Rotax 912 ULS muffler wanted

[Kyle Communications]

I am chasing a second hand Rotax 912ULS muffler. A genuine one it doesnt have to work or can be damaged even. I want to see if I can fit it to my Savannah XL. I will probably buy a new one eventually but need to get the exhaust pipes to fit and see how much modifications I will need to make to the cowl.

 

The reason for this is the XL muffler supplied by ICP is very small probably about 1/3 the size in volume to the Rotax one. The ICP is made to fit inside the cowl so is very flat.

 

This all started when I went for a fly in a friends new Technam and I couldnt believe how much acceleration it had on the ground and also in flight. I initially thought it was his prop but its a bolly the same as mine and after much discussion with much smarter and experienced people than me the thought was the size of the XL muffler choking the engine. When you look at the XL muffler and the way it is configured it is easy to see this is the reason. The engine is probably between 5 to 10 HP down on what is quoted. Rotax figures are based on using their muffler not anyone elses.

 

So chasing one down to see how I can get it fitted

 

Mark

 

 

[JimG]

Did Geoff buy the genuine muffler, I'll have his motor till the end of the week so if it is ,you could borrow that one for a look see.

 

JimG

 

 

[JimG]

If I put the 912ULS in my Karatoo , I'll be making a pair of 2 into one pipes with no mufflers . It'll be very similar to the systems most RV's are running on their Lycomings.

 

This would yield the best performance if the carby's are rejetted correctly.

 

The jury is still out here though as I'm finding it difficult to turn my back on almost 1 years work and money setting up my EA81 and redrive.

 

JimG

 

 

[Geoff13]

Mark

 

I have a Genuine Rotax Muffler as well as the one that came with the motor. Both are out of the plane ATM as Jim said my motor won't be ready before the end of the week and as we are moving early next week it is unlikely that I will need the Muffler before the following weekend. You are welcome to borrow it. I am not sure how you would go but you could possibly even try my header pipes and see if anything fouls.

 

I also have the one that came out of the Sportstar that my accessories all came from. It has the correct capacity but the holes just didn't line up for me. There are photos of an identical one on another current thread about Rotax mufflers. I have offered it for sale so I would have to give him first option on that. It could still be worth looking at to see if it fits.

 

I am not sure where I read it but when I was considering Mufflers and looked at yours to see if it could fit I did read somewhere that the 912ULS needs a minimum of 5 litres capacity in the muffler. I can't find it again but it was in one of the Rotax books.

 

Let me know, I am hoping to be at the hangar early tomorrow as I need to go to Dalby and Toowoomba. If the weather is good I hope to fly, if it's average I will ride and if it's crap I guess I will need to drive.

 

 

[Kyle Communications]

I thought you had a muffler for the Jab engine that came out. It would be could if I could borrow them Geoff to see if I can get something to fit easily ..mainly getting the pipes to it. What time will you be at the hangar?...I will be going through to work around 7am..maybe too early for you.

 

Mark

 

 

[Kyle Communications]

If I put the 912ULS in my Karatoo , I'll be making a pair of 2 into one pipes with no mufflers . It'll be very similar to the systems most RV's are running on their Lycomings.This would yield the best performance if the carby's are rejetted correctly.

The jury is still out here though as I'm finding it difficult to turn my back on almost 1 years work and money setting up my EA81 and redrive.

 

JimG

It would be nice to be able to do it that way cuz as I could get the welder at work to do it but I dont think I could get it to fit in the Sav the way it is on the ring mount. How much noisier do you think it would be with just straight outputs also rejetting might take a bit of trial and error though

 

 

[JimG]

Sure the noise will be substantially higher but I wouldn't worry too much about that where we operate with Tiger Moth's , P51 and that bloody loud prop on the jump plane..!

 

Just use a good noise cancelling head set, Bob has that in his RV9A and it is beaut to fly.

 

As for tuning, I'll approach that in the same way as I tune racing engines, safely overrich especially in the middle and WOT and then carefully work it back into tune using EGT's and AFR's . Mostly on the ground tied to a tree and when close in the air overhead the field.

