4-1 primarily for track use when you're at the top of the rev range more. I'd personally use a 4-2-1 manifold.

Also, just welding any bits of old pipe together and hoping for the best isnt really going to work well lol. Manifolds can gain, or lose you power if poorly designed. You need to think about scavenging, port sizes, lengths, diameters etc. I was going to make some manifolds for a car I once owned as the standard log ones were poor, and its ALOT of work to get right.