One of my biggest pet peeves are exhaust leaks. Single turbo rotaries as we all know are so difficult to seal up exhaust wise IMO.




My current issue is the manifold to engine block. Specifically, my brand new* turblown shorty cast manifold to brand new housings. Back when I had bought a new mazda engine, I noticed my shorty manifold was cracked and got a new one. Once everything was installed I immediately noticed a terrible exhaust leak from the inner edges of both ports. . Turbo came out, new cosmo gaskets later with new inconel hardware torqued down and still the leak continued. I drove around a bit and again turbo out, same leak. The manifold is dead flat when checking with a straight edge and light. This time painfully I used copper gasket maker which I know will probably burn out eventually but it seems better for now but not perfect. Before it sounded like an open dump with throttle.

Are Mazda housing tolerances off? It seems this could be engine block level related which is weird to me. Some rotary OG's talk about using two gaskets sandwiched together, others swear by the copper RTV, some say it is what it is.

How are you all managing your exhaust leaks?

Cheers,

 

Rotor housing dimension (or Mazda QC), seems to have declined, but wouldn't expect the exhaust outlet face parallelism to be out.

If you suspect something, I'd probably blue mating surfaces, bolt up the manifold alone sans gaskets, and see if there's anything weird happening in that contact area.

Not sure it makes a skerrick of difference, I've always done the opposite of what you've done, the flat side of the gasket facing the manifold and the side with the folded edges towards the engine.....touch wood, never a leak in that area.

 

I don't think Ive ever had this issue with new stuff torqued down. I have had issues with the stuff loosening up, which hopefully i've cured with locking hardware. Something has got to be off for a problem that severe.

 

Check for exhaust sleeves with wallowed out or broken pins into the rotor housing. If the exhaust sleeve is loose, something is wrong and sealing is compromised.

I never had an issue with engine to manifold sealing in 24 years of autox/hillclimb/sprint racing. Just manifold to turbo gaskets blowing out.

 

Working in a machine shop for a few years, I can tell you that a straight edge with light won’t always cut it. It gives a general idea, but you need it to be perfectly flat. I’d suggest going to a machine shop and getting it surfaced flat. You’ll be surprised how warped something is after the first pass of the mill. If you’re not already using a stud and nut setup, switch to that instead of just bolts for even clamping force. Also, after a few heat cycles, go back and re-torque everything with a torque wrench. This should get rid of your leak. If not, then you’re in a simulation or something.