[ScottSmith]

There are a few old threads claiming 22-23psi is the limit for a stock N20/N26. I'm wondering how much of that is due to the limited range of the MAP sensor. It's a 0.2-2.5 bar sensor; 1.5 bar boost (assuming 1.0 bar ambient air pressure) is about 21.7psi; so it wouldn't surprise me if running at 22-23 psi boost is simply exceeding the range of the sensor.

On the other hand I have seen reports of 27+psi for those with crazy builds. So maybe the ECU ignores the MAP sensor and just relies on the charge pipe sensor? I know there's also the MAF sensor but the manual says that's just for long term trimming of it's MAP based airflow model.

Does anyone have a BM3 log running high boost? I'm curious how the pre-throttle boost charts compared to the MAP value.

I ended up getting a Chevy/Bosch 0.2-3.0 bar sensor for my car (using an aftermarket ECU). It can still read the vacuum I need to read (as I'm not using valvetronic). The N55 guys have explored similar options.

[ScottSmith]

Arg, answering my own question. From this thread:
https://f30.bimmerpost.com/forums/sh....php?t=1778526
looking at this datalog:
https://www.bootmod3.net/log?id=606b...0b43224889fb15
you can see pre-throttle boost and MAP diverge significantly after 23.2psi. The throttle angle is 100%, so that isn't the limit...

Avto

[sqwinny]

Originally Posted by ScottSmith

Arg, answering my own question. From this thread:
https://f30.bimmerpost.com/forums/sh....php?t=1778526
looking at this datalog:
https://www.bootmod3.net/log?id=606b...0b43224889fb15
you can see pre-throttle boost and MAP diverge significantly after 23.2psi. The throttle angle is 100%, so that isn't the limit...

Avto

It's said the stock n20 MAP sensor is a 3.5 bar sensor.

@navardi would know more for n20 as he is pushing the limit every day with cars in AUS. I've hit 27 psi peak but it wasn't something I was tuning for (was having boost control issues at the time). bootmod3 showed it in a log all by itself. It's an old log so it's not in the cloud anymore.

JB4 with the n54 guys use it and "tick" an option to rescale the voltage calibration for the higher boost levels with n54/n55. Same happens with MHD. They tick a box, update their flash and go after connecting it. Logs show it afterwards.

[dís_f30]

22 - 23 is max on the N20 for safety reasons. It has nothing to do with sensors. Even if you have upgraded the intake, fmic, turbo inlet, charge and boost pipes, turbo, downpipe, and exhaust, even going as far as upgrading the internals as well, the engine block can only handle so much. If you up the boost any higher you risk cracking the block or worse.

[ScottSmith]

No, the MAP (M=manifold) sensor is 2.5 bar absolute. The charge pipe air pressure sensor is 3.5 bar absolute. The N55 got the same 2.5 bar sensor in both locations, while the N20 and S55 got the higher pre-throttle sensor.

The q is what does the stock computer do when the pre-throttle sensor returns values the post-throttle sensor can't return. Does it model the pressure drop across the throttle body based on throttle position, much like it must do to model the flow through the valves depending on the valvetronic position? At first I assumed the higher range on the pre-throttle sensor was just to handle boost spikes, while the ECU then used the throttle for fast-reacting boost control (you can see this in numerous BM3 datalogs, where the ECU drives the wastegate at 100%, overshoots the boost target but then closes the throttle, then brings the pre-throttle boost down and opens the throttle back again). Still though, it seems they wouldn't have put a sensor in the manifold if it didn't serve some purpose... and if it can't read the range being used then maybe it isn't serving that purpose anymore.

[D041987]

Stock turbo is the limit and the cause of bent rods and engine issues on this car. Reason why 24 is the cap is cause the turbo emits higher/ hotter gases which result in the turbo being a heat maker rather then producing more airflow so at over 24 psi the turbo is out of it's efficiency range and creates higher EGT's which result in higher cylinder pressure and cause misfires that lead to burnt piston rings and or bent rods cause of detonation. Also valve springs might be too soft to push higher PSI and can cause valve float in the head in which I would recommend upgrading them with N55 aftermarket components (NOT OEM) to push more RPM and also more PSI. Stock Head bolts should be ok to push around 30PSI but would not feel comfortable in that region and would upgrade to L19 head studs if you doing head or block work on this motor.

Stock block can make over 450 WHP just need to have a custom manifold and bigger turbo setup on these cars to push the power band over to the right past 3500 RPM to save the rods. It's all in the setup and how the turbo comes into boost and that is controlled by the tune.

We just need to tune the car like any 4 cyl and EVO and WRX boys have pushed well over 500WHP on stock blocks with keeping the torque in check as that is what kills the motor. I feel this car can do the same or close to the same power, it's just not mature enough with tuners and people willing to push the car further.

[navardi]

@scott,
To answer your question.

Here is a BM3 log we did on the world record N20 car that made 345rwkw on a load bearing dyno, which is around 530whp on Dynojet

Car is around 12.17psi baro, 16 deg C ambient temp, boost in below log is relative not absolute

https://www.bootmod3.net/log?id=6164...729b7f195b4e89

PWG N20 turbo is setup as an external wastegate setup using GFB Boost controller for boost control.

