I have an '88 Regal with a 4.3 (GM V6) Mercruiser. Anyone know whether I need to use 91 octane gas? I've been using 87 octane and I don't hear any knocking but I'd hate to find out the hard way that this engine needs 91.
You will be fine on regular. That's what you've been using to this point, right? If you notice knocking or pinging - especially under a load, then you might need to retard the timing or go up a grade or two in fuel.... but I think you will continue to be fine with regular.
If you know the engine has not been hot rodded IE:, head work, hi comp pistons, etc, the 87 will work just fine. Comp check will tell you as well. If numbers are way high, 170 psi and up, you may need the 91.
