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Old 07-22-2007, 06:45 PM
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RWHP numbers

So you have a 500hp sbc at the crank. What many people have told me is you loose about 20 to 25% at the rear wheels. That would make around 400hp.
My question is how do you limit the loss of hp or is there a way. Angle of the rearend, manual or auto trans, higher or lower stall converter if auto, aluminum drive shaft.
All of the above or none.
I put it here more as more of a discussion to learn for my own knowledge.

Thank you

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Old 07-22-2007, 07:09 PM
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good lubrication.......

there is no way to stop all the hp loss. my only suggestion is make sure you have your brakes adjusted correctly, wheel bearings lubed with good synthetic grease and adjusted properly. proper pinion angle and good u joints again with a good synthetic grease. rear end and trans filled to the proper level with good fluid. try to prevent heat.
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Old 07-22-2007, 08:21 PM
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Yeah synthetic lubes and keeping down excess heat is the trick for less hp loss
Shane
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Old 07-22-2007, 08:30 PM
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The type of rear end can make a difference. Somebody posted an excerpt from magazine article that explained the differences between the 12 bolt and 9 in. One thing they point was that, due to the placement of the pinions the 9in tended to consume a little more power but was somewhat stronger because the pinion was placed farther below the ring gear centerline than that of a 12 bolt.
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Old 07-22-2007, 09:21 PM
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There is something i don't understand about those figures. wouldn't a parasitic drive train loss be a set hp amount rather than a percentage. what i'm getting at is let's say the massive th400 uses 45 hp, wouldn't it be 45 hp weather you are making 100 or 1000 hp at the crank?
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Old 07-22-2007, 10:08 PM
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Quote:
Originally Posted by njbloodline666
There is something i don't understand about those figures. wouldn't a parasitic drive train loss be a set hp amount rather than a percentage. what i'm getting at is let's say the massive th400 uses 45 hp, wouldn't it be 45 hp weather you are making 100 or 1000 hp at the crank?
This is why I wanted peoples knowldge on this.
I know if you would go with a th350 there would be a wieght loss so in a sence you would make more power. Maybe not hp on a dyno but in a drag race, but why do the percentages go up with hp increses. I gues that is why you would go with synthetic oils. right?
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Old 07-22-2007, 10:51 PM
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rotational mass. use a percentage figure rather than a set value.
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Old 07-23-2007, 04:14 PM
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Quote:
Originally Posted by DHMag
rotational mass. use a percentage figure rather than a set value.
but why, mass would increase with centrifugal force (if its not balanced), not the power being applied. In increase in power should result (in my mind anyway) in a smaller percentage parasitic loss
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Old 07-23-2007, 05:07 PM
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im not an expert on this but i'll try to explain it

if it takes 45 hp to turn the th400 mass at 2000 rpm
and it only takes 40 hp to turn a th350 at 2000 rpm

its going to take more power to spin the larger mass another words at 3000 rpm it will take an extra 5 hp bringing the total to 45 at 3000 rpm for the 350 but it will take 8 more hp to turn the 400 at 3000 rpm. so if you put that into a ratio the th400 uses more power as a percentage as well as more power over all.


i hope i said that right feel free to correct me if im wrong.
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Old 07-23-2007, 05:18 PM
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it takes more power to move more mass.

dont forget other things that go roundy round, like tires, rear gears, driveshafts, brake drums/discs. also, make sure you account for slop in u-joints, rear gear lash, trans planetaries/sun gears/low roller clutches, and tread cupping.

besides, its easier to figure a percentage on a whole as opposed to indiviually measuring and gathering every intricate part of the drivetrain affected.

for FWD vehicles, use 15%. RWD vehicles, use 20%. its a safe bet.

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Old 07-23-2007, 05:44 PM
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right, but all factors being equal other than the horsepower at the crank those numbers would change dramatically . if you have a stock 1985 caprice with a 350 in it, that engine probably produces 160 hp at the crank and assume a 20 percent drivetrain loss thats a loss of 32 hp. take that engine out rebuild it to 400 hp leaving the drivetrain and tires the same thats a loss of 80 hp through the drivetrain. where did they go? the rotating mass of the drivetrain is the same because you left it untouched.
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Old 07-23-2007, 07:50 PM
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Quote:
Originally Posted by njbloodline666
right, but all factors being equal other than the horsepower at the crank those numbers would change dramatically . if you have a stock 1985 caprice with a 350 in it, that engine probably produces 160 hp at the crank and assume a 20 percent drivetrain loss thats a loss of 32 hp. take that engine out rebuild it to 400 hp leaving the drivetrain and tires the same thats a loss of 80 hp through the drivetrain. where did they go? the rotating mass of the drivetrain is the same because you left it untouched.
kinetic energy. a 400hp motor is going to act differently than a 160hp motor. specifically if you especially build a motor to sustain higher RPM than stock.
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Old 07-23-2007, 08:54 PM
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Would a car lose more hp with an auto trans or a manual? or how would a stall converter effect the outcome.? Higher stall less loss or lower stall less loss?
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Old 07-24-2007, 08:11 PM
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smoke a manual trans has less mass to it, so in my opinion it will consume less power. with an auto trans if you run a smaller diameter torque converter it will weigh less and consume less power than if you had the stock converter. and dhmag iirc kinetic energy is the amount of energy required to accelerate a given mass. i still don't understand your point of view on this subject because the given mass hasn't changed. i wish a physicist would reply to this thread lol.
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Old 07-24-2007, 08:55 PM
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Thank you for all your replies. It has opened my eyes to alot of new sources for hp.
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