I've always used 93 octane in my motors, but am wondering if I could get away with 89. Tthe fuel dock at the end of my creek only has 89, the nearest 93 is down the river a bit. Last time out one of the two places for 93 had broken pumps and I was REALLY low on fulel.

The motors are 454's with 9.8:1 static compression and the cams have 235/245 @.050 duration, Iron GM heads.

How much compression is anyone running against 89 octane?

-Greg

Iron heads and almost 10:1. Stick with at least 92 unless you want to retard the spark advance.
My $0.02
Gary

Hi Gary, glad your still around.

Forgot to mention that I do run a fair amount of advance, 35-36 degrees total all in by a little under 3000 RPM, and around 18-20 initial (I set the total and let the initial fall where it may). I've got the MSD's set to the shortest advance curve I could.

-Greg

OK, 10:1 iron heads, and 36 degrees? Damn, I would stick with 93, cheap insurance.
I had to put 89 in my 525SCs once (late night fill up) and I was scared to push over 1lb boost. Bad thigs happen when you start to detonate.
Gary

You may get away with using 89 if you throw some octane booster in with it. Watch your plugs for little aluminum beads!!!

Also if you just cruise and don't hammer on it 89 should be fine

Does anybody have a rule of thumb for degrees of retard for dropping from 92/3 to 89 or to 87 octane?

My MSD Digital boxes have a retard that can be wired to a switch. I was thinking of using it as a "cheap gas" retard but don't know where to start as far as degrees to retard.

Figured I would monitor it and see if it affected my cruise fuel economy. If not, I would intentionally use cheap gas on long (over a tankfull) cruising trips.

Guess I'll keep running the 93 (it really isn't much cost difference) and hope I don't need to use 89 to "get me home" anytime.
I'd hate to have to pump out 200+ gallons of fuel I can't use. It would take a LOOOONG time to burn that much waste fuel in the lawn mower


-Greg