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Old 08-19-2002, 03:05 PM   #1
js0308
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Default What is the % difference (loss) from flywheel HP to rear wheel

I cant remember what the % loss number typically is between flywheel and rear wheel HP calculations. I know most cars are rated from the factory for flywheel HP probably since the more horses they can advertise the better.
:chevy
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Old 08-19-2002, 03:07 PM   #2
Nathan Plemons
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Default Re: What is the % difference (loss) from flywheel HP to rear wheel (js0308)

For a manual tranny calc anywhere from 10-15% auto's are a little higher.

If you believe that my car was rated at 300 hp and it made exactly that at the engine it made 270 at the wheels stock. That's a 10% loss.
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Old 08-19-2002, 03:08 PM   #3
Ender85
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Default Re: What is the % difference (Nathan Plemons)

I heard somewhere that it was 17% for manual cars.
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Old 08-19-2002, 03:19 PM   #4
1991Z07
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Default Re: What is the % difference (loss) from flywheel HP to rear wheel (js0308)

Lingenfelter uses 16% for manuals and 21% for automatics.

I think they know what the loss is....based on engine & chassis dynoing literally thousands of C4 engines over the years. :yesnod:
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Old 08-19-2002, 05:03 PM   #5
FlyboyZR1
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Default Re: What is the % difference (Joe90)

Quote:
Lingenfelter uses 16% for manuals and 21% for automatics.

I think they know what the loss is....based on engine & chassis dynoing literally thousands of C4 engines over the years. :yesnod:
Does this also apply for torque?
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Old 08-19-2002, 05:13 PM   #6
UB2 SLOW
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Default Re: What is the % difference (Joe90)

[QUOTE]Lingenfelter uses 16% for manuals and 21% for automatics.

I think that number is high for Auto's. I got my dynoed prior to any mods and I was getting 253hp at the rear wheels. If it is 21% then I was making about 318hp for a stock LT1. If you go with 15% then I was making 303. The 15% puts me alot closer the stock rating. I did buy the Vette used, but the previous owner said the only thing he did was add a Tranny cooler and shift kit.
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Old 08-19-2002, 06:30 PM   #7
Mez
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Default Re: What is the % difference (loss) from flywheel HP to rear wheel (js0308)

For as long as there have been chassis dynos, I have heard about loosing 15% to 20% in horsepower between the flywheel and rear wheels. Why is it a fixed percent?? Should it not be an amount based on driveline RPM? A flat percent does not make sense to me.

For example, take two engines--one with 300 hp at 6000 rpm and the second one has 400hp at 6000 rpm. Using the 15% rule, you loose 45 hp less at the rear wheels with the 300 hp engine and 60 hp with the 400 hp engine. If the driveline is the same, 15 HP loss with the bigger engine makes no sense.

I would think HP power comsumed by the drive train is a variable on the RPM rather than a simple fixed percent. So, two engines turning 6000 rpm, the absolute HP loss should be the same number.

Another way to look at this is to totally forget about flywheel HP and only discuss rear wheel horse power.
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Old 08-19-2002, 11:34 PM   #8
sinistervette
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Default Re: What is the % difference (loss) from flywheel HP to rear wheel (js0308)

Most calculations, including Lingenfelter's, are based on averages from years of testing. Each individual car is going to be different. When I was racing stock cars, one of my sponsors had a chassis dyno and I did as much testing and changing as I could. I used B/W super T-10's almost all the time. I had a stock one a origionally with an alum. flywheel and 10"clutch, that I spent hours upon hours drilling "lightening holes" in it. My 406 dyno'd 587.4 hp @flywheel / 513 lb/ft tq @ flywheel, and after droping it in the car and 2 nights of racing(about 63 full on laps) we dyno'd it on chassis dyno = 500.4 hp @ rear wheels and 456.5 lb/ft tq @ rear wheels. I lost 87hp(14.8%) and 56.5 lb/ft tq(11%)!!! Later that week I swapped out my stock T-10 for one that we removed 1st and 3rd gears from. Back on the dyno 505.7hp/459.1tq. Hp lost 13.9% tq lost 10.5% from flywheel ratings. Later in the summer, about 3 1/2 months = 17 nights of racing, I puked the clutch/alum flywheel. Replaced it with a ram coupler, a gear type dog clutch that only weighed 2 1/4 lbs.! It bolts on with an automatic trans flex plate. This made the car very responsive to throttle position!! We ran it 3 nights and back on the dyno we went. I also installed new plugs and air filter at this time. 534.5hp / 471.9tq !!! Hp only lost 9% from flywheel and 8% loss of tq!! I messed with changing to small dia.(2" od tubing!) drive shaft, alum. drive shafts, 30w motor oil in both trans and rear dif. and some of these did change output, just not much at all. I've never run an auto trans, so I'm not sure what they are loosing, the guy that had the chassis dyno said that most of the automatic cars he tested were loosing anywhere from 13% all the way up to 28%!! He said that the biggest loss in an automatic was always the convertor. He installed a "inexpensive" racing convertor in a customers 496cid. 727 torque-flite, dodge charger and lost 28%!! After going to a "big dollar"(quality!) convertor, they only lost 16%. It is a guessing game, really. The best thing is to only compare time slips. If you want to know who's got what......run 'em!!
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Old 08-19-2002, 11:34 PM
 
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