TeeKay

obZidian, you have a darned good point, that is "What's the point of this thread?" ha ha Here's what I think is the root question:

When engine changes are made, what is a repeatable, reasonably accurate method for ESTIMATING engine chp from the observed chassis dyno runs at WOT acceleration?

The debate: Is the traditional straight percentage of engine power accurate enough for the estimate when the engine power is changed? Yes or no?

Things we know:
> Power to turn the drive train varies with acceleration - shown to some people's satisfaction, but not all agree.
> Results for the same engine/drivetrain vary with the gear it's done in.
> A trans gear ratio of 1:1 seems to give the highest readings.
> We have two measured data points: Mike K's engine dyno against chassis dyno tests at 15%. The stock 04-05 GTO whp dyno runs against advertised hp. 350 hp and 400 hp both showed 15% loss.
> A manufacturer's rated 100 shot of N2O showed 100+ at the wheels.
> Power loss changes as changes are made to the drivetrain (gears, TC's, etc.)
> There are possible dynamics at work that we haven't accounted for - we haven't identified what yet.

One thing that hasn't been said, but IMO should be obvious, is that a given drivetrain's efficiency will be different FOR EACH AVAILABLE GEAR (1st, 2nd, etc.), because more (or less) gearsets are engaged.

HTH the discussion.

trackbird

iTrader: (4)

Actually (to clarify, not picking on you, just to better explain), in lower gears (1st-3rd), you accelerate the engine/flywheel even faster (like having more power, thus acceleration losses are greater). In a taller gear (like 5th), you llose mechanical advantage so torque suffers and the numbers drop.

Ex.

My car run in 3rd and 4th gear (same day, same dyno, back to back) 4th is the upper graph (the car was stock).



My car run in 3rd, 4th, and 5th. In one long pull (same day, same dyno, same pull). 4th is the pull in the middle (and the most hp).

TeeKay

No offense taken. If the numbers show it, I can not/will not argue. I will just try to understand. Thanks for the data. That's what we need!

Re-reading this thread brings to mind the thing I heard in engineering school back in 1965, "Disregarding someone else's 'hare-brained' idea is the surest way to fatal error". I always remember that when I think of the the Feb, 2003 Columbia shuttle disaster.

obZidian

iTrader: (2)

im working on something that might help....going through some eye surgery tomorrow at 8:30am so as soon as i get better, will have...

I love this thread by the way......MORE!!!!!!!!!!

TeeKay

Hey, good luck with the surgery, see you when you get out!

HammerSandwich

That was a lot harsh, 5-7.

However, I agree with the gist of it. So, Tony, do you have an answer to the question I asked earlier?