, thought those of you versed in the topic of basic physics, but complicated application, would be able to chime in and help.
One of these guys on the thread is a real Gem.
I also got plenty of pro team engineers and physics guys emailing and PM'ing me, validating I was doing a good job, but to not waste time with these bozos.
I would rather argue with these guys in some spirited discussion than watch CSI with my wife. This way, i can do both!
mk
Later, someone posted the M5 (500hp stock, but modified to 550hp) and Caddy CTSV 550hp dyno runs. both had near the same hp but the caddy had 120ft-lbs more engine torque. The "Knowitalls" came back with the Caddy would get out of turns better. In this example, the caddy and M5 HP curves were almost identical in shape, showing almost the same HP level at any vehicle speed. this was contrdicted by the knowitalls, onw of which has driven both and thought the Caddy got off turns better and ended up with a self verified 10mph higher speed down a straight at VIR. I tolk him, great, is that proof or were those the two cars that were dyno'ed?? He has never replied to any question and just likes to bust folks chops. (ON a massive ego scale)
Sure, I could have just let it go, by out you know me. pursuit of truth!
So, I posted an interesting dyno run set of a 928 (scots 5 liter v8) vs my buddies M3 3.2 euro motor. As expected to me, the M3 had more HP at any speed that the two cars would compete at, at ANY track, off any curve, etc.
I showed the dyno rus, I showed the gearing charts and picked a speed at the 928s PEAK TORQUE level. The math was simple and shows the 928 lacking in REAR WHEEL MULTIPLIED TORQUE, at that speed and any other.
This was declared nonsense, magic and not real world. EVen though the facts that we have seen both of these cars at the track, and ewn without the lighter weight of the BMW, it has some GET UP off the curves. seeing the dyno runs, its NO surprise why.
This discussion went on for 20 pages and still the leader of the nay sayers, stick by their guns quoting that engine torque is what determines off turn acceleration , or "real world " performance. The only point to Dez, was to point out that " It DEPENDS". shape of HP curve, all other things being equal is the determinant factor for rear wheel torque, and to the pavement forces!
Anyway, thought those of you versed in the topic of basic physics, but complicated application, would be able to chime in and help.
One of these guys on the thread is a real Gem.
I also got plenty of pro team engineers and physics guys emailing and PM'ing me, validating I was doing a good job, but to not waste time with these bozos.
I would rather argue with these guys in some spirited discussion than watch CSI with my wife. This way, i can do both!
mk
02-14-2009, 09:07 PM
#12
Nordschleife Master
MK --
Here's my question to you. Why do people quote the power band in RPM? Someone could say, for example, that the engine has a 3000 rpm power band. (Let's define the powerband as the band between max torque and max power rpms, although I like the definition of the longest continuous range in which the torque is within x% of the max torque). But isn't a 3000 rpm band completely different if it's from 2000 to 5000 rpm vs. from 10000 to 13000rpm? Why aren't people quoting the power band ratios, that is the max power rpm to max torque rpm? Isn't this a much better measure of powerband (for cars with a transmission)?
Regarding the topic of this thread: Has someone explained to your opponents in that other thread the function of that big heavy box between the engine and the rear end?
Best, Tuomo
Here's my question to you. Why do people quote the power band in RPM? Someone could say, for example, that the engine has a 3000 rpm power band. (Let's define the powerband as the band between max torque and max power rpms, although I like the definition of the longest continuous range in which the torque is within x% of the max torque). But isn't a 3000 rpm band completely different if it's from 2000 to 5000 rpm vs. from 10000 to 13000rpm? Why aren't people quoting the power band ratios, that is the max power rpm to max torque rpm? Isn't this a much better measure of powerband (for cars with a transmission)?
Regarding the topic of this thread: Has someone explained to your opponents in that other thread the function of that big heavy box between the engine and the rear end?
Best, Tuomo
02-14-2009, 09:23 PM
#13
Rennlist Member
Thread Starter
They shouldnt be. it should be the ratio, as you say, of a percentage of time spent near the max HP level and directly dependent on the gear ratio spacing. Our gear ratio spacing is near 27% rpm drop per shift (besides the 2.2 5th gear of 50% )
The HP-seconds you produce will win the battle all other things being equal. (maximizing time at max HP) torque is kind of irrelevant. Its the torque at the rear wheels that matters and this is determined by engine HP.
mk
) The HP-seconds you produce will win the battle all other things being equal. (maximizing time at max HP) torque is kind of irrelevant. Its the torque at the rear wheels that matters and this is determined by engine HP.
mk
MK --
Here's my question to you. Why do people quote the power band in RPM? Someone could say, for example, that the engine has a 3000 rpm power band. (Let's define the powerband as the band between max torque and max power rpms, although I like the definition of the longest continuous range in which the torque is within x% of the max torque). But isn't a 3000 rpm band completely different if it's from 2000 to 5000 rpm vs. from 10000 to 13000rpm? Why aren't people quoting the power band ratios, that is the max power rpm to max torque rpm? Isn't this a much better measure of powerband (for cars with a transmission)?
