Also you won't want your pistons too sloppy in the hole due to rocking and you would want to check all the holes on deck height. I would probably select the .030 cometic.

Thanks for the info, Bob. I mis-typed the combustion chamber volume - actually 118 cc's as checked at the machine shop. Thanks for the heads up on the RA for the MLS gaskets - Cometic lists a required RA of 50 on their site - I will verify with my machinist that we are within those specs.

I ended up going with the cam that you ground for Brian up in Detroit - it was the one on the 114 LSA. I chose this one because it is a brand new cam, plus there is a chance that I may add a Silent Choice style thru-prop option to my Lightnings, so with the reduced overlap I assumed this would be the safer choice. Also, with my relatively low CR, would a cam with less overlap work better below 5000 RPM to maintain dynamic CR?

I am running 10 to 1 compression. Pistons are 0 decked, heads are CC'd Jim Valeakeo PRO ones, block was decked square to the crank, balanced and bluprinted 509's, intakes port matched to the heads, Holley HP 950's. Can run mid grade without any knocking but usually run Premium.

haxby, henri ricardo spent alot of his research on squish, quench and the turbulence it created. alot of early smog engines got away from squish bands and that lead to knock with unleaded gas.

Below is what i have fond on the net on another forum.
Thats a very interresting thread and i need to know what is supose to be the right squish on a blower engine.

Just note that my Merc 525sc gen 6 come with std deck height 9.800'' with a .040'' head gasket with 4'' stroke, 6.135 rod and 1.64 piston comp height give a total of .065'' squish.

What i have fond...

(Forced induction doesn't require the tight quench that an N/A engine does to keep the piston and chamber cool. There is an enormous amount of air/fuel being quenched after all. If you have 5 times the amount of air/fuel in the cylinder, you don't want a tight quench as the flame front can and will become supersonic. This is when the head gaskets take a beating. Opening that quench to accommodate the extra air/fuel helps a ton..........especially when tuning.

MLS gaskets are known for toughness as well as copper. By the time you've blown either, you've got other issues. Depending on the boost level and the engine, I personally like to run around .070"+. If it's a big blower/turbo setup, I'll run as much as .110" quench.)

Bringing this old thread up. Good info here.

From what I been researching lately, it seems that when running higher boost, a tight quench can possibly present some issues? I'm guessing mercury put their piston down in the hole so far for a reason.?

Could someone please define quench? I'm lost in figures.

Quench pad is the flat spot on the head that is exposed to the cylinder. Quench distance or squish is the distance between the piston and the flat spot on the head. The idea is to get the mixture out of this area and into the combustion chamber. As Mild stated on high boost and especially nitrous applications this area can be troublesome and micro detonation can occur due to an extreme amount of pressure. There is a point with this area when you have to throw the engine building book out the window and get the piston away from the head. At what point? I'm not the person to ask. But I can tell you it's not with your everyday marine blower motor.

Yea, not an issue for your typical 5-8lb of boost marine deal. But I would like to know at what level is it a concern? 12psi? 15 psi?

Way more boost. Probably in the 40+ area. And the design of the chamber and top of the piston has a lot to do with it.