eiter way if they both performance manifolds you will still notice the difference from standar as they should b a slightly larger bore and thye will help the engine flow better thus increasing performance
they only add up to 25 bhp on some cars most cars they only add about 5-10 bhp which you can add around 5 bhp just with a quick tune up with new plugs etc and a lil tinker with the engine timig which you should do when u get a new manifold just so you get the maximum gain out of it
I think 4-2-1 increases mid-range torque & 4-1 is less resrictive at high revs, but losses a little low to mid-range torque.
as for this i'm unsure about the difference between the 2 but as i said at the top if they both performance manifolds ur goin to get performance gain across the rev range i would have thought the 4-1 manifold would b more increase is mid range and the 4-2-1 would b better hgh end as the exhaust gas flows into the single pipe easier with the 4-2-1 and the 4-1 the exhaust gasses would build up in the manfiold just like 20 people runnin to get in a lift tht only holds 10 at a time if you thinkabout it that way
but when people tune there cars for fast road maybe a bit of rallying every now and then iv allways heard of them using 4-2-1 manifolds
hope this kinda helps
