What's in the RV-12 Muffler?

There are many good threads here about cutting the cowl and moving the oil cooler forward for better oil cooling. There is often much less than a one inch gap between the aft side of the oil cooler and the muffler.

That got me to thinking. What is inside the muffler? Because the same thing could be accomplished with a different or modified muffler without doing plane-is-finished-and-painted cowl surgery. Which gives me a bit of worry despite the great pics from Marty on THIS THREAD: http://www.vansairforce.com/community/showthread.php?t=111244

Look here - Basically, what if the existing muffler (or a replacement) had a big square"ish" dent in it? What would be the issues? Anyone know whats inside the muffler? Could a muffler shop do this mod? Basically cut a hole in it and patch it as shown? I haven't seen this posted as an idea. I guess it would be possible to flatten the entire front (?) rather than the "picture frame" kind of mod I show.



Bill H.
N412BR "Sweetie"

I had that very thought several years ago while pioneering the cowl duct mod. I chose the mod because it just seemed far more prudent for a number of reasons. The mod probably costs $20? That muffler was $800.00 at the time. In the end, I just could not see tearing up the muffler when I felt reasonably certain that the mod would solve the problem. Thankfully I was correct.

Another thought . .

You might take it to a TIG welding shop, but muffler shops are not at the level of skill you probably want.

Also, notice that mufflers don't have flat panels. That is because the blowdown pressure from the cylinder has a pretty high pulse pressure. Flat surfaces move vigorously and that does two things, it fatigues and breaks, and the motion make noise, neutralizing the function of the device.

Moving the cooler, and using a thermal radiation shield between the HX and the muffler would probably be easier. Then the next muffler would fit when needed.

Just my 2 cents.

It's not the cost of the mod - which would be much easier done before completion! It's the skill and doing it on a completed plane with a good repaint in the duct. I am wondering if a muffler shop would do this mod for maybe $200 or less, that might depend on what the muffler internals (if any?) look like. I like alternatives. I might do the cowl mod. It's also been mentioned that putting the modified cowl back on and getting the oil cooler in place on it is more difficult.

If I remember right the muffler is hollow.

There are new mufflers systems other OEM Rotax 912 users have that are the size of a soup can. The smaller exhaust would give much greater clearance without need to modify the cowling. It would however require a new exhaust system.

I see a new product line for Vetterman Exhaust.

Why spend a hundred or two. Moving the oil cooler 1" is simple. Cost - A few dollars plus paint. Did it last month. Van's will do this eventually, that is, if they have not done it. Scott has had plenty of proof that the change should implemented. Here is my info and the info from all that helped me. https://www.dropbox.com/sh/oh6xzctv990v2ed/Mbp73pOI-F

$fiberglass<<$stainless welding

MartySantic said:

Why spend a hundred or two. Moving the oil cooler 1" is simple. Cost - A few dollars plus paint. Did it last month. Van's will do this eventually, that is, if they have not done it. Scott has had plenty of proof that the change should implemented. Here is my info and the info from all that helped me. https://www.dropbox.com/sh/oh6xzctv990v2ed/Mbp73pOI-F

Click to expand...

My vote is with Marty--following his and Jetguy John's destructions, it wasn't that tough--and I generally dislike fiberglass work. I was able to pry the flange portion of the duct off, slice an inch off all around, and piece it back together without any major gaps in the fiberglass to fill. I haven't got things fired up yet, but, with the added inch of separation, combined with addition of the oil thermostasis unit, I suspect I will solve the Texas summer and unseasonably-cold Texas winter oil temp problems.

Hmmmm... Might get some help from my very knowledgeable-in-Fiberglas EAA tech advisor friend and get over the mental hurdle.

On the muffler, imagine cutting out the convex "window." Then instead of replacing it with a flat plate, turn it facing backwards - so it is concave facing forwards. That would be stronger than a flat plate. Re-weld with end pieces. Now there is no flat plate as mentioned by Bill Lane, but there is a bit less internal volume than you would get from a flat plats. No telling what the shock wave patterns inside would look like!

I'd be reluctant to cut the muffler shell unless I had a detailed drawing of the internal baffles and their arrangement. I assume it's an arrangement similar to an automobile muffler. I remember from teen age gear head days that back pressure can affect valve life. I guess I don't feel I'm smart enough to know what unintended consequences I would cause by cutting the muffler.

RFS - exactly why the title of this thread is what it is! So far only one response that it is hollow, not definitive. Overall it doesn't sound like a great idea, but one I think worth asking.

Seems to me that the muffler could have been vertically oval in cross section, equal volume, and avoided this whole clearance-cooling issue. Plenty of oval mufflers out there. Perhaps a good aftermarket opportunity.

Maybe you could use a fiber optic to scope it out and see what's in there if you can't get a drawing. I live in Phoenix, and the oil temp issue is annoying in the summer but manageable. It's not a big enough issue for me to get out the saw yet. Good luck with your plans and please let us know if it works.

Rich