the felpro allready have black sticky stuff on them, they do say they want the deck slick,RA

I dont have any exp with Cometics,though they have more choises on thickness.

Cometics all the way. Put them on dry.
Eddie

call bob at perfomance gaskets he will help you out !262 677 4690. HE supplies merc with 75% of the gaskets they use.

How about on a non blower application? I am refreshing two Mercury 525's and ordered fel-pro high performance gasket kit (17207). I originally thought that that was a direct replacement for what was on the engines but turned out that that was not correct so I ordered the gasket from Mercury that was listed (811546A04). This turned out to be a cometic MLS gasket and both the engine builder and machine shop that I have talked to say that they have had nothing but problems getting the MLS gaskets to seal. I called the distributor and Mercury and they both said that it is a new part number (old was A03) and this is what they recommend.

Any help would be greatly appreciated.

From what I've seen lately, the Cometics are standard issue from Merc Racing and for good reason.
I have never heard of nor had any sort of problem getting the Cometics to seal. I wouldn't use anything else personally.
Dave

Hey Dave...I guess what the issue is is that only the head had been finished by the machine shop and we couldn't the block clean enough to meet the recommended specs for the Cometic to seal properly.

I am not real familiar with all that goes into the rebuilding of an engine but thats what friends are for and I am certainly learning. I also may not have explained everything correctly for the same reason.

We ended up using the fel-pro high performance marine gasket (#17048 I think).

Thanx,
Smitty

I have run BOTH in my turbocharged 69 bird.

I had failures with both, if you detonate the engine either will go bad. The cometics IMO need hylomar on them or they can weep water unless the decks are perfectly falt and polished like mirror.LOL

I run the cometics because I feel they will hold a little more combustion pressure than the felpros.

But the felpros seal water way better.

Old thread indeed, but I have to make this same decision. I talked to tech support for both companies this morning to get part numbers for my 489 build.

First, FelPro:

Interestingly enough, he said that neither the 17042 or the 1037 is a MLS gasket. They do both have a stainless steel core, with the only difference being that the 1037 has a fire ring that the other one does not have. Either will work for my Gen VI block. He recommended against any of their MLS gaskets for a raw water cooled marine engine because they are not SS.

Cometic:

PN for a Gen VI 4.280 bore is C5817-040, which is a SS MLS gasket with a .040 compressed thickness. The Cometics can be special ordered in .027, .030, .036 thicknesses also.

My engine builder has run both, but he thinks the FelPro's will be fine for my application since I am only running 8.7 - 9.0 :1 CR with no plans to supercharge. For supercharged applications or aluminum head motors he prefers the Cometic.

Cometics will cost about $100 per side. I have found the Fel Pros online for as little as $34.00 each.

The Felpro 1075 and 1077 MLS are definitely stainless.

The Felpro blue teflon composite gaskets are fine for just about any n/a performance use. The Cometics would be a waste of money in your case. The Felpro's are definately a better gasket than what Mercury put in all of their HP500's in the past few years.