someone knows how to figure the diameter of the TB in a particular aplication,any formula of engine configuration or so....

 

I would say that so it isnt a restriction, go with whatever size intake piping you are using.
im using 3" piping (76mm) and I have a 75mm throttle body. 76 would be ideal, but I used what was available at that time for cheap.

 

for me: 70mm piping and 70mm TB,
Depends of your intake manifold too.

 

Last year I had a 70mm t-body and 3" piping. Mid-season I put on a 90mm and 4" charge piping resulting in zero gains....

 

ouch
prob made it laggy too. unless its a straight drag car and doesnt see under 6k rpms ha

 

Laggy? Piping size doesnt matter as much as people things it does.

 

I stand corrected. i should have know that, i remember swapping to a huge fmic and the difference in spool time was hardly noticeable..and that was with a small *** turbo.

 

Yeah you dont gain much.

Before was using oem b16 tb and it works.

Now using 3in pipes and 76mm tb. Just matching it.