John Reid wrote:It doesnt do any harm going to the bigger size when you consider how much cheaper you can pick one up for..
Think mine is a "polished out" 56mm from a rover turbo, or tomcat or whatever.
Noops has one the same, much better than the std plastic one in anyones book. Much cheaper than a 52mm one from Elise parts..
It *DOES* harm to step out;
(a) it slows airflow
(b) it causes turbulence.
Ideally you want to sleeve the new TB to have the same I/D as the plenum, though a compromise will be to blend the two together over an inch or so in each direction, or get a smaller TB.
Can you not just take a 48mm alloy body, remove the butteryfly and spindle, bore it out, source/make a brass disc of suitable OD to replace the smaller one you took out?
If so, I'll happily pay someone with skillz and access to supplies to get mine reworked.
Cheers,
Robin