Help on 408 build

OK, thanks..... I was in the ICON catalog, and they list that kit as having dish pistons but I think that is a catalog mistake based on the piston volume of -5 cc (5 cc would be eyebrows only), and the compression ratios that they list. And I am sure you would not miss a dish LOL! So I am thinking these are probably ICON IC744 pistons. Those would sit .012" below a nominal LA deck height, so was this block decked milled for zero decking the pistons? It is not a massive difference.... about 1/4 point in the SCR and DCR numbers. But we just want to be as accurate as possible here to help get you out of the woods.

I would take that 'used' gasket thickness as removed as being very close to actual as installed.

The PRH and my numbers on SCR are looking to be close if the J heads were not milled any more than just a bit to true them up. Do you have any info on any head milling? They typically are at 72 cc's + or -. So that is encouraging and you may very well get by with thicker Cometic head gaskets and some better tuning on the timing.

Not to jump the gun too much, but if it is correct that you were in the low-mid 8's for DCR, then I am not at all surprised that you had consistent detonation with that timing. I've run iron heads at 8.3 DCR WITH quench and could not run the amount of timing you had in it. So with no quench, you are going to run into detonation even more readily with advanced timing.

I'd also suggest timing the cam (if it was not already done) and making sure your 0 mark on the timing is exact with the piston stop method. You are working in a compression territory where everything needs to be known and exact to get it to work well. And the suggestion to put in an AFR meter is also spot-on IMHO... again, you are pushing the dynamic compression up there and need to know things with accuracy.