427build/compression questions

[Tom Gahman]

What is the ragged edge for compression for iron heads vs aluminum heads on pump premium?
Also I don't mind mixing cam2, my cars main purpose is "fun at the track",I'm not a every week racer,
and this isn't a max effort build.
My plan is to build a sturdy short block with flat tops and start with iron cj heads that I already have
and grow into aluminum heads and larger chambers.
Using Summits comp calculator, with an Icon flat top, compression will be
11.5 with a 70cc head(+-) and less with larger chambers.
My car is a 4000 pound Galaxie with a 4 speed and a 4.86 rear gear.
Street time is mostly for "testing".
The short block will hopefully be 4.25x3.98.
I will be using my current cam and valve train,258@.050 and 615 lift.
Is this a reasonable plan? If I have to, I may wait and pick up some aluminum heads.
Thoughts and advice?
Thanks, Tom

[blykins]

Tom, you will have to mix or run race gas no matter which cylinder head you run.

If I were in your spot, planning a car that's main purpose is drag time, I'd let her eat on the compression ratio.  Compression is a power-maker.  I'd run 12-12.5-13 and run race gas.  If you're not driving it on the street, or just doing it very rarely, you can keep some race gas on hand.

[Tom Gahman]

Thanks,thats what I was thinking,but how do I know what octane to shoot for?
Is there a formula:10.5=x,11=x,etc.?
I've used the Wallace octane calculators for mixing, but I really don't know where I should be for a given ratio.
This build will be more$$
More $$= more fear of screwing up.

Thanks,Tom

[blykins]

I would nail down the compression ratio first and then see what octane you need from there.

[Tom Gahman]

Will do.
Thanks again,
Tom.