Which octane should i use for my stock 1990 LX 5.0?

 

With stock timing (10*) you should be able to use 87. The higher octane gas takes more energy to burn and therefore you can increase your initial timing. Once you go above the factory setting you'll have to use 89 or better.

 

sometimes I used to run 14 degrees timing and 87 octane, but on hot days it would ping.
now only 92 octane goes in my beast. because of the nitrous.

 

I have a 94 5.0 - more or less the same car - and I run 87 in it with no problems.

 

Same here, I have a 94-95 HO and I run 87 no problems.

 

i use the one in the middle thats 89 right?

 

Yeah 89 is midgrade.

 

I assume 89 would be perfect for 12* timing right?

 

if you run premium you will be able to tell the difference in performance, mabye not for a stock motor, but with mods I can sure feel the difference.

 

My car is basically stock - I have headers, o/r H, and flows - and when I put in 93 I can feel a difference. Not much, and its not really worth the extra cash, but the car pulls better.