P Mack

iTrader: (6)

Is there a certain time the injector pulse starts, like say at top dead center on the intake stroke? And does the injector always open at the same time and close later to change pulsewidth, or does it also change when it opens?

Bink

Here's a good thread on your topic.Pulsewidth

critter

iTrader: (9)

I don't think anyone knows whether it always starts at the same time. You would have to put an o'scope on an injector and the crank trigger to find out. I suspect it doesn't matter much since at WOT you spend ~half the time spraying on the closed intake.

Bink

Yeah - I was shocked..to think that we're shooting at the back of the valve. But I read, for atomization purposes, hitting the hot valve Before it opens is a big help in charge homogeneity.FWIW.

P Mack

iTrader: (6)

Thanks for the link, there's a lot of good info in there, stuff i've never thought about before. I was wondering more about low rpm, low duty cycle, with a cam with a lot of overlap. It seems if the injector is firing right at tdc and there's a lot of exhaust overlap you could lose a lot of the fuel out the exhaust which would make it hard to tune.

Bink

As you can see from the htread there is alot of fuel sprayed before the Intake opens therefore with overlap some is exhausted - as well as Intake charge O2. Does screw with the O2 sensors. My cam is on a 106 LSA with 33* overlap (@.050"). It idles well, and responds crisply, at an AFR of 15 - 16. I suspect the added O2 from the overlap skews the AFR to lean.

critter

iTrader: (9)

So it would make sense to open the injector earlier as the load (pulse width) goes up rather than extending the end. I'd take a look if I had a portable scope.