Originally Posted by squawSkiBum

OK it looks like I was mistaken about the vent to atmosphere (VTA) valve on the N18. It is about 50/50 on the N14 though based on posts from people who have installed one.

The reason for either a VTA or recirculating valve is to prevent turbo "flutter", which is the impeller blades of the turbo stalling when the air stops moving because the throttle closed. This can damage the turbo bearings. N14 and N18 engines differ in that the N14 uses the throttle plate to regulate airflow into the intake manifold, the N18 uses variable valve lift. I'm not sure how this affects the overall issue but since there is a longer path in the N18 vs. the N14 (the N18 air path is all the way through the throttle body and intake runners up to the intake valves) there's likely more of a spring or cushion effect when you suddenly lift in the N18 vs. the N14. In either case there is be a boost spike as moving air hits closed throttle plate or intake valves.

With sustained full throttle, the turbo will be at maximum RPM so lifting suddenly and closing the throttle plate (N14) or reducing intake valve lift (N18) will stop the airflow out of the turbo. That airflow either has to get vented or recirculated. Venting it makes noise, which some people like, but it also means that the pressure the turbo has been working hard to build is lost and the turbo starts to slow down. Recirculating the output of the turbo back to the input keeps the turbo from slowing down which means that boost will build faster once you're back on the throttle again, so it minimizes turbo lag.

I get it that some people like to hear the noise of the turbo boost being released. I'm an engineer and tend to over analyze things, I think the recirculating valve is an elegant solution to minimizing turbo lag, and will always make my decision based on performance and efficiency. The original reciculation valve is well known for failures, there is an updated part available. But it's your MINI, you get to do what you want with it.

Originally Posted by Jason Cornelius

Since someone brought this back, I have upgraded my DV with Alta boost spring and knock off forge adapter with no issues. Holds boost all the way through rpm range, no fluctuations. This was more for the psss sound. Clubman’s are too quiet.

Originally Posted by Jeremyj

N18? I'm thinking of doing the same thing. Chinese adapter (eek) and spring.

Originally Posted by Jason Cornelius

N14, yes Chinese, Alta spring from Amazon.

https://www.ebay.com/itm/Blow-Off-Va...a-f4d370addf6d

this cost me 9 bucks and change shipped.

Originally Posted by Jeremyj

I heard they work with N18 with a little filing down. Is that true?

Originally Posted by Jeremyj

I heard they work with N18 with a little filing down. Is that true?