it all depends on your car. how it acts and how it feels and what your looking for that car to do. you will get a bit more boost out of the car with the valve and a better Throttle response, as well as taking any Yo-Yo it should have. We sell a lot of them and only have to trouble shoot problems due to vaccum leaks after install. Normally a inter cooler boot folded in or under. never becasue the valve didn't do that it should be. i personally hand make each one.
no you actually see more boost. it doesn't create it, but it does close faster, so the boost builds sooner (the throttle response part) and it closes fully so you not leaking any boost, and the combo of the two allows more boost to be made in the time you have between shifts. so if the the car sees 16 lbs before you and get 16.5 to even 17 lbs on average (some valves come really miss adjusted on the early cars, but not as bad on later cars).
over all i sell 10 to 20 valves a month on average, but only see about 5 -10 for sale used per year if that and that could be fore a lot of reason like selling the car. so i think most people are happy over all with the product and i always welcome feed back to refine any part of DT be it parts, web site, or new product idea.
At 74K miles I'd be tempted to replace the BPV on general principle. I gather you are not the original owner of this MINI so the service history is unknown.
Just for yucks you probably want to check out the condition of the other vital fluids if you have yet to address them.
But moving on..
From the look of the other bit of kit going on in 3 weeks I'm gonna go on a limb here and guess that you are buying a package deal?
Buy it yet, if not create new thread to discuss your choices...We fight nicely here, so it will make a for a good read...
I talked with someone from Grassroots Garage about this a while back and heard something similar, faster response from the valve, and reduced boost leakage so there's some credit, still, for me with a later car this upgrade isn't worth it until my stock valve is in need of replacement, there's other places I can look for power and I have no problem with the responsiveness of my car given the stock flywheel for now.
When taken in consideration of the other upcoming changes it's not a bad prophylactic maintenance item. 74K miles and we have no idea of service history. Is it a TX car, gets pretty darn hot a lot round here. Why not insure it's operation when opening up the breathing. You're gonna be in there anyway.
The $3 spring may be worth it for an extra half psi of boost and some throttle response, but I'm not 100% sure of what exactly I'd be doing once I got the BPV off so I'd have to add the probability I'd do it wrong and spend more than a little bit of time trying to get it right, time is money and right now my time's at a bit of a premium. The already done DT unit, at it's current cost, is a bit more than I'm willing to spend for maybe 1 or 2hp but at least would be an R&R job.
the DTBPV is a great mod, just feeling the difference in the spring before I got it installed I couldn't believe how weak my stock bpv spring was! Boost definitely comes quicker and I gained 1psi which is pretty much only good for bragging rights lol but it is a great mod boost is quick.
If the factory unit's always been leaking boost then you never had that last little bit of performance to begin with so upgrading a compromised factory piece is a gain. You yourself said it well:
Add in that the supercharger was added almost as an afterthought as a quick way to boost the performance of this already compromised engine and it's easy to believe that a spring BMW tried saving money on might be a place for performance improvements. This has been the nature of hot-rodding for 75 years and as long as there's accountants at a car company, there will be room for improvement.
