The Ford Barn

RKS.PA · 05-17-2023, 01:36 PM

Not intending this to stir up a controversy like a discussion about "the best oil", but I know the literature says use Premium grade fuel in the 312ci because the compression ratio is 9.0 to 1 for a 1956 Thunderbird.

For reasons unknown to me, our gas over here in AZ is quite a bit more expensive than some of our other neighboring states, with the exception of CA.

If I changed to 89 octane (the middle grade here), am I likely to damage any engine components? I don't do any highway driving. The Pertronix electronic ignition fires the engine right up. Might this change using a lower octane?

I'm interested in hearing what you Y Block gurus have learned over the years!!

Thanks in advance for your thoughts!!

(My apologies if this topic has been covered in the past..I'm still finding my way over here.)

miker98038 · 05-17-2023, 02:00 PM

Sponsored Links (Register now to hide all advertisements)

I’d give it a try. Marana is about 2500 ft. If you hear a ping from pre ignition, get your foot out of it. Most old Fords struggled to make the “static” compressions ratio stock and new. Now if the heads are milled and the block decked, you might have that. The cam plays into also of course (dynamic ratio).

My guess is it’ll only ping if you’re in it hard on a good uphill pull on a hot day. I’ve had a number of cars where that happened only in those conditions (even on premium, but it was marginal enough octane booster actually helped).

Just don’t stay in it and let it rattle. Tough on piston tops and other things.

05-17-2023, 01:36 PM	#1
RKS.PA Senior Member Join Date: Jun 2010 Location: Marana, AZ Posts: 1,194	Fuel Grade for 312 ci engine Not intending this to stir up a controversy like a discussion about "the best oil", but I know the literature says use Premium grade fuel in the 312ci because the compression ratio is 9.0 to 1 for a 1956 Thunderbird. For reasons unknown to me, our gas over here in AZ is quite a bit more expensive than some of our other neighboring states, with the exception of CA. If I changed to 89 octane (the middle grade here), am I likely to damage any engine components? I don't do any highway driving. The Pertronix electronic ignition fires the engine right up. Might this change using a lower octane? I'm interested in hearing what you Y Block gurus have learned over the years!! Thanks in advance for your thoughts!! (My apologies if this topic has been covered in the past..I'm still finding my way over here.)

05-17-2023, 02:00 PM	#2
miker98038 Senior Member Join Date: Mar 2013 Location: Kent, WA. Tucson, AZ Posts: 1,398	Re: Fuel Grade for 312 ci engine Sponsored Links (Register now to hide all advertisements) I’d give it a try. Marana is about 2500 ft. If you hear a ping from pre ignition, get your foot out of it. Most old Fords struggled to make the “static” compressions ratio stock and new. Now if the heads are milled and the block decked, you might have that. The cam plays into also of course (dynamic ratio). My guess is it’ll only ping if you’re in it hard on a good uphill pull on a hot day. I’ve had a number of cars where that happened only in those conditions (even on premium, but it was marginal enough octane booster actually helped). Just don’t stay in it and let it rattle. Tough on piston tops and other things.