sort your suspension out for the corners then you shouldn't have any issues with getting into third.
if you can get the car thru the corners better with the power on in second you should be able to hold the same sort of line with it in third ......

I just got the cam done up into a sports cam. the manifolds have been replaces with those from a a15 and same with the head but no modification has been done on the head.They have strict modificationj rules. it hasn't been shaved down or anything and the engine hasnt been bored out or rebuilt at all.

I am in Juniour Speedway driver so wile i was still inexperienced , 2nd gear was pumping out plenty of power but now after 5 years i am doing realy higfh s[peeds but i am limited because ii cant get out of 2nd gear and it gives the poor old sunny a bit of a hard time. When i try it in third it is way too sloppy on the corners and i end up going slower.

dont know exactly what you're after but i've had no trouble keeping mine moving using the standard 3.7 open centre and 185/60/13's and 195/50/15's .... now with a new 4.11 lsd and 185/45/15's it's still goes just as well ....
the A12 isn't a monster for torque so it's got to be driven higher in the revs to keep the momentum up and not rely on having the motor push the car up to speed from low revs.
what have you done to your motor ?? cam, head, bottom end etc ??

Anybody have any suggestions on weel sizes that ( with the right diff ratieo) can get a a12 racing engine into third gear wihout losing to much guts?