NewOrleansLT1

So I’m slowly getting parts to put my 383 together and I’ve been looking at head gaskets.. I’m intrested in the Cometic MLS Head Gaskets C5645-027, but it’s a 4.040 gasket.. Would it be safe to run with them with a 4.030 piston? Any advise? Thanks..

SS RRR

iTrader: (2)

Yes, but why?

NewOrleansLT1

Well I just realized they have a 4.100 gasket also.. I wanted to run some good quality gaskets that’s all..

SS RRR

iTrader: (2)

I wouldn't bother unless you are going to run crazy cylinder pressure. On a street car the odds could be stacked against you and they could end up leaking. IMO run a Fel-Pro head gasket and be done with it.

Heatmaker

HG's aren't a "Do you think this should work" part of your engine to fool around with. Match them to the right bore size. Get a quality set of 4.030 gaskets that you're setup calls for. If you're really worried about your HG's use Studs instead of bolts.

NewOrleansLT1

So you thkink that particular gasket will leak because of the material it’s made of? I know solid copper head gaskets leak slightly on 14:1 race engines but I didn’t think an MLS gasket would.. What would be a good .026-.030 gasket to run? All I know from Felpro is the 1074 which is .039..

TwoFast4Lv

iTrader: (8)

I used to think Fel-Pro was a great gasket. Then I push one out the back of the head.

Now i run custom Cometic's

NewOrleansLT1

That’s why I’m asking for advise.. I know how thin I need them.. Just was curious on how small a bore I can run.. And a 4.030 bore with a 4.030 gasket is asking for trouble imo..

TwoFast4Lv

iTrader: (8)

I would run at least .010 bigger then the bore

Heatmaker

I meant to say 4.040 The name of the game is to match your HG's closest to your engine bore size. If it fits and you have clearance without interference it's a green light. Cometic already has done the thinking for 4.030 users and put out the 4.040 that's their offering for a 4.030 bore. If you know what size and thickness you're looking for and what manufacturer you want to go with then purchase them. You kind of already answered your own question a bit. On the LT1 though using studs is the best choice for buttoning down the heads as extra security. What I was saying is that if you're worried about popping head gaskets and want extra peace of mind upgrade from head bolts to studs too.

and yes HG's or really any engine gasket can be more prone to leaking depending on what material they're made of.

http://www.jegs.com/p/Cometic-Gasket...48863/10002/-1

SS RRR

iTrader: (2)

It's just like any soft metal gasket. There is little margin for error for imperfection on the block/head surfaces, and with liquid under pressure is a constant assault on any weak points. If there are any then they will be found and leak and the only solution is to start over again. As stated, if it's an N/A daily then I wouldn't do cometics. JMO, of course.
As far as thickness, a lot of people have ran the Impala gaskets which I believe are .026.

NewOrleansLT1

It’s N/A but my car is FAR from being a daily lol.. What you think about Mr Gasket 5716G?

SS RRR

iTrader: (2)

I have no experience with them. Everything I've ever done was with Fel-Pro. I had cometics on my last engine for about two years before they started leaking. Car was pretty much dailied at that point since it was fun to drive. Do a search on those gaskets and see what comes up.

96lt1m6

iTrader: (31)

I have had nothing but great luck with FEL-PRO
12.8 compression 482" big block with plenty nitrous to euthanize a small town
406"
383"
350"

TwoFast4Lv

iTrader: (8)

make sure your pistons are .015 or more down the hole. Factory is usually .024-.028.

I have ran as tight as .035 piston to head but is as close as I would ever go.

TwoFast4Lv

iTrader: (8)

Fel Pro FTW!

SS RRR

iTrader: (2)

lol. didn’t work for you so they’re no good, br golly!11
Who is to say it wasn’t from shitty machine work?

NewOrleansLT1

The block is 0 decked with forged SRP 5cc pistons..

Nostang

iTrader: (4)

I am running Cometic .027 4.060 bore gaskets on my 383 with the piston .006 in the hole (.033 quench). The gaskets seem to work fine but my head studs seeped a little bit for the first 500 miles.

SS RRR

iTrader: (2)

rule of thumb is a .040 quench. going any thinner will be of no benefit.