pittster wrote:....While there are differences in 4-2 vs 4-1 most systems that have twin outlet pipes normally go 4-2-1-2 or 4-1-2 ..
Early model 4-cyl bikes were a fair bit different - none of these ( basically any 4-cyl bike made between the late 60's and the late 80's) - had either a 4-1-2 or a 4-2-1-2 system at all......this is something that has only come into exhaust pipe design in the last 20 years, and it is nearly all driven by cosmetics and noise limits - not good performance. Most of these older 4-cyl bikes had a 2-1 on each side, with a collector pipe across the guts, and a big single muffler out each side.....
Naked Twin wrote:......I thought, well I have seen it done of v8's is to take it 4 into 1 with a correctly designed exhaust will create a vacuum in the manifold and in effect suck the exhaust fumes out from the ensuing firing cyclinder......
and that is why they are called ......Extractors............*tuned length* headers work best at a certain rpm, and generally are worse at other rev ranges than *interference* headers - which use different header lengths for each cylinder - these pipes provide a fatter spread of power, but generally a lower peak hp maximum, than the tuned length........
as always with any engine tuning - its always about trade-offs and sacrificing one thing to get another......
