Peckster

I'm running one without O rings.

My mechanic said it was worth a try puttingn one in and I trust him. The guy's been racing and repairing 944s for 15 years. Anyway they are certainly no worse, and not much money more compared to the labor.

Evan70

When I had mine replaced I asked Tom Charlesworth (my mechnic) what was the best solution (O ring head, widefire, Cometic, stock, etc). His reply was definitely Cometic. He uses them on his own cars, and recommends them to all his customers. Condsidering how much experience he has with 944/951s I'll definitely trust his judgement.

macnewma

Evan, did you mill the block and head? What head studs are you using?

Evan70

Honestly I can't remember for sure what exact work he did. I do know he sent the head out to be machined (including port/polish), but I don't believe he needed to do anything to the block. Studs are stock. I can find my receipt over the weekend or give him a call Monday if you're really interested in the exact details.

macnewma

I imagine if the head was sent for a refresh that they checked it for squareness and milled if needed. My concern is that without a perfectly flush block to head mating surface and a MLS HG you could run into issues with leaking as the MLS doesn't compress as well.

Also, how valid is the concern that when switching to a MLS HG, you lose the safety valve of the HG when you go lean? I would rather blow my HG than blow something else. Is this a reasonable concern?

Fen

And I thought a head gasket was supposed to seal between the head and the block.

I hate that BS that's repeatedly trawled out about the HG being some sort of safety valve - of course it isn't.

Fen

One flaw in that theory: the stock studs aren't elastic, they stretch one time and that's it. That's why you don't re-use them. If anything the stretch limits the clamping force you can achieve but they aren't going to act like a spring.

macnewma

Fen, could you explain how a MLS HG seals better than a fibrous HG? (this isn't a rhetorical or sarcastic question although it may sound like it)

Fen

Search. As I said in my first post on this thread someone on here looked into this (I'm fairly sure Danno) and the finding was that WF has a single thickness of fire ring whereas stock has a double thickness. That suggests to me stock is better than WF, although that's my conclusion not a statement from Danno/whoever.

Also I've never seen the WF marketed as being for O-ringed heads so I'm not convinced that is what it is intended for.

Bill

My setup is O-Ring head, wide fire, stock studs, 22psi boost. 10,000 miles on this setup and everything is dandy so far. Of course fuel curve is spot on and I use 100 octaine.

Fen

I don't think it does seal better (in fact the fibrous surface probably seal better than steel), but I think it is more resistant to the pressure inside the combustion chamber so less likely to deform. Being steel all the way through it is also less likely to suffer a burn through of the fire ring. Lastly I believe it can (and should) be used with a higher clamping force to reduce the chance of "head walk".

In short I think it is better suited to extreme use and has better longevity. For a stock engine I'd recommend a stock gasket all the way.

Personally I think the stock gasket is not suitable for (nor intended for) high boost applications. I'd prefer my head to stay sealed and to use a proper AFR (as Bill says above) to avoid the need for a safety valve. Sure something could go wrong and make me run lean at high boost, but something could go wrong and make me veer off into the Armco at high speed too. If you worry about that stuff you'd buy a Toyota Prius and drive a 20mph everywhere.

macnewma

I see what you are saying.

I think what we may be getting at here is that there is no single HG solution that is best for everyone. There are some downsides to the MLS gasket such as the need for more precise mating surfaces. If you can get past that, you might have an advantage, but when does that advantage become appreciable?

What factors determine the proper situation to change from stock to WFHG or stock to MLS?

I think that we should first assume the car is running safe A/F and timing. Next, lets assume the HG is new and not deteriorated.

At what boost level or other factor should the person consider the MLS or WFHG necessary? Does anyone have anything other than a wild guess? Does anybody know what the stock HG's limit is (assuming it is fresh and not 20 yrs and 200k miles old)?

Chris White

Nope, the stock studs are not a torque to yield fastener so they will return to original length (elastic deformation vs inelastic deformation).
Even if they were a torque to yield type that means that they don’t return to the original length, they still some elastic properties.

Chris White

Fen

Chris, I think something in the middle is probably true. If they were fully elastic back to original length then they'd be reusable. Also even though Raceware/ARP etc. are not designed to stretch they will be slightly elastic as well.

Max, exactly. I just don't think the WF has any place, although the idea that it's ideally suited to a o-ringed head might be a change to that.

macnewma

Fen, I see exactly what you are saying. I also don't know about the validity of the WF with or without an o-ring. I know that o-ringing is popular in drag cars pushing very high horsepower, but that doesn't mean it is suitable for us. I believe the WF ring gives the o-ring the width needed to bite in the ring.