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

 

[Gravy]

Bob,

The improvement in noise control is modest. Any power increase is virtually undetectable. I believe that both the noise and power issues can be improved with a better design. I may try again sometime in the next year or so.

Carl,

The wrap might be worth trying, if only to get the heat out of the engine compartment and reduce vaporlock concerns. I'm still not convinced we've figured out the real cause of the backfiring.

I still want to find more ways to reduce the overall noise level. I find both the exhaust noise and the hydraulic whine irritating. The problem I'm having is that most sound insulators are also thermal insulators. I worry about overheating my pumps and motors. I'm afraid I don't have the R&D budget for active noise cancellation...

Gravy

 

[cqaigy2]

I worry about overheating my pumps and motors. I'm afraid I don't have the R&D budget for active noise cancellation...

Gravy

I bought a generator this year to run the well pump cause we lost power for 10 days this last winter, anyway the exhaust system on the generator is surprising good but you can still hear all the racket the motor makes now.

I was talking to a rental place and their mechanic was working on a honda generator. He started it up and man was it quiet! He then removed one of the panels and sure enough, it sounded just like my generator with all the noise from the motor but not much from the exhaust. The panel looked to have some kind of material on it that canceled the noise out but i wasn't too sure how they get the heat out of the enclosure.

 

[kmaz]

Thanks for The pictures gravy. I actually just today bought some insulating wrap...kinda like a blanket. for now I plan on at least wrapping the header. I mounted a fuel shutoff valve an filter in the same exact area you moved your fuel pump to.
Kris

 

[pairodime]

I tried wrapping my header and it retained so much heat it deformed and the muffler began to sag and twist. Replaced the whole assembly while still under warranty.

Now I control the heat be keeping the fuel line in an insulated wrap and I relcocated the fuel filter to be under the fuel tank instead of next to the engine.

No sign of vapor lock problems since then.

 

[Phils]

Dang good job, Gravy!!

And after viewing your photos, I realized I could have done what you did: move the stock fuel pump and install a longer 'pulse' hose to it. I haven't had a problem using the electric pump, but I think your solution is better. Either way, getting the fuel pump and hoses away from the exhaust has GOT to help even if it doesn't entirely cure the problem.

The only other benefit I get from the electric pump is being able to hear whether it's pumping liquid or vapor. That alone isn't worth the modification IMO, as the most important thing is whether the engine runs or not.

Keep us posted when you 're-engineer' the exhaust.

Phil

 

[Gravy]

Phil,

Relocating the fuel pump improved the fuel starvation/vapor lock problem, but didn't eliminate it. I tried an electric fuel pump, which took care of that problem until the pump failed in under 20 hours. I got a warranty replacement which failed in about 10 hours. I haven't gotten around to trying #3 yet.

The pump I'm using is a Facet solenoid type universal pump from NAPA. In my former career as an auto mechanic, I installed a fair number of Facet pumps and never had a failure. The ones I used back then looked very different from the one I've got now, though. I don't have a clue why these are failing. I suppose they might be getting too hot, or the electrical power supply may be "dirtier" than on a car. I'll need to get the latest one installed before summer gets here. I hope it survives.

Pairodime,

Except on a PT, I don't think I've ever seen a muffler wrapped, just the pipe sections. It may be that the thinner metal and more complex structure of a muffler makes it more prone to heat-related distortion than a simple tube. As far as I know, the most common use of exhaust wrap is in performance engines, where keeping the exhaust gases hot can apparently give a bit of a horsepower boost. For our application, it makes more sense to me to relocate or shield the parts you want to keep cool.

Gravy

 

[cqaigy2]

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

I thought about doing the same with a car muffler too.

I wouldn't think that low-end torque would be much of a concern if your running your motor mostly at higher rpms.

Thanks for the pictures and relating your experiences with the exhaust!!

 

[BobRip]

I was at Fun Pilot's house today and bought his concrete mixer. When loading it onto my truck, I noticed that his 425 is even lounder than my 422. Has anyone made more progress in this area? I would love to quiet my 422 and am concerned that when I get a 425 it will be way to loud for my taste.

 

[SnowRidge]

Unless you are planning on buying a 425 in the near future, chances are there will be yet another muffler design in production. It's hard to say how loud a future machine will be.

 

[MossRoad]

I was at Fun Pilot's house today and bought his concrete mixer. When loading it onto my truck, I noticed that his 425 is even lounder than my 422. Has anyone made more progress in this area? I would love to quiet my 422 and am concerned that when I get a 425 it will be way to loud for my taste.

You know, I always thougth my 2001 PT425 with the Kohler engine was loud until a few weeks ago. I let my daughter mow the lawn with it and I stood back and realized it is about as loud as my neighbor's Wheelhorse and my other neighbor's Deere lawn tractors. It may be that my steel canopy just traps the noise in there with the operator, but from a distance, it is just like the rest.