I'm looking at my boost tables. (EBL P4). I'm going for a very conservative/safe 11.5 AFR With the stock gradient in the tables I'm at 11.5+ - at 4 psi. At 3 psi and below the table drops and it is leaner. What are most folk doing-at what boost level are you hitting your richest AFR that you want to maintain on up?

 

It depends on the setup. Normally for EBL users that need help with a tune I will set AFR to 11.0 as a constant the moment boost enters the equation, and will also keep timing at 15* despite them asking for more, but this is done mainly because most users are unfamiliar with actual compression levels, quench, ring gap, plug gap, plug type, cam specs and any possible hot spots in the chamber. Plus need to consider what gas they have available in their area. When/if you know these things ahead of time, and if the setup allows... then you can get away with less fuel, and more timing overall. In my case I've been running over twenty pounds of boost running E85, but my engine is far from stock, and blueprinted for it ahead of time. Using a gasoline conversion for the sake of this thread, I'm around 10.75 to 11.0 AFR throughout, engine seems to like it, so it really comes down to your individual setup with respect to richest AFR maintained...

- Rob

 

On pump gas i target 11.5 on most setups. Pushing more of the limit? I’ll go 11.0-11.2. Richer at high torque rpms and leaner post peak hp rpm sometimes. Intercooling it can be on the leaner side, non intercooled needs richer especially the longer you are in throttle

first few psi typically dont need to be much richer than 12.0. Taper to 11.5 as boost climbs. Depends on what motor wants tho. If its low compression you can get more aggressive there. Higher compression on pump gas may want to be richer to try to keep things cooler.

 

I ran my Weiand 177 up to about 5 psi on basically the same WOT air/fuel ratio as naturally aspirated. About 12:1 at peak torque and 12:5:1 at peak horsepower. As the boost increased past 5 psi, I progressively increased the fueling until I was at about 11:1 @ peak torque and 11.5:1 at peak hp at 10 psi. It would have been ideal to have the air/fuel ratio targets a smooth linear line with boost increase, but I was running a 7747 ECM that was blind to boost. The boost fueling was merely being added by a rising rate FMU on the TBI return outlet. The timing was being retarded by a MSD 6BTM at the time. IIRC it was pulling about 1* per psi of boost. At 10 psi my WOT timing was 18* on a stock L05 short block. I never hurt the engine with that setup but it was a 700r4 executioner.