Iflyglow

My Feedback: (79)

I have a question for the guys who have run this combo before. Did you run the carb with the restricter (came in the Carb barrel), or did you take it out? I have not flown this plane for several years, but just got it back through an estate sale. The plane was put away perserved, and I am just finishing the anual, to fly it again. In the past I ran a Master Airscrew 14-6, but now I would like to spin an APC 15-6. The engine is in a GP Ryan STA-M, and is equiped with a Cline system, Tetra tank, and a Custom Tig welded exaust made from a Slimline Sport inverted muffler. Fuel draw is not a problem due to the Cline system, so it just comes down to RPM I guess. I am thinking that the restricter should stay in like it has in the past, but I am open to suggestions. Since I am trying to get alittle more out of it yet, than what it had in the past. I guess there is no substitute for the power of a YS, since that is what was in it when I first built it. I got used to the power of it, but did not like the complexity of the exhaust that I had to run to make it look decent, so I installed a ST .90 and sold it after flying a few more times.

NM2K

My Feedback: (14)

As you probably know, any .90 that was derived from a .60 sized crankcase isn't really much of a .90, power wise. Yes, I've owned several ST .90 engines myself over the years.

If you really want more power and already have a Cline Regulator in place, why not upgrade to a larger engine, such as the ST 1.40? It's biggest complaints have been about poor fuel draw and the miseries that come with that. The Cline Regulator will take care of that problem with ease.


Ed Cregger

Iflyglow

My Feedback: (79)

Is the bolting pattern the same or very close. The .90 has way more than scale power, but I was looking to get just a little more out of it.

NM2K

My Feedback: (14)

No. Unfortunately, the 1.40 (G2300) is a much larger engine physically. Perhaps your idea of obtaining a slight increase in power by staying with the G90 is a better idea. Of course, there is always an ASP 1.08...


Ed Cregger

w8ye

My Feedback: (16)

I had three of these at one time. I preferred the restrictor plate but it runs pretty good without it.

rc34074

My Feedback: (5)

I have run the G90 for 15 years in my 60 size warbirds. I don't use the stock muffler much - I use pitts mufflers - but I throw away the gasket and use red rtv between the engine and the muffler, and I use double nuts on the muffler screws to keep the nuts/screws from coming loose. So I NEVER lose a muffler and they don't come loose. I never tried tuned mufflers because they stick out too much (I know the G90 sticks out but don't mind that because it's a great engine for the money). You might look at Dub Jett's mufflers - he has some tuned mufflers that might give a little power boost for the G90 but I don't know if he has one designed for this engine.

Ed

Iflyglow

My Feedback: (79)

MY exhaust is designed for the plane, and I am not changing that. The question is mainly related to the use of a Magnum .91-1.08 carb which I recieved with a restricter in it.

Iflyglow

My Feedback: (79)

Was there a power difference? The large carb opening will not create a fuel draw problem for me, because of the crankcase pressurized (Cline) system.

rc34074

My Feedback: (5)

Changing only the carb will not increase the max power of the G90.

Ed

Iflyglow

My Feedback: (79)

It should though, since you can run a little leaner with the Cline system and not have to worry about the mixture changing according to the fuel level in the tank. Also you should be able to get by with a larger Venturi since you are dealing with a pressurized system. Pumped engine offerings from OS used to come with a bigger carb that offered a little more power (.46SF-p and .61SF-p).

w8ye

My Feedback: (16)

I experienced a 500 rpm increase using the Magnum carbs over using the original ST carbs

rc34074

My Feedback: (5)

Sorry I don't believe it - you can only get so much fuel/air combustion with a normally aspirated egnine - you should already begetting all the benefit you can get with the cline, unless you just haven't tuned it as lean as you think you can. Now if you have the benefit of a tuned pipe type myffler then you could realistically expect to get more power, but without that its just not realistice/believable.

w*ye - if you made some additional change then I will believe it but unless you can show how you took into account variations in temoperature/humidity etc I don't believe it - or unless you changed to a different muffler, or you repositioned the muffler on the engine exhaust outlet tube, then you might get a tuning effect. I found that with the quiet mufflers you could get a tuning effect on the 61 and the 90 if you moved the muffler in/out on the exhaust tube. This could be 500 rpm.

Ed

Iflyglow

My Feedback: (79)

Well I ran it yesterday for a few tanks at the flying field, and it is screaming. I was getting 11,200 with a Master Airscrew 14-6, on homebrew 5%. I am thinking the APC 15-6 should be no problem. The engine litteraly screams, and sound really cool @ 1/4 throttle. Remember this is not a stock .90. It has a Bowman ring, Cline system, custom exhaust, and a Magnum 1.08 carb. After seeing it run yesterday, I will not be looking for a bigger engine. I just want to load it down a little more with a 15-6.

My mistake, the rpms were 12,200 rpm on the first tank of the day. A later tank while the temperature was getting close to 90 deg F resulted in 11,900-12,000. The .91 really snorts with a Boman ring and all the other little tweaks that I did to it. A larger prop is really needed since the bark that it makes at the high rpm will surely make a few of the older guys pissed. It sounds as if the prop is not big enough, since its throttle responce is next to instatnt.

airraptor

My Feedback: (66)

wrong many r/c engines will gain rpm with a larger carb.

Now i will say also that the super tiger carbs are very well made and maybe the best two cycle sport carbs excluding the ones with regulators and three needles.

that APC 15x6 should run well on that plane and engine combo...

Hobbsy

My Feedback: (102)

Jim is a man of great integrity, if he says he got a 500 rpm increase you can take that to the bank. If it were something as simple as moving the muffler out on the stack he would posted that as a heads up a long time ago.

1QwkSport2.5r

+1 on that. I'll add to the discussion - RC car guys swap bigger carbs in all the time. Bigger carbs almost always boost power in that application. There is a point when too big is too big. I really think most manufacturers are conservative with the size carbs they install on their engines. The same can be said of mufflers as well. If a 46 muffler installed on an Enya 30SS can boost rpm by 1700, I have no doubt a carb could boost rpm by 500 or more.

Sport_Pilot

Quote:

My mistake, the rpms were 12,200 rpm on the first tank of the day. A later tank while the temperature was getting close to 90 deg F resulted in 11,900-12,000. The .91 really snorts with a Boman ring and all the other little tweaks that I did to it. A larger prop is really needed since the bark that it makes at the high rpm will surely make a few of

Yes the engine will have less RPM with thinner air, regardless if from temperature or altitude. Who was it that claimed it did not because the prop does less work in thin air?

airraptor

My Feedback: (66)

most carbs are smaller than the hole thru the crank. MFG put small bore carbs on engies to have great fuel draw on sport engines so the end user will have a good running engine even when tanks are not installed correctly.

now matching the carb to the crank hole will give best rpm on some engines. the carb should be just slightly smaller than the bore in the crank.

the whole engine is a matched system. the better you optimize the internals the better it will perform, but once you start getting away from the MFG set up the more you will optimize the engine for a certain application.



Off subject here but, I found out last month that a old FP 40 will turn a 15x6 APC at 6,500 and needle just fine on it. the spool up though was very slow.

Superspook

My Feedback: (16)

Help! I have a large cub (91") with an ASP 108 and I don't want to destroy the cowl. I have the engine inverted and need a pitts style muffler with the exhaust pointed downward. have talked to Jtec but nothing good happenedyet. would appreciate any help available. Regards Superspook

Iflyglow

My Feedback: (79)

I would look for a Slimline "Sport inverted muffler". That is what I used to build my exhaust.