Dumb question..... I have an 88 GTA 5.7, am I supposed to run premium gas or can I run regular or mid-grade? Thanks for the help.

 

Well assuming you have a bone stock unmodified L98 then you should be able to run regular unleaded

 

nothing saying you cant run a higher than regular grade. running a higher grade will give you slightly better MPGs.

 

The car has SLP headers and a 3" catback.

 

While you can run a higher grade of fuel its not necessarily true that youll get better mpgs but you should get better emissions lol

If thats all thats done than regular unleaded is fine... where you want to be concerned is if your timing is different then stock or if you have increased compression...