WHP vs. Crank power
- Thread starter pjork
- Start date
figure its like 15%..just count yourself lucky...AWD is huge!
- :
- 2001 Mazda MP3
not %. depends. drivetain loss. a LSD etc helps , stuff like that.
yea..i forgot to mention that
Installshield 2
Gothenburg Superiority
I think I was sort of involved in that thread...
Here is what I could find out since then...I will relate this as much to 2.0L G-15M-R equipped proteges as I can...Also assume that nothing is changed in anyway from the crankshaft out, no clutch/flywheel changes, no LSDs, no driveaxle weights changed etc...
here are the two sides of the argument more or less...A LOT of people argue that you loose a fixed percentage of hp to the wheels...meaning if we loose 22% of the factory bhp rating, that 22% holds true regardless of the engine output...so applying that to a much more powerful P5, say with about 300bhp (again assuming nothing has been done to the drivetrain, which makes this impossible, so it is all theoretical) you take 22% of 300 which is 66...so a 300bhp P5 will loose 22% or 66hp to the wheels for a whp rating of 234, and a 130bhp P5 will loose 22% or 28.6hp to the wheels for a whp rating of slightly over 100...I can't see how this makes sense...the 300bhp protege5 with an identical drivetrain would loose 66hp, compared to the stock P5 loosing only 30hp...
I argue that the percentage fluctuates with the bhp rating, and that you will always loose a fixed X amount of hp to the wheels...Meaning we will always loose only roughly 28.6hp to the wheels, and if you increase the engine's bhp rating that has virtually no effect on how much you loose to a certain point, you will still only loose 28.6hp even with a 300bhp engine in your P5...and in this case the car is loosing 9.5% of the bhp to the wheels
I ran this by a mechanical engineer and he opened up some other variables worth looking at...He told me that the % lost does change and is related to bhp, and that you more less only loose the same amount of hp through a transaxle, even if you increase that engine's bhp...But with an increase of power, acceleration within the gearbox internals also increases which can lead to flexures that will make the gearbox consume more power...But these increase are not very significant until well over 600hp, so this does not effect our level of engine tuning...
Here is how he made it make sense to me...if you would de-tune or restrict a P5's engine to make 28.6bhp...The car would not move...the engine would not be able to overcome the needed power to turn the gearbox internals and thus move the car, and therefore stall...and also at this case the drivetrain is consuming 100% of the engine's power...so you have a drivetrain loss of 100%...Now the other theory suggests that if you could restrict a P5's engine to make only 10bhp, you would still be putting 2.2whp to the pavement (22% of 10 is 2.2)...Hopefully you can see why this makes little sense, this suggests that by decreasing the engine's output you make the gearbox more efficient...and if you want to get really technical you could say that a 2bhp rated P5 is still making .44whp...I am just not buying it...
Here is why this is important...if you do a mod that increase your whp by 10, you also gained 10bhp...Some guys say that a 10whp mod will give you 13-14bhp, but I have never found an argument to justify that...
Please somebody really argue me on this, this has been bugging me for a while and still am not 100% sure about either theory...
Here is what I could find out since then...I will relate this as much to 2.0L G-15M-R equipped proteges as I can...Also assume that nothing is changed in anyway from the crankshaft out, no clutch/flywheel changes, no LSDs, no driveaxle weights changed etc...
here are the two sides of the argument more or less...A LOT of people argue that you loose a fixed percentage of hp to the wheels...meaning if we loose 22% of the factory bhp rating, that 22% holds true regardless of the engine output...so applying that to a much more powerful P5, say with about 300bhp (again assuming nothing has been done to the drivetrain, which makes this impossible, so it is all theoretical) you take 22% of 300 which is 66...so a 300bhp P5 will loose 22% or 66hp to the wheels for a whp rating of 234, and a 130bhp P5 will loose 22% or 28.6hp to the wheels for a whp rating of slightly over 100...I can't see how this makes sense...the 300bhp protege5 with an identical drivetrain would loose 66hp, compared to the stock P5 loosing only 30hp...
I argue that the percentage fluctuates with the bhp rating, and that you will always loose a fixed X amount of hp to the wheels...Meaning we will always loose only roughly 28.6hp to the wheels, and if you increase the engine's bhp rating that has virtually no effect on how much you loose to a certain point, you will still only loose 28.6hp even with a 300bhp engine in your P5...and in this case the car is loosing 9.5% of the bhp to the wheels
I ran this by a mechanical engineer and he opened up some other variables worth looking at...He told me that the % lost does change and is related to bhp, and that you more less only loose the same amount of hp through a transaxle, even if you increase that engine's bhp...But with an increase of power, acceleration within the gearbox internals also increases which can lead to flexures that will make the gearbox consume more power...But these increase are not very significant until well over 600hp, so this does not effect our level of engine tuning...
Here is how he made it make sense to me...if you would de-tune or restrict a P5's engine to make 28.6bhp...The car would not move...the engine would not be able to overcome the needed power to turn the gearbox internals and thus move the car, and therefore stall...and also at this case the drivetrain is consuming 100% of the engine's power...so you have a drivetrain loss of 100%...Now the other theory suggests that if you could restrict a P5's engine to make only 10bhp, you would still be putting 2.2whp to the pavement (22% of 10 is 2.2)...Hopefully you can see why this makes little sense, this suggests that by decreasing the engine's output you make the gearbox more efficient...and if you want to get really technical you could say that a 2bhp rated P5 is still making .44whp...I am just not buying it...
Here is why this is important...if you do a mod that increase your whp by 10, you also gained 10bhp...Some guys say that a 10whp mod will give you 13-14bhp, but I have never found an argument to justify that...
Please somebody really argue me on this, this has been bugging me for a while and still am not 100% sure about either theory...
Last edited:
twilightprotege
Member
- :
- 2001 323 Astina SP20 (P5)
very good theory, well put. i tend to agree.
i was going to say, as a general rule of thumb, what you get in whp is what the engine makes in kw. 1hp = apx 0.74kw. but that theory of yours sorta puts that to shame.
how about someone take the engine out, dyno it. chuck it back in the car and do another dyno
hehehe....
but i like the way you think about mods...obviously it is a sliding scale....i'm personally leaning towards this - you losse XXhp through the drivetrain plus XX% of the total hp you're putting out. so at 130hp at the crank, you're loosing 20hp + 7.6% of the total output (10hp), giving 100whp.....taking that further....200hp at the engine - you'll loose 20hp + 15hp...so you're making 165whp....
i'm certain those figures are wrong (ie the base 20hp + 7.6%), but that's just my idea in writing.
i was going to say, as a general rule of thumb, what you get in whp is what the engine makes in kw. 1hp = apx 0.74kw. but that theory of yours sorta puts that to shame.
how about someone take the engine out, dyno it. chuck it back in the car and do another dyno
hehehe....but i like the way you think about mods...obviously it is a sliding scale....i'm personally leaning towards this - you losse XXhp through the drivetrain plus XX% of the total hp you're putting out. so at 130hp at the crank, you're loosing 20hp + 7.6% of the total output (10hp), giving 100whp.....taking that further....200hp at the engine - you'll loose 20hp + 15hp...so you're making 165whp....
i'm certain those figures are wrong (ie the base 20hp + 7.6%), but that's just my idea in writing.
