Specs:
- 17% Alta pulley
- 400ml injectors
- JCW air box and filter, cold air from cowling and from the front (just like a regular JCW)
- Newman PH2 (250/400) cam
- BMW Throttle body
- Adrian remap
- 2.5" stainless exhaust - resonated
- Standard manifold + catalytic converter
- Upgraded intercooler
- AEM Wideband sensor pre-cat
- Shell VPower 100 petrol

So just had the cam and the 17% pulley fitted but I'm somewhat struggling with low airmass readings when I datalog.
A 3rd gear pull will only show 705kg/h just before 7.000 rpm. This should be ~200Bhp if my math is correct. This seems low for the mods I'm running, I'd expect ~810 kg/h. (boost is just under 16psi) Has anyone done some data logging with a newman cam and a 17% pulley?
I do have good AFR, from ~13 low down to 12ísh at the top. And the car pulls cleany - just not like I'd expect from the mods.

I'm running the original belt still - and the tensioner is almost fully extended, but I cannot hear or feel the belt slipping on it. The BPV is the original one with only vacum to the actuator, I plan on changing it to get the boost as well - to try and force it closed once it gets on boost.

Anything else i should investigate to find the reason for the low airmass ?

 

I have to believe you're slipping with the OEM size belt. That is wayyy too large for the application. We were fighting belt slip when troubleshooting a friend's car who was using a JCW belt (11%) with a 15% pulley.

 

That is also what I think, but I cannot hear it slipping, the power is very linear, no "bumps" or anything that would indicate a slipping belt. But you might be right.

I got a 1360mm otgether with the pulley, but that was massively shorter than the original, so looked "off". I have ordered a 1368mm one now theoretically that shouls be right for it.

 

You 100% need to replace that belt with the correct shorter belt for the 17% pulley. When you use a belt that is too long it slips so small you don't hear it, but the MAP sensor will pick it up and it looks like spikes when you datalog the boost. That is what the ECU sees and pulls timing. This was one of the biggest problems we found when we started dyno tuning MINIs all the way back in 2007, such a simple fix, but people doing the tune didn't know how to read the data and would often think it was a fuel or clutch slip issue.

also note with those big intercoolers you will see a boost drop from the stock, so that can also effect you reading.

 

I did not see any spikes in the logs I did, but update frequency might be too slow for it to pick it up.

It doesn't pull timing according to my logs. I do run what I'd expect from the maps. (IIRC 26 deg at 6.500)

I have ordered a 1368mm belt for it, the 1360 was too short for my liking, so I'll try with the 1368mm. (Which should be spot on for a 17% reduces pulley)

Yes, drop in pressure, but increase in airflow It is the air flow that is low for my liking. I intentionally steered away from boost as this is not what makes power - air flow is