What is the highest compresion that can be run with 93 pump gas in an iron headed application? Would my L98, bored .30 with 56cc heads be over that limit. I posted about this earlier and someone gave me a link to an engine calculator that didnt work. I need to know because ive seen a nice set of vortec heads cheap but they have been milled down to 56cc. This is a street car, so it must be able to run on pump gas. Can i run these heads?

 

lot of variables but 10.5 would be about the top limit but on your engine you may only be able to run 9.8 or so. a safe bet would be in the 10.2 range.

 

You can download a compression ratio calc program
that will work, from Performance Trends.

Do a search
The short answer is if you have .025" deck clearance (or more),and use a "corvette" .051" gasket and use a fairly big cam, you'll be just this side of ok.
Best check out what other mods have been done to these heads
to see if they are compatable with your plans.

 

My block was "decked" during a rebuild done by the previous owner, would i still have clearance do you think? Could i also just use a cam with a ton of overlap? I like the idea of higher compression but i dont want it to be out of hand.

 

I'm not a wizard. I can't see in your motor.

You'd have to take it apart to see.
There are ways to adjust the final cr to suite.

Copper shim gaskets ("head savers" etc)
You can also open up the combustion chambers on those heads
with a die grinder.
A long overlap cam will only help a little bit. (increased EGR
effect at low rpm) (rough idle)
A grossly oversized cam will be a pain and not worth it.

Vortec heads are cheap to buy anyways. Why not get a set
from some where else with stock chamber vol and not have to worry about it. Bolt those heads on a 305 or a 350 with dished pistons.

You're going to spend more trying to correct these heads than
you would on a new set.