[Jay S]

Just my opinion. But if I have a set of high compression heads and spent a bunch of time and money on with port work, valves, guides , ect….I would take a hard look at cutting a symmetrical dish in the flat tops to drop the compression some and run the 48s over starting over again on some lower compression heads. If it is a balanced rotating assembly I would figure the mass loss from the dish and figure the effects on balancing, might be ok yet. That or buy appropriate pistons and maybe sell those pistons and get some pistons that will put the compression in a range that works better. I don’t like doing things twice but I would rather do that than start on another set of heads. Here it is $170 to rebalance, that won’t go very far rebuilding heads, let alone port work, even if it is a DIY scenario. Our best pump gas results (so far) have been with symmetrical dished pistons over flat tops, D shape, or domes. Maybe more factors at play there though. FWIW

I mostly shoot for between 10 to 11 compression on my cast iron heads with a lot of port work in Pontiacs 450 + cid for 87 to 91 octane. FWIWz…I don’t think I am quite to the point I am at 11:1 for 87. I was looking at the new Progression Ignition distributer that you can modified the timing curve and it connects via blue tooth with a smart phone. I think that is my next step to get to 87 on the 11:1 street engines. But I think I will carry the oem HEI in the trunk, just in case…Lol.

Totally stock d port 455 on 91 octane we have been a 10.4 SCR. Might have ran on 87, never tried it. Cam was big for the head flow, it didn’t run great. It dropped the DCR to low for the RPMs the cam wanted to run, and ran out of head flow. Much better results with port work. All our D ports I run are now are 280 cfm or better with RA 4 ports or bigger. I don’t think a really high compression stock port size will work very good in a 455 on pump gas, would need 93 for sure to keep the cam from out running the heads. My pump gas 461 is a 11:1, the 6x-4 heads flow 291@28”, 224 exh, Bullet SR cam.

Most think that the HP gains are to small from the added compression to be worth the risks, most sensible engine builders won’t go there. I think just the thermal and volumetric efficiency are worth the efforts. But it only takes one thing to be overlooked and you end running more octane than originally planned. I did a cam for a friends 455 the compression was suppose to be 9.8. He wanted fo run on 87. I helped degree the cam in and I noticed the pistons where way down at TDC. Measure it at about .030” down, refigured his compression and it was in the lower 9s. He thought it was a good thing becuase it dropped the compression down, I told him it wasn’t going to work out how he was expecting (bad quench). He is determined to get it to run on 87, been helping him on it some. He may get it to run on 87, but it is not there yet. If you get to the point you get a compression target and want to run something by me, shoot me a PM. I enjoy designing high compression pump gas stuff.