[Diy_efi] RE: Diy_efi digest, Vol 1 #413 - 12 msgs

[Dave Dahlgren]

You need to think in terms of cylinder pressure. Big truck long hill same rpm
and map big cylinder pressure. same engine in a 2000 lb car going downhill at
WOT very little pressure same rpm and MAP, at least until you chicken out and
lift. But I think it Makes the point. the only time the two engines see the same
load is at terminal velocity for both at the same rpm. If you tune for terminal
velocity with no fuel or timing modifiers for the lower gears and less load you
are giving something up power wise. To a certain degree the OEMs seem to play
with gearing to make some of these scenarios equal. Small light car take gear
out,big truck put gear in.. 
Dave

William Shurvinton wrote:
> 
> I must admit in shame that there are a couple of concepts here that I am
> still having difficulty getting my head around, despite having followed it
> each time it is discussed. Whilst I understand that a truck engine in a
> truck has to work harder than the same engine in a hotrod I still have
> confusions about 'load'.
> 
> I can't help wondering whether is it because I am thinking about it from a
> MAP or TPS% perspective (NA). These are used to infer load, but are merely
> measures or inferences of the air entering the engine. So if you are
> comparing 2 applications on part throttle, for the same throttle opening,
> the light vehicle will need less fuel than the heavy one. Normally you
> modulate the throttle to match the load so you don't actually see this,
> except perhaps the drivability issues with a non-linear throttle reponse due
> to having too little 'load'. Or to put it another way TPS% is a measure of
> potential power, not actual or required.
> 
> The Dyno of course has difficulty replicating this.
> 
> It may click after a few more years tuning the car, or am I still
> approaching it from the wrong direction?
> 
> Bill
> ----- Original Message -----
> From: "Shannen Durphey" <shannen at grolen.com>
> 
> <snipped everywhere>
> 
> ."  Yet again the tune for
> > the long, heavy load isn't optimum for the short, light load.
> >
> > Gear and load corrections can be a good thing.  > Shannen
> 
> >
> > Dave Dahlgren wrote:
> > >
> . The better after
> > > market stuff has tables and corrections for what gear you are in. You
> can and
> > > should change timing fueling and boost according what gear you are in as
> it
> > > compensates for the relative load on the engine.
> > > Dave
> > >
> > > Shannen Durphey wrote:
> > >
> > > > Using a braking type dyno to tune a car for WOT can produce misleading
> > > > results.  A lightweight car with a high power to weight ratio would
> > > > typically never see the same load and duration that can be applied
> with a
> > > > brake type dyno
> 
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