BMW N54 Boost Control – PID and Tuning Limits

Given recent developments in flash based tuning we wanted to offer our insight into the inner workings of the N54 DME when it comes to boost control tuning or more specifically, PID based boost control.

Boost control in the N54 OEM DME as well as most modern electronic boost controllers out there is based on what is called a PID algorithm. PID algorithms aren’t exclusive to boost control and are applied to various systems where correction to a signal can be applied by feeding the actual value of the signal through the algorithm and adjusting control for it automatically by comparing setpoint/requested to actual and adjusting the controlling device which in the case of boost control is pulse to a boost control solenoid.

Concept of a PID algorithm is quite simple. It is based around knowing two values:

1) Setpoint – in the case of boost control this is requested boost pressure that the DME is targeting for a given Load
2) Actual Value fed into the PID algorithm – in the case of N54 boost control this is the signal coming from the OEM TMAP sensor feeding back a 0-5V value representing absolute pressure

DME converts the analog 0-5V signal coming off of the TMAP sensor into engineering units based on the Map Conversion table you can find in your maps.

OEM TMAP sensor is a 2.5bar sensor. That means it can read 2.5bar of absolute pressure. This means your actual boost will vary based on your atmospheric/barometric pressure which needs to be subtracted from 2.5bar to understand how much readable range you’ve got out of your MAP sensor. This readable range above your barometric is what is referred typically as the word we all love and we’re here for, “BOOST” (i.e. positive pressure or pressure above barometric).

The OEM N54 DME works on the principle of Load based tuning and PID based boost control. Load is a calculation based on various parameters primarily around “boost” (i.e. pressure at the MAP sensor – barometric presure) and charge air temp which in turn calculate into Mass Air Flow (MAF). N54 doesn’t use a MAF sensor to meter airflow on the intake side. It calculates/infers it based on other values mentioned.

In order to make boost from the turbos the DME regulates boost control solenoids via a PWM (pulse-width modulated) signal pulsing them and allowing vacuum to hit the wastegate actuator. The frequency of that pulse/signal is what is typically referred to as wastegate duty cycle (WGDC). This is where PID based boost control comes in and helps the DME regulate the amount of WGDC applied to the solenoids so that Target Load is hit as required.

Very few of us speak about our tunes in terms of target load and it makes sense as most are used to talking about “Boost”. While the DME targets a given load and given that Load is defined based on primarily boost+IAT+compressor maps and airflow modelling around stock turbos/intakes/intake pipes it ends up calculating a Requested Boost level. In your Cobb datalogs you can monitor this value by looking at the Req. Boost Abs. channel.

You can refer to the Req. Boost Abs. as the DME’s Setpoint for the PID based algorithm. When using Cobb’s ATR software there is a hard limit at 1.28bar in terms of maximum Requestable boost. If for any reason your car boosts past this level the DME’s safety mechanism will kick in to prevent motor damage due to what it perceives as an uncontrollable boost condition for its settings. For a tuner using ATR to get around this issue and provide a smooth tune they need to effectively remove this first DME safety by calibrating tables related to boost control and throttle management. In other words, if at any point in time the turbos were to spike boost and cause it to overshoot target to say 35psi instead of where they’ve set/expect your tune to be, given how they’ve set the DME tables up to get that extra 2-5psi out of your car, it ends up being quite unsafe and won’t have the DME intervene as it normally should/would. With appropriate PID control and DME failsafes in place the signal to the solenoids is taken way, DME closes throttle causing DVs/BOV to open and vent boost and the DME goes into limp mode.

If you’ve been around the N54 scene long enough or even owned an N54 for while, especially a tuned one, you know that there are countless N54s out there that have had an experience with either overboost (30FE) or underboost (30FF) induced limp mode issues that otherwise could’ve ended up in a tune that knocked damaging the motor potentially ending in a really unnecessary and expensive repair.

Some N54 ROMs, such as the I8A0S and IJE0S, have had support added by Cobb (i.e. race code) so that the full range of the OEM TMAP sensor can be tuned with PID based boost control and the DME safety net entirely in place. It is only available with AccessTuner Pro (ATP) software and only by request to Cobb from a licensed protuner shop.

Even with the above race code in place going past the limits of the OEM TMAP sensor with flash only tuning carries an extreme level of risk for a motor. N54 is a stout motor that we all know can take quite a beating but that hasn’t prevented engine failures in the past due to various reasons but also due to poor and unsafe tuning.

