I found a bored TB on ebay that was apparently bored to 59mm, was the origional bored size 52mm??? and would the 7mm make a big difference in horsepower, and if so how much
thanks

 

it depends on if it was an auto tb or a manual tb. I belive the manual tb's were 48mm and the autos were 52mm. I know the performance shops all sell 55 and 60mm tb's with the indication being that 55 is best for N/A motors and 60 being good for NOS or FI motors. From what I have read a bigger tb will improve your throttle response and give you better top end.

 

The hole where the TB neck meets the plenum is only 52mm at best (you can't quite fit the butterfly plate through it). So going bigger than that on the stock intake manifold will not give any extra airflow. What a larger TB will do, however, is cause a higher pressure (less vacuum, technically) in the plenum, which is what the MAP reads. So at WOT, the engine thinks there is less airflow than there actually is, and you get less fuel (and a smidge more timing advance). The Neon PCM runs very rich at WOT, so leaning it out a tad can gain a couple of ponies.

Best of luck!

 

****, the Tbs arent by any chance interchangelbe, meaning that that one wont fit on mine will it

 

don't really understand your last question but you can port match the tb and the intake so that they can match.