you are right joe,a perma torque gasket will fail,you must use a mls gasket.guess all those head gaskets i installed through the years failed and no one realized it.

question,what head gasket came on a merc 575sc?

the same ones the 500 efi’s use....the ones that toast between the cylinders when they get a little time on them

575sci, 500EFI, 525EFI, all came with the old school gaskets at some point. That has now been changed as I stated earlier, and if you walk into a merc dealer, and order a replacement gasket for any of those engines, you get a Cometic MLS gasket with a Mercury Part # on it. That part # is 27-811546A04 . All of those engines were known to have head gasket sealing issues over time before the MLS stuff.

The 700SCI, 600SCI , new 565EFI , all come with the MLS gasket.

Teagues thoughts.
'
Forced induction high performance marine engines are hard on cylinder head gaskets. Fight back and prevent torched blocks and cylinder heads with the right marine head gaskets from Cometic and Felpro, available for all generations and bores of Big Block Chevrolet. Teague Custom Marine uses Cometic or Felpro multilayer cylinder head gaskets on all engines over 700 horsepower, and Felpro Marine high performance cylinder head gaskets on less than 700 horsepower naturally aspirated engines.

https://teaguecustommarine.com/em001...tf017lp5as8f61

what brand&part number was the old school head gasket?several of the engines you listed that i removed the heads had victor gaskets and the not so good gm head bolts.i reinstalled the heads on these with fel pro marine perma torque gaskets and to date none have had head gasket issues,also replaced the head bolts with top quality arp bolts&washers.some people just don,t want to spend the coin for the mls gasket.

So in the end I went with felpro MLS gaskets...a buddy that has built several race engines agrees with everything that was said on here and said to run the MLS for peace of mind...I appreciate all your guys' help!!

Stewart

stewart,what did you use for head bolting?

ARP bolts...gonna be a bit before she actually goes back together but picked up boxes of parts last night so I have everything minus pistons at this point...gaskets, rods, bearings, timing chain, oil pump, etc....ready to start building when the work schedule allows..will post a build thread and hopefully pics when I start making progress...

Thunder....do you really think this will be 700 hp?? I was shooting for 6-650 so anything over that is a bonus!! lol

Stewart

generally agree,,but I have seen a few hp500's that had blowers put on in the 650 range start to weaken the felpro head gaskets.I pretty much use cometic at anything over 600.my personal motors and a couple of friends,Ive reused the cometics,and these were all blower motors.7-800hp.
also,seems like over time the felpro marine like to weep water out the side of the block,cometics seem to cure that problem.just did heads and gaskets on a whipple 502 and they were leaking bad at 100hrs.will see next summer how things are holding up.these motors get turned up to 5800rpm on a regular basis,36 specte cat.
food for thought.