Horsepower

[UKZR1]

Hi Guys

When Marc built my engine, and put it on the dyno it made 529hp. Just wondering what the loss through the drivetrain is on a ZR1 and what I should expect at the rear wheels.

[Jagdpanzer]

15% is the usual number most use

[Aurora40]

Sounds like a good opportunity for you to tell us the loss I don't think too many people have flywheel and rear wheel runs on the same motor for comparison.

Sounds like a healthy motor though!

[UKZR1]

Yeah, I may have the opputunity to put it on a dyno later this year. In the meantime I am going to have a play with the Gtech pro my wife bought me ages ago that I have never used - of course what I should have done was used that before I pulled the motor out and everytime I've done something but I never got around to it. Besides, when I pulled the motor out it was sick - It had eaten a screw in NO 8, breaking the rings off and causing the plug to foul from the oil when in traffic. It still ran strong though even like that, just a month earlier it still managed 180mph on the autobahn I have had the car weighed so the weight I enter will be accurate so hopefully the net hp it gives me should be quite reliable.

The motor has done around 15000 miles since Marc built it so it should be nicely loosened up by now.

[Paul Workman]

Yep. I'm all ears on this one. I find it hard to accept that the loss would be a fixed %, "15" or whatever. The only way for it to be fixed is for the parasitic loads to be a function of speed and also be very linear. But, are they??

Breaking it down for illustration sake, suppose we're measuring power at the flywheel. Two engines, one making 100 hp and one making 700 hp are turning at the same rpm. All else being equal, why would the load ratio (in %) be the same?

Something that bugs me...Example:

Let's say the water pump is consuming 15% of the 100 hp engine's output, leaving a net 85 hp - consuming 15 hp. If the same 15% applies to the 700 hp engine, the pump would have to be eating 105 hp!

This example could be expanded to include the drive train and the question remains: Does the 15% apply to any hp range, or is it more a rule of thumb within a window of "average" horsepower engine output??

I haven't had the opportunity to study this question...yet. But, I'm dubious of any "rule of thumb" factors, especially when used w/o the variables listed as well. So, if you have a FWHP of 525, I (for one) would be very interested to see how that ol' 15% factor compares to an actual ZR-1's rwhp!

P.

[rhipsher]

529hp divided by 100 X 15 - 529 = 449.65hp

[flyin ryan]

The differance i 'usually' see is 18%ish, with a manual trans. Always hard to guess-timate acuratly though.

[Paul Workman]

Originally Posted by flyin ryan

The differance i 'usually' see is 18%ish, with a manual trans. Always hard to guess-timate acuratly though.

Yeah, but I have to wonder how much of that is due to hysteresis as a function of accelerating the rotating mass of the trans/flywheel? Would it be 18% (or whatever) in a sustained output, is the question. And! IF it is, a sustained loss, then the drive train is forced to dissipate over 45kW and methinks something is going to FRY! I don't see a big radiator on our transmissions and or differentials, ya know? It just seems like a lot of loss (to me), especially in a sustained "pull".

Dynos vs. accuracy...One of those things (with a LOT of variables) that make me say "Hmmmmm....."

Don't mean to hyjack the thread, but it grazed this dyno thing; a topic that keeps me wondering.

P.

[Jim Nolan]

An article I read a few months ago stated they dynoed a new ZR1 and it put down 505 at the wheels. That's a 20.8% loss. I thought that was a pretty big loss.............but maybe not.

[Kevin]

just slap it one a dyno and find out