HP loss through drive train?
12-18-2004, 04:19 PM
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HP loss through drive train? what percintage of power is lost through the drive train on an A4 car?
My car pulled 508RWHP, I was interested in what this would translate to at the crank?
Mods are listed below.
Thanks guys..
My car pulled 508RWHP, I was interested in what this would translate to at the crank?
Mods are listed below.
Thanks guys..
Last edited by Jeremiah; 07-04-2008 at 01:19 PM.
12-19-2004, 01:23 PM
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Dyno HP is only an estimate. You can take your car to 10 different dyno machines and get 10 different readings. Every brand of dyno reads differently and even the same brand of dyno will not repeat on a different machine in a different shop, most usually. The dyno is really good to get a baseline reading. Use the same company every time you do an upgrade to see the increase/decrease in HP and torque.
BTW, cool location to shoot your car photo. I drive by there quite often on my way to visit the folks. Mustang Rd north to Reno from the turnpike. Nice car, too. Graduate of Mustang High '82.
BTW, cool location to shoot your car photo. I drive by there quite often on my way to visit the folks. Mustang Rd north to Reno from the turnpike. Nice car, too. Graduate of Mustang High '82.
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12-26-2004, 05:36 PM
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You guys need to remember too, that the estimated percentage drivetrain loss is guestimated for a stock hp rating...
Drivetrain loss as hp increases is not a linear value...
i.e. 12% loss for 350 fwhp vs. 12% loss for 500 fwhp is not a correct calculation...
Assume that the amount of engine friction between a stock LS1 and a 500 fwhp LS1 is approximately the same (even though it is not, but it is close)
Drivetrain loss is the amount of hp required to turn over the balance of the drivetrain, tires, driveshaft, axles etc...This loss really does not vary with the power of the engine...
Thus, lets just say you make 350 fwhp and 310 rwhp stock...That's a 40 rwhp loss due to the drivetrain...
Going to the 500 fwhp engine you could still expect to loose approx. 40 rwhp due to the drivetrain, so you would see roughly 460 rwhp...
310/350=.886 or 88.6% or roughly 12% loss
460/500=.92 or 92% or roughly 8% loss...
You can use the 12~15% universally if you want to brag as to how much fwhp you have...
But in reality, you would be overestimating your hp by a few percentage...
Peace...Gman
Drivetrain loss as hp increases is not a linear value...
i.e. 12% loss for 350 fwhp vs. 12% loss for 500 fwhp is not a correct calculation...
Assume that the amount of engine friction between a stock LS1 and a 500 fwhp LS1 is approximately the same (even though it is not, but it is close)
Drivetrain loss is the amount of hp required to turn over the balance of the drivetrain, tires, driveshaft, axles etc...This loss really does not vary with the power of the engine...
Thus, lets just say you make 350 fwhp and 310 rwhp stock...That's a 40 rwhp loss due to the drivetrain...
Going to the 500 fwhp engine you could still expect to loose approx. 40 rwhp due to the drivetrain, so you would see roughly 460 rwhp...
310/350=.886 or 88.6% or roughly 12% loss
460/500=.92 or 92% or roughly 8% loss...
You can use the 12~15% universally if you want to brag as to how much fwhp you have...
But in reality, you would be overestimating your hp by a few percentage...
Peace...Gman
12-26-2004, 05:44 PM
#10
Gman, by your reasoning, you are showing that as your HP goes up, the percentage loss goes down, and it makes sense to an extent. But how would you explain Mike K's car (408 stroker) that had both an engine and chassis dyno, and recorded a ~15% drivetrain loss through a T-56 and a 10-bolt, which is the generally accepted drivetrain loss for the combo?
12-26-2004, 05:52 PM
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The only way I would say his numbers reflect a true 15% loss, is if while the engine was on the engine dyno, it was set up exactly as it is when it is installed in the car...Meaning, the exact same exhaust, the exact intake, all the accessories etc.
This hp debate goes back to the late 60's, early 70's with "gross" hp vs. "net" hp...
Example: '71 SS 454 was rated at 365 gross fwhp, in '72 the exact same engine was rated at 270 gross hp...That is how much hp was lost by putting the engine into the car, hooking up the exhaust, intake, power steering, oil pump, etc vs rating it without all those items attached on the engine dyno...
Peace...Gman
This hp debate goes back to the late 60's, early 70's with "gross" hp vs. "net" hp...
Example: '71 SS 454 was rated at 365 gross fwhp, in '72 the exact same engine was rated at 270 gross hp...That is how much hp was lost by putting the engine into the car, hooking up the exhaust, intake, power steering, oil pump, etc vs rating it without all those items attached on the engine dyno...
Peace...Gman
12-27-2004, 09:16 AM
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"Drivetrain loss is the amount of hp required to turn over the balance of the drivetrain, tires, driveshaft, axles etc...This loss really does not vary with the power of the engine..."
