Canister exhaust mounting and 2 stroke cans on a 4 stroke

[Bob Cotsford]

Has anyone ever tried hooking up a 2 stroke can to a 4 stroke? I've got a couple of JMB 30cc size steel canisters and I am tempted to fit one on the NGH GF38 4 stroke in my WotsWot XL to see if I can get it under 80dBa. I just need to make up some sort of adaptor to go from M14*.75 on the manifold to the 20mm can inlet. A 3/4 AF nyloc nut has a shoulder that's a nice fit in 20mm stainless tube, drilled and tapped out to 14*.75 this would fit on the JE manifold that they supply with the engines. I just happen to have some 3/4 AF stainless nuts left over from when I rebuilt a T140V Bonneville some years ago.

Next, how to mount the canister under the airframe - a headlight clamp for a 50mm fork leg is a nice fit around the can, and I've got a couple handy, but does the can need anything to stop it moving away from the manifold or will the rigid white Teflon/PTFE(?) coupler tube hold it tight enough? What other options are there for hanging a 50mm OD can?

Or am I wasting my time with this idea?

[flight1]

Well as an experiment i have attached a 50cc canister to the end of the gf38 original manifold with some flexi steel pipe. used self tapper to hold join and cilicon tube to seal. It work well for a few flight but the original manifold did not take the strain even though the canister was suported(3 flights). in the process of trying to make a new one. use a g sonic pro prop as will be quiter. I will have to look up the db as its recorded at our club in a little black book and is required to be below 84 before flying a new model.

[Bob Cotsford]

Hi Flight1, was that with the NGH aluminium manifold or the JE steel one? Someone on RCG reported that the supplied ali manifold softened and collapsed with a can added . Did you notice any difference in revs? For reference, with an 18*8 HK wood prop and an ASP FS180 exhaust on JE's manifold I was getting 83dBa at 7 metres in the Acrowot XL but I don't recall the revs.

[flight1]

Yes it was with the ngh manifold that came with it failed , just not strong enough for the job at hand, if the previous post said it melted thy must of over resrticted the exhaust and greated too much back pressure, not good for 4-strokes.

i should have a tinker this weekend and get some trials done and hopefully some flights

[AndyD]

ive been searching the net just lately trying to sorce simular setups but with no luck,ive heard several JE setups but not overly impressed with the noise and sound so was looking for a more quiet setup,i might try something like this as used on the torq pro 70.

[Bob Cotsford]

That's interesting Andy, I wonder what size outlet he's used.

[flight1]

Andyd more details please what wrapeed around it and how its made... as I've got one of those too

[AndyD]

not many details on it but as far as i can tell its a alloy can withe the bendy pipe silconed in to it and ten 3mm holes drilled in the bottom,a bit crude but seems to work and sound nice,not sure how it would sound with just one outlet.

[Bob Cotsford]

So I took a 3/4" AF stainless nyloc nut, drilled to 13mm and tapped it 14*.75. Then I extracted the nylon insert and turned down the external hex to fit inside 20mm ss tube, leaving about 6mm of the hex intact. Silver solder the two together, bolt on in place of the ASP 180 silencer supplied by JE and attach a JMB A30 can with KS isolation mounts:

From

to

This one is on the Acrowot XL, just as a control I happen to have the WotsWot XL with the same engine, both running Aerostar 20*8 wood props:

WW, JE exhaust with the ASP 180 baffled silencer - 6200ish rpm (the meter was fluctuating +-50rpm)

AW, JMB canister - 6200ish rpm(again, the meter was fluctuating +-50rpm). I think I need a new battery in the meter!

The engine still ticks over smoothly and transitions well but the canister definitely seems to take the edge off the exhaust. Next I just need to get it up the field where I can noise test it properly as there are just too many reflective surfaces in the back garden.

and make another manifold adaptor for the WWXL of course!

edit - as the can weighs 300gm I had to put 45gm of lead in the tail to compensate.

Edited By Bob Cotsford on 16/09/2016 15:45:12

[AndyD]

ive just gone down the same route and bought a cannister for my torqpro 70 4 stroke,its not compleatly fitted yet so i dont know how its going to sound but i found a youtube clip which sounds pretty good,it really notices when the cannister drops off at about 3.42

[Bob Cotsford]

Ballpark test using an un-calibrated cheap meter - a 3dB reduction, very rewarding. In fact, in flight the loudest noise was the annoying rattle that seems to coming from the Krumscheid (sp?) rubber mount - it has steel inserts which appear to be chattering together under the effect of engine vibes. I need to adjust the alignment of the manifold to see if I can reduce this chatter. Now to make up another manifold for the WW XL.

[Ace]

Interesting Bob, do you recall the readings Front , Left, Rear, Right? only I am also looking to do something similar. David

[Bob Cotsford]

Sorry David, it really was only a quick and dirty check from the front which has proven to be the noisiest orientation in most of our club tests. Presumably this is because you are getting the full 'benefit' of the prop noise. I'm hoping to get a proper test with a calibrated meter on Sunday. Subjectively - it was much better. With the ASP silencer when flying I was very aware it was a bit loud, with the big canister I never gave it a thought.