Shortening the rod (increasing the spring pressure) has the effect of generating boost overshoot. The ecu will then try and back it off usually resulting in some undershoot. As an extreme the boost will overshoot and stay there cos the ecu can't cope but it will always try. Higher spring pressure keeps the wastegate closed for longer.

Mike Tuckwoods car was overboosting to 1.8 bar due to this.

 

Has anyone played with lengthening/shortening the length of the "rod" from the actuator to the wastegate control ?

Have heard that shimming the actuator can allow more boost, but since the actuator is bolted at the back not front this isnt an option. Does look like the rod is adjustable though.

One theory would be that shortening the rod means when the actuator opens (to close the wastegate) it can't close it as much as it would like..thus more boost.

 

Lee,

I think this might have worked with cars like the R5 GT Turbo, but the Scooby has a closed loop boost control system, so the ECU will alter the control solenoid timing to get the right amount of boost as measured via the MAP sensor.

Not a good idea probably, but then what do I know....

Cheers,

Alex

 

Hmm. this is pretty much as I guessed.

I.e. shorten the rod the ECU keeps the solenoid shut for longer allowing the actuator to see whatever pressure is needed to regulate the boost.

Until a point where the rod is so short there is insufficient travel to completely close the wastegate..boost will continue to rise regardless of ECU "panic" until cut-out or big-bang !

oh well, worth a try.