head gasket selection
 

need help choosing head gaskets...in the process of "freshening up" my 525 sc....its getting a set of dart heads roller cam and 575 sci blower...whats a good choice for head gaskets?? it will have ARP head studs installed as well...may seem like a dumb question but I know not all gaskets are created equal

thanks

Stewart

Need to know more about the setup to recommend an exact head gasket.... desired compression ratio, piston cc, head cc, etc.

I would highly recommend an MLS (multi-layered steel) head gasket though, but I cant make a recommendation on brand or thickness

oh yea sorry...shooting for 8:5:1 forged pistons not sure on brand yet....119 cc dart heads iron eagle that's about all I know at this point...looking for 7-8 lbs of boost and it does have a chiller

thanks

Stewart

you don,t need a mls gasket for you,r power leval,a fel pro perma torque would be what i would use.edit in,i also would not use head studs,arp head bolts would be a better choice.

would the MLS be added protection?? just want to make sure hopefully I only do this once hahaha

thanks

Stewart

You need to have heads and block machined to a finer RA for MLS gaskets.

so maybe just stick with the felpros and hope for the best??

What about this...lets say the engine had 9:1 compression...how does that change things??

Stewart

The Felpro marine gaskets will be fine. I ran them on my bumped up 525SC with 8# of boost.

I'm sure a stock style head gasket will work just fine but I would highly recommend stepping it up to an MLS. Especially since you are re-doing everything you can have the heads and block finished to the correct surface finish for an MLS.

I cant think of any drawbacks to an MLS if done properly. I cant actually name a modern engine that doesn't have an MLS gasket.

Also, what is your reasoning for recommending head bolts over studs?

I also just used ARP head bolts and not studs on mine.
IMO, studs are overkill for what he is doing and he will most likely have to grind the lower studs to clear the exhaust.

good to know griff thanks!! I think if I can get away with the cheaper route ill probably do that as im looking at buying a complete shortblock now possibly so no reason to tear it apart to have the head cleaned up just for the purpose of running a gasket that I probably don't need

Stewart

IMHO: Felpro HG (more forgiving and you have mild engines) and ARP Bolts. Studs harder to seal in 454 blocks, studs can interfere with other things, plus the bolts will handle pantloads of HP. Pantloads = a schitton. :)

kinda what I was thinking thanks!!

Stewart

have you ever had the pleasure of removing an aluminum head that has been on a cast iron block with steel head studs?after about 5 years when the heads need to come off it is dam near not posable because of the corrosion from the dissimilar metals.the head stud is bigger through the middle and promotes the corrosion.

steel heads... use a permatorque head gasket and the appropriate ARP bolts... IMPO

thanks guys!!

how do I determine what thickness I need??

Stewart

.039 is pretty normal. Going up or down will change compression and quench slightly.

7-8lbs boost? Dart Heads? Chiller? Upgraded cam? you're gonna be spinning the bearings out of the 177 trying to get 8lbs of boost.

better heads, better cam, drop boost and gain power. Chiller is a bit of a restriction, and blower needs to be spin faster to overcome that. That tiny blower is gonna be working overtime for minimum wage.

imo, you wanna run 8lbs on that combo, get a 8-71.

As for head gasket thickness , as long as your Pistons aren't above the deck, a .040 gasket should be fine.

He did say that he is upgrading the blower to 575 blower, still small at 250/256 but should be OK for a 454.

correct its the B&M version of the 256...I know still a little on the small side but gotta use what I can afford for now lol

thanks for all the input guys!! think I have a direction to go now

Stewart

didn't catch that . I just saw the 525sc part. I Agree, the 256 will work better than the 177.

I had both 177s and 250 on my 454s . The 250s at 7psi with no chiller were still screaming pretty hard around 10,000 rpm blower speed, but it was a nice little power upgrade to the 177. I had the single carb version of the 250, with a dominator. With that setup, the front cylinders were substantially leaner than the rears.

Sounds like a nice package over a stock 525sc , good luck

Thanks!! I plan to go dual carb on it...found a dual carb plate for it and going to run whatever carb came stock on a 900SC...have a pair of those laying around so might as well put them to good use!! theyre holleys 800 cfm maybe?? need to go through them and once this project is done start the jetting process...running an innovative wideband on both sides so should hopefully make things a little easier

Stewart

the 900sc came with twin dominator carbs. The 800sc , had twin 700 cfm if I recall

must have been an 800 then because I know theyre not dominators

Contrary to what most think, MLS are not the ONLY gasket that requires a specific RA finish. And you do not need as smooth of a finish when dealing with cast iron heads, as you do aluminum, with either MLS or Composition style gaskets. This is right from Federal Mogul

Imo, a 250 blower, dart heads, you may be in the 700hp, or even more range, out of a 454 engine. Pretty sure Felpro will tell you , at that power level, you should be looking at MLS. ESPECIALLY, if you were using an aluminum head. Its not just about whether the gasket will seal on a dyno pull. It comes down to service life. Theres a reason OEM's are using MLS gaskets these days, even on lower power engines. A good example was the 575sci engines. Gaskets sealed great...for a little while. Then by 200 hours, they were failing. The common fix was installing some Cometics.

a head gasket must conform to thermal expansion, and expansion from cylinder pressures. A MLS gasket acts like a spring, and can conform to these changes over and over. I would not look to save 100 bucks on gaskets on
A supercharged marine engine.
Head Gaskets and Fasteners - Engine Builder Magazine

when i posted my thoughts about the perma torque gasket being all the head gasket he would need it was from practical experiance,i don,t always pay attention to what should work but rather relied on what has worked for years.if he is having block&heads machined then by all means the mls would be fine.i will add that a lot of the mercury marine head gaskets problems were not caused from the gasket but rather from the junk gm head bolts they started using around the time the gen 5 engines came out.

i agree their is a reason the oem are using mls gaskets,they design the engines to go 300+thousand miles without even a head removal,part of that is very mild camshaft,s that don,t kill the valve springs.that equates to many thousands of running hours.question,what is the normal valve spring life on a mercury racing hp 500 efi or a hp 525 efi engine?hint,hundreds,not thousands.

I know quite a few boaters, and pretty rare that I see anyone running 700+HP supercharged engines, that go 300 hours without a head being yanked off for some reason, to really see how things are holding up at that point. Half the time guys with custom built engines are barely making it past the 50 hour mark before something melts down.

Being that he is using iron heads, and an iron block, he should have no issues running a MLS gasket without the need for a super fine RA finish. Fel-Pro recommends a finish of 60 to 100 Ra for cast iron cylinder heads and blocks, and 50 to 60 Ra for aluminum .My advice isn't something I am making up. Its recommendations and data right from the gasket manufacturers. Could you run a cast crank with a 2 bolt main , sure, know guys who have. Would I recommend a friend to go that route, nah.

Mercury Racing's updated gasket for the failure prone 575sci head gasket, is part #27-811546A04 . That is a Cometic MLS gasket. Used on a 575HP supercharged marine engine with cast iron heads. This is the gasket you will get from mercury if you order a HG for a 575sci. It replaces the old part # 811546A03

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.