Cometic MLS head gasket for 406 street engine? - Chevelle Tech
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post #1 of 12 (permalink) Old Dec 10th, 19, 1:53 AM Thread Starter
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Steve
 
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Cometic MLS head gasket for 406 street engine?

Had planned on FelPro 1014 head gasket with .039 compressed thickness and 4.2 bore for my 4.155 bore 406. I know the FelPro seals good, and I don't want any issues.

Now looking at using the Cometic C5248-030 head gasket, diameter is 4.165.
Compressed thickness is .030 which would make my quench about where I want it.

Will be using AFR 195 Aluminum heads.

Does anyone have experience with this or similar Cometic MLS gaskets with aluminum heads for normal 406 street driven applications?
Thanks!

TXCR13
1966 Chevelle 300 2dr Sedan
385, Flat Top Hypers, Performer RPM, S.M.I. 750 Q-Jet, 72cc Dart Platinum 200cc runners, U.D. Harold 223/233 112 LSA Cam, 700-R4, PS, Manual Disc Brakes, AC, Hedman headers with 2-1/2" exhaust.

1946 Studebaker Coupe- street gasser finally underway!
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post #2 of 12 (permalink) Old Dec 10th, 19, 4:29 AM
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Re: Cometic MLS head gasket for 406 street engine?

Hi
using thinner MLs gaskets raise the compression compared to Felpro 1014
What comp are u chasing ??
What chamber are the heads 65 or 75cc ??
What fuel ??

Use Wallace racing comp calc

MY combo
68-70 cc = machined head
4.125 bore
stroke 3.75
-5cc piston v/reliefs
.0045 piston down the bore

cam 230 upto 245 at.o50
rear gr 3.6
tire 26.2
convertor 2600---3200rpm
highest octane pump gas

compression = 10.5---10.8 depends on chamber size
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post #3 of 12 (permalink) Old Dec 10th, 19, 8:03 AM
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Mr Bill
 
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Re: Cometic MLS head gasket for 406 street engine?

Steve,
The Cometic gaskets will work fine but make sure that the 4.165 gasket bore size is large enough to clear whatever chamfer you have on the top of your cylinders. Call Cometic and ask them to be sure. Might be kind of hard to get anyone this week though because of the PRI show.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md


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post #4 of 12 (permalink) Old Dec 10th, 19, 8:31 AM
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Re: Cometic MLS head gasket for 406 street engine?

Quote:
Originally Posted by BillK View Post
Steve,
The Cometic gaskets will work fine but make sure that the 4.165 gasket bore size is large enough to clear whatever chamfer you have on the top of your cylinders. Call Cometic and ask them to be sure. Might be kind of hard to get anyone this week though because of the PRI show.
Also check the combustion chamber of the head to the gasket. A lot of times, the chamber is bigger than the bore and using small bore gaskets allows the backside of the fire ring to be exposed and it torches the gasket.
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post #5 of 12 (permalink) Old Dec 10th, 19, 10:37 AM
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Rick
 
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Re: Cometic MLS head gasket for 406 street engine?

I use Cometics on my SBC. With a 4.125 bore i use a 4.125 gasket. Part number C5271-040.

Never have had a gasket issue. 3 drag weeks and 300+ 8 second passes on this set.

1967 Chevelle Malibu 4 door


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post #6 of 12 (permalink) Old Dec 10th, 19, 11:38 AM Thread Starter
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Steve
 
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Re: Cometic MLS head gasket for 406 street engine?

Quote:
Originally Posted by BillK View Post
Steve,
The Cometic gaskets will work fine but make sure that the 4.165 gasket bore size is large enough to clear whatever chamfer you have on the top of your cylinders. Call Cometic and ask them to be sure. Might be kind of hard to get anyone this week though because of the PRI show.

Thanks, Bill. Glad to see your post and I will talk with Cometic. I have heard they recommend a certain dimension larger than cylinder bore for the gasket, but will call to confirm what it is.
a

TXCR13
1966 Chevelle 300 2dr Sedan
385, Flat Top Hypers, Performer RPM, S.M.I. 750 Q-Jet, 72cc Dart Platinum 200cc runners, U.D. Harold 223/233 112 LSA Cam, 700-R4, PS, Manual Disc Brakes, AC, Hedman headers with 2-1/2" exhaust.

1946 Studebaker Coupe- street gasser finally underway!
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post #7 of 12 (permalink) Old Dec 10th, 19, 11:40 AM Thread Starter
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Steve
 
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Re: Cometic MLS head gasket for 406 street engine?

Quote:
Originally Posted by bracketchev1221 View Post
Also check the combustion chamber of the head to the gasket. A lot of times, the chamber is bigger than the bore and using small bore gaskets allows the backside of the fire ring to be exposed and it torches the gasket.
Thanks for the helpful post. Looks like I need to talk with both Cometic and AFR about clearances.

TXCR13
1966 Chevelle 300 2dr Sedan
385, Flat Top Hypers, Performer RPM, S.M.I. 750 Q-Jet, 72cc Dart Platinum 200cc runners, U.D. Harold 223/233 112 LSA Cam, 700-R4, PS, Manual Disc Brakes, AC, Hedman headers with 2-1/2" exhaust.

1946 Studebaker Coupe- street gasser finally underway!
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post #8 of 12 (permalink) Old Dec 10th, 19, 1:19 PM
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Scott Foxwell
 
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Re: Cometic MLS head gasket for 406 street engine?

We run Cometics on just about everything. Clean and flat surfaces are necessary. They seem rather tolerant of a surface finish that's not to their spec. IMO flat is more important. X2 on all the advice on fitting. Lay the gasket on the heads and block to double check the fit.
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Straub Technologies

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post #9 of 12 (permalink) Old Dec 10th, 19, 2:21 PM
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Jim
 
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Re: Cometic MLS head gasket for 406 street engine?

There is this one too, if you need thinner.

https://www.speedwaymotors.com/Speed...ore,39728.html

Jim

77 Monte
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post #10 of 12 (permalink) Old Dec 11th, 19, 6:17 AM
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Tom Terrific II
 
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Re: Cometic MLS head gasket for 406 street engine?

jeeze, 4.156 shim, .025 thick. no steam holes, but I'll bet a guy can make those.
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post #11 of 12 (permalink) Old Dec 11th, 19, 8:48 AM
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Jim
 
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Re: Cometic MLS head gasket for 406 street engine?

Doesn't look like a shim in the pic though.

Jim

77 Monte
421 Profilers ported by Eric Weingartner, Straub HR 3200 conv. from Jake 200-4r w/ 3.73's
Machine work by Torvinen's machine
11.93 @ 112.7 & tuning
67 Imp.SS for the wife 275 hp 327-TH350
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post #12 of 12 (permalink) Old Dec 12th, 19, 7:59 AM
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Re: Cometic MLS head gasket for 406 street engine?

Quote:
Originally Posted by bracketchev1221 View Post
Also check the combustion chamber of the head to the gasket. A lot of times, the chamber is bigger than the bore and using small bore gaskets allows the backside of the fire ring to be exposed and it torches the gasket.
I ran into this problem with my 215cc Edelbrock Victor Jr. Heads on on 4.125 bore. Had to go with 4.165 gasket to get the fire ring out of the chamber. I used Cometic P/N C5031-040

Twin Turbo 400 SBC 748 RWHP in 1969 Chevelle.
Sniper EFI,Turbo 400, Victor Jr. CNC heads and 2925 Super Victor Manifold.
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