the jenvey site says, in an inlet track butterfly to valve distance should be "praticle minimum of 200mm"

does this mean 200mm is the best compromise or that longer is better.

any one with any experience or with any general comments like to give their 2p worth before i do any more work

cheers
liam Mc

IMO : It means it should be at least 200mm between the butterflies and the valves if practical.
Obviously on some cars there's just not the room available to do it like that.

Inlet tract length has an effect on inlet air pulse timing. Longer length brings the pulses into effect at lower RPM and the pulses increase volumetric efficiency of the cylinders thus making more torque/power.

The longer the inlet tract (distance from butterfly to valve) the lower the RPM at which this effect occurs.

So I think the 200mm is a minimum value. Have a search on all the usual car forums and you'll find a calculation for the relationship.

I'm not convinced that butterfly position is that critical. Certainly not for maximum power anyway as when it's wide open it should be more or less "invisible" to the airflow anyway.

The overall length of the inlet tract is the important parameter for both peak power and torque.