Fifer wrote:Thanks - looks like its a Muzzy then, in the absence of anything to the contrary.
Pipe technology was evolving at the time these Muzzy systems were manufactured. My ZXR Muzzy system on the dyno had a noticeable flat spot / plateau around the 7000rpm mark before building good BHP again. Not such a big issue on the track as you are usually above the 7000rpm range. However, air fuel ratio was a bit all over the shop throughout the rev range. Too rich in some parts of the range and too lean in others. There is a lot of turbulence in the collector - at the 4 into 1 junction that contributes to this.
On my bike, Phil Tainton, Warren and Hayden at PTR were able to gain 5.5 BHP at that 7000rpm point and stabilise the AFR significantly by welding a plate into the collector, in effect making it a 4 into 2 into 1. A highly recommended mod.