Fuel energy constant for FAST XFI questions

[quadzila]

I know the fuel energy constant needs to be set to .680 when switching to E85 on my xfi --but what about the first time fuel is switched and there is still lets say 1.0 gallon of gas left in the tank after draining tank from the fuel rail and i add 10 gallons of e-85 would that make the fuel E-75 and should i set the fuel energy constant to about .725 to compensate ? or just leave it set to .680 and the xfi will compensate what ever the fuel is e-75 or e-80 e-83 or what ever it ma bee.....?.. I do not have the flex fuel sensor. thanks in advance.....

 

[northerngn]

When I switch from .680 to 1.0 and back again I always pump out the tank and then fill to the top with whatever I'm switching to...E-85 fluctuates anyways so just pump it out, fill with new fuel from a gas can then change you FEC number and drive it ( like a grandma) to the station and fill it to the top and run it...If you'll have a knock gauge you'll be fine...no knock no worries (I always run both my tunes both gas and corn on the fat side)
-Dan

 

[quadzila]

When I switch from .680 to 1.0 and back again I always pump out the tank and then fill to the top with whatever I'm switching to...E-85 fluctuates anyways so just pump it out, fill with new fuel from a gas can then change you FEC number and drive it ( like a grandma) to the station and fill it to the top and run it...If you'll have a knock gauge you'll be fine...no knock no worries (I always run both my tunes both gas and corn on the fat side)
-Dan

ok great, thank you for your input. As soon as i get my double pump installed im going to make the switch....do you have to tweak any other parameters after its switched to e85 ?

 

[northerngn]

ok great, thank you for your input. As soon as i get my double pump installed im going to make the switch....do you have to tweak any other parameters after its switched to e85 ?

Yeah there a re a few other things such as E-85 seems more tolerant to more timing than gas is and, of course... the fact that you can run a ton more boost so your WOT tuning will be occurring on a higher part of you VE table which will also require attention the the same areas on the target AFR table as well

 

[quadzila]

I will check and verify those table settings as boost goes up, thanks

 

[northerngn]

I will check and verify those table settings as boost goes up, thanks

Yup!