Possible under-boosting issue with my remapped 20i?

[Felixlamb]

Heya,

Firstly, apologies for the long post, but I'm posting this with the hope that someone who knows more than me can offer some advice!

Back in September, I took my Z4 to Will @ Performance Torque to get it remapped on his rolling road. Thread: viewtopic.php?t=131485

I mentioned that I picked one of the worst days to get it remapped, as it was pretty warm and humid, which made it difficult to keep the temps at bay. Regardless, I think he said that it was still running the same boost levels as other remapped 18i/20i/28i Z4s he's done, just that the ECU was toning down the boost because of the IATs.

I've got an (annoyingly not so cheapo, and definitely overpriced) BlueDriver OBD scanner, which can read the data from the car. I find all the info quite interesting so keep it plugged in most of the time so I can see the readings on my phone. However one thing which is confusing me is the boost level it is quoting.

From what I understand, the stock 20i boost is around 8-9 PSI, with the stock 28i boosting to around 17 PSI. My BlueDriver app shows that at WOT, the maximum boost I'm making is around 17 PSI (app shows this as 31.5 PSI, before subtracting 1 atmosphere @ ~14.5 PSI), so the same as a stock 28i. That has me slightly confused, as I expected it to be boosting closer to 19-20+ PSI. The boost also seems to tail off quite quickly, which I don't really understand, as the IATs aren't even that high at that stage, so it does start to feel a touch breathless in the final half of a pull. I absolutely understand that the boost will decrease slightly during a pull (not just due to rising IATs), but from what I've seen, it only normally drops off by a couple of PSI at the maximum. Whilst I've only been actively recording this recently, I know for certain that it was doing the same thing even in the winter where IATs wouldn't be a problem.

Here's a couple of logs which demonstrate this (note that the throttle % never shows 100%, but these were all done with me being locked in gear in Sport+ mode, with my foot to the floor, such that the kickdown button was depressed for consistency. 14.5 PSI will need to be subtracted from all readings. All done with Costco's finest premium unleaded!

4th gear pulls:

17.3 PSI max, decreasing to 13.3 PSI


16.2 PSI max, decreasing to 12.8 PSI

3rd gear pulls:

16.4 PSI max, decreasing to 13.5 PSI


17.6 PSI max, decreasing to 13.9 PSI

And finally, a 2nd-3rd gear pull, followed by a 3rd-4th gear pull:

17.4 PSI max, but oddly drops sharply to 10.9 PSI, and only increases following gear change to 3rd decreasing to 13.9 PSI


17.0 PSI max, but again oddly drops to 12.9 PSI, and never really recovers, despite a gear change into 4th.

Maybe this isn't actually an issue, and I'm just a drama queen, but to me it definitely seems to not really be boosting as high as it probably should be? It seems that, if anything, it's boosting lower than a standard 28i? It's all very confusing as my graph printout would suggest otherwise (at least with the torque):

[B21]

Making power on a turbo’s engine like the N54,N55, N20, B48, B58 is a function of many things.

The tuner’s understanding of how the logic of the DME works and what all the multitude of tables are used for what reasons and why,

Asked for boost, asked for ignition timing, asked for fuel ratio, asked for fuel amounts etc etc

Limits caused by wear and tear on fuel pump volume , pressure, ignition, injectors

So to come to your point without being a mind reader of either BMW / Bosch and /or the tuner who knows..

You may be suffering from a hard ware related issue such as a failing boost controller, diverter valve, boost leak, tired turbo and /or an inadvertent or deliberate action of the tuner.

I learnt the hard way that technical support for N20 tuning is very limited in the UK and generally one tuner won’t touch another’s work.

So you can accept the way it is or book dyno time with a competent entity who will probably run you tune, re program it back to OE and then apply their tune.

There is not enough public body of work on N20s but now I’ve twiddling with N54s where there’s a huge body of knowledge on that and it’s just simply amazing how sophisticated tuners can be.

Running lots of boost isn’t necessarily the panacea to making power.

I’m not dissing your tuner but simply saying that the level of tuners, their understanding of what will work and what won’t is not something most buyers can evaluate.

So the question is..if you hadn’t got your OBD reader would you have been happy?

[Smartbear]

Felixlamb, how many miles has your n20 covered?
Rob

[B21]

FWIW on other turbo tunes boost dropping towards the red line is quite common to avoid overdressing the engine..

The MHD tunes for the N54 do this..I know different engine etc..

[R.E92]

The reason for boost falling off at higher RPMs is that typically OE turbos are sized to provide fast flow for response at lower RPMs. As RPMs increase the airflow demands rise and the small turbo can't keep up.

If you suspect you are getting less boost than you should it might be worth checking for boost leaks. Does the N20 in the Z4 use an electronic actuator or pneumatic? If pneumatic then check for vacuum leaks and possibly replace the boost solenoid.

[Felixlamb]

Sorry! Been at work and wanted to answer on the laptop rather than faffing on the phone! Thanks for all your responses.

So the question is..if you hadn’t got your OBD reader would you have been happy?

Until I drove the family’s B57 730D and realised that my Z4, despite being over 500KG lighter and with what I expected to be similar HP (but of course lower torque) was noticeably slower
Otherwise I agree with you - ignorance is bliss and all that…

Felixlamb, how many miles has your n20 covered?
Rob

It’s at about 46K I believe, although probably less than 4K have been put on it since the remap. Has always been run on some form of premium too.

The reason for boost falling off at higher RPMs is that typically OE turbos are sized to provide fast flow for response at lower RPMs. As RPMs increase the airflow demands rise and the small turbo can't keep up.

