First, I wanted to adjust the tune to recognize that we have E10, or gas with up to 10% ethanol. This gas has a lower stoichemic makeup, and an ideal ratio is 14.2:1 air:fuel instead of non-alcoholic gas at 14.7:1 air:fuel. The Cadillac factory tune assumes 14.7:1 fuel. I set the tune to 14.4:1 since we have an uncertain mix of alcohol in the fuel.
Second & Third, in our Texas heat the Cadillac is just on the border of heat retard from engine coolant temperature and intake air temp. I addressed each of those to move the ‘border” a few degrees higher and get that retard out. We’ll look for any sense of knock or knock retard on these runs just to be careful.
The two test runs with those changes appear to have lost 8 hp and 5 lb ft of torque. Not what I hoped. In this graph the red/blue runs are from earlier today, the green/yellow runs are from after the tuning changes.
The stoichemic setting change had the effect of moving the XLR 0.3 richer on in AFR, which is not what it appears to want. The other changes allow it run a bit more timing. My sense is we need to keep the AFR, but I am uncertain if the Wideband O2 sensors in the XLR are auto-magically compensating for fuel quality and driving to lambda for the current fuel, then reporting that as 14.7 AFR?
The calculated hp before/after is not as dramatic as the Virtual Dyno.
For the next tune I plan to replace Stoich at 14.7, and move PE from 1.176 to 1.148 (12.8:1). This will have the net effect of going the other way from baseline — taking the overall fueling 0.3 AFR leaner than factory tune from 12.5:1 to 12.8:1 in AFR terms.