mirwin

My Feedback: (1)

Can I run a 4-stroke without the muffler? I can get better scale looks on my warbirds if I can use only the exhaust pipe. Engines I'm most concerned about are Magnums and OS's.

Thanks,
Mike

nickj

Most fields have noise restrictions. Technically, you don't have to run a muffler on a 4-stroke.

mikeboyd

Many of the older 4 strokes had exhaust pipes without a muffler. Depending on your application, you might be able to find an exhaust pipe that would fit your unit. The downside of this is, that without a muffler you may have a problem with tank pressurization and engine reliability. The newer 4 strokes put out more power than the older ones and are designed to run with a muffler and tank pressure, unless you are running a pump..

Good luck with your model.

khodges

My Feedback: (1)

Don't know which 4-stroke you're using, but Saito has a flex-pipe available. Not cheap, but does allow a lot of flexibility in fitting things inside cowls, etc. They are primarily made for the twins, but work with any of the singles. It is louder than a muffled engine, but not very much so. I use one on my WACO and seem to have plenty of pressure for the tank; I just put the nipple pretty close to the exhaust port. You can order them through Horizon, you should get the elbow also.

I just noticed what you said about OS and Magnum. Don't know about Magnum, but OS also has a flex pipe.

tailskid

My Feedback: (34)

I flew a Midwest Citabra with a Saito 91 for three years without a muffler and no one noticed as it was enclosed w/i a cowl.

Jerry

flipstart

I have posted this exhaust mod on another forum-but on my Saito 91-to keep exhaust in the cowl and exit out the bottom-I cut the extention pipe from engine to muffler in half-brased on a copper 90 then a 1/2" brass tube that extends thru bottom of cowl. I added a piece of brass tube inside the 1/2" tube for some back pressure-put pressure nipple about halfway up on the exhaust tube. Engine runs good-no muffler-surprisingly noise is no louder than with a muffler-nice throaty sound.

You may need to add a Z bracket to support the exhaust tube and prevent vibration. I also added a short piece of flat brass across bottom of copper 90 for extra support. On muffler pressure I got a "slow stream of bubbles" by dropping pressure line in a cup of water.

Not sure how Magnum or OS attaches their mufflers, but it must be something similiar to Saito. Give it a try-you will love the sound. Really makes a WWI plane sound realistic.

mirwin

My Feedback: (1)

OS and Magnum exhaust systems attach like Saitos do. I actually had khodges' system in mind when I opened this forum.

I had an older OS 1.20 that wouldn't run with just the exhaust pipe, but I don't know if it was the absence of tank pressure or lack of back pressure. I sold that engine, and I now use OS 1.20 FS III engines with pumps so tank pressure is not a concern.

The Magnum .80 4-stroke is another matter. If you guys don't think I'll burn the valves, I'll try running it without the muffler, and see what happens.

In either case, I would use the flex pipe.


Thanks,
Mike

B.L.E.

It's not "backpressure" so much as it is the fact that engines tend to suck a little of the exhaust back into the cylinder before the exhaust valve closes, particularly while the engine is idleing. If the engine sucks fresh air back into the exhaust port, the fuel/air mixture goes lean. With a header pipe, the engine sucks back old exhaust gases that have had all of the oxygen burned out of them and the mixture, while it is diluted with exhaust gas, does not go lean.