excuse me for poor english.
tb 33mm is useless
I made tb 35,38,40,42 and run my car(punto 60 1242ccm) for 2000km with every of them.
If you run car without other modifications the best IMO is tb38.
If you run car with better exhaust,air intake,ported head,chip ...the best IMO is tb40mm.
tb 35 is better then standard 30mm but not very much power increase .
42 is too big
on the picture is tb 32,35,38,42(40 is on my punto)