How big to go with boring exhaust manifold

[FL-cracker]

I have a old style small bore "43mm" factory manifold and elbow. I am gona have them bored buy a friend of mine, and was just curious if anyone else has played with this. The new manifolds are 47mm, has anyone gone bigger? What effect does this have on the performance of the motor. "particularly a bigbore flat top motor".

lets discuss

 

[butti]

48mm

 

[Freestyleriverrat]

I did mine a little over a month ago. I think I went up to about 46mm but got anxious and put it on. I will finish it later. I just used a dremel and a sanding wheel.