4 stroke exhaust extension

You're better off just swinging the muffler around and having it exit out a different part of the cowl, even if it does not look as streamlined. Or rotate the engine mount to allow the muffler to exit better.

4-strokes, especially if using smoke, are particular about back-pressure and the stock muffler offers the best chance of good engine runs.

A .56 4-stroke can make good smoke but everything needs to be just right. Increasing back pressure with a muffler extension then squirting smoke oil in will cost you, perhaps dearly in engine performance.

There is some info about smoke and small 4-strokes on my web page:

An aluminum or brass tube, sized to just fit over the stock exhaust with a slit in the tube (easy to cut with either a Dremel tool or a Zona saw) as long as you can make it and still be slid onto the straight portion of the stock exhaust tube. Then get a small automotive type hose clamp and clamp the extension tube to the stock exhaust tube. Shim around the exhaust extension tube with sheet aluminum to build up the diameter if you can't find a hose clamp small enough. JB Weld will NOT hold on a exhaust system extension.

Right now it's looking like the exhaust isn't even long enough for that. The plane (AK Models PItts) has a very strange construction in that it doesn't have a soild firewal, but more of a half firewall on the top and half, further back, on the bottom. Horrible description, but I have some pics.

I was going to use a tube that was as much bigger than the stock opening as I could get and still secure it. I was hoping to avoid any back pressure problems by using a large piece of aluminum tubing. I was even considering a piece of very large tubing, the same size as the bigger part of the muffler body.

I've had the plumbing pic from your web page hanging up for awhile in fact.... The new OS 4 stroke mufflers (F-4040) look more like 2 stroke mufflers than "traditional" 4 stroke mufflers. Supposedly this is because of noise restrictions in Europe, but everybody has an opinion...

My main reason for wanting the extension is so that the exhaust doesn't go up inside the body of the plane. I need to get it back further, past the opening in the bottom of the body, to make sure that doesn't happen.

Thanks, Steve

Can you modify the construction to close the opening?

In message , Steve writes

I think Mick Reeves a UK scale champion and model kit maker may sell the sort of tubing you want.

Have a look at the site

HTH

Potentially, but it'd be a lot of work. That's where the smoke pump is mounted now. I have pics if you (or anyne) want to take a look at the construction...

Steve