When the bypass valve is removed from the engine, the center flap should be fully closed. If not, you should replace it.

I just checked the by pass valve. I watched as my wife revved the engine for me. She got it to about 3k rpms and the valve never closed all the way and it slowly opened all the way again, without her letting off the throttle. But the valve don't feel super loose when opening it manually with the engine off either. Would this be a sign of a bad by pass valve?

Our 15% pulley typically produces around 14.5 psi of boost, so the 17% should be more than that.

It sounds like you have a boost leak, which would explain the sluggish performance. The first thing I would check is the bypass valve.

It has a 17% reduction pulley on the supercharger and the max I've seen it push is maybe 11 psi. What boost should it be pushing with the 17% reduction pulley? 

The throttle on the MINI is definitely not lightning fast because of the heavy dual mass flywheel, but it shouldn't be 'sluggish'.  Since you have a boost gauge, it's probably not a leak in the intake system, although it could be a small leak. You should see a maximum of around 12 lbs of boost with the stock supercharger.

When I hear of sluggish acceleration, I usually suspect the bypass valve. You might check this to confirm that it is closed in steady state. If not closed, you are loosing boost pressure under acceleration....
 

Probably no code would set, you can remove the feed gas o2’s leave them or it connected, wired up out of the way to get a quick sense if that’s the problem.

Cat crossed my mind, but it has no check engine light. Then again it could be normal on the MCS and I don't know. I was reading other post about the sprintbooster. Maybe what I am feeling is what people are putting the sprintbooster on for. 

Melted cat exhaust restriction? Not a real one!

Yes it is the Supercharged version, and yes the supercharger is working. I have a boost gauge that shows boost. 

My first thought - is it a supercharger engine? If it is not working then the engine has little power.

When i first looked at BMW minis, an early model was normally aspirated. Unbelievably non-sporty slug. I did not buy .

When 2004 came around, the supercharged engine was an astronomical leap forward . I bought it .

Hello Everyone, 

I'm new here to Mini Mania and this is also my first Forum to be part of. I just bought a 05 Cooper S with a manual transmission. I highly enjoy it and I believe everything to be in working order, but I have a question. If free revving the engine, it is EXTREMELY slow. It feels like it takes A LOT of work to get the rpms up. Drivablity is good, power seems good, but when you are taking off from a stop (just normal driving, not racing) it feels like it takes a lot of work to get the rpms up to take off. Is this a normal characteristic of the car or is there something that possible needs to be repaired? It doesn't feel normal. I have never driven a car (even slow cars) that takes so much work to raise the rpms.