Blown 565 compression question
 

I have built many big blocks for drag cars and NA marine but only a couple blown marine engines, I am building a replacement for my good running 575sci and need some advise on compression.
Running afr 315 heads, for the moment i will continue to run the stock blower because of it only having 55 hrs, yes i know it will be a restriction, however i am only shooting for 725-750 hp so it should get there with the stock blower at about 6.5 lbs boost and not make to much heat. The stock compression ratio is 7.5 on the 575sci, I am thinking i can get away with 8.5 on 93 octane fuel if boost stays below 8 or so.
At some point i will convert to a 871, i already have installed the young performance injection upgrade which uses 8 injectors. Amazing difference in running. I have most of the parts already so i figured i might as well just build the boat engine. My 575sci only has 55-60 hrs on it and is bone stock besides a 3.5 pulley. You guy's think 8.5 compression is ok??

Just going from memory here so numbers may be a little off. I believe the standard JE dished blower pistons come in either a -20cc dome or a -28cc dome. With a standard setup of .010 deck height and .040 head gasket and around 119 cc head i believe the -20 will put you at about 8.5-1 and the -28 will put you at around 8.2-1 compression. I have done both setups on blower motors and either will work just fine. If you are really going to throw some boost at it later, i would probably go with the -28's

Since you already have the upgraded EFI from Young Perf, I would call and discuss it with Eddie Young

I 2nd what Griff said. Eddie will let you know what will work the best for your setup.

I thought of that after I ordered my je pistons. -21cc will put me at 8.35. Perfect, I'm also doing the dyers 871 conversion. It will be a very reliable 800hp set up with more available when needed.

Very easy 800hp. I made 900 with my last 565 with a 420 megablower. It has been trouble free for 6 or 7 years now.

I'm in a tough spot, engine has very low hrs but also has stock head gaskets still and they were a issue with these engines. It sucks you can't change cam with engine in boat. For now I think I'm going to just pull heads and do Cometic gaskets, I have a set of merlin heads that have flat tappet springs so I might just bolt those on and go. Easy to do heads in this boat, plenty of work room. Then do engine swap next year.

Just pull the engine. Most of those singles with plenty of working room you can have out in 45 minutes.

The Merlins might not be any better than stock if they haven't been heavily modified.

I have ported many bbc iron heads, i have a flow bench. A stock 088 head like what is on the 575 sci flows decently good on the intake, 320 at 600 lift but the exhaust is TERRIBLE, less than 200 cfm stock. The merlin heads as cast will flow 350 on the intake and 235 on the exhaust out of the box. I did some work on the merlin heads years ago and they flow 367 at 600 and 247 on exhaust. Back in the day we used the merlin oval port on 468 builds before the afr oval port ever was though of.