I'm using my innovate MTX-L to track AFR and my car has just been mapped with the new turbo on. The fuel ratios are great on boost, 11.5 and good coming on to boost too but something that's concerning me is gentle boost fuel ratios.

I'm running a GT40 now; it's fairly laggy but has one hell of a hit. The problem is when on gentle boost, it's staying at stoich, 14.7AFR. Apparently this is absolutely fine as there's no load on the engine even though I'm at 4000rpm and 0.3-0.4bar. Throttle maybe 20-30% down.

I've contacted the mapper who specified that this is safe and I shouldn't worry about it.

Any opinions? I thought it should be around 12-13 if the boost gauge shows any kind of boost, no matter what the load.

 

At that level of boost I wouldn't be worried about it even on the big turbo - you probably start to richen when you stick your foot to the floor or increase the engine load. That's when the car drops out of closed loop and starts reading from the MAF or MAP scale to work out fuelling. These parameters will be set by your mapper so you'll have to trust they are safe for your setup.

It would be a different case on a smaller turbo that's running hotter - then you'd have to worry about EGT's rising due to the lean conditions and higher boost, but if your mapper says your safe then you should be happy.