EF B20 swap, Which exhaust manifold to use to avoid cutting and welding? 91 integra's? Or are there any aftermarket ones?

 

I have the stock manifold that came with the B20 and it was close but it fit without cutting. You should consider an innovative traction bar set up. It is an incredible handling improvement over stock and allows for a lot more space in front of the engine. They are also not too expensive for the improvement you get. If you ever go turbo, or even if you want a nice 4-1 header, you will need to mess with the crossmember eventually. I've read a 4-1 works well on the B20 because it provides better top end, which is what the B20 lacks. A believe a 4-2-1 gives you more low end torque, but with the B20 the top end is where you need improvement.