Injector Sizing: REALLY dumb question

[Zack]

OK, 'nuther dumb newbie question.  How can injector timing have any 
effect on torque??  Torque, I thought, is directly related to BMEP, 
which would in turn be almost directly related to the amount of air 
ingested into the cylinder (assuming for the moment that the injector 
duration is adjusted so A/F ratio is constant throughout the RPM 
range).
	The only thing I can think of related to injector timing which would 
affect the amount of air getting into the cylinder would be, if fuel 
is squirted into the manifold before the valve opens, the 
vaporization of the fuel there would tend to displace air from that 
portion of the manifold and lower the final charge density.
	Looking at it this way I could easily tempt myself into believing
that the best approach would be to delay injection until the last 
possible moment (uhh...), or even better, to inject the fuel into the 
chamber directly only after the intake valve is closed.
	OTOH, if you're squirting methanol in, for example, 
the cooling effect due to the high heat of evaporation easily
dominates the displacing effect of the vapor, so that you are much 
better off overall if the vaporization is already complete by the 
time the intake valve closes, because the cooling effect of the 
mixture caused by the evap of the methanol draws additional air/fuel 
mixture in behind it.
	Gasoline lies somewhere between the two ends of this continuum, on 
the one end the fuel with no heat of vaporization whatever that 
you'd like to inject only after the intake valve closes, and on the 
other end the fuel with a very high heat of evap. that you'd like to 
inject well before so that the evap & cooling is complete by the time 
the charge reaches the cylinder.
	I don't know exactly where gasoline falls on that continuum, so it's 
not clear to me how y'all are coming to conclusions about when's the 
best time to inject the fuel.

 Hints?  Thoughts?  Data?   All welcome...

Z


> I'm aware that what I suggested is'nt how most current systems work -
> The 
> injection event is fixed at whatever advance the designer feels will
> accomodate 
> the rpm range he has in mind.
> Per matching "squirt" with "inhale", the idea of advancing/retarding the
> injection 
> event is to improve the low-end torque characteristics of motors
> designed to 
> produce HP at high rpm - Free low-end torque is not a bad thing.
> 
> Regards, Jack 
> 
> Tom Sharpe wrote:
> > My ProFlow fires before the intake stroke, hoping that the hot intake valve
> > will vaporize the fuel. Edelbrock calls it "settle time". Above 5500 RPM at
> > WOT, the injector is open 100% of the time. So much for matching the squirt
> > with the inhale.  Just more brain food! Tom
> 
>