LZKS

RX8 is rated at 234hp at crank, but only ~180hp at wheels.
Close to 25% drivetrain power loss.
Why is that?
Some say, it's the computer that reduces power when only rear wheel is spinning without the front.
Some say it has something to do with the catalytic converter; US regulations limiting carbon dioxide emission.

For one thing, it makes no sense that a car that only makes ~180whp and weighs 3000lbs do less than 6.5sec from 0-60mph.

So, I'm guessing Rx8 actually makes more than ~180whp??

jasonrxeight

its about 180rwhp
drivertain usually reduce 10% if FWD or 20% if RWD.

fyrstormer

The cheap gearbox oil doesn't help, and the right-angle gears in the differential waste a lot of power as heat. In fact, right-angle gears are the biggest reason why RWD cars are less efficient than FWD cars. I don't know if pre-2009 RX-8s have limited-slip differentials standard, but those are also good for losing a little gas mileage if your driving involves lots of long, sweeping curves.

Switching to the best full-synthetic gearbox oil you can find should help a bit.

LZKS

What I mean is... most other similar rwd cars lose about 15% through drivetrain.
Why does Rx8 lose so much?
It can't be that rx8 has such a terrible drivetrain.
Plus, like I said, if it DOES produce only 180rwhp, how can it do less than 6.5sec from 0-60mph with 3000lbs to lug around?

jasonrxeight

3000lbs isnt really alot. and because of the torque is just about right, very little tire spin as well.
plus the short ratio gearbox also is part of the reason. LSD. in a mustang you have 250hp with open diff, one tire spins you getting no where.

fyrstormer

Three words: Flat Torque Curve.

Looking at the maximum horsepower rating on an engine is pretty much worthless. You need a torque graph to tell what's really going on. The Renesis engine produces >90% of its maximum torque from 3000rpm all the way to redline. Very few piston engines do that. Because it can produce such a consistent amount of torque across such a wide range of RPMs, it can accelerate smoothly and quickly without the "punch in the back" that big piston engines create.

Anyway, high RPMs equal high drivetrain loss, because the drivetrain loss comes from the gear teeth rubbing together, and when the gears are spinning faster on average, that means the gear teeth rub together faster too. Each pair of teeth that rubs together wastes a little power, and when the gears are spinning fast, that means the wasted power adds up fast too.