VVRC 40cc Twin

[Alky6]

Had to add some paint... Very pleased with the performance and noise reduction.

 

[Ohio AV8TOR]

Looks awesome Alky. I am so glad to hear that there is no power loss. The U shape design concerned me over the typical Y design because with the cylinders offset one exhaust make the single point before the other. I just could not see that being the most efficient but apparently it does not. I am remembering back to my racing days of Hooker headers where every tube was an equal length ti the collector.

 

[Alky6]

Thanks. Yep, 2-strokes are funny animals and the exhaust is even more strange. What we think intuitively usually doesn't hold true. Have had many many "good" ideas for the two-stroke boat racing exhaust that failed miserably. Had some others that were often odd that seemed to work! It's crazy! I am just pleased this exhaust system works well. I do have a couple points on the curve with a slight delay, but I think it may be due to my throttle curve and some jetting issues to still work out (or could be attributed to what you have already pointed out). Other than that, it's great.

 

[Alky6]

Since the weather has been great I temporarily suspended the JTEC build to get out some do some flying! Here are some updated results. I got the throttle curve and jetting squared away and now have excellent throttle response and linearity. I also tried a falcon 20x9 carbon. This prop on the ground turned 7050 and in the air unloaded to 8200. Compare to a Xoar 20x8 laminated at 7100 & 8600. The engine was much happier, uplines were much happier, and surprisingly, in-air temps were down about 15 degrees. Bonus, the prop is quieter also. So far, the Falcon is the best match of what I have tried, IMHO, for this engine and IMAC style flying. I have tried a xoar 20x8 (beech & laminated), the VVRC 21x8 beech, and the Falcon 20x9 carbon.

 

[Ohio AV8TOR]

I am liking the 20x9 Falcon carbon as well. Performance slightly better than the Vess 20B I used first and quieter.

 

[Flyingjon]

I am running a xoar 20x9 beech on mine but haven't installed any telemetry so I don't know what it's doing in the air. Also I just installed bowman rings so it's still breaking in and hasn't reached full rpm potential.

 

[Ohio AV8TOR]

I am running a xoar 20x9 beech on mine but haven't installed any telemetry so I don't know what it's doing in the air. Also I just installed bowman rings so it's still breaking in and hasn't reached full rpm potential.

What rpm do you get on the ground?

 

[Flyingjon]

I've checked it but it's been a month or 2 since I've ran it and I can't remember. Been too cold!

 

[stangflyer]

I've got a couple of questions for those that know about these lil twins. I have decided to convert my 96" Cessna over to gas and originally planned for a DLE 30. Maybe a bit much, but the 20 would probably not be too spectacular. On the other hand, a 40 twin would be really cool in the plane. It flew very well with the Saito 180 four stroke, (more than enough hp.) but just can't do the glow any longer. So here are my questions. First, Any of you out there that have experience with this motor, in your opinion... is the 40 a little much for the 96" 20lb. airframe? Second question, anyone have exact measurements plug to plug of these little guys? Any suggestions for a nice scale three blade prop?

Thanks everyone....

 

[Flyingjon]

Well as far as being too much I can't really say. Mine is in a 79" freestyle 260 at 11.5 lbs but yours is a scale plane and I would think it should be plenty. Mine is the SMALL 1/4-32 plug version an it measures 7-7/8" from cap to cap.