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Old 08-13-2003, 04:09 PM   #1
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Question Rear Wheel Horsepower to Flywheel Horsepower Conversion

Just curious...I know most Dyno Test report the Rear Wheel HorsePower value. How would you calculate flywheel horsepower? In other words, how much flywheel HP would 300 RWHP be with a manual transmission? Is there an easy formula? Thanks.
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Old 08-13-2003, 04:13 PM   #2
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The average manual trans will lose 15-17% drivetrain loss.
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Old 08-14-2003, 10:20 PM   #3
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No easy or definative formula, just consider ~15% for manual and between 20-25% for autos. But the RWHP is more important anyway because that's how much HP is accelerating the car/reaching the ground.
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Old 08-15-2003, 11:32 AM   #4
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TRU DAT.... FLYWHEEL HP DONT MEAN ****E. IF IT AINT AT THE WHEELS THEN DONT WORRY ABOUT IT. BUT 300RWHP EQUALS ABOUT 345 FLYWHEEL.
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Old 08-15-2003, 01:13 PM   #5
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If you go with 15% for manual and 20% for auto, divide the rwhp by .85 for manual and .80 for auto. 300 rwhp would equal 352.9 flywheel hp manual or 375 auto.

In my case I'm making about 368 flywheel hp. Before I went to the dyno, I added up the minimum claimed hp increase for each of my mods and it came to 370 hp. I was pretty impressed it was so close.
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Old 08-15-2003, 01:40 PM   #6
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hey guys does this make as much sense to you as does me? i read in 5.0 a little while back, say you have a car that makes 500RWHP with a C-4 behind it, well with your 20% that puts you at 588 FWHP correct? now lets say you have a 300RWHP with the SAME C-4 with the 20% loss that puts that motor at 352 as stated above. now does it make sense to you that a 500RWHP car looses 88HP and the 300RWHP car looses only 52?????? i dont go with the 15% and 20% figures, why in the world would a motor making MORE power loose MORE power than a motor making LESS power????? to me and as 5.0 said too i think the actual lose is more like 30-35HP for a manual car and 40-45 for a auto car, it just makes more sense to me.
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Old 08-15-2003, 02:03 PM   #7
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One of these magazines needs to test this and be done with it. I understand what you're saying BLOWN1989SALEEN, but I've also heard the argument that internal friction and other forces go up with added hp. The truth is probably somewhere in the middle.
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Old 08-15-2003, 03:17 PM   #8
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Quote:
Originally posted by Blown95GT
One of these magazines needs to test this and be done with it. I understand what you're saying BLOWN1989SALEEN, but I've also heard the argument that internal friction and other forces go up with added hp. The truth is probably somewhere in the middle.
yeah never thought about that hey man i see your right down the road from me. im right in oxford, pa im like maybe 25min from hockessin, de. you go to cecil much?
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Old 08-16-2003, 04:26 AM   #9
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No way around it. With my RWHP, my car's still a slug.
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Old 08-16-2003, 09:50 AM   #10
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Wink

BLOWN1989SALEEN is correct. %of power doesnt really work. Hp loss also varies by what automatic your running. A c6 will absorb more hp than a c4. So it would be hard to make a list of the loss for every transmission. BLOWN1989SALEEN numbers are as close as any.
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Old 08-16-2003, 12:05 PM   #11
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and flywheel does not = what hp your block is making.a blower producing 14 psi can draw 50-80 hp off your crank,add accys and your 400 rwhp car can have a motor thats actually producing
550- 600 hp - power adder,accy, and drivetrain loss.imagine that out of a stock block
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Old 08-18-2003, 07:22 AM   #12
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Quote:
Originally posted by BLOWN1989SALEEN
yeah never thought about that hey man i see your right down the road from me. im right in oxford, pa im like maybe 25min from hockessin, de. you go to cecil much?
No, I don't run my car. I'll be showing it at the Winner Ford car show in Newark in Sept. though.
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Old 08-18-2003, 01:25 PM   #13
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I made 560hp all motor at the wheels. Thinking that's around 700hp at motor with C-4 trans. with 3;73 gears I run 9.80's.
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