If you suspect you are getting less boost than you should it might be worth checking for boost leaks. Does the N20 in the Z4 use an electronic actuator or pneumatic? If pneumatic then check for vacuum leaks and possibly replace the boost solenoid.

Mine is electronically actuated, although I’m aware that there’s a cut-off where they used to be pneumatically actuated instead. I might see if I can get any of the intake hoses off and check for leaks.

I might try and raise this with Will and see if he has any thoughts on it all. It’s very odd as other guys who have had their Zeds remapped there are closer to 260hp, and their torque curves remain flatter for far longer. As it stands, there isn’t really any point staying in the same gear once I get past ~5k RPM.

[B21]

As R.E92 says the boost runs out but generally this engine doesn't want to rev, even when I ftted a 20% bigger volume turbo..

There's something wrong with your set up as the lowest I've seen is about 255 bhp and the best especially with an EWG is up in the 285-295

I'd say that a well sorted N20 with the 8 speed auro should feel like a pretty rapid affair..

HPFP may be an issue..maybe leakage some where, boost controller valve, diverter valve..unlikley to be coked up.

Here's how the others looked..

[R.E92]

It's a bit of a myth that holding peak boost is all that matters. Although the boost might taper off at higher RPM, you are still getting more power out of the engine because of the higher revs. It's only in scenarios where torque is artificially limited, usually as your approach the limiter, that it becomes beneficial to shift slightly earlier.

If your tool can log the wastegate position then you have an idea of the turbo utilisation. Just looking at boost value doesn't tell you if the tune is bad. Your power output shouldn't be limited by intake temperatures unless they are above 50C.

[Felixlamb]

As R.E92 says the boost runs out but generally this engine doesn't want to rev, even when I ftted a 20% bigger volume turbo..

There's something wrong with your set up as the lowest I've seen is about 255 bhp and the best especially with an EWG is up in the 285-295

I'd say that a well sorted N20 with the 8 speed auro should feel like a pretty rapid affair..

HPFP may be an issue..maybe leakage some where, boost controller valve, diverter valve..unlikley to be coked up.

Here's how the others looked..

Thanks for this Pete - that’s a very useful table. Yeah mine definitely appears to be lacking compared to the others listed.
It’s certainly far quicker than it was stock, but I do feel that it probably should have a bit more oomph.
I’m also now running a resonator delete, so whilst the effect would probably be negligible, there should be a touch less restriction in the exhaust vs stock, but I don’t think this would have affected the performance at all.

It's a bit of a myth that holding peak boost is all that matters. Although the boost might taper off at higher RPM, you are still getting more power out of the engine because of the higher revs. It's only in scenarios where torque is artificially limited, usually as your approach the limiter, that it becomes beneficial to shift slightly earlier.

If your tool can log the wastegate position then you have an idea of the turbo utilisation. Just looking at boost value doesn't tell you if the tune is bad. Your power output shouldn't be limited by intake temperatures unless they are above 50C.

I’ll have to see what info my reader can record. From what I remember, it’s quite limited on the info it can obtain, but there might be something which can give an indication of any issues. If this tool can’t get this info, are you aware of another one which can?

[R.E92]

If ProTool works on an N20 then that's your best bet. Pete has it and also owned an N20 at one point so may be able to tell you for certain.

[B21]

If ProTool works on an N20 then that's your best bet. Pete has it and also owned an N20 at one point so may be able to tell you for certain.

Yes Bimmergeeks Protool does data logging, upto 10 channels displayed real time or more of just recorded to a csv type file..

The N20 DME doesn’t output some of the ‘traditional’ sensor outputs but should allow sufficient understanding..

The resonator delete would have zippo effect on the numbers..apart from a nasty drone ..

I have the feeling of a duff tune..ny first Celtic one was bad, nobody including Celtic ever explained it..

[Felixlamb]

If ProTool works on an N20 then that's your best bet. Pete has it and also owned an N20 at one point so may be able to tell you for certain.

Yes Bimmergeeks Protool does data logging, upto 10 channels displayed real time or more of just recorded to a csv type file..

The N20 DME doesn’t output some of the ‘traditional’ sensor outputs but should allow sufficient understanding..

The resonator delete would have zippo effect on the numbers..apart from a nasty drone ..

I have the feeling of a duff tune..ny first Celtic one was bad, nobody including Celtic ever explained it..

Balls. Don't have any android devices in our household
I think I'm about due for a spark plug change, so this might have a small effect on things - Literally in BMW now for my MOT and asked them for a quote... 500 quid for oil, filters and spark plugs... absolute joke.

Can't hear the drone over the road noise on the RFT 19s - every cloud and all that
Joking aside, the drone honestly isn't that bad at all, for me it's absolutely manageable.

I'll look into changing the sparks myself I think... can't be too difficult. Any recommendations on spark plugs or is OEM going to be best for this application?

Cheers

[B21]

You really need Protool if you are into that level of tinkering…I’m a 100% Apple household..just bought a cheap ruggedised Chinese android phone for this and xHP and MHD..

[Felixlamb]

For reference, a pull I did yesterday on a disused runway. This time I was able to get a full 5th gear pull, which I assume would have been the gear used on the dyno when it was remapped.

[Felixlamb]

You really need Protool if you are into that level of tinkering…I’m a 100% Apple household..just bought a cheap ruggedised Chinese android phone for this and xHP and MHD..

Gotcha - I'll look into that then. If only XHP supported the 8HP45 in the Z4 . They flat out said to me that there wasn't enough demand for them to justify it. I do also massively envy the hassle-free fiddling you N54 lot can do on MHD.