Racing Beat sells the early style 76-80 exhaust gasket with it's 12A RB systems for the 81-85 12A-powered FBs.

The early style gasket is shown below on the left and the stock 81-85 exhaust gasket is on the right.

The stock gasket is actually a bit cleaner fit to the RB header flange, with a little trimming it could fit the flange just about perfectly. On the other hand, the early style gasket is a bit undersized in some places, although not enough to make a difference I'm sure.

The only other difference I can see is the early style gasket has a beefier lip around the main exhaust port on one side (top pic) and around the auxiliary exhaust ports on the other side (bottom pic, the smaller holes, not used with the RB header).

Also, if the beefier lip on the early style gasket is preferred with the RB header, why and which way should it face, toward the engine block or toward the header flange?

The instruction sheet provided by RB doesn't say anything about this.

Incidentally, the 81-85 stock gasket, at $17, is about half the price of the earlier 76-80 gasket at Mazdatrix (http://www.mazdatrix.com/e6.htm).

Thanks!

 

It shouldn't matter. The little holes are for the air injection ports, since airflow to the thermal reactor goes airpump => ACV => heat exchanger => extremely expensive double-wall downpipe => passages in the thermal reactor => those ports in the exhaust gasket => passages to the exhaust ports in the engine.

You're eliminating all that by putting the header on. You MAY POSSIBLY have an issue with exhaust leaks if you use the late gasket on the early engine if the exhaust gases work down through the passages and burn through the gasket. But probably not, since there is no airflow so exhaust gases shouldn't ever get there in the first place. They'd have to push the dead air out first.


Personally, I never had terrific luck with any gasket, I just use a bead of high-temp silicone and call it done. I've also used Right Stuff with success.

Right Stuff is like Red Hot. I put that s- on everything

 

I have used both gaskets with success on 12a cars from 80-85. I have also cut them in half for 13b use... both the header and the gasket...


Isaac

 

Do your rotor housings have thermal reactor ports?

 

Sounds like the gaskets are interchangeable, as long as a good seal is established. Nothing special about the gaskets. Good stuff guys, thanks for your expertise.

Jeff I have some housings with thermal reactor ports, what I call "old school" from '76-'80 12As, and some without, the "new schools" from my tear downs of '81-85 engines.

This does bring up the interesting question of what do you do with those thermal reactor ports if you're installing an RB header. Especially if you want to mix and match an old school housing with a new school housing in the same engine.

I guess like peejay says, the reactor ports will be blocked off by a new school gasket backed by the header flange, or at least by the header flange in the case of the old school gasket, so it shouldn't be a problem, especially if lots of hi temp gasket sealer is used in that area. But then with the new school gasket there wouldn't be that special rim to seal around the reactor port opening to make a tight seal, so maybe that's why RB goes with the old school gasket when they sell their systems, to avoid problems with installation on old school 12As.

FOP, what's a good way to cut those exhaust gaskets to get a nice clean cut?

 

I would use a sheet metal shear to cut them up. They're pretty tough.

 

That's what I was thinking too, but I think it will leave a burr and maybe even twist the mettle. What about a jig saw with a metal blade and good backing? Cleaner cut, maybe?

 

Tin snips are what I use. Then a grinder to trim down any burrs.

Do not use any kind of goop to seal the area. These gaskets install dry.

And use the gasket that matches your rotor housings.

 

Tin snips it is.

Jeff you're contradicting the RB header installation sheet when you say to install the gasket dry, they recommend a high temp silicone sealant.

And peejay recommends the same in his post above.

But since you're almost always right, let me ask what the advantage of a dry installation would be?

 

Tin snips or a thin cutting wheel on the angle grinder, either way will need a little deburring with the grinder. FWIW I have always installed them dry, and have a few with 50K Mi+

Isaac

 

RB is often wrong. Remember what they said about the so called 'high volume' oil pumps found only in the GSL-SE? They're wrong. Every 83-85 12A with a beehive has the exact same oil pump, as do all modern nitrided R5 engines; 12A and 13B. So there's one example. I have others but don't feel like typing a lot right now.

So you can intall them dry. If you do use RTV or whatever, just know that it will shrink and harden from rotary exhaust heat and will leak worse than if it was installed dry. And yes I've done several high mile setups that don't leak which were installed dry. The gaskets look about dead but didn't leak. Or if there was a leak, it was slight and only lasted that long because they were installed dry.

 

Composition gaskets should never be installed with sealer because composition gaskets work by adhering itself to the metal.

Jeff, my experience with high temp RTV says it works just fine at the engine. I do blow it out at the pipe flanges when I get the exhaust hot when running it lean at the top end, but what can you do. The engine flange doesn't get nearly as hot as the pipes.

 

i've always used the stock gasket, and never had any trouble at all...

 

That's what I'm thinking, for RB header installation on an 84/85 12A the stock gasket is the way to go.

Also I'm thinking the silicone sealant is something the shops use to impress the customers.

Looks good going out the door, 6 months later you got some really fried waffles that ain't doing their jobs.

Kudos to Tim and Jeff, no goop for me! I'm going dried installation with the best gasket that fits, like the Rotary Gods intended.

 

I used the one on right with rb header on my 85 success.. Also used on 12a turbo 8 psi on 35r success but only for about 2-3k miles...

Never used any sealant since the highest temp copper one I've seen is rated at 700 deg and rotary exhaust can be about a thousand degrees hotter than that... I know the engine block is oil and coolant cooled but still..

Has anyone had issues dry and reinstalled with sealant and had success? That would be a better determination..

 

Good to know Mr. Z, I'm thinking the stock gasket is better for the 84/85 RB installations as well. Better fit, more happiness.

And since the sealant cooks, it makes sense that the dry installation is the way to go. Less mess.

 

I put a rb header on my gsl-se about 2 years ago i reused the original gasket and it leaked bad (it wasn't in the best of shape as it was the original) I put a stock gasket on it dry i first wiped down the mating surface of the header and block/keg with a rag and some brake parts cleaner to get rid of dirt and grime from age. I put on the stock gasket DRY and tightened it evenly. I then took it for a good spirited drive and came back and checked the bolts again (just to be sure expanding metal and all) they were a tad bit loose tightened them up and been driving daily for about a year and a half now total and no exhaust leaks at all. Couldn't be happier.