seeing this on dave's web www.davesmotors.com/z-rc-tall-...e-manifold.html
it is written only take effect on low end torque only
does it give more torque on high end RPM also by preventing fuel air mixture spitting out?
longer manifold create bigger resonance effect at 18k rpm?

Longer intake manifolds on these engines will reduce spit back at low rpms when the throttle is cracked wide open and give some bottom end do to the mixture staying in the engine. Top rpm maybe sacrificed somewhat depending on the exhaust pipe being used.
As far as providing a thermal insulation with the Teflon gaskets is a hoax, since the heat will travel to the carb by the screws that bolt on the manifold, then from the manifold to the screws that bolt on the carb and one must be careful not to over tighten the manifold and over compress the Teflon gaskets and of course they do not warp as easily as the stock manifold.

ok thanks Les

so longer will not create resonance effect
but rather slow down intake in top end

The resonance is still there and there is more of a change with timing numbers, port areas & shape. Depending on the modifications done to a specific engine a longer intake track will make minor tuning changes that the pipe length maybe required. One will have to test and tune their own engine for the slight change. It is all about the flow..... Two-stroke engines are very sensitive to this concept and use expansion chambers that return the escaping air-fuel mixture back to the cylinder. VE is key.