I'm building a 454. Probably going to be .030 or .060 over. I have Edelbrock Performer RPM Marine cylinder heads with 2.250 intake and 1.89 exhaust valves. I am going with forged aluminum pistons from SRP. I plan on having the pistons custom made by SRP, it's only a little more than off the shelf stuff, and I can get exactly what I want. Now....here is the question you have all been waiting for, lol. How much compression can I run using 90 octane gas that has no ethanol in it on an engine with these items?

Mine should be 10.25 to 1
I use pump gas from the local station and for the most part use the 92oct but a few time I have dumped 89 in it (I figure the 92oct after sitting in the 100* sun for a week or so is prob close to 90 by the time I use it) with no issues to report.

Srp is the economy line of J/E racing pistons made from mass produced piston blanks and there is no custom srp versions so I think you must mean regular J/E custom pistons? About 10-1 is your safe limit (depends on cam and cylinder pressure) and that is pushing it, with efi you could run no stat and wide open cooling at about 100 degrees with extra fuel to help you push the compression to the edge, Smitty

Why would you have custom pistons when SRP has a great selection of forged pistons? Those heads are 110cc? You can get nice SRP pistons in 0.020, 0.030, 0.060 and 0.070 over.
I run the small dome SRP open chamber pistons 9.7:1 Dart aluminum heads. I just started running 89octane. I checked my AFR's this weekend and I'm running 11.7-12.1 NA so that is a little fat I might jet down a little this weekend.
http://www.jepistons.com/Catalogs/SR...me_closed.aspx

I run 93oct with 10.25:1 with aluminum Dart heads and CP pistons. Open crossover cooling, so basically no water temps to report. Havent had any problems yet, and it has about 60 hours on it now.

I'm running 10:1 with Diamond forged pistons, AFR aluminum heads, and my distributor locked at 36. I have a very healthy cam which tends to bleed off pressure at low rpm. I run 93 pump gas from a known good station only. No problems so far and I've loaded my boat pretty good this past week.

Smitty, you are right. I meant custom J/E pistons. My heads have been shaved .080, and are 104cc now, so I want to make sure I get exactly what I need in a piston. I'm thinking of going with CompCams XM284HR cam. 284/290 duration and .547/.547 lift. Although I would like a little more lift, but the cams I have been looking at have much more duration than I want when you get up close to .600 lift. Any suggestion on A good cam? Keep in mind, I am going to be running a Gill wet exhaust with no mufflers or flappers. My exhaust exits the sides of the boat about 8" above the water line. Thanks for any help or suggestions.

And don't forget that the piston is only a part of the equation. You can don real compression calculators online. We did an air test and got the exact comp rate through the cycle and max cam lift.
I have 10.1 and alum heads 34 locked timing and use 93. I have used 90 a few times and didn't not ping.

You cut the heads down .080???????

There is not that much HP to be gained with .5 more compression. If you're running 90 octane, I probably would not go higher than about 9.6