i dont know much about boosted applications and their optimal afr but why is it sooo rich? i know optimal AFR n/a is about 13:1, is it different for FI?

IMO, the intake valve has to do with how much air is getting sucked in so just cuz there is alot of air in the back of the intake doesnt mean its all going in but im not totally sure

 

I am not really sure but I don't think it is only to do with the fuel runner. If it is why not #1 having a problem as well? It is known that any dirt or rust that gets into the fuel rail seems to settle at the end of the line. This may foul out the injector or create a poor spray pattern from the #7 injector.

I think it also has to do with the internal shape of the intake manifold. It seems likely that more air can be forced into the back corner creating a leaner condition in #7. This is a situation that high boost pressure may aggrevate.

Just a couple of thoughts on the subject and why we run a little richer AFR for protection purposes. Not much you can do except use a good filter, replace the filter more often, buy gas from a known high volume supplier and don't fill up when the truck is filling the tanks. Maybe we should think about flushing out the fuel rail as part of regular maintenance.

 

Nothing is getting "sucked in" when there is a pressure differential forcing the air in the cylinders.

I think the problem is the intake, which is why most everyone that is looking to really push their engines is going to the Vic JR. set ups......
I also think that is why Radix guys (Radix intake) can run more timing and also don't have the lean #7 issue as bad as the rest of us FI guys.

 

Makes sense to me, they don't run the stock manifold so they don't have the issue. I suppose under stock air flow conditions none of this will ever show up. How about anyone who has upped their redlines, done a cam swap, or added a real ram air set-up on a NA engine?
Something with considerably more air flow than stock, but not FI. Do they have similar issues, yet less pronounced?

 

I read and investigated for about a year before I went FI. I don't recall any NA guys having problems with #7.