Boost spike on mid/ high rpm gear change

[Steve4012]

Hi all. When I'm on full boost with the boost gauge needle vertical as it should be and then change gear I get a momentary flicker of the gauge needle to around 2 to 3 o'clock on the gauge. It's just an instant and doesn't stay there. The wastegate has been dismantled/ rebuilt as part of the rebuild and holds the boost steady until I depress the clutch/ come off throttle. I actually have this on both my G Turbo's so pretty sure it's normal but would appreciate confirmation. The blow off valve on the plenum is also fully functioning with the plunger moving freely. I'm thinking it's a momentary crossover between closing throttle and the blow off valve venting the excess pressure?

Thanks in advance, Steve.

[jonwat]

Isn't this is what a dump valve us meant to alleviate, the pressure spike that occurs with the snapping close of the throttle? 

[Escape]

The boost sensor is located in the plenum before the throttle bodies. If you lift off, boost will momentarily peak in the plenum, as the air has nowhere to go but it still being pushed in by the turbocharger until the wastegate opens and pressure drops. So the spike is normal, I get it on my SE as well, even with a blow-off valve fitted. Not much, certainly not a problem, but noticeable if you have your eye on the boost gauge when shifting.

Filip

[Steve4012]

Thanks gents for the confirmation. I've learnt to accelerate with one eye on the gauge and one on the road! I'll look at the road more in future☺