Randy Webb feels that his TB is best because of the variable bore - larger, funneling-down to slightly smaller, sort of like a velocity stack... As far as price goes, Peter at M7 should be contacted...
Some info for you that I have concluded during design of my TB;
The std 57mm TB actually has a cross sectional area equivalent to exactly 50mm,
this is due to the 57 by 10mm throttle spindle bar that resticts it at WOT.
The plastic SC inlet manifold is 63mm in dia once you have removed the messy 'rag'
just inside it ,therefore IMO 63mm is the best diameter for the TB to be.
The accuracy of the bore is critical in ensuring no jamming and good idle. This includes
roundness,squareness and on same c/l to spindle axis,zero taper,and fine surface finish
eg better than CLA16.
The replacement butterfly is of equal importance, to be machined with correct bore clearance
AND turned at the same angle as OEM. The reason for this is if you machine it at a greater or smaller angle than OE then at WOT the butterfly will not be vertical but slightly
under or over vertical in other words not full throttle!
Done properly thinning of the butterfly spindle is worthwhile too.
In essence all big TB s are not the same (once the engineering hat goes on )but may appear to be .
Best Regards Roland Gt Tuning ltd.