New Homemade Exhaust for the Sub 2.2L

bmoore2156

Active Member
Joined
Dec 21, 2008
Messages
1,005
Location
Siletz, Or
Aircraft
Converted RAF
Total Flight Time
300 hrs in my RAF
I got the idea after looking at a Sparrow Hawk gyro at ROTR.
The original RAF exhaust has cracked a few times and it was time to do something different. I made a pair of these. One of them has a nut welded on for the o2 sensor. They are made from 304 SS. I rolled the main can out of 16G sheet metal. It's 4'' dia. I used 1.5'' tubing for the pipes. The inlet pipe extends down about 3/4 of the way through the can. The outlet extends up about 3/4 the way up the can. They seem to be fairly quiet and are making good power.
Brad
Sorry guys.. I cant figure out how to rotate the photo right side up on this Mac. They say their easy to use???
 

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Very nicely done Brad!

Very nicely done Brad!

You stepped around two challenges we had with the muffler Smokey built for the Predator and we had problems.

He made the first one out of 22 gage stainless to make it light and after several cracks developed he made a second one out of 16 gage and we haven’t had any more trouble.

The other thing we did badly was to make the muffler oval because we were trying to fit it in a space so we could get better airflow to the propeller. We ended up with a flat section to get the volume we needed and that exacerbated the challenge with the thin material and it would oil can each time the engine would fire. It is all a compromise.

The Lycoming is more challenging than the Subaru to muffle because the cylinder displacement is so much bigger we need more volume to manage it.

Running the tubes into the chamber the way you did is cleaver because it acts like a one way valve.

The volume might be a little small for best performance but it looks like you have come up with a first class solution.

Thank you for showing us a job well done, Vance
 
Vance,
Thanks!
I was worried about the small size. The best way I could come up for testing was putting them on and running it wide open throttle, then comparing it to the old muffler.
They are within 10 rpm according to the stock RAF engine tach.
I also forgot to mention that I built the top and bottom out of 12g because I was worried that the constant pounding from the exhaust would crack it. I tend to over build things. It's a wonder it still makes it off the ground!
My main concern with more length was that the vibration would crack it. The longer they are, the more force from vibration it will see.
I havn't weighed them yet, but they feel about half of the weight of the stock setup.
Brad
 
Brad,

That's a great looking muffler and excellent workmanship.

What's the dimension of the can top to bottom?

How much pipe sticks out top and bottom?

Thanks, Noe
 
The cans are 4" top to bottom. 4" dia. 2" from the flange to top of can. 2" of pipe hanging out of the bottom.
Brad
 
Nice workmanship, but a horsepower robber. Small diameter equal length primaries, an efficient 4 into one merge, and a carefully selected collector/muffler is widely preffered.:sorry:

I am interested in learning. What would be the best way to "tune" a small exhaust like this? I just tried to build it small, plenty of flow, light weight and hope it performed well for power and noise reduction. It's quiet and the engine makes the same rpms at wide open throttle as before. Where should I go from here? The big bulky ones that sit under the engine are prone to cracking out and are heavy.
Brad
 
Brad, if it turns the same prop with the same pitch settings the same rpm, then you ain't lost any power!

There may possibly be more power available with some fancy tuning of pipe lengths and chamber volumes, but ... that's a "bird in the bush". :)
 
Nice workmanship, but a horsepower robber. Small diameter equal length primaries, an efficient 4 into one merge, and a carefully selected collector/muffler is widely preffered.:sorry:

Ok guys, after more testing, I don't think my stock muffler is making as much hp as a tuned exhaust could. I think that's the reason the engine rpms were close on the test. I called up delta cam and talked with Ken. He claimed that you need 26" long primary pipes to make the best power. I am all for making more power, so back to the drawing board I go. Let's hear your opinion on the perfect muffler! My next idea is a rotary style muffler. Maybe a 8" round x3" thick muffler. The primaries would enter through the side and the exhaust would flow in a circle until it exited through the end.
Need ideas guys!
Brad
 
Hi brad...
A design I know that works very well (along the circular design you described) is a pair of old freon recharge cylinders. Whack the tops off, weld together. Make a reinforcing plate (times 2) for the pipes going in.
You only need one out bound of a slightly larger diameter (I had 2- 1.5" going in...a single 1.75" out).
It's important that the In & Outs are mounted similarly around the outside circumference.
I used stock Soob manifolds...chopped @ about 12"...continued with custom pipes...mounting to the cylinder toward the ends of the cylinder...out pipe in the near middle of the cylinder.
You should not have any pipe sticking inside, it will screw up a nice circular swirling flow.
I found that the sound is amazingly quiet...back pressure is appropriate...and power is not diminished.


M-M.
 

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Brad, I have seen a website for a company that offers pre-welded 4into1 merges, and mandrel bent tubing pieces. I will try to find it and post it. As far as the muffler, I would use a proven design, rather than a freon can or something. A stock muffler from a modern superbike would be ideal. Some are even carbon fibre/aluminum, and should offer the most performance. Check Craigslist, as most guys replace their stock system with aftermarket.
 
Earthbound.... I would be interested in the web site your talking about.. I need some 1.5'' mandrel bent 304 SS 90's.

I removed my stock exhaust because it had cracked. I was going to weld it up yesterday but when I got it in the shop I noticed a rattling sound coming from inside. I got the piece out and it was part of the muffler that had cracked inside. I decided not to fly on that muffler anymore. I headed for Napa and got some exhaust pipe so I could throw one together just to get back in the air. I have cut into a stock exhaust before so I had a good idea what it looked like. I replicated the stock muffler but I used aluminized tubing and did not put any flex joints in. $60 bucks at Napa and a couple hours of work got me flying again. I was making good rpms with this muffler and it is very quiet.
The way the old flex joint worked is it put most of the weight of the muffler on the one side that was welded solid. This was the side that cracked out. I will keep a very close eye on it for cracks but I suspect that with good support from both sides and using the aluminized tube that it will hold together well.
This should keep my flying till I can get a stainless one made up and tested.
Brad
This picture is while I was welding up the internals, before I slid the 5'' pipe in place.
 

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