Sorry ahead of time if this has been talked about, i cant do a search on my phone. Got a 4.8 that im goin to put a 5.3 crank and rods in and leave the stock 4.8 flat tops in. With milled .030 243's what would be the compression? Pump gas safe?

 

Around 10.5-.6 with .04 gaskets

As long as you tune it for premium it will be fine. For 87 octane I would not go over 9.7ish, Other wise they will have to tune the cam with no advance and power sucks that way

I have a 67 camaro with 11.6 compression that runs great with 93 octane

 

That compression should be fine with a good tune, although we don't recommend going over 11.5:1 with pump gas (93 octane).