After making 4 exhaust for this airplane this works the best, extreme silence, excellent performance.

Free hp is available in a good exhaust system. I have operated with the cast iron manifold that comes with the engine but it is heavy, about 10 lb. a small section of pipe and using a Suppertrapp stainless muffler 2" id, 4" case 18" long less then 6 lb. with discs, total 18 lbs, it is acceptable for noise. Performance only better then 14" exhaust stacks.

I also experimented with a muffler within 3" from the engine (very quite), about 280 cubic in. in volume. Performance was 75 engine rpm better then the cast iron manifold. . Using 16 gauge mild steel sheet metal 12" x 20", drilled four 1.5" holes to match the cylinder head using a bi-metal hole saw on the drill press, rolled the sheet to make a tube welded the seam, squashed the tube to clear the cowling, (no longer round), made end cups and welded them on. I had spare exhaust flange, welded four 4" long by 1.5" round tubes to this flange then welded the muffler to the flange.

The muffler was bolted to the engine to determine the place of a tail pipe at the center of 2 and #3 cyl and drilled a 1.75" hole. The 18" tail pipe was also welded to the muffler. A brace from the tail pipe to the engine connected (bolted) to keep the vibrations in check. No baffles just an open chamber, the hole thing was less then 7 lb., in 60 hours of flying #4 cyl burned a hole in my cowling and caused a fire, this was after take-off at about 800 ft or less, landed all OK, I almost made it to Oshkosh. Today I would use stainless to builder the muffler.

Engine coolant temperature was about 7° F. higher when operating with this system.

This was a good time to try 4 stacks, since the cowling had a hole for number 4 cyl and I needed to continue my trip as I only need to drill 3 more holes to complete the trip to Mecca, then 600 miles home. The burnt muffler had to stay in Aupum WI. Don't try this; it is extremely loud very fatiguing even the engine will not like it.

When I got home I tested four 14" long stacks pulling my Maple tree with the big fish scale (my wife does the reading), worst case possible for hp and thrust.

A simple header, 4-2, 2-1 works well, the engine becomes happier, and when I replaced the cast iron manifold with this type of collector I gained 200 rpm on the engine. Built by Gary Wolf, thank you Gary.

My system was made of seamed (welded) mild steel tubing 16 gauge, don't use the muffler shop stuff it has aluminum it difficult to weld, that is my opinion.

This system is 31" long plus the 18"Suppertrapp, primaries 1.5" x 12" long , connected to 1.75" x 9"secondary into a "Y" into the 2" id SupperTrapp.

4-2, 2-1 Tuned exhaust, primaries 1.5" x 32" into secondary 1.75" x 9" into 2"OD "Y" 6" long. This gained 150 engine rpm on top of the 4-2, 2-1 short system, this was all tested with the same prop same setting pulling my Maple tree. Weight 15# no muffler.

Muffler 5.5" diameter by 22" long 2" outlet and inlet with no guts just an open chamber, quite at idle and up to 3000 rpm, noisy above and at 5000 ranges, it was ringing.

After flying for a couple hours, I cut open one end and installed a perforated core rapped with stainless and steel wool, I was happy, extremely quite, airplane needs a horn to move on the ramp. This was made from 304 stainless. Next step is to make a stainless header this will save weight.

You will fly more and longer if your engine installation is quite and people on the ground will be happier! Since I live on my owner airstrip my neighbors go out their way to express how they appreciate my quite airplanes.

Look for a local racing shop that builds their headers. Remember you are looking for mandrel bent pipes not the automotive muffler shop bends. The 32" tune system that I built; my friend Gary Wolf sold me the following:

Chassis Shop Performance Products Inc., 1931 N. 24Ave., Mears, MI 49436, www.ChassisShop.com, 1 800 530 9494

Making exhaust flange. You will need steel bar, hot or cold rolled 3/16" or 1/4" x 4" wide by 12" long, using the factory gasket as a pattern, I machine (I used a milling machine) one may use a drill press, lots of filing and grinding or. If you have access to a Dillon torch it will be a piece of cake, I'm sure that a regular cutting torch will work, possible plasma cutter. Since the cylinder head port is not round one needs to make 4 short pieces of 1.5" round about 1.5" long to convert the rectangular port into round. Using a bar about 1 square, about 5" long pinched in the vice (envil). One inch working area and a small ballpean hammer with practice you will end up with rectangular adapters, then weld them to the flat flange, caution check the sides of the flange to weld on.

A metal band saw is nice to make cuts on pipes in particular the bent ones. It is not difficult to create a header, you if have access to a small MIG to spot weld the joint as you assemble is the best. If not, using hose clamps and small 1/8 by 1/2" strap bar to hold the position as you tack-weld, it will work out. Trimming of the pipes may be done by filing, grinding or even a pair of aviation metal snips.

I used oxygen acetylene (gas welding) to weld my mild steel collector, if you're a good welder and a good fitter, you will be able to fuse the pipes together with out filler rod, I used mild steel rod. MIG will probably work; some people prefer TIG.

Last notes: A four into one is not as good because it operates in a narrow rpm band.

32" tuned system dropped the fuel burn also; it helps evacuate the combustion chamber, the cylinder fill up with a good charge of air/fuel.

Try to join the pipes with out sharp bends or steps in the pipes, you want a nice flowing system with out obstructions.

jim@nessaaircraft.net

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