I am starting a new project, which will be my first N/A adventure, and was planning to build a LS3 variant (418?) I want to strictly run 91 octane, but can't figure out what the maximum compression I can use.

I am at 4600ft of elevation, and I know a 11.5:1 engine will pump low, but how low?

Thanks for any help!

 

What is the typical DA?

 

http://www.altitude.org/air_pressure.php

air pressure at sea level = 101 kpa.
at 4000 feet air pressure is 88 kpa.

the website says 87%.
whatever your compression ratio say you see around 200 psi when doing a cranking compression test, you would expect to see only 87% of that at 4000 feet altitude = 174 psi cranking compression.
I wanna say going from memory you don't want to go over 200 psi cranking compression because that's the max 93 octane gas can take before compression and heat is too high and you get detonation, and this cranking compression number (which is not compression ratio such as 10:1 or 11:1) takes into account camshaft profile and running compression. other thing you need to take into account is if your fuel has 10% ethanol or more and what the air/fuel ratio is.