Venturi length on an Evolution .36?

venturi sizes - .225 in (5.7mm), .235 in (6.0mm), .275 in (7.0mm)

It seems all have the same internal diameter that I can research

so the only diff is length and they recommend staring with the 6mm middle size but give no hints why you would select the shorter or longer one

My guess is that you could swap around until you found the strongest power given a certain fuel or propeller or even a certain fuel tank or location

I have never fussed with different LENGTH venturi. Usually we experiment (or copy someone else formula/recipe) with internal diameter. Larger diameters pass more air at the cost of flow velocity. The loss of flow velocity will usually make it hard to draw fuel from a hard tank with no pressure. Smaller diameters speed up the flow and help fuel draw dramatically but limit the air ...both changes have significant effect on torque and rpm

I bet Ken Cook may have some recommendation on what would suggest using the shorter or longer stack...

I love to tinker so I would start in the middle then experiment with the short, and then the long to see what changed....

Then there is fiddling with 10, 15 or 25% nitros, and then there is experimenting with prop diameter and pitch, and then back to fiddling with the venturi to see were best power, reliability, and fuel economy fall

Fun to be sure for a tinkerer....but real frustrating for someone who just wants to start the damned thing and go fly