What octane fuel for a 427FE
 

Got the oil thing figured out, now how about fuel. What octane and should it be leaded or unleaded? Anyone know where to find the good stuff in St. Paul, MN. area? Thanks!

Need to know your compression ratio, cylinder head material (iron or aluminum), and camshaft specs to provide a meaningful answer.

Do you have a small airport close by ;-)

93 octane, I doubt your over 11:1 compression. You can probably get away with 91 if you have a mild 427.

There is a free phone app for Ethanol Free fuel. It is free and called "Pure Gas" and it located ethanol free gasoline. Some marinas sell this.

Crop dusters are a good resource for 100 octane low lead here in Arkansas.

Figure out what you need and keep notes. There is summer and winter gas. High altitude, etc., so watch out.

There are about 21 different "recipes" for what passes for gasoline these days.

Not is Arizona there is not, I think we use the most ethanol ratio next to California, we can't get just gas anymore.:mad:

10.1 Comp ratio, aluminum heads and a Comp Cam with 589 in. 615 ex. I do have a small airport 4 blocks away.

It's the duration of the intake valve that matters. The longer it stays open on the compression stroke the less "true compression" you really have. FWIW, I have a 10.6 comp ratio, aluminum heads, and 245 degrees duration at .050 on the intake valve and I run just fine on 93 octane gas with the ethanol mix (which is all I have in my area). The ethanol does clog up the air bleeds from time to time by flecking the zinc off the bowls, and that will make you think your engine has one foot and three toes in the grave.... Do a quick search on this forum to find the threads on that so you know what to look for.

91/93 octane should be fine, if you hear any pinging,try adding some 100 octane AV gas....
My old 351-W with iron heads and 10.6 to 1 compression ran fine on 93 octane...Once when running low on fuel,all I could get was 89 octane,it ran fine except slight pinging when acceleration in high gear to pass another car on the highway,as soon as I could fine 93 octane, finished filling it up with 93 and was good to go.......

David

Essentially, the purpose of "octane" is to prevent detonation. You need enough octane to prevent that. How much that is depends on a variety of facters.

The most important is probably dynamic compression. Dynamic compression includes factors like static compression, intake valve closing point, altitude, etc. There are a number of calculators on the web that will get you the right numbers. For 93 octane, you generally want less than 8.5.

As the intake charge temp goes up, so does the detonation.

Lean mixtures detonate more than rich one's. Partly because of the additional fuel, but also because it has a cooling effect. Yes, you'll spend a little more in fuel, but pistons sets are pretty darned expensive.

Too much timing will ignite the fuel too soon, and that causes a significant amount of detonation. Some people think you need to run 36-38* of timing to make good power in a small block Ford. But the truth is that many engines will make more power with 32-34*. Keep the timing conservative if you need to, and don't worry about the little bit if power you might be giving up.

And, finally, engine load is also a big factor. Not usually much of an issue with a big engine in a light weight car. But if your power band is 2,200-6,200 rpm's, pulling a big hill in 5th gear at 1,800 rpm's is putting quite a load on the engine.

Be careful, dynamic compression and low cylinder pressure can be a false sense of security. At high rpm's the real dynamics come into play here and with engine load you can get detonation and won't necessarily hear it.
I have roughly the same set up as patrick. All good at 34* and high rpm's:3DSMILE: