I have a 92 RS with the LO3 and a T5 transmission, what should I be putting in for gas? Currently I have always been using 91 but I am wondering if I may have just been wasting my money. The only mod is a high performance cat and an 80 series Flowmaster.

i think 87 oct. would be fine for you . i have an 89rs with same eng. and gears . 87 is all my car has ever seen . runs good , 27+ mpg when hwy. traveling .

These cars were designed to run on 87 octane, that's all they should need in stock (or mostly stock) form.

Mine likes to knock all over the place on 87 and all it has is a flowmaster 3 inch catback and a magnaflow cat...

Well I do have a three inch exhaust cat back so I am afraid of it knocking. I guess the only way I will know for sure is to try running 87?

Would I get better fuel mileage out of a tank of 87?

i have a 3' exhaust also , headers , roller rockers , MSD ignition parts [ no box ] , homemade intake sys. , other mild mods. . 87 oct. is good . don't waste money on 91 oct. . use money to have a cool one at the PLANK or OFFICE . used to live in IB .

The only reason you would need anything higher that 87 octane on the stock compression ratio is if you have your base timing bumped up. I have read that could give you a little better power, but usually requires 93 to keep the knock away.

Also, you might have carbon build up in the motor. Try running a can of sea foam, or squirting half a can of carb cleaner down each bore and starting the motor.

Would Carb cleaner hurt the throttle body since it is a carb cleaner? I have run a tank or 87 before and I have noticed less power as weel as more knocking, I did have my timing re adjusted.

What should I use to try to clear out the carbon deposits and also is it worth it running say Shell vs. Arco?

Shouldnt need to use anything over 87 with it properly tuned up and the engine in good working order. Carb cleaner wont hurt, but try to keep it off the sensors. The loss in power is likely from the computer trying to control the knock. Could drop the y-pipe and give it the water treatment. You basically slowly pour water into each bore with the motor running at around 2000 RPM at operating temp. You pour in enough that the motor will complain, but not so much that it slows down a lot. It will get the excess carbon out of the chambers and off of the backs of the intake valves.

Well thank you all for your replies. I will definitely get the carbon out or at least try to. Thanks

Could drop the y-pipe and give it the water treatment. You basically slowly pour water into each bore with the motor running at around 2000 RPM at operating temp. You pour in enough that the motor will complain, but not so much that it slows down a lot. It will get the excess carbon out of the chambers and off of the backs of the intake valves.[/quote]
PLEASE , elaborate on this procedure . old man that i am , i've never heard of this . never too old to learn . please explain . how , why , benefits , etc. . thanks .