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Discussion Starter #1
is hp loss through the drive train calculated on a % basis or a fixed number?

ie: if you have a 500hp crank engine and lets say you loose 100hp through the driveline and parasitic loss. and then you switch out to a 700hp engine, would you still have a 100hp loss through the drive train and parasitics, or would it be a % change...
 

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Where are all of the engineers? My gut feeling is that the number would be somewhere between the 100 figure and the % figure.
 

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is hp loss through the drive train calculated on a % basis or a fixed number?

ie: if you have a 500hp crank engine and lets say you loose 100hp through the driveline and parasitic loss. and then you switch out to a 700hp engine, would you still have a 100hp loss through the drive train and parasitics, or would it be a % change...
http://www.carcraft.com/techarticles/ccrp_0311_drivetrain_power_loss/index.html

In summary, anything that gets hot under load (diff., trans.) eats horsepower. More load = more heat = more loss. So, yes. Higher h.p. = more drivetrain loss %.
 

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What i get out of that article is a % figure. Also you need to get rid of the belt driven fan and run a manual tranny.

So if you loose 20% of 500 hp at the crank to the rear wheels you would end up with 400 RWHP

Same drive train loosing 20%, but you up the motor to 600 hp you have 480 RWHP
 

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Interesting read taken from a DynoJet article:

"A combination of two laws of physics, force equals mass times acceleration and work equals force times distance, gives us this equation: W=m X a X d. "W" is the work, in pounds-feet, the rear wheels are doing, "m" is mass equivalent (the drums), "a" is acceleration (increasing drive wheel speed) and "d" is distance (drum circumference). Once we have the work, we can find horsepower. One horsepower is 550 pounds-feet of work done in one second so, we divide the work number by the length of time measured, then divide the number we get from that by 550. To simplify: we get horsepower by multiplying the mass, acceleration and the distance, then dividing that product by time multiplied by 550. This can be expressed by: hp = (m X a X d) ÷ (t X 550).

Torque can be figured by multiplying the horsepower by a constant, 5252, then dividing that product by the speed at which the thrust force was measured. Generally, with rear wheel numbers, axle ratio is not considered in the torque computation. For comparison purposes, this makes more sense. The computer factors out the axle ratio by using engine speed data in the torque derivation."

"While Dynojet can measure "coast down" power consumption by a vehicle’s powertrain, they cannot accurately measure parasitic loss for the purpose of figuring flywheel power output from rear wheel output. Differences in power losses during acceleration and deceleration prevent this."
 

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Discussion Starter #6
ok.... read everything i could with the time at hand... read everyones statements, stayed awake last night about 3 fraken hours with this running through my mind.... here is my thoughts and ideas...


I believe it is a combination of both percentage and base.
ie..... items on the engine; fan, alternator, water pump, A/C etc will pull a flat amount of power at a given RPM and that number would be about the same from car to car from engine to engine...

then you have the drive train itself, which would be a percentage. why? friction and heat loss, the more power you try and put to the ground the greater the friction through the drive train, and thus the greater the loss of power, if you are loading down for 100 hp (got to be under load) you will have a certain amount of friction in the drive train, if you increase the load for a 1000 hp engine the stress loads increase, thus the friction goes up and and so does the lose of power....it will loose more power through the drive train, thus a percentage loss....

so both.... thus it would be something like this, parasitics loss + %(drive train)= total hp loss.
 

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The guy that asembled my enging calculated that it should be at about 430 HP at the flywheel. On his chassis dyno it only put 290 to the ground. I have a FI 383 roller cam stroker with electric fans, electric water pump and a 700R-4 trans with a 2600 RPM stall 10" converter, with 3.73 rear gears.
 

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Discussion Starter #8
The guy that asembled my enging calculated that it should be at about 430 HP at the flywheel. On his chassis dyno it only put 290 to the ground. I have a FI 383 roller cam stroker with electric fans, electric water pump and a 700R-4 trans with a 2600 RPM stall 10" converter, with 3.73 rear gears.
not to bang on your builder, but guesstaments seem to always be high... especially from the guy building it.

if you are putting down 290hp, i would bet your engine is no where close to 430.... even at 20% loss that would put you at around 350hp....

i never got an engine dyno, but have had several chassises dynos, and I am laying down to the rear wheels 436tq, and ~440+hp....

without good heads, you have limited flow.... thus restriction in the higher RPM range, thus less hp.....

hp=(tqXrpm)/5252....
 

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He didn't "build " it, he just assembled it. I took him all the components. He's been building dragster and circle track engines for about 20 years, so I'm guessing he is pretty close to the mark. In the article earlier in the thread, it stated ( as far as I took it) that with an auto trans. you could expect as much as 33% loss. That was the last paragraph on page 2 of the article. That would put it almost right on the money.
 

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Discussion Starter #10
He didn't "build " it, he just assembled it. I took him all the components. He's been building dragster and circle track engines for about 20 years, so I'm guessing he is pretty close to the mark. In the article earlier in the thread, it stated ( as far as I took it) that with an auto trans. you could expect as much as 33% loss. That was the last paragraph on page 2 of the article. That would put it almost right on the money.
the highest numbers i have seen are around 22%, the lowest around 15%... if you have a 33% loss, i would start looking for other problems.... maybe exhaust???? but 33% seems very high. if i am putting ~440hp to the ground, that would make me have around 640hp... which I wish i had... but i believe it to be more around 500-550....
 

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ok.... read everything i could with the time at hand... read everyones statements, stayed awake last night about 3 fraken hours with this running through my mind.... here is my thoughts and ideas...


I believe it is a combination of both percentage and base.
ie..... items on the engine; fan, alternator, water pump, A/C etc will pull a flat amount of power at a given RPM and that number would be about the same from car to car from engine to engine...

then you have the drive train itself, which would be a percentage. why? friction and heat loss, the more power you try and put to the ground the greater the friction through the drive train, and thus the greater the loss of power, if you are loading down for 100 hp (got to be under load) you will have a certain amount of friction in the drive train, if you increase the load for a 1000 hp engine the stress loads increase, thus the friction goes up and and so does the lose of power....it will loose more power through the drive train, thus a percentage loss....

so both.... thus it would be something like this, parasitics loss + %(drive train)= total hp loss.
I'm not sure I buy this argument. If you have a hypthetical hand crank that needs turning, it takes a finite amount of torque to turn that crank. Lets say it takes 10 ft-lb to turn the crank. If you apply 10 times that much torque, the crank doesn't get harder to turn. The source of power just has an easier time turning the crank. Other than minor variables, I don't think higher power causes the drivetrain to absorb significantly more of the power as the power goes up.
 

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Parasitical loss is already measured at the crank. If you lower
your drag on parasitcal loss it will increase your at the crank HP which in turn increases rwhp. Like using under drive pulleys. It is an overall percentage loss at the rear wheels but I think as HP increases at the crank the percentage of loss is a little lower at the rear wheels. So at 500 crank HP you now have 400 at the wheels with an A4 and
415 or so with an M6. If you bumped it up to 700 at the crank
loss through the drive system would be a little less than 20% with an A4.
 

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It shouldn't be an exhaust problem, I'm running lomng tube headers and 3" basically straight pipes, no cats. I have 3" I.D. chambereds under the car, but you can look through them like a telescope, no restriction there. Probably the 1 worst component in my engine is the heads. I'm running Edelbrock Performer RPM's.
 
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