Cometic head gasket better than Mopar?

[GLHSKEN]

Ken will disagree with me but ARP studs should be the first thing you install.

The engine for the GLHS is studded....

[BadAssPerformance]

So which will hold better, bolts or studs? I've always thought that all bolts or studs stretch a little when torqued.

Bolts = stetch and yeild = inconsitant

Studs = strecth but do not yeild = consistant

[puppet]

^Not quite right JT.
TTY is actually very consistant in providing an equal clamping load. Not as accurate as being able to use a stretch gauge but being in a blind hole that's all we got. TTY/angle bolts are calculated to provide a set clamped force based on the amount of stretch produced by the degree or turn. Go past that and you kill 'em.

Also, aluminum heads expand at a greater rate than iron heads do. Might be that some of the fellas having problems with MP bolts aren't following instructions? ... like torquing to a number? ... guys?

Studs or torque read forces are dependent on a lot of variables. 80-90% of torque readings are measuring frictional forces in the bolt, thread hole and underside of the nut. ... not very precise unless you cycle the fastener a half dozen times to minimize the friction.

What might not be obvious to a lot of people is that the final reading on the torque wrench doesn't equal the clamping force. (90ftlbs isn't 90lbs of force under the nut) it's much, much greater. Just another reason why torque reading errors can produce vastly different clamping forces. The difference between a couple lbs reading is increased exponentially to thousands of lbs of actual clamping force applied under the nut.

Care has to be taken with either bolt/stud solution used.

[glhs875]

I've always had good luck wth bolts and MP headgaskets for that matter. Haven't blown one in 4 +years of very hard driving. Of course back in the mid 80's when I first started playing with TD's, I blew alot of them before I fiqured out how to tune better. I think I'm getting close to finding the reliable limit of the MP gasket. The only thing I can see that might need to be changed on the tune is a touch of timing retard in the high boost levels (28+psi) And I think the #4 coolant mod (didn't have) is also needed for this level of power and boost. I will go with a Cometic and studs this time, along with the coolant mod. So I guess if the tune is far enough off next time, it's bye bye engine!! But that's okay it only a test engine anyway. One has to pay to play and sometimes pay alot! I think it's kinda funny, that on the way home from the store I was thinking since my boost was sky rocketing (stuck BOV allowing boost creep) and I was going to have to pull the head to fix some things anyway, that I'm gonna run thing this out for all it's worth to see what will happen when I get close to house!! I'm glad I was close!

[turbovanman²]

The engine for the GLHS is studded....

You always throw me a curve ball,

[BadAssPerformance]

^Not quite right JT.
TTY is actually very consistant in providing an equal clamping load. Not as accurate as being able to use a stretch gauge but being in a blind hole that's all we got. TTY/angle bolts are calculated to provide a set clamped force based on the amount of stretch produced by the degree or turn. Go past that and you kill 'em.
...
Care has to be taken with either bolt/stud solution used.

The inconsistency I emntion is because of the "1/4 turn" and varying torque resultant by design. Yes, if they all yeild teh same thay will hav eteh same force, but it can be difficult to make them all yeild the same. With that said, I have never had a problem with MP bolts until the head started to lift.

+1, head torquing has to be done very carefully to be succesful!

[OnLooker]

Studs are superior, they clamp so much better that if you use main studs, that you have to have the bores checked for roundness. They don't stretch like bolts do.

I am in the middle of building a motor and all machine work is done. I was thinking about running main studs to help the 87 T2 bottom hold a little better. So does this above statemant mean I am stuck using main bolts and not studs?

Thanks
Andy

[TurboJerry]

I check stock bolts with 95 ftlbs after the 1/4 turns. If any move more, only those are replaced. I torque ARP bolts/studs to 90 ftlbs. The ARP torque specs is with Cometic gaskets though. I'd never go that high on a MP/felpro, etc. gasket. The reason studs clamp better is the fine threads at the top. It takes less torque to get the same clamping force. Seems like .006" of strecth is ideal.

[glhs875]

The inconsistency I emntion is because of the "1/4 turn" and varying torque resultant by design. Yes, if they all yeild teh same thay will hav eteh same force, but it can be difficult to make them all yeild the same. With that said, I have never had a problem with MP bolts until the head started to lift.

+1, head torquing has to be done very carefully to be succesful!

That's why I've always torqued the bolts to a number, 40, 65 than 85 ft lbs. going over them many times. Too me that way seems more accurate than the number plus 1/4 turn way. Maybe I needed to final torque them a little higher like 90 to 95 ft lbs. Probably won't ever find out if a higher final torque number would help or hurt. I'm making changes.

[turbovanman²]

I am in the middle of building a motor and all machine work is done. I was thinking about running main studs to help the 87 T2 bottom hold a little better. So does this above statemant mean I am stuck using main bolts and not studs?

Thanks
Andy

Due to the better clamping force and the way they do it, they could deform the main bores, so you need to have a machine shop check it and it could need a align bore. My 89 CB was ok but Will's TIII block needed it. Weird huh?

