ChevyChad

iTrader: (50)

I am looking at a set of 225 AFR's with 72cc 'big bore' heads. Will these fit on my 347 with a 3.903 bore? Right now I am running stock GM 6.0L heads. Just want to verify that the AFR big bore heads are the same as the heads I currently have as far as the bore size is concerned...

Tom@SpeedInc

iTrader: (5)

they will but you have to use a FEL PRO 1041 or cometic 4.125 bore gakset.

ChevyChad

iTrader: (50)

I actually have a set of the new GM 5-layer MLS 6.0/6.2L gaskets waiting to go on. Will they not work? Thanks.

Tony Mamo @ AFR

iTrader: (13)

Yes they will if the bore size of the gasket is at least 4.125 in diameter (or larger).

Tony

ChevyChad

iTrader: (50)

Thanks guys. IIRC the bore of the 5-layer MLS GM gaskets is 4.100 but I guess I will have to measure to be sure. I hope they are 4.125 because I've heard bad things about cometics. If they are not big enough, how good are the fel-pros compared to the GM MLS's?

Tony Mamo @ AFR

iTrader: (13)

For N/A applications the Felpro's are fine....if your spraying or boosting the MLS style is better.

You could squeeze by with 4.100 but the gasket will be dead even with the chamber bore. I prefer it a bit inboard so the head has a little more aluminum there to better clamp the fire ring...

Tony

ChevyChad

iTrader: (50)

This is a boosted application... Hmmmmmmm This may deter my decision on the AFR's if I can't use the MLS gaskets and the fel pros won't work. I'll go measure them right now...

helicoil

iTrader: (104)

Felpro MLS 1162R and 1162L are 4.175" bore with a .053" compressed thickness (11.9 cc's)

Tony Mamo @ AFR

iTrader: (13)

Whats up with your fear of Cometic gaskets?

They are no different than the GM MLS in design and function, not to mention thousands of people have used them with great success, myself included.

Tony

PS....They have alot more to offer in thickness, bore sizes, etc....easy to get what you need and get the right quench based on your piston to deck height etc.

ChevyChad

iTrader: (50)

I've just known people personally who have had problems with getting them to seal completely. In fact, I don't know anyone personally who has had success with them. Also read of a lot of mixed reviews here on tech about them. Seems like its hit or miss really... And with my luck, thats about as certain of a miss guaranteed

I measured the GM MLS's and got anywhere from 4.102 to 4.107 Could be maybe the precision of my calipers or simply within the tolerances of the gaskets themselves.

silverZ98

iTrader: (6)

if the heads and the block is stright no dips the Cometic should have no problems sealing.

Jeff@TotalPerformanceEng

iTrader: (6)

Well, the information about the cometics is about as false as you can get. Not saying that your friends didnt have issues, but there are ALOT of guys running cometics in boosted applications..Probably thousands.. I personally have used cometics exclusivly, and have NEVER pushed water, or had a problem with the sealing. On my last car, I went to 18psi @ just under 900rwtq and 900rwhp without ANY issues. As a daily driver, it was 800rwhp 850rwtq.

My LSx 454 w/NX direct port runs cometics with no problems as a daily driver in Las Vegas's 117* heat.

99.9% of all the bullshit you read about on the internet is from some kid who had a friend of a friend that knew a guy once. Thats how almost ALL of peoples setups are built nowadays. Everything is based off of unfounded information..

I say, go with the cometics and *** worrying about something that isnt gonna happen..

ChevyChad

iTrader: (50)

LOL I know better than to base all of my decisions off the internet, but its just that I have personally seen people with problems getting them to seal. I dunno... I need to give it some thought before pulling the trigger. What could be the absolute worst case scenario if I did attempt to run the AFR's with the 4.100 GM MLS gaskets?

speedracer5532

iTrader: (8)

I have ran 4.160 bore and .040 thick cometic gaskets in my boosted application (18 lbs) with no problems as long as you don't have any detonation. If you experience any detonation, it doesn't matter what heads, gaskets, fasteners, pistons, etc you have you will have problems.

ChevyChad

iTrader: (50)

Would LS7 gaskets work? Anyone ever used those on a 3.9 bore engine?

PREDATOR-Z

The issues with Cometics are due mostly to poor surface preparation.
Clean the block and head decks real well, spray the Cometic with Copper sealant, use head studs and don't look back.
They are the best gasket for your application.

speedracer5532

iTrader: (8)

I don't know the bore size of the LS7 MLS gasket but it has to be larger than 4.125 so I would think they would work. GM gaskets are definitely cheaper than the cometics. I like the cometics because then I can run the thickness I want.

ChevyChad

iTrader: (50)

I'd rather stick with the GM gaskets personally. Just found out the LS7's are 4.150 x .056 that would be good for me. It'd bring my SCR down to 9.3, but thats no big deal. Thanks again guys for all the help.

ChevyChad

iTrader: (50)

Welp, just ordered the LS7 gaskets from SDPC and I'm going to pick up the AFR heads this weekend. Can't wait to see how much power the AFR's make compared to the stock 6.0L heads I was running!

Tom@SpeedInc

iTrader: (5)

Cometic gaskets work fine, lot of people clean the deck surface with a die grinder which leads to problems.

gasket scraper and honing stone are better choice for prepping a deck surface.