I have a 1985 trans am 305 TPI what type of gas shoul i use it has 9:5:1 compression. 87 89 or 93 octane???

 

Check th owner's manual if you have it. My 87 305
TPI was recomened in the manual to run PREMIUM UNLEADED 93
OCTANE. Or Run what the engine will accept without a knock or ping.

 

Your 87 305 TPI calls for Premium? These cars are 9.3:1 compression or less... that should call for 87 octane (regular). My 89 L98 calls for regular, 87 octane gas.

However, I find that the price increase of getting premium gas equates to about an extra $1 per tank. Therefore, even though my car calls for 87 octane, I find it a worth while investment to use 93.

 

It should run just fine on 87.

 

Generally the detergents added to the premiums generate less ash when burning, so long term, the exhuast vales will last longer.

For component life, things always seem to last longer with the higher octane fuel (this based on fleet management). If you only care about a limited service life, then any ol thing will work.