e85 can make great power on these cars but just throwing some in the tank without tuning for it or upgrading the fuel delivery capacity isnt advisable . stoich for gas is around 14.7 to 1 stoich for e85 is around 9.8. boosted applications rely heavily on power enrichment fuel to stay together.
while in open loop getting feedback from your 02 sensors it will compensate to a point as long as the fuel supply can keep up ( injectors/pump/lines ) but over a short period of time your fuel trims will peg and when you put it back on gasoline it will be trying to run pig rich from these learned trims until it settles back in
in closed loop which gets commanded when you go WOT you will get what is commanded in the tune for fueling with no regard to the 02 sensor readings so in the case running pure e85 you would be comanding 30+% too lean ouch!!!
I have done some tuning using e85 blends on a friends 3800sc rock crawler which we are currently running it at e25 (25% ethanol) and its as far as I have recommended him going without replacing the stock injectors as the duty cycles are around 90% at wot when running a safe 11.2 afr on my wideband using a gasoline scale .
he loves the results so far and plans an injector upgrade soon so he can pulley down further , its currently able to run a 3.4 pulley on stock fwd rear manifold ( pass side) and plog on drivers side with no knock on 18* timing - he gives the guys with stock 5.3's in their crawlers fits ! on premium pump fuel it was not able to run a 3.5 pulley safely due to KR
