Join Date: Sep 2011
Location: Manchester, England
It shouldn't be taken for granted that flow will increase.
Wider, more open "hi-flow" pipes can accommodate more gas but that means the gas travels slower.
This reduces engine scavenging and reduces performance compared to the OEM pipe.
A lot of what people believe to be issues of tuning the mixture are really issues with the harmonic shock wave reflections and the amount/ timing of scavenger pulses due to the shape/length of the replacement exhaust.