injector Timing {B3702}.... when to tune?

[joecar]

Interesting observation...

the one must be timing in crank degrees wrt to an absolute crank position,
and the other must be timing advance relative to some cam/valve event
(which is also wrt to absolute crank position since the cam degreed to the crank...
ah, I just went in a circle... ...lol).

[jfpilla]

Joe
I think I'll leave it alone. The car tuned easily and runs well, so unless I can find a good reason to change it, I won't.
It would seem that both should be timed to the crank. Cam positions are often changed.
(theory: 2ms before something would be in the same position as, say, 500 degrees of something.)
Thanks for your thoughts
Joe

[NASABlue]

Center line of the cam lobe will depend on both timing and any ground in advance. A longer duration cam will nearly always result in the valves both opening earlier and closing later. Think of it in terms of overlap and the problems of big camshafts having both the exhaust and inlet open at the same time. FWIW, Hymey and I have spoken a bit about this.

We looked at injector timing vs cam timing and what happens with bigger cam shafts. The theory was that for big cams with lots of overlap, you could delay the injector timing to fire when the exhaust valve closed to minimise fuel being lost out the exhaust at low RPM. Then ramp the advance up as the RPM climbs to give the fuel time to fully vaporise for combustion. The issue was that it will probably effect transient fueling a bit and that would need a lot of work to correct for sharp throttle movements. It certainly needs lots of WB use when playing.

In latter tunes, I think GM have gone for very high injector timing to take advantage of the heat in the head / valve to vaporise the fuel in an effort to increase fuel economy. However that also means that the intake charge warms up a lot while sitting in the intake. I think that dropping the timing may allow for some "chemical cooling" of the charge, allowing that charge to be used before it's taken on too much heat from the head. The risk is though, that some of the heavier components of the fuel may not vapourise and remain in liquid form. So the timing needs to ramp up again as the RPM climbs.

Simon.

Awesome info and thread. I don't know if there is already injector timing info in the sticky section, but if not, this should be a candidate...

I have the Lucas and THeres a lot to just to get the correct conversion for the flow rate between pressure and rating with the test solution vs US gas.

[Sid447]

Anyone notice,

The Injection Timing Table {B3702} is different in the LS1-B HSV GTS tunes (see holdencrazy.com) ......when compared to all the other stock tune files?
Especially the 2002 GTS M6 which is considerably different and wonder if it might be a mistake in the tune file. Though {B3703) IT Trim has been adjusted too.

[5.7ute]

Just to try keep this thread going. Has there been any advances on where the reference pulses for the injector are in relation to TDC ( or whatever piston position it uses)?