I have a question for all you guys. Is that number based at the crank or rear wheels?

If it is based at the Crank how much of the 250HP are we losing at the rear wheels. I'm hoping not much.

 

from the factory, engines are always rated at the flywheel, 'cause it's obviously higher... who would give up a marketing advantage by quoting a number 10-15 hp lower than it would be at the flywheel??

 

the RX-7 gives about 217 - 220 to the wheel with rated 255 at flywheel....

 

Well I plan on putting mine on the Dyno as soon as get it. I plan on documenting all mods with the HP increase each time. I have a bud that works at a car shop.

 

Nice RotorGeek! Think you can hook up us locals with your bud so we can dyno too? Maybe have a "dyno day"?

 

I will see what I can do. If he can I will let you know. I am also looking into some Home Dyno kits. I'm also looking into some Home dyno kit that allows you to do it all with a Laptop. I don't know how good that system is.

http://www.charm.net/~mchaney/roaddyno/dyno.htm#what

 

Would there be more drivetrain losses with a longer wheelbase?

 

only if the longer hardware to get the power to the wheels, which are further from the engine, are heavier or have significantly more friction than the car you're comparing with the shorter wheelbase... in the case of the RX-7 vs. RX-8, i have no idea... but i do know that the 8's driveshaft is pretty nifty (and light...)
plastic and carbon, i think.

 

Yeah it has a carbon fiber driveshaft

 

Typical drivetrain loss is on the order of 18 percent, so figure around 205 at the rear wheels.

 

Typical drivetrain loss isn't a percentage, and varies depending on drivetrain configuration (ie FWD vs. RWD vs. AWD). The best model for drivetrain loss would be a fixed amount for the majority of it, and then a much smaller component that varies depending on the power level being transmitted through the drivetrain.

For example, a Miata in the 100 - 200 rwhp range has a drivetrain loss of about 26 hp. It isn't 26% or 13%, it's close to a fixed 26 hp. In the 200 to 300 rwhp range, it might be 30 hp, maybe up to 35 hp loss.

Regards,
Gordon

 

However 26 HP is still out of the maximum HP which can be converted to a % loss.

 

IIRC-The 8 also doesn't have an intermediate U-joint, that should help keep the losses down.

Rob

 

Yes, for that particular HP number only - but that certainly is not the appropriate way to express that loss. For example, a Miata that can generate 102 rwhp has drivetrain losses of 26 hp, and it's flywheel hp would be 128 HP. So, I've got 20.3% drivetrain loss. As soon as you express it as a percentage like that, someone will come along and say "Gee, if I add this Jackson Racing Supercharger to my Miata and dyno test it at 140 rwhp, then 20.3% drivetrain loss would mean that I'm getting 177 flywheel hp. But that's not true - in fact, that Miata would still be losing only 26 hp in the drivetrain, and the correct flywheel hp would be 166 hp. Does that mean that the Miata's drivetrain loss has dropped to 15.7%? Yes, for that particular HP number only - but the drivetrain really hasn't gained efficiency, since it's still costing the same 26 hp. And that's why expressing drivetrain loss as a percentage is wrong, since the percentage is not constant.

Regards,
Gordon