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Username Post: Composition vs. Steel Shim Head Gaskets?        (Topic#143683)
AmericanPie 
Senior Member
Posts: 477

Loc: Camarillo, CA
Reg: 07-28-01
11-04-06 11:22 PM - Post#1029155    

I'll be rebuilding my 327/300 motor soon. Since it's a matching-numbers car, I WON'T be having the block decked, but I would like to get the static compression between 9.5 to 10.0:1. Are there any disadvantages of using a .015" steel shim gasket (which I believe is OEM) vs. an aftermarket composition gasket? Are the composition gaskets supposed to be more durable/less prone to failure?

Also, how much difference in compression would there be between the two gaskets? Thanks!
1965 Impala SS 327
1985 BMW 635CSi
1987 BMW 535is


 
shawnlee 
Senior Member
Posts: 459

Age: 43
Loc: so.cal
Reg: 06-19-06
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 06:57 AM - Post#1029156    
    In response to AmericanPie

The compression difference is 0,most gasketts are listed at there compressed thickness or have the specs for compressed thickness listed.The steel gasketts do not compress enuff to measure.The key to the steel gaskett is a flat surface and using the copper spray to get it to seal good ,maybe even a little sealer around the water ports.The standard gasketts go all the way down to .025 I believe ,maybe even a little thinner. Hope this helps. There may be some other gasketts I do not know about and issues with the steel I have not run into.
Its gunna cost more and take longer,trUst me!!


 
bobb 
Super Senior Member
Posts: 4931
bobb
Loc: paradise
Reg: 09-05-03
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 07:27 AM - Post#1029157    
    In response to AmericanPie

compression change is small maybe .4 or so. one option is corteco ss shim gasket, i am running them now. i dont know about pros and cons of the two but the thin gasket will give you a better quench since you wount be decking the block. i dont think shim gaskets go with aluminum heads too well. some shim gaskets come with a coating of rubber or something to help with the sealing.
70 L camino 350 all forged,174 baby blower, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
Rick_L 
Honored Member
Posts: 25785

Loc: Katy, Tx, USA
Reg: 07-06-00
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 08:17 AM - Post#1029158    
    In response to AmericanPie

The compression ratio difference is not zero, and I don't think a difference of 0.4 is negligible. To safely get .4 more compression ratio with a better quench for $0 is significant to me. I believe the 327s came with a .018" thick gasket.

When a steel shim gasket is spec'd at a certain thickness, that is usually by the thickness of the steel it's stamped from. If you measure over the beads it's much thicker. The beads don't compress away completely, the final compressed thick is usually .001-.002 thicker than the material.

Steel shim gaskets are less forgiving than composition gaskets to things like warpage and finish. They also require the use of sealer. I use Permatex Hi-Tack (hard to find now) or K&W spray Copper Kote. Let the sprayed sealer dry about 10 minutes before you install the head.

I've never had a problem with steel shim gaskets. They are good on a drag race small block with cast iron heads to 600-700 hp.

 
Vaughn 
"13th Year" Gold Supporting Member
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Loc: Colorado Springs, CO
Reg: 08-08-04
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 08:29 AM - Post#1029159    
    In response to Rick_L

If you are careful with steel shim gaskets, they work fine. I ALWAYS use a sealer with them - Copper Kote is good.

If there is ANY warpage on the block or heads, they will not seal.

The composite are much more forgiving - especially if you have something you don't want to machine if you can help it.

Back in the early 80's I had a small block Mopar that would lose oil pressure as soon as it warmed up. THe rocker oiling goes through the head gasket (a tremendously bad design feature), so if ther was ANY PROBLEM with the stock steel shim gasket, block or head it would lose oil pressure. I had the heads off 3 times trying to fix the problem. I finally had to deck the block, heads and used a special thick gasket to solve the problem.

 
AmericanPie 
Senior Member
Posts: 477

Loc: Camarillo, CA
Reg: 07-28-01
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 10:58 AM - Post#1029160    
    In response to Rick_L

Quote:

The compression ratio difference is not zero, and I don't think a difference of 0.4 is negligible. To safely get .4 more compression ratio with a better quench for $0 is significant to me. I believe the 327s came with a .018" thick gasket.




Some real good replies to my original post here; thanks!

A difference of 0.4 isn't negligible; that would put me pretty close to 10.0:1. I think I'd prefer to use shim gaskets, but I won't know for sure whether I can use them until I measure the warpage on my block and heads. Since I'm not planning on having the block decked, any warpage would probably require the use of composition gaskets.

Bottom line: can anybody tell me what my approximate static compression would be on a .030" over 327, with -461 (64 cc) heads, and flat top pistons with two valve reliefs, using shim gaskets? And what would it be using composite gaskets? Obviously this will greatly influence my cam selection. Thank you!
1965 Impala SS 327
1985 BMW 635CSi
1987 BMW 535is


 
shawnlee 
Senior Member
Posts: 459

Age: 43
Loc: so.cal
Reg: 06-19-06
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 12:24 PM - Post#1029161    
    In response to AmericanPie

My bad ,I thought he was talking about gaskett compression ,not staic compression Its all in the terminology!!

 
Rick_L 
Honored Member
Posts: 25785

Loc: Katy, Tx, USA
Reg: 07-06-00
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 12:43 PM - Post#1029162    
    In response to AmericanPie

The 10.0:1 that you estimate is about what you'll get. The advertised compression ratio on that engine was 10.5, but it realistically didn't have it without milling the heads and maybe decking the block too.

And the 10:1 is about the most you want to run with today's premium and a mild cam. So - you're good to go.

 
MikeB 
Senior Member
Posts: 9485
MikeB
Loc: Plano, TX
Reg: 08-28-03
Re: Composition vs. Steel Shim Head Gaskets?
11-05-06 03:57 PM - Post#1029163    
    In response to AmericanPie

I'd get the heads decked and use a composite gasket. No numbers lost that way, and you have a better chance of a good seal on that old block surface.

Or get a modern cam with shorter seat duration to make more cylinder pressure with your existing CR.

1982 C-10 SWB pickup -- Unmolested, original paint, 250 six, 3-speed (soon to be 350 Vortec & TH350)

Sold my 55 sedan in June 2014, having owned it 11 years.


 
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