idle questions

[Yves]

This is for an MS2, SBC with 247/249 @ .050 and 106 lsa on itb's.

I was working on my idle to see if I could improve it incorporating the IAC.

When warmed up completly I've been gradually using a higher amount of ignition timing at idle. I went from 18° all the way to 26°at the same time trying to lower my idle vacuum. Originally I had 69-70 kPa and around 24-25° I managed to get to 67 kPa. Rpm stayed virtually the same. I idled mostly around upper 13 to 14.5 AFR. Now and then I got some lean spikes.

The odd thing is that going towards 26° my AFR started to go lean in the order of 15.5-16. How should I interpret that ?

[Matt Cramer]

[Yves]

sorry, I didn't log it.

[Yves]

Ok, I was thinking the following : this is on an itb crossram manifold which sits on top of a SBC. The injectors sit just before the heads, but due to the proximity of the stacks, the injectors and rails have very little room, so the manufacturer placed them at an angle of 90° to the airstream into the engine. Although I have not noticed any real big adverse effects I think this creates a lot of wall wetting. Might this play a role at idle where air speed is low ? If so how could this be combatted ?

[Rick Finsta]

Wall-wetting EAE is designed to deal with that exact issue by tracking the amount of fuel being added to and removed from the puddle over time and conditional changes, so while EAE isn't exactly the easiest or most intuitive thing to tune, it will allow you to make the effects of the puddling basically negligible relative to engine performance.

IMHO the effects of injector angle are overstated; most engines address it as a packaging concern simply because it doesn't make enough of a difference to change other areas of the design to suit more injector angle. If you can, then yeah aim at the back of the valve, but don't reduce effectiveness somewhere else (like manifold design) to get there.

I seem to remember reading something recently about some testing with intentionally aiming the injector at the opposing port wall but can't for the life of me find it now.

[Yves]

Wall-wetting EAE is designed to deal with that exact issue by tracking the amount of fuel being added to and removed from the puddle over time and conditional changes, so while EAE isn't exactly the easiest or most intuitive thing to tune, it will allow you to make the effects of the puddling basically negligible relative to engine performance.

IMHO the effects of injector angle are overstated; most engines address it as a packaging concern simply because it doesn't make enough of a difference to change other areas of the design to suit more injector angle. If you can, then yeah aim at the back of the valve, but don't reduce effectiveness somewhere else (like manifold design) to get there.

I seem to remember reading something recently about some testing with intentionally aiming the injector at the opposing port wall but can't for the life of me find it now.

I've seen the EAE but it seems terribly difficult to tune.

Would appreciate the test about the injector aimed at the oposite wall.

BTW : we have talked on speedtalk about timing at WOT