Drive train losses
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Drive train losses
I know this topic has been beat to death, well sort of.
Many typically use a percentage instead of a solid hp number.
I have read that on a stock car, you can normally use a percentage (15-18 % stick, 18-20 % auto), but on a modded car, it's more of a number than a percentage.
Okay, I've heard that my 89 6 speed will lose roughly 40-50 hp from crank to wheels. I'm ok with that, not questioning that.
I'm basically asking is torque loss equivalent to hp loss? Would I lose about 40-50 ft. lbs as well?
Is there any stock dyno numbers to go by. Or any LPE engines that have stated hp figures and dyno to see the difference?
Many typically use a percentage instead of a solid hp number.
I have read that on a stock car, you can normally use a percentage (15-18 % stick, 18-20 % auto), but on a modded car, it's more of a number than a percentage.
Okay, I've heard that my 89 6 speed will lose roughly 40-50 hp from crank to wheels. I'm ok with that, not questioning that.
I'm basically asking is torque loss equivalent to hp loss? Would I lose about 40-50 ft. lbs as well?
Is there any stock dyno numbers to go by. Or any LPE engines that have stated hp figures and dyno to see the difference?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Drive train losses (black_89_vette)
On the evening I first had my L98 on the dyno it showed 247 RWHP; just 1/2 hr before that trap speed showed it to be building a peak of 297 CHP.
That amounted to a 17% DT loss with my A4 and stock 2.59 rear, or a 50 HP DT loss.
The dyno pull is on my site so you can calc. peak torque from the trap speed HP nunber if you like.
If I ever get the heads & cam change into her it would be interesting to do the dyno pull & trap speed comparsion again to see if the % loss holds of if the loss is indeed a fixed HP amount.
That amounted to a 17% DT loss with my A4 and stock 2.59 rear, or a 50 HP DT loss.
The dyno pull is on my site so you can calc. peak torque from the trap speed HP nunber if you like.
If I ever get the heads & cam change into her it would be interesting to do the dyno pull & trap speed comparsion again to see if the % loss holds of if the loss is indeed a fixed HP amount.
Melting Slicks
Joined: Jan 2002
Posts: 3,159
Likes: 0
Re: Drive train losses (black_89_vette)
its a combo of both. it takes X hp to spin Y at Z rpms.
if you dont have enough hp to turn Y, it wont turn.
However more load causes more losses. Friction is also not linear. I think its not quiet squared, but something like ^1.75... I read it somewhere, probobly a forum but cant remember.
So its a lil of column a and a little of column b :cheers:
if you dont have enough hp to turn Y, it wont turn.
However more load causes more losses. Friction is also not linear. I think its not quiet squared, but something like ^1.75... I read it somewhere, probobly a forum but cant remember.
So its a lil of column a and a little of column b :cheers:
Instructor
Joined: Oct 2003
Posts: 128
Likes: 0
From: Puyallup WA
Re: Drive train losses (65Z01)
How are you figuring crank HP based on your time slips? You should be able to figure out wheel HP from the time slips, but not crank HP. It's entirely possible to improve your times by swapping in a more efficient transmission or rearend without changing the weight of the car or the horsepower of the engine.
Trey is mostly correct. The HP losses vary with load and speed. So, as you increase your horsepower, you will lose more to the drivetrain. As you spin the drivetrain faster, you lose more power. However, it's certainly doesn't increase linearly, but I'm not sure what the rate is.
Assigning a percentage doesn't really work because of this. And different transmissions will lose different amounts of HP (this is part of why powerglides are so popular in drag racing) so it's more guesswork than anything. The only real way to know is to use an engine dyno and a chassis dyno and compare the graphs.
As for torque losses, keep in mind that horsepower is directly proportional to torque. So, if you lose HP, you lose the exact same percentage of torque by definition.
Trey is mostly correct. The HP losses vary with load and speed. So, as you increase your horsepower, you will lose more to the drivetrain. As you spin the drivetrain faster, you lose more power. However, it's certainly doesn't increase linearly, but I'm not sure what the rate is.
Assigning a percentage doesn't really work because of this. And different transmissions will lose different amounts of HP (this is part of why powerglides are so popular in drag racing) so it's more guesswork than anything. The only real way to know is to use an engine dyno and a chassis dyno and compare the graphs.
As for torque losses, keep in mind that horsepower is directly proportional to torque. So, if you lose HP, you lose the exact same percentage of torque by definition.
