Thin Head Gasket and Comprtession Ratio

[Ronno6]

5.7L engine from 1993 C1500
Bored .030", aluminum 64cc heads, GM LT4 Roller Hot Cam
No dish pistons w/4 valve reliefs
The head gaskets that came with my kit are .041" thick.
Near as I can figure I will have a C/R of about 9.25:1.
I had hoped for higher.
Fee-Pro makes a SS gasket that is .015: thick.
This would boost the ratio up to about 9.8:1.

Not much $$.
Would this be worth doing?
Any caveats?? Would they need re-torquing?

 

[Matt69olds]

Mill the heads? Mill the heads and use thin gaskets? If you do cut the heads and use thin gaskets before torquing the head bolts trial fit the intake. Depending on how things fit you may have to cut the intake side of the heads.

 

[bucket]

GM often used steel shim type gaskets. I've been told by more than one engine builder that when using a shim gasket, it's best that the block and heads be resurfaced to prevent failure.

 

[Ronno6]

GM often used steel shim type gaskets. I've been told by more than one engine builder that when using a shim gasket, it's best that the block and heads be resurfaced to prevent failure.

Heads are new...block is not.
Probably sage advice, but too late for that now.

Would I realize much performance gain from the C/R increase??

 

[bucket]

I wouldn't think you would gain much from it. But 'not much' is still more than nothing.

Personally, I'd give the shims a whirl.

 

[Ronno6]

I wouldn't think you would gain much from it. But 'not much' is still more than nothing.

Personally, I'd give the shims a whirl.

The Fel-Pro 1094 is a Stainless Steel shim gasket that has a sealing compound on both sides, It is .015 thick ans suitable for use with aluminum heads. It might just be the ticket.
I am concerned as the LT4 hot cam was designed for use with a 10.4:1 compression ratio. I fear that 9.25:1 may be a tad too low. 9.8:1 would be better.

 

[Shorty81]

I would run it as is. Why fret, enjoy your truck.

 

[Rusty Nail]

9.8>9.2

Yeah...it's a frigging small black chebby dude- it'll handle it. Check the oil and run it LOL.

I am a fan of steel shim head gaskets ..the 1094 is /win.
Caveat is to use Permatex brush-on gasket sealer around water passages on both sides of the gasket and always new bolts.

You WILL see a marked and notable performance increase, without doubt.

 

[shiftpro]

Deck the **** out of the block...

 

[Rusty Nail]

For your reading pleasure:

https://www.hotrod.com/articles/ideal-quench-height/

I used to have a buddy named Squish..

http://garage.grumpysperformance.com/index.php?threads/quench-squish.726/

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Every (all three) engines I put together with SHIM gaskets required hi-test (91) to stay out of ping and I live 1200 feet above sea level.

Hope this helps!

 

[Ronno6]

My pistons are not dished, but have 4 valve reliefs.
Much of my lack of C/R stems from the fact that my pistons are .040" below deck level
at TDC.
My decks also exhibit some pitting around head bolt holes and/or water passages.
This may make it too rough to use thin gaskets.
Not crazy about the notion of disassembling the short block to have it decked.
I need to figger out how serious I am about getting the most out of this setup.......

 

[shiftpro]

My pistons are not dished, but have 4 valve reliefs.
Much of my lack of C/R stems from the fact that my pistons are .040" below deck level
at TDC.
My decks also exhibit some pitting around head bolt holes and/or water passages.
This may make it too rough to use thin gaskets.
Not crazy about the notion of disassembling the short block to have it decked.
I need to figger out how serious I am about getting the most out of this setup.......

Well there you go, it needs to be decked (and always should) anyway... go nutz. .020 easy without effecting the manifold to head port alignment.
Maybe more, talk to your machinist.

 

[Matt69olds]

Hmm, 0.040 deck clearance is quite a bit. Decking the block might be the best choice if you really want the best performance.

As to your question about how much milling the heads will help, with my Olds engines every .006 machined from the heads equals 1 cc of chamber volume decrease. Most 455 Olds heads displace about 80cc. I’m sure there is a rule of thumb for Chevy heads.

 

[Ronno6]

The pistons which came with my "rebuild kit" are Sealed Power 345 NPS. these have a compression height of 1.54". That contributes to the problem.
Going to 1.56" or so would eat up half that depth...

 

[Ronno6]

In the real world, how does one get to a zero piston deck height??