Originally Posted by ShawnQ
Another thing to keep in mind is that headers are 'tuned' using header primary lengths, flow, curve, etc.
You can't just take 3 pipes, collect them into one in such a way that they will fit into the car, and hope for a huge gain. The flow characteristics must also be better than the stockers.
Race headers are indeed tuned to their particular engine. Several engine parameters are needed to build a set of "tuned" headers.
Now taking a look at those Supersprint headers you will notice that they aren't equal length. That is most always the case on a "tuned" header design.
So to argue that
"You can't just take 3 pipes, collect them into one", sure you can and it would make a great street header (see Supersprint design). Anytime you remove turbulances (by utilizing individual tubes) and increase the scavaging (by adding a true collector) you will increase exhaust flow which in turn creates more horsepower. But if you wanted the most out of a header a "tuned" header such as the ones that HDDP had built are the way to go.
Folks I can't believe we are even debating whether headers will produce more horsepower.
This has been the case since headers were first made. Come on!