I too had felt a significant difference on the track, changing from a 2 inch to a 2 1/2 inch system.. A14 had much better mid to high response.

Benny

i'm running a 2 inch on my rally car but i'm soon to upgrade to a 2 1/2 inch as i have heard from another with a 1200 rally car that he noticed an improvement going from 2 1/4 to 2 1/2. His a12 is out to about 1600cc though. This is all press bent, so probably a mandrel bent 2 1/4 would be fine but probably more expensive.

i've got 2 1/2 inch mandrel bent exhaust on an a12 it works fine.

if you get extractors put on.
don't get hitech ones they rub on the bellhousing

i run a 4 1/2" 'zorst' on my car, with 3" system :) and its a rotary. even though its broken atm.

Most of it's Australian. Even I have trouble with it sometimes

Ok thanks sorry not familar with the wording over there yet I am working on it

Zorst - Defined in the Datsun owner dictionary, as an uncommonly used noun for an A series engines way to release combusted materials, commonly known in the english language as an exhaust

What is a zorst?

i ran a 2" Zorst on my A14 coupe, it was great single lukey muffler with a bit of a gurgle on down gearing. i love it.

what are you planning on doing to the motor? What extractors/cam/carbs? If your building a racecar with twin sidedrafts, Uber cam and 4-1 extractors then a 2" will be more than enough in my opinion but if its going to be a daily driver get something smaller to fit or maybe go to a performance zorst dealer like powerflow or something and ask them to work out a nice system.