my 598 NA made 760hp at 5950 on precision's dyno. boat runs pretty good, 112 on gps speedo, but takes forever to get there.

with a CR of 10:1, i plan to use a thick cometic gasket, about 0.100", to get the CR to 9.

with the new whipple 4.5L, should make around 1050 with 7-8psi.

i am using the holley HP EFI and will creep up on the timing and AFR.

The important part of being successful with what eddie young mentions above is setting the quench tight. .037-.040 is a good place to be to prevent detonation. Putting on a .100 th head gasket is exactly the wrong direction to head with what you want to do.

Bad idea with the headgasket imo. Ideally blown you wanna be somewhere in the .040-.060 quench area. A little less is ok, but .100 or more, I wouldnt do it.

Just a bit of trivia on the quench deal. I'm rebuilding a couple of Merc 1075's. I was a bit surprised to find they run the pistons .060 down in the hole with .060 head gaskets, so a total of .120. Goes against everything I've believed for over 50 years.

Interesting. Wonder why? I'm sure there must be a reason for it

Hi David, I'm glad to hear the self tuning Holley HP made so much more power and speed then the MEFI system did out west.. (Shameless plug) :thankyouthankyou:

On a boosted application the squish height is not as critical as an NA deal and can be dangerous if too tight. There are also a lot of variables; it's not as simple as one size fits all. However, the preferred method is to run the piston deeper in the hole. Once you get up in the .100" sizes on the cometics they have a tendency to squirm around on the inner layers and can cause sealing issues between cylinders after lots of heat cycles and extreme pressure. SCE makes a nice copper gasket with a built in fire ring that doesn't require O-ringing the block. I'm trying some but don't have any run data yet. I think for what you're trying to accomplish performance wise I'd run a .060 or .080 Fel Pro MLS and start at about 5lbs boost. I think you'll be pleasantly surprised at how much acceleration you pick up.

I have always been told by numerous engine builders just the opposite....that it is more critical on a SC engine than an NA engine. I've always shot for the .050-.060 area, so I don't have any first hand knowledge of how it would act if the quench were any larger. I've always heard that it would be a detonation monster once it got over about .075, assuming it was an already aggressive piece. Not arguing, just trying to get to the bottom of it.

How aggressive of a build have you done with a larger quench (over .075)?
Eddie

I'm very curious to see what comes of this. I always thought 80's emissions motors knocked and pinged easily cuz the quench always sucked on the low compression emissions motors. Always seemed like a few miles and a little carbon build up and all you could hear was rattle!

It really depends on the application. On 2000+hp stuff I'll run .150 in the hole with a .060 gasket. On stuff where you're gonna run meth injection a little extra will help too. AFR of the intake charge, chamber efficiency, piston design, rod material, pin thickness, target rpm, piston to wall clearance, fuel quality, etc. all effect optimal squish. When the engine is not in boost is the only time detonation may become an issue but can be eliminated through proper tuning.

if you run a hemispherical head the rules change again, but most here run BBC so "status quo"