By default the factory DME targets boost on the tmap 3.5bar sensor, the map 2.5bar sensor is used mainly as a safety sensor incase the tmap fails or for large variances in boost across the throttle body. Typically speaking as you'll see in the above log, once the map sensor maxes out the car keeps on going, from the DMEs point of view it still has a way to measure the boost pressure. There is an option within tuning the factory DME to use the map sensor for boost target/reading over TMAP however thats very rarely used, and typically only used if there is a huge variance in temp between the two sensors such as water to air intercoolers etc much like how the B48s etc are setup.

[ScottSmith]

Originally Posted by navardi

@scott,
To answer your question.

Here is a BM3 log we did on the world record N20 car that made 345rwkw on a load bearing dyno, which is around 530whp on Dynojet

Car is around 12.17psi baro, 16 deg C ambient temp, boost in below log is relative not absolute

https://www.bootmod3.net/log?id=6164...729b7f195b4e89

By default the factory DME targets boost on the tmap 3.5bar sensor, the map 2.5bar sensor is used mainly as a safety sensor incase the tmap fails or for large variances in boost across the throttle body. Typically speaking as you'll see in the above log, once the map sensor maxes out the car keeps on going, from the DMEs point of view it still has a way to measure the boost pressure. There is an option within tuning the factory DME to use the map sensor for boost target/reading over TMAP however thats very rarely used, and typically only used if there is a huge variance in temp between the two sensors such as water to air intercoolers etc much like how the B48s etc are setup.

Awesome, thanks! The log is interesting.

1. Is that a pneumatic wastegate car? Wastegate duty cycle is much lower than I would expect for EWG. I guess it probable is since it's an aftermarket turbo.
2. The throttle never closes despite pre-throttle boost exceeding the boost target. Did you disable that functionality or did the ECU automatically decide not to do that? I've seen other logs where the ECU closes the throttle in what I assume is a short term intake manifold boost limiter.
3. The MAF value seem to saturate. Maybe you need an upgrade or is it just a datalogging issue?
4. The Mass Flow (HFM) value also seems to saturate, but at the same time as Load Target and Relative Air Filling. Maybe these are calculated numbers?

but it seems none of that is affecting the stock computer's ability to run the engine. Guess it's just me that needs an upgraded MAP sensor!

[navardi]

Originally Posted by ScottSmith

Awesome, thanks! The log is interesting.

1. Is that a pneumatic wastegate car? Wastegate duty cycle is much lower than I would expect for EWG. I guess it probable is since it's an aftermarket turbo.
2. The throttle never closes despite pre-throttle boost exceeding the boost target. Did you disable that functionality or did the ECU automatically decide not to do that? I've seen other logs where the ECU closes the throttle in what I assume is a short term intake manifold boost limiter.
3. The MAF value seem to saturate. Maybe you need an upgrade or is it just a datalogging issue?
4. The Mass Flow (HFM) value also seems to saturate, but at the same time as Load Target and Relative Air Filling. Maybe these are calculated numbers?

but it seems none of that is affecting the stock computer's ability to run the engine. Guess it's just me that needs an upgraded MAP sensor!

Hey mate I'll answer your questions below:
1. It is a PWG N20, however the precision 5858 is setup in an external wastegate setup and as such had to use an external boost controller to control the external wastegate (We used a GFB boost controller) hence why wastegate duty cycle is so low in the log as its trying to read the factory pwg controller data which was left plugged electrically but not connected to anything.

2. Boost target caps at 22.5psi at sea level or in this example around 24-25psi due to Baro being around 12.17psi DME automatically calculates this change. The boost target caps at 22.5psi this is an issue with the datalogging component of the factory DME, to view above that we often use "Boost deviation", Torque Target % and RAM Boost Target datalogging channels to see load & boost targets over 22.5psi (24-25psi in this example) and 191.25 load (as you'll see load target was maxed out). The DME still calculates above but DME datalogging refuses to display higher than these values for these channels (boost target and load target)

3. MAF caps around 37.4-38 this again is another datalogging limitation, this is the Calculated MAF by the DME. The DME still calculates above this 37-38lbs/min however datalogging component of this DME again just doesn't show it. N20 MEVD17.2.x DME maxes out alot lower on this channel than say the S55 which uses the same MEVD17.2.x DME but of a different hardware/software sub class.

4. MAF HFM, which is reading true MAF from the MAF sensor typically most stock N20 MAF sensors cap out at 38lbs/min or 1080 KG/H you could retrofit a N55 one if you wanted. But considering during WOT the factory DME goes into closed loop mode, the MAF sensor is basically ignored and MAP/TMAP sensors become the primary focus of the engines operation and internal calculations.

Boost Target in these logs are based off the 3.5Bar TMAP in the chargepipe. MAP datalogging channel as you see maxes out around 22.5psi, when I've tried 3.5bar sensors in the Manifold, the MAP channel seems to only show data up to 22.5psi despite the sensor being able to read higher and the correct sensor calibration data added into the tune. Again manifold sensor not really used as a boost target sensor in the DME calibration unless you specifically specify it.