Octane rating based on CR??

[MikeTaylor]

I'm rebuilding the 59A in my '48 tudor and am planning on a 4" crank, 8CM cam & alum heads. I haven't made up my mind yet on carbs, 2 deuces or a 4 bbl setup nor what the bore should be.

This will be (So. Dak. winters permitting) a daily driver and, as I live 30 miles from anywhere, will see a lot of miles. In addition, there'll be a least one trip to CA and one to the east coast.

I mention this because you can't always find 91 octane and anything without ethanol has pretty much gone by the wayside.

Soooo..... what's the best CR for this 87 octane crap they call gas???

Thanks in advance , all replies appreciated
Mike

 

[Ol' Ron]

You ask a good question and I'm sure several people will jump in here. I try to limit my CR to 8.5 to 1 for 87 Oct gas. However, The combustion chamber design determines the mechanical Oct of the engine. I keep the piston to head clearance very close to form a quench area that increases the turbulence of the chamber. This also allows for more spark advance for better economy in cruise. I have a 280 ci engine in my truck with stock EAB cam and so far it;s working well but I haven't had it into the hills of Vermont yet.

I made a mistake here. changed the 9 to an 8. Thanks for correcting me. I do all this "Studd" with magnifiers and text to speech programs and still screw up.

 

[Charlie ny]

MT,
Based on JWL's book and input from Ron I built my 4" 8ba with EAB heads
and made sure I had zero piston to chamber clearance with NO head gasket in
place. With head gaskets installed and heads torqued I knew I had .040 between
the chamber and piston crown. I use 87 octane corn gas successfully. I did have to
dial in my sbc/8ba distributor in a bit , no big deal, and set the ancient Olds 4 barrel
up with an A/F meter.
Charlie ny

 

[JSeery]

You ask a good question and I'm sure several people will jump in here. I try to limit my CR to 8.5 to 1 for 97 Oct gas. However, The combustion chamber design determines the mechanical Oct of the engine. I keep the piston to head clearance very close to form a quench area that increases the turbulence of the chamber. This also allows for more spark advance for better economy in cruise. I have a 280 ci engine in my truck with stock EAB cam and so far it;s working well but I haven't had it into the hills of Vermont yet.

Ron, a question. 8.5 to 1 should not require that high an octane, do you think it is the CR or the timing advance you are running that is requiring it?

Note: I agree the combustion shape has a lot to do with it, there is a lot of difference between an overhead valve engine and an L-head engine.

 

[HCO41]

For those that are traveling the following site may help in finding non-ethanol gasoline through-out the country. As you'll see, most is 91 Octane.

Pure-gas.org

Howard

 

[supereal]

The problem is that all gasoline now contains some alcohol. It is in the hose of the multi choice pumps, and/or the transport trucks. If all parts of the fuel system in your car are "fuel proof", you should be safe. Where you (and I) live, fuel line freeze is likely due to the water in gasohol. I add Heet or other methanol product to take care of that.

 

[itslow]

...I try to limit my CR to 8.5 to 1 for 97 Oct gas...

Ron, a question. 8.5 to 1 should not require that high an octane, do you think it is the CR or the timing advance you are running that is requiring it?

I suspect that's a typo - considering 97 octane is not likely to be available at any gas station in the US - and he meant 87, instead.

 

[Ol' Ron]

Yepa doodle. Thanks. Another thing that JWL did was relocate the spark plug. I did the same thing to a set of heads for a 239 engine I wanted to check mileage on. Unfortunately the block was no good. By placing the plug in the middle of the transfer area and a power ti plug a very lean mixture can be burned in cruise. I keep putzing to make it better.

 

[JSeery]

The problem is that all gasoline now contains some alcohol. It is in the hose of the multi choice pumps, and/or the transport trucks. If all parts of the fuel system in your car are "fuel proof", you should be safe. Where you (and I) live, fuel line freeze is likely due to the water in gasohol. I add Heet or other methanol product to take care of that.

That is not the case here, Not alcohol fuel uses a separate hose.