It doesn't make much of if any difference but every little helps too:)
If you want to get it done, any machine shop should be able to do it.
Its just a case of mounting the throttle body on a lathe and boring out by about 3mm
then making up a new butterfly to fit.
I've been getting one or two and an M20 one for a mate ready to work on in the next week or two.
its not needed.
the metric mechanic 2.1L ralley motor makes 250 hp and uses stock throttle body.
EDIT:cone filter setup and you'll be set.
What? this one?
http://ie.youtube.com/watch?v=MjrKaFgd190&feature=relatedTo be honest, it seems very slow for what they cost and the power they are suppose to be producing.
Cone filters make no difference whatsover apart from more noise unless used with a decent heatshield too