[Shotimes] Re: Rotating mass and dyno tests

[Alan Fanning]

Mark,

I went through this dilemna myself a few years back, on one of the Ford
truck lists. What I didn't understand at the time is that most dyno runs are
not performed at constant RPM, and thus there is hp lost in accelerating
heavier brake and wheel components up to peak rpm.

   Alan


wrote:

> But for HP at a constant RPM I can't figure where it would make the least
> bit difference, even if you are measuring it at the wheels.  Since the  engine
> isn't accelerating the spinning weight, no HP is being lost.   (Although, if
> you had rims with "turbine fan" spokes, the parasitic drag  would kill ya.
> But 
> that's not a weight issue.)
>  
> Maybe it's as simple as when they increased the rolling diameter, they took
> the engine out of the sweet spot of its power curve by changing the actual,
> final drive ratio.  It was running flat out but at a different RPM and just
> not on the sweet spot anymore.
>  
> Cheers
> Mark LaBarre
> 94 atx 130k