[hpp]

I have a '75 400 block .30 over the deck was not zero decked just re-surfaced for a good clean up and to make sure it was square.

Pistons are L2262 TRW's advertised at 6 cc./Tomahawk rods

Heads are 061's about or around 78 cc.

Im looking at the Cometic's head gasket's 4.160 x .027.

Cam is a Comp 224 230 @ .50 .477 .480 lift.

I figure comp ratio should be around 9.65-9.75:1 or so.

My question is about the cometic gasket's,there very pricey. Around $200.00 for the pr. But they have the bore size and thickness I need.

Anyone use these?

[Old Man Taylor]

I have reused my set several times. They're great.

[TIN TIGR]

ditto..they hold up well and are re-usable..just make sure the surfaces are super smooth..and follow directions

[Steve C.]

MLS head gaskets are very durable because their solid steel construction retains torque very well and doesn’t take a compression set like composition gaskets. But the rigid nature of MLS gaskets also means they have very little conformability. That’s why MLS gaskets require an extremely smooth, flat surface finish on both mating surfaces (typically 20 to 30 RA or less).


Question.... for discussion. Does the Cometic gasket have a traditional fire-ring ? I ask because I read here on a PY post the distance of the fire-ring should not be too close to the piston bore. A minimum distance was mentioned, .015 ?, .020 ?, I don't remember. It had to do with potential detonation issues with it being heated up, or someything to that effect. Your proposed 4.160 gasket bore leaves about .005" per side. Also the inside diameter may not be a perfect circle.

[hpp]

The deck of the block and the heads have a good finish"RA".

I wanted to use a thinner gasket because the pistons are kinda down in the hole,block was not decked. So the .027 will improve the quench.

Far as the bore size from 4.15 to 4.160 distance,Im not 100%sure about that? I didn't want a bunch of dead space up top.

The Cometics do have a fire-ring.
I am concerned about the cost,I know 1016 fel-pro's would be alot cheaper. For what this engine is and what it will be used for the Fel-Pro's may be fine for now,It would help me out right now to save some money.

Any tech info would be great.

[BVR421]

dont waste your money
a $20 gasket is all you need

[goatasaurus rex]

bvr is right. the 1016's are probably overkill. the standard fel pro should do the job. spend the cash on something else because there is always something else.

[67drake]

I'm running the 027" Cometics on my 71' 400 bored .030" over.Only have 1000 miles on the rebuild so far,no problems.
After talking to a tech at Cometic,and my engine builder,they said to get a gasket bore of 4.185" for a 030" overbore 400. I remember that I questioned this at the time also,wondering why the extra bore diameter. To be honest I don't remember why the Cometic tech suggested this,I was only making sure that he was not mistaking it for a .060" overbore rebuild. So if you do order them you may want to talk to a tech before you buy them. The 027" are considered a "special order" item,so they are not returnable. BTW,mine were $202 shipped.

[Cliff R]

"I wanted to use a thinner gasket because the pistons are kinda down in the hole"

How far down in the hole? Most of the TRW forgings we've seen were .028-.032" down in the holes at TDC on stock blocks.

The money best spent here is to have the block zero decked, then use the stock $20 Felpro head gaskets.

I wouldn't even consider trying to run any sort of steel/shim type gasket on an engine that didn't have both the block and heads machined. Even then, you had better make sure that the shop had sharp cutters on their machines when they did the operation.

Looks like you may have chosen the XE268 camshaft? We built a 400 several years ago with ported #16 heads, and tried that cam. I was NOT overly impressed anyplace with that camshaft, not nearly big enough for a 400 engine up near 10 to 1 static compression ratio. It acted like a stock 066 cam, dead smooth idle, DONE by about 4500-4800rpm's....FWIW.....Cliff

[hpp]

The block and heads were machined.

They have almost a mirrior finish,although I dont remeber what the RA finish was.

I read O61 heads dont have much squish pad area. As the deck was not zero decked,I thought a thinner head gasket would help.

Also as I read the TRW's wind up around .026,but mesure closer to .20"-.022".

The cam is a Comp XE268H,lobe seperation of 110.

Comp claims RPM range is 1600-5800,also says there will be a slightly rough idle.
I have not used this cam before,so I cant say.


If this cam isn't suggested,what would be? I already have the matched springs installed on the heads,there Comp 995-16 that may also work w/a different Comp cam.

[Cliff R]

Idle quality in the 400 engine mentioned above was dead "smooth", just a deep/heavy sound. Kind of took me by surprise when we first fired her up, as the similiar sized Crower 60916 (221/229/112) cam has a slight "lope" at idle in similiar engines.

The "basic" power range is just a blanket statement given by the cam manufacturer's, what cid is the "basic" power range estimated by, who knows? I'll bet they don't even know if you asked them! Anyhow, that "range" is NOT accurage for a 400 engine, that cam is all done WAY before 5800rpm's. I know a guy running the next larger XE274 cam in a RAIV 400 engine. He's "OK" with the cam, as the car is only street driven, but he did tell me that it doesn't pull anywhere near as hard as, or as far into the rpm range as his "old" RAIV camshaft.....Cliff

[Geoff]

hpp,
The Cometic style MLS gaskets' main benefit is the type of material is better suited for use with dissimilar metals, such as iron & alum. With alum heads on an iron block, the alum expands more than the iron, which causes minute movement & sliding action [ & wear over time ] of the head across the gasket surface. The very smooth surface [ 20-30 RA ] of the head & gasket, plus the hard gasket material maintains the best seal & minimises wear.
With an iron block & heads there is no relative movement, so the traditional composite gasaket & slightly rougher surface finish would probably be a better choice.

[hpp]

Originally Posted by Geoff

hpp,
The Cometic style MLS gaskets' main benefit is the type of material is better suited for use with dissimilar metals, such as iron & alum. With alum heads on an iron block, the alum expands more than the iron, which causes minute movement & sliding action [ & wear over time ] of the head across the gasket surface. The very smooth surface [ 20-30 RA ] of the head & gasket, plus the hard gasket material maintains the best seal & minimises wear.
With an iron block & heads there is no relative movement, so the traditional composite gasaket & slightly rougher surface finish would probably be a better choice.

I've decided not to use the Cometics gasket. It's not needed for my application,plus the cost. Thanks,guys

[Tim Corcoran]

Cometic multi layer steel (MLS) head gaskets are a great product and work well for aluminum headed pontiacs with high compression. They are not a bandaid for warped or poorly milled block and/or head surfaces. As previouly stated you need a clean flat smooth surface for optimum results. For your combo a standard Felpro gasket would work just fine. If your goal is to improve quench and raise compression Cometics would work. If you decide to go with a Cometic gasket I recommend that you call Bill Takanabe from RSB Motor Sports. He has a very competitive price and you can custom order from him. You can specify your bore size and gasket thickness. He has great customer service and of course he is a total Pontiac guy.

Tim C

http://www.rsbmotorsports.net/dept.asp?dept_id=21