Contour Enthusiasts Group Archives Forums Branches Kentucky Parasitic loss....

This has recently started to bug me. I'm gonna post it to several boards and see what it stirrs up. Should make for interesting conversation anyway.

Most people, when refering to rear wheel horsepower claims v. flywheel claims, will say there is anywhere from 15-30% driveline, parasitic loss. What bugs me is, how can we state this as a percentage. Assuming a Miata motor makes 100hp at the flywheel (easy math number, give me a break :)) and it's drivetrain saps 30%, we should get 70hp at the rear wheels. Now let's pull the I4 and drop in a small block Ford tuned to 300hp at the flywheel. It magically bolts to the Miata driveline. What will RWHP be? It cost the I4 30hp to turn it. If it only costs the V8 30hp we end up with 270 rear wheel hp and about 90% efficiency. If the drivetrain is said to be 70% efficient, how can it make the V8 waste 60hp more than the I4? It sould only take a given amount of hp to turn a drivetrain to a given speed. What am I missing?

Chris

good question...

too bad Physics class just ended or i would ask Prof.

The only solution that I can possibly think of is the fact that in order to handle the hgiher amounts of poer created by the V8 those transmissions have to be more sturdy. Thus creating more drag.

V8 has 300hp withbeefy tranny so it gets 15% driveline loss = 255rwhp (loss of 45hp)

I4 has 100hp with wimpy tranny so gets 15% driveline loss = 85rwhp (Loss of 15hp)

This way the percentage stays the same, but hte actual amount of power needed changes, Due to the stronger gears/bigger flywheel/heavier duty driveshaft.

That is the only thing I can think of that would cause us to use a percentage. I will ask a couple of the car Gurus at work today and see what answers I can come up with.

it doesnt matter, as long as it goes fast and put a big smile on your face

Mainly 2kwik is right. However, one thing that should be looked at is the amount of weight each component has. For instance on our cars SVT's have a 20lb. flywheel and the standard V6 has a 22lb. flywheel. The SVT is going to get more power out because it take the engine less time and power to turn the flywheel over. Hence, buying an aluminum driveshaft for a Mustang allows more power to be transmitted to the ground because it takes less rotational force to turn over the driveshaft so more power is transmitted through. Mostly it's weight that drags down the engine. Now imagine how much power we can make if we could make, and get to the ground if every internal and external engine component out of the lightest material possible. That's how some cars make 10,000+ RPM and make a large power band.

exactly

You guys are comparing apples and oranges. Notice I didn't say anything about using a heavier/beafier tranny with the big motor. Same drivetrain. The point is that when most generalize and say "typical driveline loss is xx%" there is no way to make that generalization.

Chris

i hear the more your car breaks, the faster it is... btw the firebird broke again... at this rate im going to break the sound barrior

I guess thats why I dominated the group at the fun event

Thats true I can't see anythign really being Typical about that system