 

JimG

 

 

[Blueadventures]

I am chasing a second hand Rotax 912ULS muffler. A genuine one it doesnt have to work or can be damaged even. I want to see if I can fit it to my Savannah XL. I will probably buy a new one eventually but need to get the exhaust pipes to fit and see how much modifications I will need to make to the cowl.The reason for this is the XL muffler supplied by ICP is very small probably about 1/3 the size in volume to the Rotax one. The ICP is made to fit inside the cowl so is very flat.

 

This all started when I went for a fly in a friends new Technam and I couldnt believe how much acceleration it had on the ground and also in flight. I initially thought it was his prop but its a bolly the same as mine and after much discussion with much smarter and experienced people than me the thought was the size of the XL muffler choking the engine. When you look at the XL muffler and the way it is configured it is easy to see this is the reason. The engine is probably between 5 to 10 HP down on what is quoted. Rotax figures are based on using their muffler not anyone elses.

 

So chasing one down to see how I can get it fitted

 

Mark

Hi Mark

 

Have you considered the CKT mufflers? http://www.cktengineering.com/

 

They are popular in UK etc with 912ULS installations. Scott Hendry had one on his Skyranger Nynja. Not sure if its still at Caboolture. I've have a CKT on my build underway at present. They are a bit flatish with two outlets.

 

Cheers

 

Mike

 

 

[Kyle Communications]

Hi Mike

 

Just checked their list..they do not have any for the Sav or the Zenith 701

 

Mark

 

 

[Geoff13]

Mark

 

I hope to be up there around then. Give me a ring around 6-630 let me know how you are travelling, I should know by then which way I am going.

 

 

[Kyle Communications]

Sure the noise will be substantially higher but I wouldn't worry too much about that where we operate with Tiger Moth's , P51 and that bloody loud prop on the jump plane..!Just use a good noise cancelling head set, Bob has that in his RV9A and it is beaut to fly.

 

As for tuning, I'll approach that in the same way as I tune racing engines, safely overrich especially in the middle and WOT and then carefully work it back into tune using EGT's and AFR's . Mostly on the ground tied to a tree and when close in the air overhead the field.

 

JimG

I was looking at some pics I have here and that way with the 2 pipes into one could work. There would be 2 exhaust outlets of course and you could direct them further under the fuselage. I would be concerned with how much noise there would be though

 

 

[Kyle Communications]

MarkI hope to be up there around then. Give me a ring around 6-630 let me know how you are travelling, I should know by then which way I am going.

Thats great I will call when I get in the car to see where you are probably around 6.45 or so. It would be good to see if it makes an easy fit...no problems modifying the bottom of the cowl that will be the easy part

 

 

[Blueadventures]

Hi MikeJust checked their list..they do not have any for the Sav or the Zenith 701

 

Mark

OK. Let me know if some images and dimensions of one on a 912 ULS is helpful and I'll take some and send so you could see clearance to engine from frount and side view plus the dimensions if required.

Cheers

 

Mike

 

 

[rotax618]

If you want an efficient and very quiet muffler that takes the heat out of the cowl, look up "Swiss Muffler"

 

A Swiss muffler would be easy to fit to a Sav and would also lower the chances of CO poisoning.

 

 

[rankamateur]

If you want an efficient and very quiet muffler that takes the heat out of the cowl, look up "Swiss Muffler"A Swiss muffler would be easy to fit to a Sav and would also lower the chances of CO poisoning.

Is that this one?

 

https://www.backcountrypilot.org/forum/swiss-muffler-is-a-maintenance-nightmare-12929

 

 

[facthunter]

The higher revving motor may make a lot of noise. I would try an open system even for a ground run, before I went to the trouble of going down that road. Nev

 

 

[rotax618]

Yep, the homemade Swiss Muffler only lasted 800 hours because a flexible pipe broke. Maybe Swiss Mufflers should be banned. - honestly. Read Tony Bingles' Book Firewall Forward.

 

 

[Kyle Communications]

Geoff13 kindly lent me his Rotax muffler and I did some prelim work at how I might fit it. I took a couple of pics to show the difference in size of the ICP one and the genuine Rotax one, you can see the massive size difference. The rear pilot side will be a bit of a issue trying to get the exhaust pipe down to the muffler the front ones will need a different shape but should be easy and the rear pax side should go straight on.

