does it make a big difference with my 88 RX7 GXL what type of gas i use? i've only used regular. should i fill it with the better stuff every once in a while or does it matter?

 

use 87

 

regular here IS 87. You can either use 87 or mid-grade. I'm not sure of the number, but I guess it's between reg and premium. I've only see it on gas stations once that said "mid-grade" .... other than that.. i've seen reg, something reg and premium.

 

In the rotary world, only modified turbo's & race cars have any need for high octane.

 

Your car is rated for 87 octane. If you notice any knocking, then either change brands or go up to 89 octane. Putting higher octane in it for no reason is just a waste of money.

Read all about it:
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm