InfernalVortex

iTrader: (4)

I learned a lot since I put my build together, and now I'm wanting to do a cam swap and along with it Im thinking I need to do a head gasket swap while I'm there.

If my pistons are around .025 in the hole (1.560 height pistons, 9.025 deck height) on average, I am currently at around .065 quench. This is, from what I can tell, just a hair shy of horrible.

So I need a head gasket in the .015-.030 range to get it manageable I think. Clearly the thinner the better from a quench point of view, but my build has been running in my car for 2 years, and I know it's never overheated, but I also know that it wasn't decked when I took it to the machine shop. My machine shop guys told me the deck was flat, and it didnt need to be decked at all. What that really means as far as flatness, Im not sure. What that means for the block as it sits in the car - I'm not sure.

So I read that MLS are the best head gaskets for performance engines, but I also read that MLS is VERY picky about having VERY flat surfaces. Im not sure I can get away with taking that gamble, to be honest.

Would I be better off with copper? Or should I just leave it well enough alone at that quench?

Current cam SCR = 9.7:1, DCR = 8.2:1
New cam SCR = 9.7:1, DCR - 7.9:1

With a .045 quench (fudging head gasket bore diameter):
Current cam SCR = 10.2:1 , DCR = 8.6:1
New cam SCR = 10.2:1, DCR = 8.3:1

So given that this is in a running 350 that's got a "good enough" deck for a composite gasket of .040 inches, what kind of gasket material should I be looking at to drop .020 off of the gasket thickness? I was looking at Cometic, but they only make MLS, which I want to avoid because of what I hear about how picky MLS gaskets are about deck smoothness.

Is it even worth pulling the heads to swap them out? Starting to think I should just build a 383 or a Gen III motor for the long haul and run the cam swap as is.

Anyone used those "nitroseal" gaskets? They're in the .025-.028 range. Graphite over a perforated steel core.

five7kid

iTrader: (14)

I ran .015" compressed Felpro shim gaskets when I put the World heads on the 305, then used the same type (new) when I put the World heads on the 350. I sprayed the gaskets with Copper Coat when installing.

With that much quench distance, you probably can't run as much ignition timing as you could with the proper quench distance. But, if you've got a new build in mind soon (a couple of years), I would probably leave it as it is for now if it's running okay otherwise.

InfernalVortex

iTrader: (4)

Was it a plain steel shim? Or a rubber coated one? Fel Pro has 3 steel shims that thick, just curious whether I should go with the plain steel one or the rubber coated ones. What spray is it that youre supposed to use?

grumpyvette

http://forum.grumpysperformance.com/...er+coat#p11603

http://forum.grumpysperformance.com/...=quench#p13147

http://forum.grumpysperformance.com/...sealant#p17369

http://forum.grumpysperformance.com/...=studs+sealant

five7kid

iTrader: (14)

The Fel Pro was rubber coated, the 2nd one (Hastings, I believe) was plain.

InfernalVortex

iTrader: (4)

Crunching the numbers after reading your links grumpy, looks like I should go for at 4.100 bore, .015 head gasket.

That, with the xe274 cam I'm planning on is looking like it iwll bump me up to 8.4:1 dynamic compression. Is that a bit too high? Seems like it to me...

Is it better to run a thicker gasket and worse quench to get the DCR down? Or should I go with a different cam? I was thinking about a Magnum 280H from comp. 230/230, .480/.480. It's a smaller cam, but for some reason according to the caclulator I'm using it gives me an 8.22:1 DCR, which seems a little safer. I was hoping to have my power band kick in under 2000 RPMs though just for street crusing - the xe274 starts at 1800 RPMs, the 280H at 2000, and I'd rather not advance the cam to move the torque down lower, it's probably already ground in 6 degrees advanced like the Comp xe line and I worry about deviating too much.

dimented24x7

iTrader: (2)

GM makes (or uses) a gasket with .028" compressed thickness. This gasket is used on the crate gen-I SBCs. http://www.summitracing.com/parts/NAL-10105117/ These are the steel core/graphite type.

That would shave some thickness off for the current motor. One thing Ive always worried about with the shim gaskets is that most heads/decks dont really have a clean enough surface for them. There are shops that can deck the block to a very good finish, but most factory blocks Ive seen have imperfections (coarse finish, casting voids, etc) and such that would make me think twice about running a steel shim gasket.

grumpyvette

a good quench distance to try for is between .040-.044, your better off with the correct quench and a bit higher dynamic compression ratio (obviously theres limits) a wider LSA like 112-114 on identical duration tends to reduce effective compression, and retarding the cam 4 degrees will raise your whole power curve and reduce the effective compression, in your case thats the route ID suggest (good quench & retarding the cam 4-6 degrees to a strait up index) cams normally run best that way any way, cam companys got into the habit of advancing cams 4 degrees to compensate for customers almost always selecting cams a bit longer in duration than the engine can really use.
to lower customer complaints