the Jett Stream muff is a tuned system for high RPM applications they aren't designed or intended for torque applications which is what you are/were after. the Turbo Jett on the other hand is designed for more torque oriented applications.

as far as pricey goes, the Jett Stream is very cheap in comparison to a full length tuned pipe and only a few hundred RPM shy of it in performance, to most of use who are after all out speed we tend to conceder the Jett Stream very cheaply priced

kc

Yeah, Id say try the turbo-jett to get more from the ST90. Works well with that engine. Generally you can go up one prop size, and keep the same rpm you had (say jumping from a 14x6 to a 14x8 or 15x6).

The ST90 is a pretty good engine, but if the plane really needs 108, 120 or 160 class power, i think the answer in that case is clear.

For an example of the turbo-jett installation, take a look at the following link. This shows a Jett 100L and turbo install, but you will get the general idea - its about the same size/fit for your application
http://www.jettengineering.com/edge/edge.html

When I bought the muffler I asked the Jett folks which muffler would give me more torque. I asked about the Jett Sream and the turbojett. The turbojett would have been a lot easier of an installation bc I wouldnt have had to carve up the belly of my plane so much.

The folks at Jett told me my best bet to increase torque would be the 120 sized muffler on the ST90 as oppossed to the 90 sized muffler.

So I went with their recomendation.

bob27s is the Jett guy him and Dub and Dub you have to call on the phone to talk with him, are you sure it was one of those two who told you different? I've never seen them not give great information and bend over backward to answer any questions asked, to me the customer service at Jett both before and after the sale is worth the extra cost of an engine in comparison to any other brand.

kc

Positive, I called and talked to someone on the phone. I remember him giving me the measurements over the phone while I measure my plane to see what would work. I went with the 120 muffler on their recomendation. I have been happy with it, its light years ahead of the stock muffler.

I will agree customer service was great. If I recall right he put the muffler in the mail the same afternoon.

The 120 size jett-stream is a good solution for a torque install. That muffler boosts well from about 10000 to 13000 rpm - lower range than the 90 size muffler - so its better if you are running larger props.

The turbo-jett has a bit different torque boosting characteristic, especailly with the big engines. Plus I prefer it on the in-cowl applications.

Gringo, what size props did you utilize?

reference here... this is a large Pitts with OS160 and turbo-jett. Again, visualization of how one installs.

I have tried a 14X6MA and APC and a 13X6 APC. Dont remember off hand what they tach at. The engine runs well with all of those props and I do remember a boost in performance I just dont remember how much. I´ll tach it next time I run the engine. With all of those props I am sure it is staying in the 10 to 13K range.

Bob, will that muffler fit the new OS120?

I went back and found my before and after tach readings.

14X6 MA 10,300 on 5% stock muffler
10,800 on the Jett.

13X6 APC I am getting around 11,200 with the Jett. I dont have any before prop numbers with that prop.

Thanks for the info - that looks about right - 500 rpm gain is a pretty significant HP gain when dealing with a 14" prop.

If the opportunity arrises, try an APC 15x6 too. Might surprise ya

Technically the muffler will work on the OS120. Just matching up the bolt pattern is the key here. Im not sure if either sets of fastern holes on the muffler match the OS120.

I do know that Dub has an OS120 for testing, but he has been busy on a couple of other projects... not sure how much test data he has so far.

What does all of this talk about Jetts have to do with getting more power out of a ST 90?

Jett is branching out making mufflers and such to fit certain sized Super Tigers. I don't think he would waste his time on the engines if he didn't think it all had potential.

Bruce, those numbers are on a ST90 with stock muffler and a Jett muffler. So the 120 Jett muffler is good for about a 500 rpm boost on a 14X6 prop.

Bob, if you find out the bolt pattern is the same on the OS 120 would you let me know?

Bruce, do you have any productive discussion to add or just criticism for everybody elses responses.

I asked a question "What does all of this talk about Jetts have to do with getting more power out of a ST 90?"
What does that have to do with criticism? Oops, another question. Am I criticizing again?

Its just so far in this post you have only criticized other posters.

The Jett muffler has everything to do with getting more power out of an ST90. So far the turbo jett and jett stream muffler have been suggested. One even with tach numbers.

I believe Performance Specialties also makes a Ultrathrust muffler for a G90. I have some for other engines and they increase the power significantly. I also have some Jetts and a Jettstream for a ST. I would go with Jett merely for the customer service.

Question here is answered easily. It is in direct response to the "how to".

In fact this answer can be expanded to nearly all 2-C glow model engines.

The exhaust system of a modern 2c engine is where the greatest performance gain (or loss) is realized. Switching to a tuned exhaust system can increase actual HP by 10-20% with this engine. The tuned system must be matched to the aircraft/engine/application/prop and can be optimized with everything considered. It also represents a "bolt on" solution with no other changes to the engine. Additionally, the nature of the tuned system provides a proper balance of backpressure for the engine - this is essentail to proper fuel delivery.

Tweeking the engine, messing with port timing, changing head shims, increasing fuel nitro, even swapping the carb can gain some performance, but often at the expense of reliability if not done properly and with due consideration of the intended use. And in most cases, the gain here is limited compaired to the gain that can be realized from a tuned exhaust system.

Bob

I have a ST G90 with Magnum 108 carb and JTEC header on a 7.5lb AW Edge 540 46-91. The combo is excellent for 3D with 5% fuel and 15x4W apc. Excellent throttle response and power with the Magnum carb.