[GLHSKEN]

That's why I've always torqued the bolts to a number, 40, 65 than 85 ft lbs. going over them many times. Too me that way seems more accurate than the number plus 1/4 turn way. Maybe I needed to final torque them a little higher like 90 to 95 ft lbs. Probably won't ever find out if a higher final torque number would help or hurt. I'm making changes.

nope... do the final 1/4 turn.. that is the way tho blts are designed!! Set the torque wrench to 95 ft lbs and then test them... should "click" immediatly

[johnl]

I check stock bolts with 95 ftlbs after the 1/4 turns. If any move more, only those are replaced. I torque ARP bolts/studs to 90 ftlbs. The ARP torque specs is with Cometic gaskets though. I'd never go that high on a MP/felpro, etc. gasket. The reason studs clamp better is the fine threads at the top. It takes less torque to get the same clamping force. Seems like .006" of strecth is ideal.

Agreed - fine threads.

As I imagine it, there is another thing to consider about studs vs bolts.

With a long bolt the force is applied at one end and the friction is at the other - so - torsion. The thing twists and that takes up some of what your torque wrench is reading. Then too the torsion may cause deflection of the threads that you are trying to twist into the block - more friction. Then the bulk of what your wrench reads, of course, is compression of the head onto the block.

With a stud, we care less about the stud's torsion and the friction of the threads at the other end. The torque wrench is measuring the amount of compression of a short section of the stud (not a long section) upon the head.

Also measured - as for both stud and bolt - is the friction, through the moly lube, at the nut's threads and at the joint of the polished nut/polished washer.

So, all things equal, by eliminating the torsion, IMO a stud will apply more clamping force, at the same "torque," as compared to a bolt. Also, as TurboJerry points out, the finer thread has less friction.

[glhs875]

Do you guys spray the Cometic gasket with anything, (what) or install as is? I also see where the Cometic gaskets come in different thicknesses. Even custom thicknesses can be made. One could decrease or increase the quench area in the combustion chamber if desired. I'm looking into that.

[87csx2.4]

I am in the middle of building a motor and all machine work is done. I was thinking about running main studs to help the 87 T2 bottom hold a little better. So does this above statemant mean I am stuck using main bolts and not studs?

Thanks
Andy

If you run main studs you have to have the block line bored with studs installed dont install them now or you will possibly have some serious problems.

[csxtra]

Do you guys spray the Cometic gasket with anything, (what) or install as is? I also see where the Cometic gaskets come in different thicknesses. Even custom thicknesses can be made. One could decrease or increase the quench area in the combustion chamber if desired. I'm looking into that.

I had issues getting my cometic to seal (coolant leakage out the back) when I put it in without any spray. Did some research and supposedly the best spray sealer is Hylomar spray, but it is nearly impossible to find.

Since I couldn't find the Hylomar spray, I used the old standby copper spray, and it sealed up and held fine for 2 years until I lifted the head on a 1/4 mile pass with some detonation at >29psi (not sure how much actual boost, 5V on 3-bar sensor was all I know). I lost a bunch of coolant during the run. I let the car cool down, refilled the radiator, and the car ran fine again (it made another good pass and drove home that night without any issues). I think I got REALLY lucky. I need to go out and retorque the ARP studs after that just to be sure.

So does this mean that the head flexing was my "fuse"?

On another note, I'm, running the standard thickness Cometic.

Hope this helps,
Warren

[glhs875]

I just ordered a custom Cometic gasket .036 thick. That will bring my compression ratio up to 8.2 to 8.4 to 1 from 7.98 to 1 with the #005 MP gasket (.068 thick), depending on what my combustion chambers cc to when I done with them. That will also decrease the quench area from .078 to .046. All together I think this will be a definite improvement in performance. My combo seems to be very detonation resistant, the tighter quench should help it even more. We shall see!

[crazy1eye]

I just ordered a custom Cometic gasket .036 thick. That will bring my compression ratio up to 8.2 to 8.4 to 1 from 7.98 to 1 with the #005 MP gasket (.068 thick), depending on what my combustion chambers cc to when I done with them. That will also decrease the quench area from .078 to .046. All together I think this will be a definite improvement in performance. My combo seems to be very detonation resistant, the tighter quench should help it even more. We shall see!

Did it cost more?

I too could use a thinner head gasket since I also run a G head with JE pistons, not to mention my combustion chamber cc's are high because of de-shrouding the valves, etc.

Thanks.

[glhs875]

Did it cost more?

I too could use a thinner head gasket since I also run a G head with JE pistons, not to mention my combustion chamber cc's are high because of de-shrouding the valves, etc.

Thanks.

I ordered direct from Cometic. 148.00 and some change + shipping. Basically the same price.

[Mario]

Hylomar Spray http://www.dougherbert.com/hylomar-spray-p-10844.html

[slasky]

I was told not to use the hylomar but use the copper spray.