I need to add approx 8" of high temp hose to end of my black can zenoah exhaust to exit the rear of a scale fuselage. Will this negatively affect engine performance? Will it not run right if I do this?

yes it will effect the engine performance. It will not be a horribly negative effect but you will notice a drop in high RPM power from the engine. You may even need to retune it slightly. This is where the thinner the diameter the worse the performance thing comes in....The best thing to do is go with as wide a diameter tubing as you can to minimize this effect...like say 1" diameter...

The can muffler itself does fine with anything under 9,000rpms...which is why plankers have no issues with it as most props on gasser engines in the 20cc plus range stay well under 10,000...but once you start to go over 10,000 rpms, where heli engines are normally used the back pressure in the muffler builds up and effects the intake/exhaust flow through the engine.

showing a preference will only get you into trouble, 90% of everything is crap...

Damn RM3...

I didn't know you looked like that...! Scary

Going back to the subject, it might reduce top end power a bit but its not a big deal anyways, you're flying a scale heli so have at it.

-=>Raja.

MA 1005 Hanson 280, 4225 flts
Spectra 27 3DMax, 3325 flts
Whiplash V1-2 Hanson 300, 1650 flts
Whiplash V2 Hanson 300, 504 flts

I'm building a Bell 206B & I'm using the black can muffler with 2 outlets instead of the 1 supplied (welded that one closed). So I can route the exhaust to the actual outlet points on the 206B. The cross section of 2 holes is better than the one. If that's an option for you.

RM3 don't you think a 1" tube is overkill? I've never seen any muffler with more than approximately a 3/8 hole? A 1" tube would be kind of drastic to route inside a fuse!

gyan...

1 inch is no where near over kill...

look at it this way....take your typical soda straw...cut a piece 1 inch long...now blow thru it hard...pretty easy....now find a bunch of soda straws like 10 or so tape them together one after another into one longe straw and blow hard thru them...you'll notice its a little harder..., your now having to push the extra volume of air thru...thats some what the concept except that two stroke engines don't just deal with a constant flow of exhuast...there are sharp pressure pulses that occur and the less the restriction near the outlet of the engine the better the flow. if there is a longer column of air the inertia of that volume increases with length as does its ressistance to flow. The 3/8 outlet on the tuned pipes (stingers) are flowing at more of an even rate but they do this AFTER a large internal expansion chamber and are tuned to flow for the specific volume of the expansion chamber. Since the can muffler has a very small expansion volume, there is back pressure inside it...so if you use a smallish diameter but also long tube, the backpressure increases and that messes with the intake flow into the combustion chamber, especially at higher RPMs where there is less time to push those exhaust gasses out.

like I said earlier...it will not big a terrible change, but it will be noticable, and there will need to be a slight tuning change.

now if you don't think 3/8 inch tube nearly a foot long will not hurt the power output of a gasser or Nitro for that matter...test it for yourself, you'll see.

showing a preference will only get you into trouble, 90% of everything is crap...

Great, thank you guys very much- you just made my life a Lot easier The can has a 5/8 outlet so that is what ill get at the auto store to finish it up. The power issue really isn't a big deal to me as long as it will run ok.

Thanks RM3 the soda straw analogy helps. I'm using the can muffler but have 2 exhaust holes each the size of the original 1. I'll see what happens with it.

Ok guys, this is what I ended up going with. The tubing is high temp heater hose (5/8id) and the elbow is 5/8id as well. The rear section is approx 8" and the short coupler to elbow is approx 1.5". Curious what the opinion is on my addition of the elbow. Without it, the bend in the tubing was very sharp and the only way to keep it from kinking was to increase it's length by adding a few more inches.

that hose may melt. test it on another heli before trying it on the scale ship. i understand its hi temp but no coolant is going to reach the heat of the exhaust also the exhaust gas may react with the material of the hose

R I P Roman Jr. Team SKOOKUM SRW EFC

+1 on the temp issues. High temp in a cooling system might be 250F. Your EGT even at the muffler outlet might be over 500F.

On the bend... its going to add a significant restriction. I believe the typical flow calculation is that a single 90deg elbow adds as much restriction as a straight length of pipe 30x the diameter - so you are talking the equivalent of another 18inches of run. You can reduce the restriction if you can find a larger radius bend or find some pipe you can bed into a sweep, or use a larger diameter for the elbow. (remember the old 2 stroke dirt bikes that had those big fat sections in the curves of the exhaust pipe? same idea)

But as said above, the loss of power due to the increased backpressure might not be an issue in scale. One thing to keep an eye on is head temp & cooling, sometimes 2 stroke engines run hotter with more backpressure. I had a plank motor once that overheated consistently till I removed a muffler baffle.

-Jeremy
Whiplash-G
Helix 700G
T-Rex 450 fbl conversion
alot of planks

> that hose may melt.

I was thinking the same thing. I don't think it will last long at all.

- John

RR rules!

Ok guys, I had no idea gasser exhausts got that hot... I have done this on glow before but I guess since I'm still fairly new to gas im dealing with a whole different animal.

Is that a plastic elbow?

Yes gasser exhaust is very hot, close to 1000 degrees actually. I remember putting the temp sensor for my fpv taylorcraft in the exhaust stream and it was too high it wouldn't register. Later I moved it to the outside of the exhaust can and it would read around 400 +/- depending on climb on glide.

That looks like its not going to work out. But you could make it work with copper pipes. A hose kills the motor worse than a pipe which can shed heat from my nitro days when I used to extend exhausts 3 feet to get all the mess out by the rudder.

-=>Raja.

MA 1005 Hanson 280, 4225 flts
Spectra 27 3DMax, 3325 flts
Whiplash V1-2 Hanson 300, 1650 flts
Whiplash V2 Hanson 300, 504 flts

Raja is on the right track, What I would do is, cut the small exhaust pipe off, cut a hole for 3/4" copper tubing, then have someone or yourself weld a short 1 1/2" long piece of tubing comming off you muffler, then use a piece of the white flexable hose that the rear muffler system uses (Vario or Xcell) then, all you have to do is bend the 3/4" copper tubbing to fit your needs, then use the clamps on each end of the white flexable tubing and your done,, Good luck.. XGM/VGM

P.S. You can use what ever size you need, but I would not go under 1/2" exhaust,,,

Ok I finially saw your pic's and all you really need is the white flexable heat tubing that comes with a vario or zimmerman muffler, I think it is 1/2" maybe bigger, not for sure, Get 2 clamps, and bend your copper tubing how you need it with a tubing bender to make smooth curves, should be good to go,, XGM/VGM

John Crotts
www.soonerhelicamproductions.com

Raja, yes it's a high temp plastic used in plumbing/boiler hookup. Dangit I may just have to rethink the exhaust all together now. Im thinking I may be able to shoehorn a v5 style pipe in there with a minimal piece on the end to exit where I want. I was hoping to just retain the stock can but at this point I want it right so a few extra $$ for a pipe will be ok. Nothing worse than issues and stuff not working right at the field when you are there to fly.

I feel your pain Jack.....

Success! Ok guys, I took out the elbow (after the tips on restrictive flow and being plastic) and just used the high temp heater hose with a gentle bend. It runs great with only a slight richening of the high speed needle. The tube gets warm but I had no issues with melting or failure. I flew three, 15min flights today. I will still watch it closely in flight but hopefully it will have no issues.

...

Thank you for that link. Its good to know of a specific tubing designed just for this application. I may switch it just for piece of mind.

I'm surprized there isn't a scale pipe ( low profile) for gassers. there is one for nitro helis.

R I P Roman Jr. Team SKOOKUM SRW EFC