05-07-2015, 12:04 PM
Alright, I've discussed this a lot on hot rod forums when it comes to headers and free-flowing exhaust. You want to flow as much air out as possible for big power. Backpressure on modern four strokes is nearly irrelevant and is not needed. I've seen people say 'Oh I dyno'd more power on the 1-3/4" headers over the 2" headers, backpressure matters!' The truth is, if you get headers that don't match the head, you get turbulence and that causes reduced flow. People with 2" exhaust ports that use a 2" primary do see big gains over a 1-3/4" header. Anywho I tangented, you don't need to worry about backpressure. Pipes have a head loss caused by friction between the passing air and the rough surface of the pipe. With as many bends as there are in the pipe, you're going to get some backpressure no matter how much you try to alleviate it. So worry not. It will be there and it is not needed. Keep your primary size consistent with exhaust port size, you'll be fine.
Though, if you want to make more power, a nicely designed collector will provide a scavenging effect. A really nice example is how automotive headers are made, but your 4 in to 4 shouldn't lead to any significant loss in power (or any loss at all IMO) but I HAVE BEEN WRONG and you should never trust me
Though, if you want to make more power, a nicely designed collector will provide a scavenging effect. A really nice example is how automotive headers are made, but your 4 in to 4 shouldn't lead to any significant loss in power (or any loss at all IMO) but I HAVE BEEN WRONG and you should never trust me