I've had good luck with the Felpro mls gaskets up to 25lb's boost, never tried Cometic though.

 

I had nothing but trouble with the Cometic gaskets, switched to MLS and made not tune up changes and they sealed great. Some people love the Cometic and some love the MLS. Go with the correct surface finishes and both should work no problem.

 

I used them with nitrous, not boost, never had an issue, but............... Why in the world did Fel Pro make the gasket so short where it heads towards the china wall? If you don't pay attention during assembly (or read the instructions, who does that....), you're going to have four big crankcase leaks!!! My builder made that mistake. Lucky for me I decided to vacuum test the crankcase while the engine was on the stand. I was not pulling it all apart at that time and simply gooped the heck out of the four corners. The Cometics don't have that issue.

 

Only used the Cometic in SBC and BBC as well as a few Ls...some boosted, some nitrous. Never any problems. Surface prep is key as well as we never install them dry, always use sealant on them. On iron head BBC and SBC we also reused them a couple times, no problems. Never used the FelPro, never had a reason to switch.

 

Only used the Cometic in SBC and BBC as well as a few Ls...some boosted, some nitrous. Never any problems. Surface prep is key as well as we never install them dry, always use sealant on them. On iron head BBC and SBC we also reused them a couple times, no problems. Never used the FelPro, never had a reason to switch.

Fel-Pro issued a bulletin last year to install there gaskets dry.
No copper spray or anything.



SICKFOX

 

We run the felpro MLS on our procharged BBC 45lbs from a F3 no problems

 

Spray or dry use?

 

Cometic MLS here, dry on properly prepped head and block.

 

stock mls gaskets for a 5.4 modular and arp bolts, keep on the tune up and no issues at 28psi

 

Why don't you guys use copper and o-ring? Thats what ive always done and haven't seen any issues. Just wondering what the benefits of these other multi layered gaskets are over copper and o-ring.

 

I use copper /rings/receivers . Just interested in the prep or no prep that's being used.
Those mls hold well until they don't and scorch the deck or head. Tune up is the key.
Copper is IMO more forgiving but can be tricky in prep and retorque. I'd rather push, pinch , slide a copper gasket under boost rather than decking , surfacing the head or buying a new block/head if a problem occurs.
To each their on.

 

I agree, thats my thinking also. I have always wondered why people went the other route. I guess they dont want to o-ring the block or heads.

 

i tried the felpro severe duty on new build- blew gasket in 7 semi passes-- cometic went 3 years and never blew-- but we probly did hurt the felpro going lean a couple passes before it blew-- so can really say..lol so went back to cometic when i went back together last week.. went lean before on cometics-- so?

 

Used fel pro 3 layer mls. 18lbs of boost on a roots 871 sbc, no complaints here.

 

Ive used felpro mls gaskets dry and with copper spray. No issues with either n/a, nitrous, or boost..... but ive also had no issues with the Chinese head studs and not resizing those silly crack capped rods while installing arp rod bolts. (strictly LS series stuff)

 

I've run both copper and MLS gaskets, and I can tell you from experience that if your tune is off, copper will just push, but MLS if it blows, takes out a channel through your aluminum head and maybe the top of the block between cylinders!

 

True statement.

 

I've used both felpro does have a better sealant on them than cometic in my opinion. but I always use copper spray and put a couple coats on the gaskets' just for good measures. never had a problem with either I use a cleaning solution and prep the block and heads so the gasket can make a good contact. most head gasket problems comes from improper installing or improper torque imo...... like previous post said " if your tune is off mls gasket doesn't give much it wipe out the heads, chambers ,pistons etc.... trust me i've done it a couple times when I first started my blowthru setup

 

just some advise...... get the gasket that's closet to the cylinder bore for example if your running4.030 bore get a gasket with 4.040 or close instead of a 4.125- 4.200 bore gasket. sounds like common sense I no but you want believe the number of people that make this simple mistake... reason for doing it is.... you want to keep as much head gasket material between the cylinders....

 

That's exactly what I was looking at. This is a 4.53 bore and the Cometic is a 4.54. Not sure I trust .005" on a side for gasket clearance. The FelPro is 4.58 which is only .025 a side. Next step is to a 4.6x gasket which I won't do. One of the main reasons for keeping the small bore on this build (TT big block Chev) is to have some head gasket between the cyl's.
Thanks for the input.

 

i like the Felpro MLS-SD gaskets.

 

Felpro also wants the surface as slick as you can get it, but most shops ive seen cant slow down their machines enough

Rob

Felpro

We do not recommend a surface finish coarser than 60 Ra or 360 Rz with MLS. With a coarse finish it is very difficult for the thin rubber coating to seal off the peaks and valleys in the machined surface. I suggest having the finish on the block and heads measured. If the finish does not exceed 360 Rz you should be good to go. We do offer a .061" thick version of 1075. It might be best to use the .061" thick gasket and re-deck the block with a smoother finish. The 60 Ra/360 Rz values are maximum values. If you re-machine the castings, I suggest going as smooth as possible. The smoother the better with MLS. Seeing that this engine had problems in the past, if there is any question on the surface finish, I would re-machine the block and heads as smooth as possible.