I've had a Cooper S for a week. I know nothing of it's mods other than the SC pulley looks to me to be aftermarket. So I've assumed I've a 15% pulley.

The Android app "Torque", connected to OBD2, reports that the boost pressure at idle is 7-8psi. That seems kinda high. Idle speed seems reasonable to me. Don't recall the exact rpm, 700rpm maybe.

The gain of boost pressure vs. RPM seems odd to me. I would have expected boost pressure to always go up with RPM in a linear relationship. Is that reasonable or am I missing something? Maybe I'm being fooled by the sluggishness of the OBD2 data?

 

Another anomaly. On the way to work this morning I accelerated from 3k to 4k rpm at maybe half throttle. The boost went from 15psi to 12psi. What sense does that make?

 

We'd get there when we get there message relaying.

 

Huh?

I figure there's 3 possibilities.
The Torque app doesn't accurately interpret the OBD2 data for boost. Is there a Torque app user here that is seeing boost info that makes sense?

The OBD2 stream has bad data because of a bad sensor. If so, what's the impact of this. Does boost pressure play into engine management apps? BTW, what's the acronym for the engine management computer in Mini parlance? They use "DME" like the BMW types use?

The boost pulley or maybe the belt is slipping.

How common are the latter two issues?

 

Means there's no service level agreement on the low-speed bus, it'll get there when it gets there

In my experience the OBD data is highly delayed, by 1-2 sec, and the delay is inconsistent. That can really throw off your visual reading of the info. It's not a Torque issue, it's just that there's no high speed CAN bus available. Best bet is to chart it and pull at WOT. Anything other than WOT and the system is feathering the bypass valve.

Are you sure you're reading 8psi and not -8psi? At idle you should have manifold vacuum.

 

The apps like that ( I have Dash Command) does have a very noticeable amount of lag in the signal. For most things it’s not that big of a deal, but for boost the lag bothers me enough that I installed a real gauge, but use the app for lots of other parameters.
Yeah, at idle you should be reading vacuum. Boost is read in psi, but on the negative side, vacuum is read in inHg (inches of mercury)

 

I run Torque App and adjusted the settings to read at 0. In normal config -14.7 it seemed the boost was really high. This way seems normal and when I left off it will read vacuum. It will drive you mad due to the lag. I am going to install a gauge but keep Torque for other stuff.

 

'What are you? A FAE or sales engineer? You are too smirk for that, and please take that as a compliment.

 

Mid the lag drives you as crazy as it did me, a real gauge is the only way to go.
I do the same, I use Dash Command for everything but boost.

 

On the way home last night I played with RPM and boost pressures, as indicated by the Torque App. There was no difference worth noting between 3k and 4k rpm. Both showed 12-13psi of boost. Surprisingly, boost pressure seemed to be sensitive to throttle position. A little more throttle and the boost goes up. A little less throttle and the boost goes down. But think about how intake vacuum corresponds with throttle position.

More throttle means pressure goes up (less vacuum because butterfly is open a bit more). We do have a butterfly in our intake, yes? Remember, I've had the car a week.

Less throttle means pressure goes down (more vacuum because pistons sucking air and butterfly is closed a bit more).

Here's where it gets weird. I did a couple WOT tests from 3-4kpm and indicated boost went to 25psi. Woah, that seems way too high. The app indicated this almost immed, which rules out OBD2 data lag as the culprit here.

I need someone in this thread that is also reading boost psi from the OBD2 stream. If you know someone doing that, pls point out this thread to them. Their experience would be valuable to hear from.

I need a 2nd opinion. I've got a vac/boost gauge stashed somewhere. I need to find it, T it in to the vac line, flex tie it to a windshield wiper, and do some more testing.

 

Your bypass valve is closing under more throttle, dumping more boost air into the manifold. Remember, you're reading manifold pressure.
You are reading absolute pressure, so you have to subtract local atmospheric pressure. It's closer to 11 psi.
Close, though I think the FAEs have rubbed off on me

 

Re. bypass valve. I had to go look that up. I understand the idea but less so about how it functions in practice. Does the bypass valve function like an on/off switch or does it modulate with changing intake vac? How much vac triggers the bypass valve closed. Like maybe it's something that happens only at high intake vacuum or it happens at more moderate levels?

Re. absolute pressure. YES! That totally makes sense. I owe you a beer for that.