Looked for a "head gasket" thread didn't really see any, so I'll ask, are these gaskets good to use are they just higher price for very little gain?

https://www.summitracing.com/parts/cgt-c5809-027

Cometic MLS Head Gaskets C5809-027

Head Gasket, 4.200 in. Bore, .027 in. Compressed Thickness, Oldsmobile, 330, 350, 400, 425,

 

In today's world the very best out there.

 

Excellent gaskets, but do you really need them? The regular old FelPro head gaskets may be fine for your application.

 

I just bought the Fel Pro head gasket set for my 455. If you aren't racing your Oldsmobile there's no need to spend the big bucks on gaskets.

 

As others have pointed out, that's top of the line and priced accordingly. Do you really need it vs. FelPros at under $20 each? I've built a lot of street motors with FelPro head gaskets and never had a problem.

 

X2, just out of curiosity, do you install the gasket bare or do you spray the Permatex copper spray?

 

Depends on the gasket. I follow the manufacturer's instructions. FelPro blue doesn't get anything sprayed on it.

 

I thought the thinner gasket would give you some more compression?
Not worth it or??? Joe Im listening..

 

Yes it will. Is an extra quarter of a point of compression ratio worth 4x the price of the head gaskets? Keep in mind that the MLS head gaskets really want a perfect sealing surface on both the block and the head. Are you milling both surfaces? If you are just doing the heads, have an extra 0.025 milled off the head to make up for the CR difference. Done.

 

Check.

 

this is what I had done when I had my heads redone, used the Fel-Pro 8171 Head gaskets .042 gasket thickness -.025 head milling = .017, back to stock

 

Yes thanks Joe, I was just thinking 140 Canadian for 1 is beyond what I want to pay lol, I will be having some work done to the heads and now I can save some $$

 

Dave, what were you planning on for head gaskets? I know Mark suggested the Mahle MLS head gaskets for aluminum heads, $120 each😱 Canadian through somewhere like Jegs. There are a couple of other options besides Felpro Blue.

 

I was thinking using Joes advice, Just mill a hair more off the heads and use the Felpro.

 

Talk to Mark about gasket options as well. Mahle and Mr Gasket have full sets available, comparable to the the Felpro in price. The Mahe are .040" and the Mr.Gasket are .045". The Felpro fall in between at .042" compressed. I actually have all three sets in my garage, I can take pics this weekend. They are all a bit different, especially the Mr.Gasket head gaskets.

 

Thanks brother, I appreciate that. We have the same pistons and on the chart it was calculated at 0.013" below deck and 0.027" head gasket thickness would yield 9.7 Compression with a 65cc Head.

 

Yes, supposed to equal .013" without decking. It depends on how much was removed from the block to square the deck, where you currently sit. If they sit .010" below not the end of the world with a .040 head gasket. Factory Olds sit .020" to .030" below deck. The early motors had .017" shims. Late were .042" Felpro. Some of Dodge's pistons sit .100+" below deck! Mine needed .016" removed to square the deck. They honestly looked even with deck, .003" isn't very much. Your machinist should be able to tell you how much was removed and also be able to measure how far below deck the pistons currently sit.

 

Thought I would post pics of another of couple of options, especially iron heads. The Mahle 3436VC are .040" compressed and the Mr.Gasket are .045". The Mr.Gasket directions actually say to paint the metal side with aluminum paint, no sealers on the other side.

 

The only benefit to running the .027” is a better quench.

Only calculating comp ratio without taking into account for quench is missing a good part of the picture. You want it as close as possible.

 

The Beauty of the Mr. Gasket is they're 1/2 the price and on sale at the moment:
https://www.holley.com/products/gask...ts/parts/5788G

Those Cometics are expensive and have a looong lead time if they're not currently in stock (Summit said won't ship until Mar. 3 at least for the size I needed).

With .013 in the hole and .027 gasket you're right on the money with the Quench of .040 though. The .027" Thick Cometic also has a 4.125 opening which further helps with compression as long as you're not more than .030 over (ideally you want your gasket opening .030-.060 bigger than your bore per Cometics instructions).

I went back and forth on buying Cometics, but between the cost and lead time, I'm going to sacrifice a little CR and save some bucks and the Mr. Gaskets do work.

 

I had my block bored for the Mahle 4.100 pistons, so would that make Cometics wrong since the bore will fall below .030?

 

I’ve been able to get Cometics reasonably fast. Don’t believe that international ship date when it says they are on the shelf for U.S. residents

They usually have the standard bore sizes ready to ship. Don’t worry about being bigger on the bore diameter

Amazon shows the .027” available in Canada at $143.00 C with free shipping, ships in a week

 

it’s not jus the final comp ratio. The quench is very important. I would gladly give up 1/4 of a point for a much better quench than the other way around.

is the cost of stripping down two heads and surfacing them less than the extra cost of Cometics? No

 

Thanks for the tips, appreciate that.