 

I got some pricing on the net so I can make up new pipes...holy crap the fittings are expensive to go into the Rotax head and the muffler end then you get the pipe and bend it and weld the fittings how you need. Most complete standard kits will need modifying to put into the Sav and a full kit is about $1000 US

 

I am thinking seriously now of trying the 2 into 1 pipe on each side of the engine and exhaust it under the floor it will be a easy try except as Cuz suggests that the engine will need to be rejetted in the carbs. I will look at it a bit more this weekend to see what will be the best way to approach it

 

Mark

 

 

 

 

[facthunter]

Running the exhaust as you suggest is wrong for even pulsing. I don't even like doing it on a Continental or Lycoming. Nev

 

 

[JimG]

Yes Big Fella, not that simple ,the 2 into one system crosses over underneath the engine .

 

Frt left joins right rear and frt right joins left rear. The biggest mistake is making the pipe too large.

 

Keep the primary pipes the same dia as the std rotax pipes then to a merge collector ( 2 to 1 ) and the secondary pipe only 1/8" larger . That's it, the plan is to be unrestricted high velocity to promote good scavenging and minimize pumping loss.

 

I'f you are serious about trying this I have a few pipe design programs, I can run the numbers through.

 

The pipes on Bob's Lycoming RV9A look disproportionally small and they are purpose designed for power and economy and they definitely deliver on both with a smooth idle.

 

JimG

 

 

[Geoff13]

I have a doughnut and I think a couple of other bits you can have Mark. The muffler came with 2 but we only needed the one to make it work.

 

 

[Kyle Communications]

Yes Big Fella, not that simple ,the 2 into one system crosses over underneath the engine .Frt left joins right rear and frt right joins left rear. The biggest mistake is making the pipe too large.

Keep the primary pipes the same dia as the std rotax pipes then to a merge collector ( 2 to 1 ) and the secondary pipe only 1/8" larger . That's it, the plan is to be unrestricted high velocity to promote good scavenging and minimize pumping loss.

 

I'f you are serious about trying this I have a few pipe design programs, I can run the numbers through.

 

The pipes on Bob's Lycoming RV9A look disproportionally small and they are purpose designed for power and economy and they definitely deliver on both with a smooth idle.

 

JimG

Hmmm that would be a difficult exercise I think. I didnt realise that they needed to be configured like that then. The other option then would be to extend the Rotax muffler lengthways. The reason is that it is about 5 inches short to allow the rear pipe on the pilot side to come down in the same position it is in. I could cut the muffler down the middle and fit a new outer in the middle to get the required distance. this will also allow for more expansion and I would think allow more output to flow easily. Maybe I am wrong on this. Danny has a boroscope I can use to go inside the muffler to see how the inner section of the muffler is constructed. If it looks ok then I can just fit a new outer into the middle part then it really is only just a matter of getting the 2 front pipes in at the angle. The Rotax mufflers input ports are 90 deg to each other where the ICP are only about 70 deg.

Mark

 

 

[Geoff13]

Did you look at the other one i had there. You need the be careful. To large could be as bad as to small.

 

 

[Kyle Communications]

The other one looked a bit smaller Geoff. I am off there this morning before I have to get sliced and diced this morning to get some skin cancers removed I think Mark G is helping Roger with his fuel tanks today so will have a better look at it as well

 

Mark

 

 

[flyvulcan]

On our Lightning Bug fitted with a 912ULS, we have used the Downwind Technologies Toucan system. I cannot report on whether it has any effect on power because it is too early in our test flying phase to determine how the engine is really performing but it is certainly quiet.

 

Here are some pics that might give you some ideas. The routing of the pipes is flexible.

 

 

 

 

As you can see, we had to do a lot of cutting and welding to get our pipes to fit within the very tight engine bay of the Bug. Now that we know the routing for the pipes, we shall be able to get custom pipes fabricated to remove all the welds that are in the current system. Using the two smaller mufflers has given us more flexibility than using the single larger muffler which we simply didn't have space for.