bitter old man
Joined: Jul 2002
Location: La Porte, Texas
If your car was really "tons" faster, then your timing is being retarded when using 87-octane. If 89-octane really was faster, you'd notice an improvement in gas mileage, too. So, if 87-octane requires the ECU to retard timing, 86-octane would require even more timing retard. Less power, lower mileage. If the lower grade is 7% less cost, you need to get at least 7% better gas mileage with the higher grade to make the economics work for using 87-octane. Of course, if your SOTP dyno can't stand the power loss, who cares about economics.
Bruce in Houston
'94 Nissan Sentra SE-R w/ $tuff, converting to ITA
'98 Suzuki Bandit 1200S w/ $tuff
'02 Dodge Dakota SLT 4-dr tow beast, stock!