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Old 06-12-2010, 03:44 PM   #21
VetteNo2
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Darn, im just trying to figure out what my 640rwhp Z is making at the crank. Who knew this would be such a difficult formula to figure out.
How good an estimate do you need? The fixed number posts have indicated a range of 55-75. If you are just curious and an answer plus or minus 10 is okay, call it 65 and you have 705 or, call it 705 plus or minus 10.

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!
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Old 06-12-2010, 09:37 PM   #22
BOB EAGAN
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A C6Z makes 505 at the crank and lets say 430ish at the wheels which would be a 15% loss and 75hp. So are we saying if my car is putting down 640rwhp and we use the same 75hp loss it would be around 715hp at the flywheel?.
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.
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Old 06-12-2010, 09:43 PM   #23
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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....
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Old 06-13-2010, 11:49 PM   #24
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http://forums.corvetteforum.com/c6-z...engine-hp.html

Post #5.
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Old 06-14-2010, 12:15 AM   #25
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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
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Old 06-15-2010, 10:06 AM   #26
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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.
I never knew this. Thanks!
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Old 06-15-2010, 11:34 AM   #27
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each car is different, like the ZR-1 is about 7-8%, Z06 is about 10% the M6 LS3 is about 12% and A6 is about 15%, LS2 M6 is about 15%.. that is just my observation
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Old 06-15-2010, 11:36 AM   #28
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if you want to tell people how much HP your ride has, I would say a little over 700hp..
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Old 06-15-2010, 12:15 PM   #29
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Thanks for showing up on this thread with real facts. It was kinda funny while it lasted though.
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Old 06-15-2010, 01:00 PM   #30
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"...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.
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Old 07-05-2010, 04:00 PM   #31
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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?
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Old 07-05-2010, 04:14 PM   #32
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625rwhp translates to about 720(+-)bhp. So either its a typo or very optomistic LPE advertising.
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Old 07-05-2010, 04:33 PM   #33
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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.
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Old 07-05-2010, 04:42 PM   #34
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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.
Man, you guys really want to drive me nuts now huh? 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.
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Old 07-05-2010, 04:51 PM   #35
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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
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Old 07-05-2010, 05:21 PM   #36
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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.
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Old 07-05-2010, 08:16 PM   #37
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Man, you guys really want to drive me nuts now huh? 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.
It's real easy. Always under-estimate your HP. That way when you beat someone, you have them scratching their head wondering how they lost to a car making only XXX hp. The same thing works if you lose. Then they'll wonder why they only beat you buy X amount of lengths, 1/10s, mphs, etc. Never show all your cards.

Point is, you make a lot of power so exact numbers aren't completely necessary.
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Old 07-05-2010, 08:16 PM
 
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