Jett Muffler insides
 

Just wondering what the inside of a Jett type muffler is like, if anyone has opened one up? Is there a tube going to the front from the rear, or whatever. I have never heard of anyone using the bell type muffler that they sell either. An inside view of that would be interesting too.

Hi!
The Jett muffler is made as any other half wave tuned pipe. That means it has an outer shell and inside is a tube that goes from the opening (where the exhaust gas goes in) and ends appr 10mm from the wedged rear opening.

OK, now I can almost see it on a few of my MVVS mufflers. I was thinking of making a new tailpiece for a standard muffler, but now see it would be better to just use a header and maybe some other regular pipe, or even a car style? Maybe a mousse can. Just thinking out loud. It is kind of hard to make a header without welding. I can only machine stuff at home, not weld aluminum. (steel yes) Too cold to fly now, but still thinking about stuff.

The Jett style mufflers are 1/4 wave tuned pipes. Super tiger was the first to make one as far I know then Jett and nelson came out with them. The jett mufflers have changed quit a bit on the inside and out side from early days until now. I have about 20 different sizes and but buddy has over 200 and has about every different style made from early on. From the testing I have done on most sport engines and Jetts engines is that a full tuned pipe will only give around 200 to 400 more over the Jett mufflers. that really isnt that much when you look at the convenience of the Jett muffler over the full tuned pipe, with mounting and couplers. I would love to see a small jett muffler for the .10 and .15 size engines.

on the insides I for got to post lol. you have the front part that mounts to the engine. then an inner tube of 1/2 to 3/4 is threaded in to the front part. then you have the outer tube that threads into the front part also, and then the end cap is threaded into the outer tube. Jett has a patent on the design.

200 pipes, I thought I was bad for collecting stuff. I am too. It seems like the .10 to .15 size is overlooked now with the leckie revolution. Just the FAI Russian stuff which is leaps and bounds over the mere mortal stuff. Looks like a big project to make the front part of a muffled pipe just to play, I am sure there is quite a way to go with pipes and quietness even. Have to get my mill going again. Needs a motor mounted.

Its cheap to buy a jett muffler and save time or spend more more money this way. get a long header from MACS then make a cone that fits over the header then machine a step in that cone and weld on a aluminium tube and then an end cap with a small stinger. hard part is finding the length of header you need for the 1/4 wave pipe you just made. easiest is to just order the jett muffler. you can get the red ones, gold ones or the black quickie ones. red is 15,500 to 17,000 on ground. gold is around 17,000 to 19000 and the black is 18500 to 21000. all these are average numbers as I have seen some red one go as low as 14000. oh these are for the 25 size and 45 size cased engines. The red one for the 90 to 120s work well in the 9000 to 11000 range

I believe, based on the sheet that came with my red Jett .90 muffler, that the tuned range for that one is 12,000-15,000rpm. I'm guessing the larger 1.20 Jettstream muffler is 9,000-11,000rpm? I have the JS-90 pipe.

yes there are two different red pipes in the 90-120 size range. most 90 dont turn up high rpm unless on a tiny prop

Yeah; the Jett site lists a pipe for the .90 engines and a different pipe for the 1.20's.

Yes I have three 90 size and 2 120 size ones I think. if you go to run a 120 size you need a mount for the rear of the pipe or it will break near the bolt holes.

Prop most 90-95 size engines for 11,000 to 12,000 or so on the ground for most sport planes. a 12x8 on the 95 AX is a good combo. most should run a 10x10 around 15,000 plus as a few 90s will get 17,000 on the 10x10

My JS-90 is on a box stock ST S90. I don't fly it, just run it on the ground and prop it for around 13,500-14,000rpm for my intended purpose. It works pretty good for me. I think it would liven up some with a bigger carburetor. I tried an Enya XF-IV Heli carb on it and it ran the same top rpm as the stock ST carb with Jett muffler but the midrange and idle were horribly rich. Adjusting that carb to clean up the rich idle and midrange caused it to go lean on the top end that the needle couldn't be adjusted rich enough for. I might get a cheap ASP 1.08 carb to try on it at some point.

Well for the .45 to .60 size small case engines. Jett actually makes one pipe tuned for higher RPMS. But their Evolution engine tuned pipe is setup for lower RPMs though to match the Evo engines better. Granted they make a inside the cowl tuned muffler too.

Earl the have a gold muffler for high rpm as I stated. the blue evo muffler is about 500 rpm less than the red mufflers. qwk measure the hole in the crank as that can limit the size of carb. so if the crank hole is .400 then a carb bigger than doesnt help. all of the Jett mufflers will load up on the midrange on most engines i have seen. just something we have to live with. Jett mufflers are for boring holes lol I have used them on some fun fly planes and work well just have to run to full power for a couple of seconds to clear engine. Something else on engines with enough clearance I like to run the four stroke plugs as it has helped on some engines.

My S90 is awaiting breaking in a new ring, so I'll check the crankshaft channel size. Some guys have used the 10 or 11mm ASP 1.08 or OS 7D carb and picked up 1,000rpm with it. Stock carb is 9mm I think with the thin spraybar. I have a jig for boring the crankshaft, so if it needs more volume, it can easily be fixed. I just did a Picco .28 crank - went from 9.5mm to 10.2mm. Those are some hard crankshafts in those little boogers.

that is cool you can bore them i may have to send some cranks in to you for some work lol

Haha.. I'm no professional. It took me an hour to do the Picco car engine crank. Not something I can do on any real scale. Plus I'm moving soon.

I noticed on the Fora .049, that they do not have a really large crank bore, but flare out the sides larger, so the fuel/air gets around the rod. Looks like about 20 degrees each side. They don't do the "turbo" cut like a lot of the car guys seem to like. I am guessing that this leaves the crankcase volume lower than opening up the whole crank bore. I noticed on an Axial motor that I have the the hole is bored off center, otherwise it would hit the crankpin. I like the Fora plan better.

The nelson engines are like the fora also. you dont want a lot of empty space in the engine for sure. filling the front helps some too

What is a good material to use for filling the front of the crank with?

I use Scotch weld 2216 but that is expensive stuff. JB weld has been used by some people with no issues. just has to be clean and roughed up.

I don't want to try a filler and then have it start coming out, if the 2216 scotch weld will stand up to fuel then that's what I will get, thanks.

I use solder, clean with acetone, scratch up the front cavity with a dremel and a little bit, then add flux, and heat it up just enough to melt the solder. I hold the crank at an angle that I like, and clean up any excess when it cools. I keep the heat away from the crankpin.

solder is cheap and easy buy some cranks may be harder to get to stick. The epoxy stuff seems a little more resilient in sticking than solder plus its lighter.
Some engines I have seen no gain in power but a better fuel draw. The ramp will help some engines get on the pipe easier too.

I think the solder will stick to pretty much any steel that cranks would be made of as long as it is shiny clean. Yes it would be heavier than epoxy, but not a lot more than steel, which it should be if machined correctly in the first place. I heard throttling may improve, but overall speed may not, by too much. I have done the solder thing, and radiused the back of the window, and sharpened the edges, and only got 200 and 300 rpm extra in unpiped motors. Still it is better than nothing, if it idles, and ramps up better.