What octane for a 239 flattie?

KEITHS 1950 F68 · #1 (**permalink**) 02-16-2003, 05:56 PM

Hey guys and gals;

Should I be putting the really expensive gas, or the really, really expensive gas in my flathead 239?

I haven't done anything about the no lead thing yet; but apart from that, should I be burning premium or regular fuel? Anybody with any suggestions about what works for them?

Thanks.

mtflat · #2 (**permalink**) 02-17-2003, 12:09 AM

If you're running a 52 or 53 without hardened valve seats you might want to use a lead substitute, but otherwise it'll run on anything.

I just returned from a 550 mile trip and ran 85.5 octane regular unleaded with no problems including pulling hard up mountain passes with about 500 lbs in the box.

Unless your motor is built for performance - high comp heads or radical cam, you should be good with regular pump gas. IMHO

KEITHS 1950 F68 · #3 (**permalink**) 02-17-2003, 01:28 AM

Tim;

Thanks; I'll go with the 'cheap' ($0.83Can per Canadian gal) stuff.

Keith.

STEVE1103 · #4 (**permalink**) 02-19-2003, 08:02 AM

My 53 Merc seems to run better with the 87, costs a little more than the 85 but does eliminate the stumble I was getting.

41Clay · #5 (**permalink**) 02-27-2003, 05:45 PM

As I hear it, you are subbposed to use the octain in occordance with your compression, 8.5:1 compression=85 octane gas. Since the falttys came with about 6.5:1 compression the cheapest would be fine, unless you upped the compression and timming (alot) then the higher octane would be wise.

Clayton

KEITHS 1950 F68 · #6 (**permalink**) 02-28-2003, 02:42 PM

Clayton; Sounds like a good formula. Thanks......Keith.