Take .040 off your 706's

 

Find a new machine shop then...milling heads on these engines is common practice

 

What kind of comp ratio would that give me?

 

Got it...

5.3 with .040" milled 706 head = 10.13:1 with a 3.910 bore .054" thick head gasket.

5.3 with .025" milled 706 head = 9.87:1 with a 3.910 bore .054" thick head gasket.


Thinking I might want to go .025" to keep using regular 87 octane fuel.

 

You can use 87 with 10.13:1 static compression depending on what cam you choose and how much overlap it has. You need to figure out what your dynamic compression ratio will be, and you can also play around with the timing tables to keep the engine from detonating. As much compression that you can run without detonation will be beneficial to your low/midrange that you're looking for. Considering that the SilvySS came with 10.08:1 from the factory, with the factory bumpstick, I'd have to *guess" that 10.13:1 with a larger cam would be good to go as long as you don't get crazy with ignition timing. I do believe that GM recommended at least 91 octane on the SS's, but I'm not 100% sure on that.

Maybe split the difference between .025 and .040 and go for like a .030ish mill or something