In the intercooler thread I mentioned that I have fitted an aftermarket diverter/blow-off valve on my QV.
Since I can't find anything on this topic here, I thought it might be interesting for you guys if I shared a bit of my experience.
The reason I started looking into aftermarket diverter valves was that some internet reading suggested me that the stock valve might not be all that happy with increased boost pressure following remapping. Also, the original valve is of the membrane type which is prone to deterioration over time and boost leaks even at stock boost levels.
BUT in a modern car such as the Giulietta, the diverter valve is actuated by the ECU which is much faster than the external aftermarket valves which are actuated in pressure differences. Also, the valve has to recirculate the air in order to avoid screwing up the air/fuel ratio when going back on power.
So, enter the DV+ valve from Go fast bits. It retains the ECU control over the diverter valve, fits as a straight replacement of the stock one, reformulated vented air and is able to hold far more boost. In addition an additional spring in the assembly retains some residual boost pressure in the intercooler, allowing going on boost quicker as the turbo doesn't have to start "from zero" on upshift.
The unit that fits the QV (at least the ones with the 940A1000 engine that I have) is the T9354
. When I contacted them about it they first said that they had no clue. After a few emails back and forth with them we concluded that it should probably fit. I ordered it form the German site with the thought of returning it should it not fit. Fortunately this didn't happen.
So, what is the result? More power early in the rev range, quicker boost and much better throttle response, especially in N mode. In D the retained boost is visible in the dynamic display as the boost graph never goes empty on upshift or liftoff. I also get the (subjective) impression that it holds boost better towards the redline.
One caveat to my impressions is that I fired a larger intercooler at the same time as the valve, so I cannot swear what effect is attributable to which mod.
I liked to this article
In the other thread where they describe the turbo lag reducing function of the valve.
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