Exhaust Flange Thread Size?

[edwardc]

A quick question.

I'm about to rebuild my exhaust system. Does anyone know the diameter and thread pitch of the internal threads in the MMI exhaust flange?

[Dave Neptune]

Flange

Ed, I think it is a 1 1/2" NPT.

Dave Neptune

[sastanley]

Sorry Dave - 1 1/4" NPT. I must have bought every piece & combination of 1.25" pipe from about 3 different stores until I found a good combination for my hot section.

Ed, check out my thread from last year.

http://www.moyermarine.com/forums/showthread.php?t=2974

[hanleyclifford]

Ed - 1 1/4" is the correct answer for the stock flange. But if you want to upgrade your system, the flange can easily be opened up to 1 1/2" for a huge gain in performance. Regards, Hanley

[edwardc]

Ed - 1 1/4" is the correct answer for the stock flange. But if you want to upgrade your system, the flange can easily be opened up to 1 1/2" for a huge gain in performance. Regards, Hanley

Thanks, guys. I got in there with a caliper and confirmed that it's a 1 1/4" on the flange.

On my existing system, it has a short nipple into a bushing that takes it up to 1 1/2, and the rest of the plumbing up to the muffler is 1 1/2".

Another question.

Having fought with too many rusted-solid exhaust systems, and broken off many bolts & studs and had to hacksaw things apart, I was planning to do this system in red brass & bronze. But I found that McMasters has the same parts in stainless steel for almost the same price.

So my question is: Ignoring price, is there any reason to perfer one material over the other? I'm guessing that stainless is stronger, but brass & bronze are easier to make a tight connection. Is one more corrosion resistant in a hot, salt-water environment?

[hanleyclifford]

Ed - Interesting that your system goes up to 1 1/2" via a nipple and bushing. That is exactly how I did my first upgrade when I started re-engineering exhaust systems. I currently have a flange opened up to 1 1/2", then a close nipple, then a bushing up to 2". It was an evolutionary thing. Your decision to go to bronze or stainless is a new one for me. I know that stainless does not like an anerobic environment so if you are planning to wrap it you might get some corrosion. Bronze on the other hand has a very different rate of expansion from cast iron so you might get some fitting issues there. What ever you decide to use, I would go to studs and nuts on the manifold.

[ndutton]

Edward,

You might want to review this thread from a few months ago.

http://www.moyermarine.com/forums/showthread.php?t=3995

[67c&ccorv]

The only thing that I would say about stainless is that some grades of the stainless steel stand up to the continual hot/cold expansion/contraction cycle better than others.

I would look through a properties chart and select based on that charachteristic over all else in this application.

Cheers!

[David Masury]

I am chuckling

for a huge gain in performance

... and then we ask it to push water out a long tube.

David

[67c&ccorv]

All 30HP of it!

[Dave Neptune]

30?

In a direct drive A-4 I doubt you'll ever see 30 HP, maybe a lil over 20. You can't get the RPM's for that much power.

Dave Neptune