Robin Exhaust

[Gravy]

As promised, here's my experiment with exhaust modification on my PT 425 with the Robin engine.

I don't have a very good photo of the original exhaust. Here's what I do have. It was taken to show the proximity of the muffler to the engine cover where the fuel pump used to reside.

 

[Gravy]

I bought the side mount exhaust kit listed in the back of the parts manual available on the Robin site.

The new exhaust manifold required modification to exit through the existing cutout in the engine cover and to permit mounting of the muffler. I first made a cut.

 

[Gravy]

Next, I welded the threaded end of a 1" pipe nipple to the new manifold. I screwed on a couple of elbows to bring it out through the engine cover cutout.

 

[Gravy]

The other end of the nipple was welded to the new manifold flange. I cut the muffler bracket apart and rewelded the pieces at a different angle to attach to the tub.

 

[Gravy]

Looks like I didn't succeed in attaching a bunch of photos, so I'll try again. They should be pretty self-explanatory once you've read the text.

 

[Gravy]

A few more:

 

[Gravy]

Then I added the heat shield and tailpipe.

 

[woodlandfarms]

Pretty cool. I saw a note earlier that someone did not want to pay for powercoating. Based on my car, Powder coating really reduces heat. It is a totally worthwhile investment if you are having heat issues. Also, there are few wraps out there (they come out the motorcycle world but are now in performance shops) that work well also...

Carl

 

[BobRip]

Looks good. How do you like it? Quieter, more power?

 

[Gravy]

The results: The new muffler is a little bit more quiet and has a mellower tone than the PT muffler. It's about the same size as the PT muffler. I had expected it to be considerably larger and quieter.

I haven't noticed any difference in the power, and the backfiring hasn't changed. The location of the new muffler seems to be less protected than the factory one, as it's collected several dents in the heat shield since the photos were taken. This may also be due to the fact that the heat shield is thin sheet metal, rather than the heavy-wall material of the original muffler.

If I were going to try again, I would try to fabricate a system with fewer bends, and find a small automotive muffler with 2 to 3 times the internal volume. If I knew a motorcycle exhaust fabricator, I'd get an equal length header with fairly long primaries to try to improve low-end torque. As it is, if and when the muffler needs replacing, I'll probably retain the current manifold and work up something with a car muffler.

In summary, I'm not terribly displeased with the results, but it probably wasn't worth the cost and effort.

Gravy