I've been running 87 octane in my 3.8 track here in the great state of Oklahoma, without any problems. I usually go to shell stations and make sure that its pure gas, none of this part alcohol bs. Trust me, as has been said, if your running below 11:1 compression (which you are) you dont need high octane gas. You are just throwing money away.
Buy, 87, tell your friends who dont know any better that your running 91.
Owned a 1984 Trans-Am with a rebuilt 305 with a 600cfm Holley carb. Car made 360 horsepower and about 320 pounds of torque (it was a monster) and It ran on 87 just fine. But, my buddy with an Acura RXS-S has a scrawny 2.0 litre, but the compression is way high, like 11:1 and the motor will knock like hell with anything less than 91. But these cars are nowhere near that compression so, really no need.
If you absolutely must, buy 89. But, I (with a bit of car knowledge, but by no means an expert) will tell you that you are throwing away your money on 91.
Put your savings into cheap light beer.
Rule of thumb that I've learned. If the motor revs over 7,000 rpm, you need 91 octane. You can take that to the bank.
By the way, if anyone else out there is studying for the bar exam and drinking by yourself. My hat goes off to you.
Last edited by Tufast; 07-11-2009 at 08:54 PM.