Well, I went flying. Mechanically the engine sounds very healthy, first flick start, no black oil, no overheating and good needle response. So after 10 minutes of running-in I decided it would be less boring to fly the thing.
Fuel is 80% methanol, 15% Aerosave synthetic and 5% Racing Castor #927.
I had a pile of cylinder heads to test, all prepared so that starting point is same (squish area, squish clearance, head volume), and all with the same weird bathtub combustion chamber. So, same layout with 3 main differences:
-Standard with nothing else special.
-With a titanium umbrella a'la Yuriy to protect plug and perhaps pre-heat and stabilize the burning process.
-Twin plug.
It was quite windy and turbulent so I could not fully focus to the engine but it seems to run very well. Much better power at richer mix than with older version, and allmost perfect running symmetry. I still need time to optimize the venturi/head volume ratios and play with tank position, but it looks very promising.
As I guessed, heads with Ti-umbrella and two plugs need slightly bigger head volume and give slightly better running stability, including outside/inside symmetry. I think that kind of proves that with horizontally mounted engines with healthy, efficient scavenging, those issues are closely related to burning stability during load variations.
I also found that Merlin 2004 plug works a little better than Enya #3. I have ordered Merlin flat-coil plugs too, it will be interesting to see if they offer any advantage. L
Topic: Allmost there.. (Read 2016 times)