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...

Good question!..I believe it will be the same loss..tests show that parasitic drivetrain losses do not increase proportionally with drastic increases in horsepower..it remains relatively constant..if its the same driveline, why would it require additional horsepower to turn the same rpm..and better drivetrain components and synthetic lubricants can actually reduce losses.. the new Corvettes only lose 40-50 HP to parastic loss due to reduced friction.

.tests show that parasitic drivetrain losses do not increase proportionally with drastic increases in horsepower..it remains relatively constant..

What test? proof.... not beliefs...

I believe it to be a % loss,,,,,

ok, here one, Hendricks motorsports , Nascar, took a 2009 ZR1, 638 HP rated Corvette and put it on the dyno..now we all know all dynos are not exactly identical reading, they vary..But the 638 HP pulled 567HP at the rear wheels ..which is a loss of only 71 HP,or 11% which I contend is what that specific driveline consumes to spin it under those conditions...if you use your formula of 22% loss regardless of HP, it would have only pulled 497 RWHP. it is not proportional, it is constant..

nope.... sorry... %.... but not just a%.... something inbetween

http://www.carcraft.com/techarticles/ccrp_0311_drivetrain_power_loss/tests.html

poster on another forum:
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 %.

also..... we loose about 3% through our IRS rear end.... over a solid axel.

Is the horsepower loss through the drive train calculated on a % basis or a fixed number?

If you have a 500hp engine and 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?




If you lose 100 horsepower through your drive train and you have a 500 horsepower engine, then you have lost 1/5th or 20% of your horsepower.

If you have a 700 horsepower engine, the loss through the drive train remains the same. But as the engine's horsepower is higher, the loss is now only 1/7th or 14.2%.

So the frictional loss is a fixed amount depending on what kind of transmission you're running. Automatic transmissions eat up more horsepower than 4-speeds do and the TH400 eats up more than either a TH350 or 700R4. That's why you seldom see a TH400 behind a small block (although they were used for several years on the high-horsepower 327's and 350's).

a post from another forum... interesting.....

I have had my engine on two different engine dynos where it made 662hp/675tq STD corrected on one, 657hp/672tq STD corrected on the other. That was with 2" shop headers and no exhaust, no water or fuel pump, no pullies. Oil temp 190*, water temp 120-130* and the dyno's air turbine (big blue velocity stack) which added 10hp over an open carb... Pretty damn close right??

Put that in a car with full accessories, 1 7/8"x3" headers, 3" mandrel bent exhaust with free flowing muffs and going through a T400 w/10", 3600-3700 flash converter and it made 445rwhp/450rwtq. Take the 7 blade clutch fan off and it made 460rwhp/455rwtq.

That is 30% loss from 657 down to 460hp...or about 28% if you don't count the 10hp gain from the air turbine on the dyno(say 645hp actual)...... That's a lot of loss...

My actual mph numbers at the strip are 126.08 at 3700lbs. That's only showing about 570 crank HP at the track.....that's a lot of loss.

No doubt the T400 and stall converter are eating 75-100hp by themselves....

there is no doubt that a high converter stall and a th400 rob horsepower..but that doesn t change reality..increase that car to 1000hp and the loss will still be near the same 202 hp. adding exhaust and accessories is not parasitic driveline loss..yet he counted it as part of the 30% loss..thats why engines are no longer rated at gross hp,what engine in any car runs with nothing bolted on the front? they are rated now at net hp. The Ls1 in my 99 is factory rated 345 net hp, and is well documented by several magazines to pull 285 rwhp..thats a parasitic loss of 60hp, or 16%..if I bolt on a procharger and make 600hp , the driveline loss will still be 60 hp.and now that becomes a 10% loss. the percentage decreases as the power increases

Tire friction and accessory parasitic losses probably are constant, but the energy lost through heat loss in the transmission, differential, u-joints does not. As torque/hp are increased, like on my supercharged 'vette, the dyno spins (accelerates) at a much faster rate, compared to when it was normally aspirated. This increases the bearing loads throughout the drive-train. Check the differential temp. on your tow vehicle after a long haul. I bet you can't touch it. The heat comes from friction within the unit (power loss). Tow the load at a much lower speed, and the diff. will stay cool. On an auto. trans. car, the increased torque presented to the converter will cause additional slippage (power loss) due to frictional losses, also converted to heat. Losses may only be a few percent, but it is real.

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."