If you’re running a flash-only tune on your N54 today, with or without the N20 3.5bar capable TMAP sensor, the hard limit is in place for the readable boost range of 2.5bar absolute (~21.5-22psi at sea level) inside which the DME’s boost safety mechanism works. This is also the range in which PID based boost control has authority to adjust your boost. If your tune is pushing past 22psi rest assured that even though some tuners love throwing the word PID in their descriptions that PID simply doesn’t exist and is virtually eliminated. Why? As mentioned before, PID based boost control revolves around knowing the actual boost. If you’re seeing boost flatline in your logs at ~21psi it is at that point that PID based boost control and safety has basically gone out the window for your car/DME and all you’re left with basically is the wastegate duty cycle which is mapped based on what is now a really skewed MAF calculation.

Can you make power in this way? You sure can, but so could the old versions of popular piggybacks before CANBus days. There will always be multiple ways of making power on any given motor. We’ve also shown that pushing past the TMAP sensor limit is quite doable setting a former N54 HP/TQ record on a beta Stage 3 VTT twin setup. However, the difference at least with us is that we explicitly stated that such tuning is not recommended and WILL NOT be provided for any customer car given boost control safety mechanisms aren’t in place. We are not ones to hand responsibility of appropriate tuning and throw risk into customer hands or make them stare at a boost gauge in hopes that they’ll react in time to save their motor from uncontrollable boost spikes. It is also why we recommend going with an external form of boost control when tuning any car past its OEM TMAP sensor as there simply isn’t any other proper way of doing it and certainly no way of using PID based boost control.

Dyno glory numbers and tinkering are always fun and certainly help marketing buzz but its one thing to make power and another to do it with appropriate safety and control in mind. Bottom line is, if you see anyone claiming PID based boost control while going past the TMAP limit you can refer them to this thread and let them know they’re missing a key piece of information to claim effective PID based control. You can also ask them what happens if your wastegate actuator sticks (not uncommon especially with wear on the turbos) or a boost control solenoid fails in the open position or when the car is already tuned to the edge at altitude and you drive down to sea level with the same map and heavily overboost. Not pretty, potentially very costly, irresponsible and just plain unnecessary given how far the N54 has come.

New Porsche 997.1 Turbo 60-130mph record – 6.700secs on pump 93 octane – OEM turbos + boltons + PTF custom Cobb tune

We are happy to report that a protune customer of ours from Alabama, US has just set new 997.1 OEM VTG turbo 60-130mph record at 6.700secs on pump 93 octane. The car has minimal bolton modifications including an AWE exhaust, OEM 997.2 intercoolers and do88.se turbo inlet pipes with a Sachs 2.5 clutch that drives just like the OEM clutch. This is your ultimate sleeper setup. The car has had ID1000 injectors as the car will be running on E85 soon. We’re looking forward to even faster numbers with E85!

Congrats Greyson, all the best!

http://www.6speedonline.com/forums/997-turbo-gt2/355173-6-93-60-130-07-997-6mt-93-octane-oem-vtgs-cobb-ptf-custom-tuning-2.html#post4269016

Porsche 997.2 Turbo 60-130mph World Record – 5.90secs – Cobb custom tuning by proTUNING Freaks

We’re excited to share a recent vbox verified 60-130mph time of 5.90secs done by our customer Costas in Greece that looks to be a new World Record.

What really makes this impressive is the car is running pump gas with our custom Cobb protune and the only hardware modification being a 100cell exhaust.

Congrats once again Costas!

Click the image to open in full size.

Here’s a link to his 6.0sec run previously:

http://www.6speedonline.com/forums/996-turbo-gt2/259006-6speedonline-s-official-1-4-mile-60-130-100-150-standing-mile-thread-94.html#post4231743

And his 5.90sec record setting run:

http://www.6speedonline.com/forums/996-turbo-gt2/259006-6speedonline-s-official-1-4-mile-60-130-100-150-standing-mile-thread-95.html#post4241464

BMW N54 30FF Underboost Code – Boost Leak Testing – DIY

We decided to share this great DIY on boost leak testing that was contributed to the N54 community a long while back and is still very useful for those running into issues with underboost codes, limp mode due to a boost leak in their charge piping.

