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Old 04-20-2007, 03:50 AM   #1
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Default MLS "thin" v. FelPro head gasket; gains worth $?

Cometic MLS "thin" head gaskets versus Fel Pro OEM style head gaskets for the L36.

According to my calculations, the MLS can raise compression on the L36 from stock 9.4:1 to as high as 9.6:1 to 9.75:1 (depending on how thin you go, MLS 0.051" or 0.045" vs. Fel Pro 0.062" stock).

zzp claims this gains like +9 (or more) hp; other net research indicates maybe +3-5 hp at best.

So, what kind of gains could really be expected?
What other mods might be needed to really get the most out of the increased compression?
Are the MLS as hard to seal as I've heard?
Ultimately, are the MLS worth about $120-$130 more than Fel Pro'*?
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Old 04-20-2007, 07:55 AM   #2
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The thinner a head gasket, the less material to seal. You might gain 3-5hp.. but at the cost of having issues sealing?

In the eternal search for more HP, my opinion is this is best left to someone that is willing to tear their motor back apart at a wimp to change the gaskets. My daily driver will have a litttle more robust gasket to ensure it'* reliablilty.
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Old 04-20-2007, 09:08 AM   #3
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I ran the 0.054" gaskets for 3-4k a couple of years ago. Now that I look back on it, I probably would have been better off spending the money elsewhere. Although they didn't show any signs of leaking or letting go when I pulled the heads off, I felt uneasy about putting a set back in with the horror stories popping up at the time. I went back to felpros.

You don't get as much compression per hundreth of an inch, but I would much rather mill the heads and keep stock gaskets. You can go as far as 0.020" without having to get shorter pushrods and as far as 0.040" before you run into LIM fitment issues.
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Old 04-20-2007, 10:48 AM   #4
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i remenber when i was drag racing my small block chevy we had thinner head gasket and what we did was to spray them whit aluminiun paint .but that was 25 years ago don, t know if its still good
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Old 04-20-2007, 10:54 AM   #5
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if you want just a plain old opinion, it would seem more worth it to me to swap out the pistons to higher compression, stroke it, or something of that sort, using a thinner gasket seems like a bad idea exactly for the previously mentioned reasons.
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Old 04-20-2007, 11:46 AM   #6
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Thanks for the advice, all.

It'* about what I figured...risk outweighs potential reward on the MLS head gaskets (at least for a daily driver).

What might I expect to pay a shop to mill 0.020" off of a set of L36 heads?
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Old 04-20-2007, 11:58 AM   #7
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Quote:
Originally Posted by agrazela
What might I expect to pay a shop to mill 0.020" off of a set of L36 heads?
It should be somewhere between $50-100 depending on the shop. You might want to get a 3 angle valve job while they are in there.
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Old 04-20-2007, 12:22 PM   #8
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Just call around about milling the heads... I would expect it to be toward the lower end of the range that Mike estimated, but that'* also an estimate . My heads are milled .040", but I can't tell you if there was much gain attributed to it because we did a cam at the same time. Like Mike said, up to .020" should be alright on the stock valvetrain, though you might be pushing the envelope a little. And when we did my heads we had the LIM milled .010" to fit nice and snug. It worked out nicely.

And by the way, I used regular thickness Felpro head gaskets.
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Old 04-20-2007, 01:17 PM   #9
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Cool, so it sound like milling plus Fel Pro'* versus not milling plus MLS is about a wash cost-wise, and a bonus reliability-wise.
(Probably ultimately a bonus cost-wise, as I'd feel better about using TTY head bolts with the FelPro'*, rather than "needing" reuseable studs with the MLS)

As to stock valvetrain, IF I was to go through with all this (and that'* a gigantic "IF" right now), I'd be going with upgraded springs and retainers for sure...whether LS6'* (90#) or CompCams 105# (and the choice of standard vs milled / "thin" retainers) is not yet decided.

So the inevitable flood of more questions:

What other valvetrain improvements might be needed?
(Current plan is stock lifters and pushrods, stock valves and locks, viton valveseals, and no change to valveguides unless they need replacing due to scoring and/or slop, in which case I was going to go with stock valveguide replacements)

What should I expect to pay to have new valveguides pressed in?

What might a 3-angle valveseat job cost me? What advantage over a "standard" valve-job (or even a plain-Jane home-lap job, if the seats are good enough for it?)
Would a 3-angle valveseat job require the valves to be re-ground, also? Expected cost?

Milling 0.020" wouldn't change spring install height / seat pressure, right? And the stock lifters and pushrods can absorb that difference, right? What about the 3-angle valve seat job...what will that do to spring install height?

Am I asking too many questions?
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Old 04-20-2007, 03:19 PM   #10
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Agra, I gotta hand it to you... you leave no stone unturned in your line of questioning

Stock valvetrain should work if you have the heads milled no more than .015" to .020". If you go more than that, buy pushrods that are the appropriate shorter length for the mill job (i.e., if you have the heads milled .050", get pushrods that are .050" shorter). When I had my original head work done, we reinstalled the stock lifters, pushrods, and rockers, and the valveguides stayed stock as well. Valve seals were replaced, and since the valves were pulled out we lapped them when they were reinstalled.

Milling the heads will have zero effect on install height, but I'm not sure about a 3-angle job. It should have a negligible effect, unless the machine shop takes an unusual amount of material from the valve seats. I've always heard the lifters can accomodate about .015" of valvetrain slop, but now Mike is saying .020" is alright .... not sure which number is correct, but Mike usually knows his stuff.

As far as costs for all this stuff, just call a machine shop and get some ballpark figures. It may vary, but generally this kind of basic machine work is quite affordable.

And you're asking good questions... I would be more concerned if you were totally ignorant about this stuff and trying to do it all
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