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.

both are interesting... I read somewhere, I d have to look for it, that there are some dyno s that can actually spin the drivetrain with engine off , using an electric drive motor,and thereby measure loss more precisely..and therefore the horsepower of engine is irrelevant in its calculations..and Paul ,if you stayed up all night thinking on this, you need a hobby.LOL

Paul ,if you stayed up all night thinking on this, you need a hobby.LOL

the vett is my hobby, and my mistress....:banana:

wife knows:happy0045:

I think thats the case with most of us here..Well, I think it is safe to say , there are just to many variables, to say with absolute certainty what the loss on any given situation would be.. the best we can do is only a guess.. even on a dyno, temp, humidity,etc change the results..and even different dynos read different numbers..

The horsepower loss remains the same as long as the rpm remains the same. But yes, the drive train DOES eat up more horsepower when it's spun faster.

NOT just faster, but with more force also, thus the percentage.

still not buying it , sorry. I just cant see a 1000 hp motor losing 250 hp to spin the same driveline that a 300hp motor in the same car only needs 60hp to turn. even if you say, yeah maybe if you accelerate it at a faster rate, there could be more drag, its just not gonna be proportional to hp increase.

I think the hp loss is proportional to the rpm and the rate of increase of the rpm. The higher hp motor will increase rpms more rapidly than a lower hp motor and therefore meet with slightly more drag as it obtains top speed (faster than a lower hp motor).
At top speed and say 6000 rpms, a high hp motor will be going faster than a lower hp motor, which, for the sake of argument, cannot attain a top speed at 6ooo rpms; and so have slightly more drag, still proportional but now only to the level of rpm.
So, to sum-up, there's more drag to optain speed faster, and there is more drag at higher rpm.
Just trying to keep you up late tonight Paul.

still not buying it , sorry. I just cant see a 1000 hp motor losing 250 hp to spin the same driveline that a 300hp motor in the same car only needs 60hp to turn. even if you say, yeah maybe if you accelerate it at a faster rate, there could be more drag, its just not gonna be proportional to hp increase.


As long as the rpm remains the same the horsepower loss remains the same. And you're right fish, it will never be proportional.

As long as the rpm remains the same the horsepower loss remains the same. And you're right fish, it will never be proportional.

At a steady-state rpm and load the loss would be the same. That's not what we're talking about. We are accelerating a 24 or 48 inch drum to a specific rpm. Turning it at a faster rate generates more frictional loss than accelerating at a slower rate does. I will say that I bet the percentage is small, but measurable none the less. :cheers:

it is really not minimal... thank about it, every gear in the transmission, all the u-joints, the rear end, all the bearings, everything is under a heave load and that load increases with tq. Also angles change with tq, which causes even more hp loss, which causes more friction and more loss, now do you really think that it will be a minimal difference if 400 foot lbs of tq ran down the drive train compared to 800 foot lbs tq? there is a reason that for ever, people have been estimating power loss in % not a flat number. if it were a flat number all you would hear is something like 100hp loss.... now thank about it... been many many people that have run both engine dynos then a chassises dyno directly after installation, with losses in the 22% range for moterhead on another forum, he lost like almost 200hp through parasitic and driveline loss. now, as we know, a 150hp engine can push a vett down the street (california 305 l48 lol!!!) ~1981.... now if the loss was constant at ~200 hp that car would never budge!

think about it..... it is a % loss, at least through the drivetrain, and more of a fixed loss for parasitics.

Don't misunderstand me, pauldana, I know it is real and present, but it will be minimal compared to the static parasitic and driveline losses.....just guessing but maybe an additional 1 TO 2% per 50 hp? It would be interesting to test an engine on an engine dyno with locked out secondary barrels on the carb. for one pull, then full open secondaries for the second pull. Then do the same tests, but this time on a chassis dyno. That would tell all.

Don't misunderstand me, pauldana, I know it is real and present, but it will be minimal compared to the static parasitic and driveline losses.....just guessing but maybe an additional 1 TO 2% per 50 hp? It would be interesting to test an engine on an engine dyno with locked out secondary barrels on the carb. for one pull, then full open secondaries for the second pull. Then do the same tests, but this time on a chassis dyno. That would tell all.


I just accept the loss and enjoy driving my car. The best advice I can give everyone is check your tire pressure at least once per month. You can't do anything about the horsepower loss through your drive train but you CAN keep your car's rolling resistance to a minimum.

that s a good test to try.. I still have to believe that , tho some increase is accrued if the drivetrain is accelerated at a faster rate ,it is not equal in percentage to the increase in Horsepower.. A stock Corvette loses to the drivetrain alone,50-60 hp, while a ZR1 with nearly double the power, only loses 71hp, according to Hendricks Motorsports tests... a difference of 21% loss in the lower power engine and only 11% loss in double horsepower...if it were to continue at 21%,as Paul believes, it would be a loss of 134hp, not 71 as it dyno d