ST 90 help
 

I would like to get more power for my ST 90. There are few alternatives to going bigger than the .90 2 strokes as the next step up significantly adds weight. The only real alternative I have seen is the new O.S. 120 AX, however, I don't think it's worth the money to shell out for 20% more power. I don't do 4 strokes either.
Basic question: What are some basic ways to get more power from a 2 stroke engine? I know a 'tuned' pipe will give you more, but how hard are they to mess with? Any other suggestions would be appreciated.

RE: ST 90 help
 

larger carb with a pump,higher nitro fuel a pipe will add some power but it depends how the engine timing is setup as to how much.usually when using a pipe the exhaust poets are timed to open/close a bit soone and a bit later.material is removed from the top of the exhaust port.

RE: ST 90 help
 

i have 2 friend's at my field that run saito 125's in there's they fly awesome..

RE: ST 90 help
 

What kind of plane?

RE: ST 90 help
 

Actually, believe it or not, I've found that I get better performance with 5% nitro in my ST's. 5% and a #3 plug. And it's the same from my 45 up to my 90. For instance, on my ST 70 mounted on a Katana with a 13X4W prop, I got about 420 more RPM with the 5% than I did with 15%. Both had 18% castor. It pulls out of hovers better, the midrange in the throttle is smoother. As far as the tuned pipe, there are threads on here on building them. Or, you can be lazy and cheap like me and modify an oversized pitts ...

RE: ST 90 help
 

If you want to run a higher nitro fuel in the st you may need to add a shim under the head to lower the compression ratio.They used to be included with the older engines

RE: ST 90 help
 

There are guys in the tach reading forum that had things they did to ST90's . One of the best was a 1.08 Magnum carb for about $39.00,some claimed almost a 1000 rpm increase. My ST90 also ran better on 5 % turned a 14x6 APC 10400 with a pitts muffler. Nothing to brag about. It has since been replaced by a Saito 100 that turns a 15x6. The ST are higher compression and without shims you might not want to go above 15% nitro.

RE: ST 90 help
 

I have the ST .90 with a Saito 125. It's a good Power to weight compromise. It will pull straight-up out of a hover, but it's not a rocket.

The OS 120 is a bit heavier, I think. You might try experimenting with props before you buy a new engine. BUT...if you buy a new engine, don't compromise. Get the best engine you can afford.

I have 13 gallons through this plane...on my second engine now. You'll love it with more power.


OH YEAH....and don't confuse RPM with power.

RE: ST 90 help
 

Ya'll a giving advice and have no idea what kind of plane it is. Your wasting your time

RE: ST 90 help
 

Golden Skies Bampf 3D

RE: ST 90 help
 

doesn't matter what plane it is the question is about how to get more power out of the st 90 engine.the mods will work no matter what plane it's in.

RE: ST 90 help
 

http://www.goldenskiesrc.com/newbampfpage3.html
Here's the plane Happy Feet.

NOW let's hear YOUR sage advice.

RE: ST 90 help
 

that's a nice looking plane.

RE: ST 90 help
 

Jett 90 = more power problem solved.

kc

RE: ST 90 help
 

Nice looking plane. Sorry no sage advice but engines perform differently on different planes. You should know this. A simple 46 fx on a trainer pulls it around just fine for a huge no aerodynamic flying box but put the same engine on a Shrike with a simple prop change and you now have a sweet 100mph plane.

How can you give advice when you don't know what your talking about (meaning the application). I see this here all the time. Some guy innocently asks "hey will this work?" We don't even know what he's talking about but everyone is replying "oh yeh it'll work just fine but make sure you do this and make sure you do that" For all we know the guy is building a boat and your telling him to use a 16/8 prop.

I think this qualifies for Khodges "Dumbing Down" theory

Thanks, "Sage"

RE: ST 90 help
 

Part of his power problem is that Golden Skies recomends minimum engine displacement of 1.08 for this airplane and up to 1.60 based on their video. The booklet says 90 is ok for sport flying.

A Performance Specialties Ultra Thrust Muffler would probably help increase the 90 output.

RE: ST 90 help
 

the question was how to get more power out of a 90 sized glow engine (a Super Tigre) without going to a larger displacement and regardless of the application be it on a boat, plane, car, of bolted to the picnic table in his/her back yard the answer is still going to be the same.

kc

RE: ST 90 help
 

kc pretty well stated what my response would be. You could always say "changing the prop MIGHT give more usable power". But even then you would be dodging the original, and only, question asked.

One more thing. Can you please point out the post in this thread where someone/anyone said "oh yeh it'll work just fine but make sure you do this and make sure you do that"?

IMO you STILL haven't given any usable advice in this thread.

RE: ST 90 help
 

or any other one :)

not that i'd really notice it anyways :eek:

kc

RE: ST 90 help
 

For some reason idk why i thought ST stood for showtime here lol my bad i shouldnt have commented without knowing full details..so yea my commetn was also useless

RE: ST 90 help
 

Me too. ST 90 sounds like um. ST-90. Oh well.

RE: ST 90 help
 

Never mind.........................

RE: ST 90 help
 

There ya go!

RE: ST 90 help
 

Reading through this forum you have at least four ideas - 5% fuel, magnum 1.08 carb, large volume pitts muffler, ultra thrust muffler for more power from your ST90. These suggestions might give the increase your looking for.

RE: ST 90 help
 

I researched going with the larger carb a while back for this same engine. What I found is that the carb gives higher rpm on the ground but in flight doesnt give any drastic performance boost. I am not an engine guru and cant explain why this is so but that is what I came up with after hours of reading through post and PMing other RCers.

On my ST90 I put a jett muffler (similar to the ultrathrust) on it. I went with the 120 sized muffler because I was after more torque rather than top speed. It gave a power boost but not a huge one. The plane really sings on a 13X6APC now but is a little too fast, I was really looking for something to boost my performance on a 14X6. Those mufflers are pretty pricey too.

I am looking into the OS 120 now. Weight wise its almost equal to the ST90 and has gobs more power. If my 120 jett muffler will fit it I think I going to go for it.

RE: ST 90 help
 

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

RE: ST 90 help
 

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

RE: ST 90 help
 

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.

RE: ST 90 help
 

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

RE: ST 90 help
 

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.

RE: ST 90 help
 

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.

RE: ST 90 help
 

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?

RE: ST 90 help
 

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.

RE: ST 90 help
 

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.

RE: ST 90 help
 

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

RE: ST 90 help
 

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.

RE: ST 90 help
 

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?

RE: ST 90 help
 

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

RE: ST 90 help
 

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?

RE: ST 90 help
 

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.