Originally Posted by bradleyland
To be fair, and I can't believe I'm even offering any explanation for this viewpoint, Clarence isn't claiming that the variation accounts for the full difference between the engines. As far as I can tell, he's claiming that some engines, when dyno'd, do not produce the full baseline horsepower expected from the N20 240 HP version. So for example:
- Engine rolls off the assembly line and dynos 228 HP (5% lower than expected)
- This fails to meet the benchmark, and the engine is then "binned" as a 180 HP version
This is where things get janky. We must assume at this point that the engine will circle back in to some stage of the production where it is re-flashed with the 180 HP ECU package and re-run on the dyno, because we can't simply sell the 180 HP version with "just under" the output of the 240 HP version. That isn't supported by user submitted dyno evidence either.
In order for the scenario described above to make any sense at all, the following conditions must be true:
- BMW's engine manufacturing has a high defect rate
- Producing, dyno testing, reflashing, and dyno testing again is less expensive than simply engineering two versions of the engine
I find both of these claims dubious at best.
So it's either all this bullshit, or BMW simply engineered the two engines accordingly and we haven't discovered exactly what component it is that they changed yet.
Which is more probable?
Thank you, I've never said the variations can be that big. All I've said is anything less than 245ps can be sold as a U0 after reflashing. Reflashing can be done at the dyno station & after that the engine can be tested again. The engine can stay at the dyno station thruout the process. Also, peak power & torque are not the only criterias, there's also the power & torque curves, amongst other things (e.g. whether the engine produces at least the baseline power & torque thruout the rev range). Strictly speaking they cannot sell the engine as a 28i even if it misses one of these measurements by a hair (e.g. <1%, & I assume that's the biggest variation they're going to get). We have no idea how strict their standards are, & judging by the dyno plots of various O0s in stock form, it can be that by just meeting the baseline is for them considered a failure.
We've already discovered long ago (early last yr to be precise) that there are 2 versions of the U0 engine - one with 11:1 compression & the other with 10:1 compression. The high compression version (fitted to most F30 & F10/11) have unique pistons as described in the Chinese article above. In fact the technical training staff from BMW China confirmed that, for the high compression version, the only physical difference between a U0 & O0 is the pistons. All other mechanical components are identical. Therefore the high compression version is always destined to be a U0 from the very first step in the assembly process.
What's interesting is the low compression version. That engine, fitted to all E84, F25 & some F30s & F10/11s (namely the xDrive version & some specific markets), is identical to O0 part for part. The low compression version did use a different turbo during periods of time in late 2011 (according to ETK), but after that the turbo is the same. For this version of the N20 it's up to u to think how BMW chooses which ones have the priviledge to be a U0 & not a O0.
So far nobody has posted a dyno plot of the U0 in stock form, but the Chinese article did suggest that, like the O0, the factory claims are conservative.