What is Spiking? Creeping?
"Spiking" occurs during your turbo's initial spool-up when the boost
level momentarily "spikes" past your set boost level. Let's say
your
boost is set for 12psi. You hit the gas and boost pressure builds-up
past 12psi to 14psi and then immediately comes down. The usual
cause is
that your boost control system is reacting too slowly. Solutions
include using a G-valve and keeping the vacuum lines very short and
unrestrictive. Experiementing with the G-valve vent or wastegate
spacers may help as well.
"Creeping" occurs after your initial spool-up when the boost slowly
creeps up or down as engine RPMs increase. Causes range from
turbo
size, to wastegate actuator spring stiffness, to wastegate port size,
to
intercooler restrictiveness, to leaking BOVs. I have been able
to
minimize creep by "tuning" my G-valve using a needle valve instead
of a
restrictor for the vent. You can also shim the wastegate actuator,
which effectivly changes the spring stiffness.
From an email posted by Russ Knize on the FMML