BHP vs. RWHP
06-12-2010, 03:44 PM
#21
Racer
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As Powelabs said, the only way to know for sure is to put it on an engine dyno. But remember, you still have variables like testing standards, correct procedure, calibration and and other issues to consider.
The real answer is that you have so much power, I'm jealous!
06-12-2010, 09:37 PM
#22
Burning Brakes
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About a year ago this was discussed a lot. Dyno's vary and results vary due to temp., alt., humidity etc. Most stock C6 Z06,s dyno 440-450 rwhp. (Dynojets.) The basic results were manuals loose approx. 55 hp and auto's loose 65 hp through the drivetrain.( this applies to LS2's, LS3's and LS7's) When adding power these values don't seem to change much. Allowing for a plus or minus 10 for the variables would be close. Your Z is probable running 695 + or - 10. I'd say you can claim 700 and be accurate. Must be nice to have 700 hp.
06-12-2010, 09:43 PM
#23
Burning Brakes
Thread Starter
700 is a nice round number I guess. My FI setup is still being tuned so I have not driven it yet with the new power so im just assuming 640ish will be the rwhp. I could be wrong. Stay tuned....
06-14-2010, 12:15 AM
#25
The first dyno was invented in 1821 by Gaspard de Prony. It was called a Prony Brake Dyno and used an actual "brake" to drive the engine against and the "reaction" was read off a pound scale from a spring loaded arm of known length to get the LB-FT of torque. The term "Brake Horsepower" was used to indicate the stated/advertised HP was measured by a Prony Brake dyno. We actually had one of these ancient machines in the engine lab at Georgia Tech along with all the modern engine dynos of the day (circa early '80s). It worked pretty good for low HP engines...once HP went over a certain amount, heat would build quickly causing the friction lining to glaze and the brake couldn't hold the engine. It wasn't exactly automatic either, forget about stepped RPM tests!
http://en.wikipedia.org/wiki/De_Prony_brake
http://en.wikipedia.org/wiki/De_Prony_brake
06-15-2010, 10:06 AM
#26
Drifting
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The difference between crank[shaft] horsepower and rear wheel horsepower is around 12% for a manual transmission car and 15% for an auto. Take the RWHP and devide it by either .88 or .85 and you will have an estimate of the horsepower at the crank[shaft], or as some call it, at the flywheel.
example...640 RWHP divided by .88(manual trans)= 727 crank[shaft](flywheel) horsepower. Remember that is an estimate.
example...640 RWHP divided by .88(manual trans)= 727 crank[shaft](flywheel) horsepower. Remember that is an estimate.
06-15-2010, 12:15 PM
#29
Race Director
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C6 of Year Finalist (performance mods) 2019
06-15-2010, 01:00 PM
#30
Burning Brakes
"...measured at the cars brakes without wheels and tires!!" rotl!! That is a classic. I want to use that as my signature. I hope the person who posted this can see the humor in this.
07-05-2010, 04:00 PM
#31
Burning Brakes
Thread Starter
Update!!! Has anyone read the new Vette magazine? Page 40 has a caption that says the LPE car is making 625whp which is 820 at the flywheel????????? That has to be a mistake, that would be a 24% powertrain loss which would mean my car is making 890 at the crank and 677rwhp. And I know im not making 890 at the flywheel. What gives here?
07-05-2010, 04:33 PM
#33
Melting Slicks
I like to divide by .88 for manual as mentioned already.
But to throw another wrench in the works and add confusion. On a boosted car if you're converting from SAE corrected numbers you will be off b/c those numbers are generally good for N/A cars b/c atmoshperic pressure is considered.
Boosted cars are less susceptible to atmoshpheric pressure changes b/c they make thier own pressure.
But to throw another wrench in the works and add confusion. On a boosted car if you're converting from SAE corrected numbers you will be off b/c those numbers are generally good for N/A cars b/c atmoshperic pressure is considered.
Boosted cars are less susceptible to atmoshpheric pressure changes b/c they make thier own pressure.
07-05-2010, 04:42 PM
#34
Burning Brakes
Thread Starter
I like to divide by .88 for manual as mentioned already.
But to throw another wrench in the works and add confusion. On a boosted car if you're converting from SAE corrected numbers you will be off b/c those numbers are generally good for N/A cars b/c atmoshperic pressure is considered.
Boosted cars are less susceptible to atmoshpheric pressure changes b/c they make thier own pressure.
But to throw another wrench in the works and add confusion. On a boosted car if you're converting from SAE corrected numbers you will be off b/c those numbers are generally good for N/A cars b/c atmoshperic pressure is considered.
Boosted cars are less susceptible to atmoshpheric pressure changes b/c they make thier own pressure.
What does a guy have to do to find out the crank hp? lol I think I will just say 775 and call it a day.
07-05-2010, 04:51 PM
#35
i found an equation online a couple weeks back....
to find out the cars Crank hp you simply take the rwhp hp divide it by .85 and add 10 to the end result to get the cars crank hp
you do the reverse to get rwhp
to find out the cars Crank hp you simply take the rwhp hp divide it by .85 and add 10 to the end result to get the cars crank hp
you do the reverse to get rwhp
07-05-2010, 05:21 PM
#36
Team Owner
Open your calculator on your computer. You will see one of these %. Take your RWHP number and add 15% then hit =. Thats all you gotta do. Dont overthink it. It aint NASA aerodynamics we're doing here.
07-05-2010, 08:16 PM
#37
Point is, you make a lot of power so exact numbers aren't completely necessary.
