A 28mm pull cable actuated butterfly valve from Ecotron UAV was selected. No caming was done at the pedal side or the throttle side. What I mean by "camming" is trying to linearize the S curve nature of a butterfly valve so Manifold Pressure vs Pedal Position is more linearized.

 

In our car PF22, Angular Position of the pedal was directly porportional with Throttle Position. We did this out of simplicity. The 28mm size did help linearize the first 40% of the throttle position.

 

(In Formula SAE the throttle body is upstream of the 20mm restrictor.)