I agree that it is not a direct percentage but I disagree with the above statement. If it were true, we would just do a coast down test, compute the HP loss and add it to the tested HP. But in reality, as we increase the pressure and velocity of the frictional components, the losses increase dramatically, not directly but closer to a squared mathematical formula.
The early 70's gross to net HP ratings changes also included other factors. GM also lowered compression for unleaded fuels and changed other engine internals such as cam and spark timing for emissions considerations. Before the manufacturer's "net" rating system of the early '70s' there were no HP measurement standards from company to company, same company, yr to yr or model to model. The numbers were fabricated from marketing pressure and/or insurance rates.
One major point that most everyone misses when talking "drive train losses" is the other loss caused by a different testing proceedure. When we compare to auto manufacturer's "net, brake HP" ratings, their test proceedure locks (brakes) the engine at each RPM then records its measurement. This alone adds another 5-10% to the reading as compared to a chassis dyno's RPM sweep method. This is why many brands of chassis dynos on the market read lower.
EJ
I agree that it is not a direct percentage but I disagree with the above statement. If it were true, we would just do a coast down test, compute the HP loss and add it to the tested HP. But in reality, as we increase the pressure and velocity of the frictional components, the losses increase dramatically, not directly but closer to a squared mathematical formula.
The early 70's gross to net HP ratings changes also included other factors. GM also lowered compression for unleaded fuels and changed other engine internals such as cam and spark timing for emissions considerations. Before the manufacturer's "net" rating system of the early '70s' there were no HP measurement standards from company to company, same company, yr to yr or model to model. The numbers were fabricated from marketing pressure and/or insurance rates.
One major point that most everyone misses when talking "drive train losses" is the other loss caused by a different testing proceedure. When we compare to auto manufacturer's "net, brake HP" ratings, their test proceedure locks (brakes) the engine at each RPM then records its measurement. This alone adds another 5-10% to the reading as compared to a chassis dyno's RPM sweep method. This is why many brands of chassis dynos on the market read lower.
EJ
12-27-2004, 08:10 PM
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dynocar...
Frictional losses due to increased accelerative forces are relatively small when compared to the losses developed by the rotating mass of the engine, accessories, tires, axles etc.
That is why I say they really don't change as hp goes up...The frictional loss is a small fraction of the total loss encounted in the drivetrain...
My net vs. gross hp comparison was between two identical GM engines from '71 to '72...Identical 454 LS5 engines, CR, smog pump etc.
Only thing different was in '71 GM was not required to rate hp as SAE NET, it was GROSS HP...365 fwhp rated, then in '72 manufacturers were required to rate their engines using the SAE NET...This is when the same motor went to 270 NET HP...
Follow this link for an example...Go down to the Drivetrain area and read his ratings...
http://www.traceyschevelle.com/about.html
My '72 SS 454 was listed the exact same way has this on...365 gross/270 net...
Peace...Gman
Frictional losses due to increased accelerative forces are relatively small when compared to the losses developed by the rotating mass of the engine, accessories, tires, axles etc.
That is why I say they really don't change as hp goes up...The frictional loss is a small fraction of the total loss encounted in the drivetrain...
My net vs. gross hp comparison was between two identical GM engines from '71 to '72...Identical 454 LS5 engines, CR, smog pump etc.
Only thing different was in '71 GM was not required to rate hp as SAE NET, it was GROSS HP...365 fwhp rated, then in '72 manufacturers were required to rate their engines using the SAE NET...This is when the same motor went to 270 NET HP...
Follow this link for an example...Go down to the Drivetrain area and read his ratings...
http://www.traceyschevelle.com/about.html
My '72 SS 454 was listed the exact same way has this on...365 gross/270 net...
Peace...Gman
12-28-2004, 12:23 AM
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actually, in talking with our powertrain engineers a few years back, they told me the driveline loss was 18% on both A4 and M6.....I did a double-take because it is unusual to have the same loss with two different transmissions...they assured me it is 18%.
go figure!!!
go figure!!!
01-06-2005, 12:23 AM
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My motor on the engine dyno was exactly the same as it was in the car, I have thought about this alot myself but think about this for a minute,
A stock car takes 15% drivetrain loss, my car also did the same. The reason for this is because any car as it makes more power will spin the drivetrain quicker but on that same note is it also takes more power to spin the drivetrain quicker i.e. since you are spinning it faster than you are with a stock motor it must take more power to spin it faster. And we know its spinning faster because you are moving quicker.
good comparison
go outside and take a basket ball and spin it, then spin it faster and notice how much more energy it takes to do so.
A stock car takes 15% drivetrain loss, my car also did the same. The reason for this is because any car as it makes more power will spin the drivetrain quicker but on that same note is it also takes more power to spin the drivetrain quicker i.e. since you are spinning it faster than you are with a stock motor it must take more power to spin it faster. And we know its spinning faster because you are moving quicker.
good comparison
go outside and take a basket ball and spin it, then spin it faster and notice how much more energy it takes to do so.
