Drivetrain loss

[Downshift]

Ok, I have been wondering this for quite a while and just thought I would post it up. I always here 15% or 18% or whatever depending on if it is RWD, FWD, Auto, Stick... Anyway what I do not get is that the percentage of the power is always the same.

If a guy puts his car on the dyno and makes 200hp but with the 15% loss his engine is making more around 230hp. But another guy goes on the dyno and makes 600hp but with the 15% he is making 690hp??? Say they are both mustangs with the same drivetrain..... Why does the same drivetrain lose 60 more hp just because the engine is making more power?


I am probably just missing something really simple, I just thought I would see what you all think.

 

[Passenger]

Its math.
10% of 100 is 10.
10% of 1000 is 100
10% of 10,000 is 1,000

 

[trav_19]

im not entirely sure but it seems a lot of calculations use the 18% ....but with a auto the numbers higher right?

 

[realitygt]

yeah from what i've alway heard it's 18 for a stick 23 for an auto rwd

 

[OnyxCobra]

This argument can and has gone on forever, but I do not believe drivetrain loss is a percentage. I feel the "percentage" was adapted to be able to get a rough estimate of a car's engine power vs whp.

I disagree with the percentage idea because it simply does not make sense that as a car makes more power the drivetrain uses more power. If it is a percentage then it's an inverse relationship.

 

[realitygt]

This argument can and has gone on forever, but I do not believe drivetrain loss is a percentage. I feel the "percentage" was adapted to be able to get a rough estimate of a car's engine power vs whp.

I disagree with the percentage idea because it simply does not make sense that as a car makes more power the drivetrain uses more power. If it is a percentage then it's an inverse relationship.

of course it's a rough estimate because you can reduce powertrain loss by more lightweigh parts like aluminum driveshaft or lighter flywheel. It is less weight to move so it will result a lower drivetrain percentage loss.

the only true way to find out your drivetrain loss would obviously be to put your engine on a dyno then put your car on a dyno

 

[trav_19]

i agree......but more power means more slippage of parts...(auto's) so i can see that number changing endlessly

 

[AaRoN]

:dunno: Who knows...

 

[xsoutherngun89x]

i think the original percentage is correct, but in reality, it takes a certain amount of HP to rotate the drivetrain, if you lose 30 stock, expect to lose that much extremely modded but not lose more. i could be completely wrong however.

put it this way, it take x amount of power to rotate the drivetrain, its gonna take that same amount whether your makin 3, 4, 5, or 6 hundred HP

 

[Twista]

im so freaking confused its not funny :dunno:

 

[Paul]

There is no usable "percentage" that can be used for all applications, combinations, and hp levels. It's comparing apples to hand grenades. If you want to know flywheel horsepower, the engine must be dyno tested seperate from the chassis. Period.

 

[OnyxCobra]

i think the original percentage is correct, but in reality, it takes a certain amount of HP to rotate the drivetrain, if you lose 30 stock, expect to lose that much extremely modded but not lose more. i could be completely wrong however.

put it this way, it take x amount of power to rotate the drivetrain, its gonna take that same amount whether your makin 3, 4, 5, or 6 hundred HP

exactly my point, here's a quick example of how I'm looking at it.


Stock: 300bhp, 270whp. That's a 30hp loss.
Same car modded makes 500whp, so add the 30hp loss would make it 530bhp.

 

[griffin7t1]

<--(L?O?S?T?)

 

[Downshift]

i think the original percentage is correct, but in reality, it takes a certain amount of HP to rotate the drivetrain, if you lose 30 stock, expect to lose that much extremely modded but not lose more. i could be completely wrong however.

put it this way, it take x amount of power to rotate the drivetrain, its gonna take that same amount whether your makin 3, 4, 5, or 6 hundred HP

exactly my point, here's a quick example of how I'm looking at it.


Stock: 300bhp, 270whp. That's a 30hp loss.
Same car modded makes 500whp, so add the 30hp loss would make it 530bhp.

That is my point exactly. How could the same car lose more hp through drivetrain just because the engine makes more power? It made no sense to me. I thought it might just be a rough percentage just to give you an idea, but when you start getting up there in the numbers it starts to seem ridiculous.

 

[Downshift]

Its math.
10% of 100 is 10.
10% of 1000 is 100
10% of 10,000 is 1,000

I get that, that is why I put an example in my post lol.

 

[Passenger]

i think the original percentage is correct, but in reality, it takes a certain amount of HP to rotate the drivetrain, if you lose 30 stock, expect to lose that much extremely modded but not lose more. i could be completely wrong however.

put it this way, it take x amount of power to rotate the drivetrain, its gonna take that same amount whether your makin 3, 4, 5, or 6 hundred HP

exactly my point, here's a quick example of how I'm looking at it.


Stock: 300bhp, 270whp. That's a 30hp loss.
Same car modded makes 500whp, so add the 30hp loss would make it 530bhp.

Thats where your wrong.

As Paul stated every individual car has a different drivetrain loss for the most part. But lets say you had two Mustangs that had the same drivetrain.

We'll say Car 1 makes 250whp. It has 18% drivetrain loss according to RealtyGT's previous post. Thats 45hp. Which means it has 295 at the flywheel.

Car 2 makes 630whp. If it has an 18% drivetrain loss, then it actually makes 743.4 at the flywheel, which means it loses 113.4hp through the drivetrain. Its all math.

 

[Peter]

Its not a simple percentage about drivetrain loss.

It takes power to move parts. Most people just say 10% because its easier then breaking down how much friction HP loss there is in the transmission and rear end.

If 2 cars have the same drive train but are making different amounts of power their power loss will be the same. How would it make sense that 2 different cars using the same transmission lose different amounts of power through the same piece of equipment?

 

[Downshift]

i think the original percentage is correct, but in reality, it takes a certain amount of HP to rotate the drivetrain, if you lose 30 stock, expect to lose that much extremely modded but not lose more. i could be completely wrong however.

put it this way, it take x amount of power to rotate the drivetrain, its gonna take that same amount whether your makin 3, 4, 5, or 6 hundred HP

exactly my point, here's a quick example of how I'm looking at it.


Stock: 300bhp, 270whp. That's a 30hp loss.
Same car modded makes 500whp, so add the 30hp loss would make it 530bhp.

Thats where your wrong.

As Paul stated every individual car has a different drivetrain loss for the most part. But lets say you had two Mustangs that had the same drivetrain.

We'll say Car 1 makes 250whp. It has 18% drivetrain loss according to RealtyGT's previous post. Thats 45hp. Which means it has 295 at the flywheel.

Car 2 makes 630whp. If it has an 18% drivetrain loss, then it actually makes 743.4 at the flywheel, which means it loses 113.4hp through the drivetrain. Its all math.

So how come two cars identical in drivetrain lose different amount of horsepower? Why would one car take 45hp to turn the driveshaft, rear end, trans and the other one it takes 113hp?


How does that make sense to you?

 

[Passenger]

I'm wrong, but thats how it was explained to me, and thats how I've always looked at it. I'd definantly like to know exactly which is true. I just don't see how two cars with the same drivetrain can lose the same hp from the flywheel to the wheels.

Wheres the smart ones at?

 

[Paul]

I don't believe that there is a consistent hp loss for two cars at different hp levels with the same drivetrain either. Viscous couplings in automatic transmissions and associated heat (energy) losses will vary with power levels. In other words, there will never be a consistent "number" or "percentage" that can be used for varied combinations, even with identical drivelines.

Paul.