Any info on these pistons? 3991476..Its hanged on X rods and a cast crank (3932442).The block is 4 bolt from a truck though..Its under crappy 462624 heads.

Im planning to port some 416 heads and put it on top and Im worried about too much compression.Its going on a heavy daily driver so I dont want it to be an exclusive 92 octane deal.

Send me some data

 

Can only find specs on the Silvolite pistons that suitably replace those pn's.

They are either 11 or 13cc dished pistons that may be .045" down in the bore at TDC (the silvolites are) You'll have to check the compression height yourself to be sure.
Pin C/L to piston top 1.54" = a .020""destroked" piston ( .045" from top @TDC.
1.56" standard compression height 350 piston typically .025" from top @ TDC

Yours could be either /or.

estimate worst case 58cc would be 9.77:1. Piston .025" below deck@TDC

IF the piston is in fact .045" below deck@TDC then 58cc head would get you a 9.2:1

You will be deshrouding the chamber in order to physically fit a large than stock valve in those 305 heads which will open up the chamber some. you can add some hand grinding to easily end up with a nice deshrouded, polished 64-66cc chamber which will get you about 9:1 . may work on 87 octane or may need a mid grade gas.
use champion RV8c plugs.....available at CTC

You'll want to go for the larger valves anyways.
1.94 x1.60 is best.

Useing a EGR intake manifold will help prevent pinging at higher compression ratios using cheaper octane gas for commuting . If you can find a egr performer get it.
Helps keep the smog ****'s off your back too.
The egr shares the ported vacuum source with the vacuum advance on the carb. the egr system and vacuum advance work together to get efficientcy and knock supression.

A cam with a little large than nessessary overlap can help too ( built in EGR effect) but easy to get too carried away and end up with a gas hog.
Something like this should work well . Worked good for me before. Blue racer cam

What is the compression height spec on your pistons?

 

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..... egr control valve