Old b pipe head pipes vs newer head pipes

[Storbeck]

On older b pipe head pipes with the smaller diameter at the manifold, is the only difference the bore at the manifold? So if that's bored out to the larger diameter performance will be there same as a newer head pipe?

 

[Quinc]

Correct. Unless it is a SN pipe then the headpipe only has 2 screws.

 

[Pro-pulsion]

Additional note, the headpipes that are actually inscribed to say "B-Pipe" have a reduced bolt hole thickness and do occasionally fracture at the outter bolt. The older headpipes that were not marked on the I.D. flat with anything more than Factory Pipe had to use longer bolts for the thicker bosses. If I remember correctly the reason for reducing the flange thickness was because they found with that slightly shorter height, the pipe responded a little more instantly but it came at the cost of some structural integrity...hence the breaking off at the bolt holes