One of the loudest valves in the GFB range can now also be
one of the quietest - choose between silent and stealthy operation, or
an ear splitting WHOOSH!
The Mach 1 and Plumback valves have now been combined into one
affordable unit - the new Mach 1 kit comes complete with the parts
required to make this valve vent to atmosphere for maximum noise, or
plumb back for silent - and very importantly - LEGAL - operation.
Most early EVO models have no problems with atmosphere-venting, however
the later EVO VIII-IX, in particular the US models, can sometimes be
sensitive to full atmosphere venting, more so if using the factory AFM
with high boost. The problem that can arise in such conditions is
"jerking" or "bucking" during a partial throttle lift-off. This does
not usually affect stock or mildly modified engines, but if it is a
problem then generally recirculating at least some of the vented air
and softening the spring pre-load will help.