Pete,
I will try 12x5 APC or/and MAS and if I can get 9,600 RPM perhaps it will be enough.
By the way: my old Magnum PRO 45 turns 11x7 APC propeller at 10,250 on the ground using the same fuel as Jett60 so either this Magnum is quite "powerful" or my Jett60 is rather "weak". Again, only 8,500 RPM from this Jett on 12x7 propeller yesterday. I know that "weak" and "powerful" are not precise technical terms but this is the best description at this moment.
Brett,
Jett60 was straight from GMA in 2000 when I bought it and it had white, short, "plastic" venturi with the throat airflow diameter of 0.226" and the fuel delivery hole of 0.100". The spray bar fuel delivery hole was (and still is) 0.080". There was only one shim below the cylinder head but, unfortunately, I did not measure it so I do not know if it was "thick", "thin" or "normal".
When I got this engine from George Aldrich sixteen years ago, I knew very little about stunt and the complexity of two cycle ICE. I run this Jett only once in 2002 or 2003 using 12.75x4 Zinger propeller with Windy's carbon composite pipe, having straight end with a very short stinger. I did not measure the ground RPM at that time.
Then, the engine sat on the shelf for 11 years and I was working hard to build my retirement fund.
In 2014 the engine was dusted, inspected, cleaned and I started learning flying my IntrepidXL renamed Great White. I used 12.75x4 Zinger (cut from 14x4 therefore it was wide), Windy's pipe and 10% nitro Omega with some castor added. in 2014,I could not get launch RPM higher than 10,000 using this setup - the best was 9,300-9,600 so I was never sure if the pipe was actually doing anything except of muffling the noise. One hot day in 2015 Spring, the engine slowed down suddenly while the plane was overhead. The guy flying the plane, a very good stunt pilot, regained the control of the plane falling vertically on him and landed safely.
Jett60 lost almost the entire compression and it was very easy to turn the prop using pinky.
I mailed the engine to Dub Jett who replaced the worn out piston and installed the new Ro-Jett liner. I also got the brand new, black "plastic" (what is this material...is it Rilsan?) stock venturi with the throat airflow diameter of 0.186" and the fuel delivery hole of 0.060".
I partially broke this hybrid Jett flying my Great White but, in the end of 2015 Summer, I destroyed the plane. Jett60 survived with minimal damage and I am using it now to fly RToucan ( former name Score).
I know now much more about stunt and ICE and hope to move in small steps to fine tune this engine. I have finished the engine break process, compression is excellent ( Dub installed only one thin shim) and I will be experimenting with venturis and props. Like I wrote before, I need more launch RPM therefore the first step is to open up the venturi airflow - I will use again GMA white venturi with 0.226" opening and we will see.
Personally, I like 12x7 APC setup with the muffled Jett60 as I will be able to compare it to my Magnum Pro45 turning 11x7 APC but, again, I need more launch RPM.
If GMA venturi gives me this 1000 RPM I am looking for ( 9,500 RPM on 12x7 APC will be enough for sure as RToucan weights RTF dry 65 oz. and has more than 700 sq.in. wings area with flaps), the problem will be solved for a while. I like to have a lot of lines tension everywhere as this gives me this good feeling that the plane will not fall from the sky when there is a wind gust. Only when I learn the entire pattern, I will be looking for true fine tuning of lap times, tension and so on.
Best Regards,
M