Regarding the topic of this thread: Has someone explained to your opponents in that other thread the function of that big heavy box between the engine and the rear end?
Best, Tuomo
Here's my question to you. Why do people quote the power band in RPM? Someone could say, for example, that the engine has a 3000 rpm power band. (Let's define the powerband as the band between max torque and max power rpms, although I like the definition of the longest continuous range in which the torque is within x% of the max torque). But isn't a 3000 rpm band completely different if it's from 2000 to 5000 rpm vs. from 10000 to 13000rpm? Why aren't people quoting the power band ratios, that is the max power rpm to max torque rpm? Isn't this a much better measure of powerband (for cars with a transmission)?
Regarding the topic of this thread: Has someone explained to your opponents in that other thread the function of that big heavy box between the engine and the rear end?
Best, Tuomo
02-14-2009, 09:27 PM
#14
Rennlist Member
Thread Starter
Flat HP curve is not really something that you need to look at , nor want. you want a flat HP curve , after all its HP that determines acceleration. your use range for racing will be as wide as your gear spacing, and will revolve around your max HP. use aveage HP as a rule of thumb.
mk
mk
Here's my torque question to everyone.
I am planning a turbo engine, and generating or reducing torque with boost is not a problem. My plan right now is to run a gear-based boost controller, and shoot for 80% of the peak torque from 3500 to 7000rpm, a power band ratio of 2. In my opinion, powerband of two is going to be wide enough for even a bad driver like myself. With the control unit, I can also shave off all peaks in the torque curve.
By the way, is my understanding correct that a perfectly flat torque curve would be the ideal torque curve, and perfectly linear power curve equivalently so?
To the question:
How much torque can the '87 s4 transmission take? Specifically, how much on the engine side and how much on the drive shaft side? Another way to ask the question is how high traction tires can I run and how much torque can I put thru the transmission at each gear?
The clutch will be Spec 3+ (SP143F), so it should hold a bunch. A bunch beeing 775 lbf-ft. At 7000 rpm, 775 lbf-ft equates to 1033hp, so it's safe to say that the clutch is not going to be the limiting factor. My worry is the transmission.
I am planning a turbo engine, and generating or reducing torque with boost is not a problem. My plan right now is to run a gear-based boost controller, and shoot for 80% of the peak torque from 3500 to 7000rpm, a power band ratio of 2. In my opinion, powerband of two is going to be wide enough for even a bad driver like myself. With the control unit, I can also shave off all peaks in the torque curve.
By the way, is my understanding correct that a perfectly flat torque curve would be the ideal torque curve, and perfectly linear power curve equivalently so?
To the question:
How much torque can the '87 s4 transmission take? Specifically, how much on the engine side and how much on the drive shaft side? Another way to ask the question is how high traction tires can I run and how much torque can I put thru the transmission at each gear?
The clutch will be Spec 3+ (SP143F), so it should hold a bunch. A bunch beeing 775 lbf-ft. At 7000 rpm, 775 lbf-ft equates to 1033hp, so it's safe to say that the clutch is not going to be the limiting factor. My worry is the transmission.
02-14-2009, 09:38 PM
#15
Nordschleife Master
Flat HP curve is not really something that you need to look at , nor want. you want a flat HP curve , after all its HP that determines acceleration. your use range for racing will be as wide as your gear spacing, and will revolve around your max HP. use aveage HP as a rule of thumb. mk
Here's why I think this is the case for my project. I am building a turbo car, and the reason why one should want this for a turbo car with basically unlimited power within reason. I say within reason because a Subaru 2.5 liter engine can be tuned to put out 800 hp. With similar tricks, one could take out 1600 hp from a 5.0 s4. Of course, wheels would just spin for a momentum before everything would break. The point being is that with a turbo, the problem is not generating torque or power but it's keeping the traction.
For a given gear, the torque limit imposed by tire traction measured at the flywheel is approximately constant. If the tires can handle a certain torque limit without lighting up, then the max useful engine torque at 1st gear is lower by the factor of ratio-to-ratio on a higher gear.