Hi there Hans,

Vibrationwise, I see not much difference, if any at all. Both engines run very smooth.
I run the 35cc on my 9 kilo Multiplex big lift, using the 3271 muffler and Mejzlik 18x10 prop at 7600 rpm. To get a 4 meter glider up to release height I need about half to three quarters of a flight pattern circle.
Using a tuned pipe, the header is 22mm outer diameter, and substantially longer than the 26cc header. To reduce the heat at the coupler end, I replaced a part of it with corrugated stainless, brazed in between. That allowed the use of Glass fibre reinforced silicone hose instead of Teflon tubing. The GFR silicone hose is more flexible.