pt 425 robin engine pipes glowing

[Rivco]

A couple of questions....

1. I measure the existing stubs between the flange and the square manifold on the PT muffler as 1" OD, which probably means 3/4" pipe (rated by ID). Did you have a problem fitting 1" pipe on the flanges and still getting bolts through? Obviously bigger is better for this application.
2. Why did you use the 1" to 1 1/4" 90 degree elbow instead of just keeping it at 1"? And where did you find butt-weld 1" to 1 1/4" 90 degree elbows?

Thanks... just trying to follow in your footsteps here.

Tim:
The short nipple I welded to the new exhaust flanges was 3/4". I then connected that nipple to a 1-1/4" to 3/4" std. cast 90' reducing elbow. Then I attached a 6" 1-1/4" nipple to the elbow. On the other end I added a 1-1/2" to 1-1/4" std. cast 90' reducing elbow. The elbow was positioned just outside the engine cover. I then added a short 1-1/2" nipple and welded that to the Glass Pack. The shortest Glass Pack I could find was 12" with a 1-3/4" inlet and outlet. Hence the reason for increasing the pipe size. I looked into using seamless butt weld fittings but the cost was to high ( especially the 90' seamless reducing elbow ), But if I were to do it over again I would bite the bullet and go with Schedule 10 butt weld fittings and pipe. The schedule 40 pipe and fittings is over kill for fabricating a dual exhaust system. Hope this Info. helps

 

[Marks481]

But if I were to do it over again I would bite the bullet and go with Schedule 10 butt weld fittings and pipe. The schedule 40 pipe and fittings is over kill for fabricating a dual exhaust system. Hope this Info. helps

rgr, I appreciate your insights on building this.

I think I will probably go with schedule 10 butt-weld piping. $7 per elbow isn't too bad since I only need 4 (except for the extra 3 that I will slag when doing the welding... haven't pulled out my torch in a couple years... will have to go get some argon before I start).

I am still wavering on two vs one muffler. I think I will start with just trying to fabricate a decently smooth header feeding into one muffler. If I don't like the result, it will be easy enough to hack it apart and go with the dual muffler setup.

Looking at the stock Robin side discharge header, it looks like it would be better to start from scratch, since that header does an un-neccessary upward 3" jog... where the PT application would allow a straight discharge to the side.