gas octane question

here in So. Cal. Whittier area, the gas is costing quite a bit lately so I was thing of changing from 91 octane to 89.

The engine is a '72 350-4 stock but with all a/c and smog removed including EGR valve. PVC is still in place. Car is power timed and runs great no ping when wot and no run on when motor is shut off.

What do you think, should I try a tank full of 89 octane?

Thanks,

Brad

 

Depends on your compression ratio. If your engine compression is below 9.5:1, then 89 octane should be fine. I have 10.25:1 in my 430, so I have to run high-octane.

 

Try some, see if it rattles

 

72 is only 8.2 compression if it’s all original. So you could go 87 and should be ok. But you could try it first like mentioned, then advance timing alittle to get the most out of it , but obviously spark knock means you will have to either use higher grade or reduce timing back down.

 

Thanks guys, I think I'll try a tank of 89 and see what happens...

 

Any more Octane then what you need only cuts back on power and in turn mileage!

 

I wouldnt try a full tank right away, I'd start with maybe a 1/4 tank. Get a 5 gallon can, fill it up, drive around, run the car and bowl dry, fill up with the 89, save a mouthful to pour into the carb to aid in starting if you wish.

 

Thanks for the suggestion. I'll try that..