I own a 98 Mustang GT with minimal mods and have a Predator tuner, I run Exxon 91 octane fuel. The Predator tool comes with tunes for 93 octane (written for a minimum 91 octane) and 87 octane. When I run the 93 octane tune (even adjusting the spark retard) it runs terrible, flat, no acceleration, and terrible gas mileage. But, when I run the 87 tune (adjusting the spark retard upward) it runs much better with better gas mileage. I live in Utah so I don't know if altitude is an issue, but anyone have any idea why this may be the case? Seems illogical to me unless there is a mechanical issue, or perhaps quality of gas??
I am on the most current version, performance on the old version was actually better. I'm inclined to think its a mechanical problem, but I don't know what, my mechanic can't find anything and says the car feels fine to him on test drive. But...I know it's just not quite right. I've posted the question one the Diablo website, first go round all they said was that it sounded like "bad gas" (I know the feeling!!!), but I've run three tanks of Exxon through it with no change.
Base 240 HP 258 TQ
Diablo performance tune 235 HP 275 TQ
Dyno Tune 259 HP 281 TQ
Max gain +89 HP and 160 TQ at 3K RPM and +55 HP and 160 TQ at 5700 RPM
Picked up 19 HP & 23 TQ over base and 24 HP & 6 TQ over caned tune at the peak.
I actually lost 5 HP with Diablo canned tune but Brent said that was because I was running way lean due to C&L MAF.