Genset exhaust tip

[Jim Blackwood]

This came up at the Nappanee gathering and I think could be helpful for anyone who would like to try it. Those stacks were popular, I guess they are on their way to becoming mandatory almost and also seem like they may help some with the noise but a few guys on my sports car forums have been experimenting with 1/4 wave traps to control drone at highway speeds and because a genset runs at a constant speed it would be a great way to get rid of the "pops" of the individual cylinders firing. Done right it can be extremely effective.

The idea is to put a T in the exhaust pipe and add a stub tube with a closed end. The sound wave travels down the tube, bounces back and cancels out the next wave. Properly called a Heimholtz filter it was developed for microwave (radar) technology but applies equally well for sound waves and exhaust pulses.

As a starting point, Phil McConnel used a pair of 32" traps to totally eliminate a bad drone at 1750 rpm on his LT1 SBC V8. A 4 cylinder genset operating at higher speed would use a shorter tube, for example if it ran twice as fast it would need a 17" tube. So there is your likely range. Best practice would be to use telescoping tubes and clamp it after you had adjusted it for maximum noise reduction. For a smaller number of cylinders it would probably need to be longer. I'll know more about that after I've got my generator operational but that may be awhile.

Also best practice would be to put the resonator as close to the engine as is practical. From what we've seen it still works as the last element but it works better if there is a muffler behind it.

So there you go, have fun experimenting and let us know your results.

Jim

[windtrader]

Dang Jim,
I swing the the other way. I leave my Jakes on all time and always smash the pedal to the metal in anticipation of then let off and hearing the lovely sounds of the Jakes slowing the bus.

[Jim Blackwood]

In the campground?!  Dang! I think you're my new Hero!

Jim

[chessie4905]

That would be more of an issue with a gas engine.

[Jim Blackwood]

Should work equally well with either type, the trap doesn't know or care what the source is. Also I didn't mention it but the final configuration does not have to be straight as long as the centerline distance is the same. Phil curved his up around the differential to get them out of the way. I could see making a loop inside the genny bay if needed. It would radiate more heat, but you could also ceramic coat it to cut that down.

A two cylinder running at the same speed as a 4 would need twice the length I'm pretty sure. 3 cylinders would be somewhere in between, so a single cylinder might need a folded chamber to get the necessary length into a compact enough package. I think it would be pretty easy to test it out. If you guys wait for me it is going to be awhile though and I think my genny is a 2 cylinder. We did find that using a tube the same size as the exhaust is more effective.

Jim

[windtrader]

Jim - I do but the jakes dissble when speed slows to under 5-10, just not enough pressure to kick them in. The regular 2 stroke sweet growl is enough to get most heads turning.

[luvrbus]

You can drill 1/4 inch holes and make a cross with bolts in a straight pipe and get the same effect, I never had a muffler on my generators and all you could hear was the air intake   

[Jim Blackwood]

Um... no? I'd hate to hear how loud your air intake is.

Granted some engines seem to run quieter than others but with no muffler at all any of them are loud. I don't think there's any getting around that, not even with 1/4" bolts.

Jim

[luvrbus]

Um... no? I'd hate to hear how loud your air intake is.

Granted some engines seem to run quieter than others but with no muffler at all any of them are loud. I don't think there's any getting around that, not even with 1/4" bolts.

Jim

They done it on Harleys for years too for the look of straight pipes 

[RJ]

Granted some engines seem to run quieter than others but with no muffler at all any of them are loud.

Jim -

Years ago there was a fellow in Hanford, CA, with a 4104 that had a clever idea for his genset's exhaust - he used one of the flatter Corvair mufflers off a 140hp engine mounted to the bulkhead between the duals, with the tailpipe exiting right in front of the driver's side tires. Was extremely quiet to the point you couldn't even tell the genset was running, at least until you got up next to the old HVAC compartment, where the remote radiator's squirrel cage blower made more noise. But a Corvair muffler? Who would have thought. . .

Some of those old pioneers in the conversions hobby, the ones who converted 4103s, 4104s and 4106s back in the late 50s and during the 60's, really came up with some unique ways of solving problems, mostly along the lines of the KISS principle. That seems to be a lost art nowadays, everyone's going for the glitz, glamor and automation.

[luvrbus]

People never pay attention to Kubota's specs for a exhaust system, you install a long pipe system without in larging the size the back pressure from the small pipe will make it run hot and shut down because the KW's drop,Same happens on the Aqua Hot   

[Jim Blackwood]

I'm not saying it would replace the muffler, just another way to decrease the noise level. It's a way to specifically target a specific part of that noise. Now just about any IC engine you come across is going to give you that "pop..pop..pop..pop..pop.." sound at the exhaust pipe, even with the best of mufflers and exhaust systems. They will also usually have an element of drone to them. If your genny is so quiet you can't tell it's running obviously you have no need for this, but many and dare I say most of them aren't quite that silent. So it's a pretty simple thing to try and we've seen them work very well on a couple of cars now. Of course if you'd rather use 1/4" bolts and a Corvair muffler I'll not argue with that. I've got a big canister muffler I've been thinking about using that was pretty quiet on a big Toro lawn mower. But I look at it this way: If the noise pulse has already been cancelled the muffler can do a much better job with what's left.

Jim

[luvrbus]

I'm not saying it would replace the muffler, just another way to decrease the noise level. It's a way to specifically target a specific part of that noise. Now just about any IC engine you come across is going to give you that "pop..pop..pop..pop..pop.." sound at the exhaust pipe, even with the best of mufflers and exhaust systems. They will also usually have an element of drone to them. If your genny is so quiet you can't tell it's running obviously you have no need for this, but many and dare I say most of them aren't quite that silent. So it's a pretty simple thing to try and we've seen them work very well on a couple of cars now. Of course if you'd rather use 1/4" bolts and a Corvair muffler I'll not argue with that. I've got a big canister muffler I've been thinking about using that was pretty quiet on a big Toro lawn mower. But I look at it this way: If the noise pulse has already been cancelled the muffler can do a much better job with what's left.

Jim

Most new diesel generators today have turbos with no mufflers,the new small diesel generator are just easier to deal with the noise,the older Perkins powered no way can you make one quite.Exgaust noise is the last thing you worry about a generator, my QT 12500 Onan in the hush box does not have a muffler all is has is SS flex coupling with  small deflector inside the coupling about 2 inches long with a twist  and it is quite
   

[chessie4905]

Just plumb it into engine exhaust.

[Van]

Anyone try and plumb a Kazoo in the exhaust?