Re: Calculation for "CRANK" HP when you already know WHP (1fastmk3)
WHP / .85 = CHP <--- using the accepted 15% loss
Example:
121 whp / .85 = CHP
142.35 = CHP
To go the other way.......
CHP * .85 = WHP
115 * .85 = WHP
97.75 = WHP ( I had 96 whp when my car was stock)
Re: Calculation for "CRANK" HP when you already know WHP (AllMotor8v)
Quote, originally posted by AllMotor8v »
WHP / .85 = CHP <--- using the accepted 15% loss
That's only asuming 15% is accepted. I've heard 12% thrown around alot but we'll never know unless someone dynos their car on a chasis dyno then takes out the motor and dynos that on an engine dyno, then we can find the true driveline loss %.
Re: Calculation for "CRANK" HP when you already know WHP (MikeBlaze)
my thoughts:
if you had a baseline, good tune and no mods dyno. then you could calculate the loss from the WHP to CHP.
if you dont have one then its a guess mostlty. i have heard anything from 12% on really efficient 5speeds. to near 25% for crappy autos.
15% is a good thought. but it could be +/- a few percent.
Re: Calculation for "CRANK" HP when you already know WHP (dunhamjr)
Quote, originally posted by dunhamjr »
you can get better guesses by using the stock rated output...
but yes they are still guesses http://****************.com/smile/emthup.gif
Oh, now I see what you and Jeff are talking about with the stock manufacturers figure. Didn't pick that up before. One of these days I'll dyno a motor and drop it in a car and dyno it again, see what the deal is. I know of at least one shop with an engine dyno in PA.
Re: Calculation for "CRANK" HP when you already know WHP (MikeBlaze)
Quote, originally posted by MikeBlaze »
One of these days I'll dyno a motor and drop it in a car and dyno it again, see what the deal is. I know of at least one shop with an engine dyno in PA.
I think alot of us on here would be interested in seeing what you find out. http://****************.com/smile/emthup.gif
However, make sure you don't take any shortcuts and use like just the exhaust mani w/ dp, no airbox..etc etc etc. If possible, try to replicate the under-the-hood situation...but I'm sure I'm just ramblin' about stuff you already thought of. Still though, I'd be interested in seeing what happened...
Re: Calculation for "CRANK" HP when you already know WHP (mk3dub)
Quote, originally posted by mk3dub »
I think alot of us on here would be interested in seeing what you find out. http://****************.com/smile/emthup.gif
I would too for sure. Half the reason I bought the Rabbit was to be able to test stuff out like this and learn from it. As far as test conditions are concerned I don't see a problem nearly duplicating the parts that are used. The intake would remain the same, exhaust isn't a big deal either even if the engine is dynoed with just a header (my rabbit has one), I can always disconnect the rest of the exhaust for the chassis dyno.
Re: Calculation for "CRANK" HP when you already know WHP (mk3dub)
my 1 cent- Drivetrain loss also depends on what oil is in the gearbox, size of wheels, and god knows what...so u r basically gonna be wrong no matter what u do. Also, I have heard from numerous sources that VWs crank "estimates" are not very accurate at all. They say that they are higher tha reality.
Re: Calculation for "CRANK" HP when you already know WHP (AllMotor8v)
Does anyone wonder why we just accept 15% as law? For example..Lets say you have 100 hp. 15% give you 85 hp. So your drivetrain is taking 15hp. So now you get a turbo and make 200 hp. Your drive train still only takes 15hp but under the 15% rule it would say your drive train now need 30 hp to do the same work as before. Now what kind of sense is that?
Re: Calculation for "CRANK" HP when you already know WHP (GTIRACER2.0t)
In my Watercooled Performance book it lists a different formula to calculate crank hp.
crank = (whp / 0.8) + 8
But my problem with that is my stock engine would've had an indicated 128 hp.
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