Cylinder head gaskets. What is better for a street/strip engine??? - Third Generation F-Body Message Boards

paulmoore · 06-28-2006, 03:10 AM

OK, guys, I have been doing some computing with my new engine, but need some help/input on something. I am unsure about which head gasket to run. I need something that is gonna give me AT LEAST 9.5:1, but I'd prefer 10.0:1. Also, what type is better? By type I mean, embossed shim, steel, copper, etc. I need something that is gonna seal and be reliable, but can handle the abuse of the car running at the track. I have always been partial to Fel Pro gaskets. I am pretty sure that I don't wanna run their economy head gasket for obvious reasons. This isn't going to be a grocery getter engine. Any suggestions???

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mnorton · 06-28-2006, 03:35 AM

I think that you have to change to something other than stock pistons in order to have a reliable gasket "and" get to even 9.5.............

You'd have to get a gasket that is at least .010 thinner than the stock gasket to get to there. I believe that would put you at a .018 steel shim, if you can find one like that.

I hope that you decked the block "and" milled the heads if you use one that thin. A leak would be a bummer....

paulmoore · 06-28-2006, 03:52 AM

Hmm, I guess it would have probably helped if I would have given my engine specs. I have an all forged internals 383 stroker short block with flat top pistons with 5 cc valve reliefs. I will be using AFR 195 street heads with 74cc chambers. I also have a COMP cams 12-433-8 cam that is .520/.540 lift @.050 and 236/242 duration@.050 110 LSA. The machine shop that built my short block parallel decked the block by .010 so my deck height is now 9.015 inches. I'm having a hard time finding a gasket that...

1. Gives me enough quench distance

2. Will keep the compression ratio up to AT LEAST 9.5:1

3. Promotes decent cylinder sealing and has some kind of longevity

As of right now, I am leaning towards this copper gasket made by SCE. It's called the Titan. It has a bore size of 4.060 and it has a compressed thickness of .032 inches. Now if I use that gasket(I plugged all the number into a dynamic compression ratio calculator) I will end up with 9.8:1 compression with a quench distance of .047. Is a copper gasket OK to use on a street/strip engine? Ever since my first engine blew up, I find myself second guessing EVERYTHING. Man, I just want this thing to be perfect and not give me any hassles.

Neil87Z28 · 06-28-2006, 09:47 AM

Optimum quench distance is around .040". This will maximize your compression ratio and also increase your resistance to detonation. Here are a few gasket choices to use with your .015" deck height.

Summit # NAL-10105117 is a GM .028"
Victor Reinz #5746 is .026"

From GM Performance Parts:

10105117 Composition Head Gasket (Cast Iron or Aluminum Head)
This composition head gasket with stainless steel faces is recommended for stock and mildly modified engines with 4.00" cylinder bores. Its compressed thickness is .028".

3830711 Steel Shim Head Gasket
Recommended for stock and mildly modified engines with 4.00" cylinder bores. Compressed thickness is .026".

You can always give Cometic a call and they'll make you anything you want.

Tibo · 06-28-2006, 12:51 PM

I was about to suggest the same gaskets. I have used the GM 1010 on three engines and I love it! The price cannot be beat. Since it is a comp gasket you do not have to of just had the deck milled (though I always do) and it can be run on aluminum heads. I have run it at a 10:1 static (that is valves closed right?) compression with no problems.

As a side note if you go to the chain automotive stores (autozone, Napa) they say that they carry that GM gasket, but they do not. They just substitute in a Fel-pro and say it is that GM gasket.

paulmoore · 06-28-2006, 01:08 PM

The gaskets say that you can run on a 4.00 inch bore but I am at .030 over. Will that still work?

Neil87Z28 · 06-28-2006, 04:20 PM

You'll need to verify the gasket bore size before buying, but you should be fine.

paulmoore · 06-29-2006, 12:25 AM

Well, I was a little unsure about the piston to deck clearances so I had the machine shop e mail me all the specs. Come to find out that my deck clearance is not .015 like I originally thought. Right now, the pistons are sitting .005 in the hole at TDC, so I have alot less room than I thought. I guess the only bright side is that now I can run a thicker gasket.

paulmoore · 06-29-2006, 02:01 AM

Well, after doing some more research and plugging in a whole lot of numbers I think that the best way to go is gonna be the custom made Cometic gaskets. So, for me the optimum gasket will be...

.028 compressed thickness which gives me a quench distance of .033 which is probably in the realm of the lowest (.030) that I'd want to go. I was thinking about getting the gasket bore to be 4.060 seeing as how the ACTUAL cylinder bore is 4.030. Does anyone forsee any issues with that? If that is gonna be an issue, then I can still use a gasket whose bore size is 4.110 inches and still keep the same compression(within a couple hundredths of a point). When all is said and done, my final dynamic compression should be 10.1:1

Although, I have read that the Cometic gaskets are very particular about the quality of the block and cylinder head mating surfaces. Has anyone run into this issue? The short block that I have has been freshly machined, and I am going to be using brand new heads so hopefully gasket sealing won't be a problem. Another plus is that they are resuable.

Neil87Z28 · 06-29-2006, 11:14 AM

The machine shop is probably just telling you the deck height based on how much they cut off the deck. It will be close, but there is no way to know for sure without measuring it after the rotating assembly has been installed. If you have the short block at home, I would recommend measuring the deck height yourself. No matter how good the machine work and rotating assembly, you'll have some cylinder to cylinder variance. It's easy to check, just put the piston at TDC and check with a deck bridge/dial indicator or it can be done with a straight edge and feeler gauge. Rock the piston side to side and take the average.

Cometic will advise you on the proper gasket bore size. Obviously, using the smallest possible gasket bore will maximize compression.
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Also, if you really are .005 in the hole, I'd use the off-the-shelf .039 Fel-Pro.

Stephen 87 IROC · 06-29-2006, 08:55 PM

GM has used steel head gaskets for years in vehicles that now have a lot of miles on them. If you want to bump up the compression slightly, you can use a .018" steel shim head gasket. A typical composite head gasket is around .039". Just make sure you still don't have any piston to valve clearance problems.

My engine only gets the high end Felpro composite head gaskets. The high end ones are not carried by my local parts stores. I need to get them from the speed shops. Felpro makes many different grades of gaskets.

V8Rumble · 06-29-2006, 11:01 PM

Quote:

Originally Posted by Neil87Z28

If you have the short block at home, I would recommend measuring the deck height yourself. No matter how good the machine work and rotating assembly, you'll have some cylinder to cylinder variance. It's easy to check, just put the piston at TDC and check with a deck bridge/dial indicator or it can be done with a straight edge and feeler gauge. Rock the piston side to side and take the average.

Wouldn't you also be able to measure it at the "centerline" of where the wristpin goes through the piston? This isn't a criticism, but the way you're describing seems as though there could be a fair bit of room for error...

(Unless you're trying to get the "absolute" measurement that includes piston rocking motion...)

I dunno, it's entirely possible that there's something I'm not seeing...

Neil87Z28 · 06-30-2006, 10:35 AM

Quote:

Originally Posted by V8Rumble

Wouldn't you also be able to measure it at the "centerline" of where the wristpin goes through the piston? This isn't a criticism, but the way you're describing seems as though there could be a fair bit of room for error...

(Unless you're trying to get the "absolute" measurement that includes piston rocking motion...)

I dunno, it's entirely possible that there's something I'm not seeing...

Even when you measure on the wrist pin centerline, rocking the piston will move the dial indicator a thou or two. It will vary even more if the mockup is without rings. Also, you can't always measure on the centerline based on the shape of the piston top and valve reliefs.