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Spent a lot of time the past week trying to diagnose a 30FF. (Boost Log is NOT matching Target)
Since 30FF can be from a leak in the pressurized section of the intake track and/or the turbo just isn’t putting out enough, I broke this up into 2 areas:

1. Turbo compressor (COOL side) to intake manifold/head interface.

a. Test entire intake system.

b. Test Diverter Valves

2. Turbo compressor operation(HOT side) –

a. Vacuum system & line integrity

b. Wastegate actuator & line integrity

c. Solenoid functionality

The sequence of the tests is not so important. You can start with the tests you already have the tools or time for and stop if you are lucky enough to detect & fix the problem. Just remember that there can be more than 1 source for the 30FF. You’re not done till the 30FF’s stop popping up.

OK, I had already made several fittings to tap into, plug and pressurize sections of the OEM intake system.
After removing sections of the intake system and checking them independently, it was obvious they could leak when they were put back together.
So after playing with all the new gadgets I wanted to test the system w/o removing any parts that are exposed to boost pressure.

Step 1a Tools & Equipment
• Compressor w/ regulator, GOOD pressure gauge, hose
• Very quiet garage to listen for leaks – beware of neighbors watering the lawn
• Squirt bottle w/ Dish soap & water
• (2) – 1-1/2” PVC pipe cap ($0.77 each @ Menards)
• (1) – ¼” NPT male hose fitting ($0.25 @ Harbor Freight)

Prep work:
Remove any bumps (injection molding gates) on the OD of each cap w/ a file (if necessary, depending on mfg.). Make it smoothed.
Drill & tap 1 cap to install air fitting. (7/16” drill, ¼” NPT tap)

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Next,
Get front wheels off the ground – ramps, jack stands or lift
Car off and cool
Remove the 14 screws & engine splash pan
Remove the DCI’s (or air filter box) to access the 2-1/4” accordion intake tubes.
Install plain PVC cap in the F tube and the other cap w/ air fitting into the R tube and tighten hose clamps.
**If running OEM crankcase venting system you must Plug the rear air intake tube at the PCV return tube heater element**-edit on 8/25/11
Set the air pressure regulator to ZERO and connect air hose to cap fitting.

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You are now “in Theory” ready to pressurize the whole intake & exhaust system from the air inlet to exhaust tips. Not sure why but didn’t need to use exhaust tip plugs I made cause air was not exiting the exhaust. Only thing that comes to mind is no overlap between intake & exhaust valves. Ideas welcome…

SLOWLY increase regulator air pressure to 10 psi (it’s high enough to find a pretty small leak).
Filling up the whole system takes some time and can sound like a leak when filling. Give it time & let pressure stabilize.
The air intake tubes are not designed to hold pressure but they do hold some. Mine held to 12 psi B4 rear turbo inlet started hissing. This is NOT a boost leak but the weakest joint in this test method.
Don’t go leak hunting if a turbo inlet is leaking @ 10 psi. You may need a buddy to hold intake tube onto turbo @ 10 psi if leaking there or get creative and wedge it in place.

Reference Picture from Hotrod’s post, I did NOT remove my engine!
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Listen & look, squirt soapy water anywhere/everywhere you suspect & look for bubbles to confirm leak. Get under the car & check both turbo connections, piping, connectors, FMIC, elbow, DV or BOV & recirculation tubes, vacuum/boost lines to DV’s, Charge pipe, Throttle body, intake manifold to engine head. Fix any leaks & retest. If air tight @ 10psi you are done with this step.

Here’s what I found!

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Step 1b.Test DV’s

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I also rigged up a way to pressurize the DV’s , CP & elbow as an assembly. Used syringe w/ Tee to both DV’s.

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Step 2a. Vacuum system & line integrity – Tools & Equipment
• Vacuum gauge
• Pick or small pry tool to remove vacuum hose

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Vacuum to Wastegate solenoids
Follow hose from the top a canister to a solenoid. Remove hose at the solenoid and connect vacuum gage. Start car, gauge should read about 26” Hg at idle. Don’t know acceptable limits but if it’s much lower than 26” trace ALL hoses all the way back to vacuum pump (behind oil filter). Replace leaking or pinched hose.
Reconnect the hose and repeat the vacuum test on remaining solenoid.

Step 2b. Wastegate actuator & line integrity – Tools & Equipment
• 100cc or larger syringe
• 5/35” Tee
• Towel Clamp or long nose vice grip

Test can be done w/o a Tee by connecting syringe directly to braided hose going to wastegate actuator. (Easier said than done)
Since a Tee is needed for Step 2C you can save time & aggravation if you:
Cut the 5” long hose that’s between the 2 OEM tees (see below)
Use clamp to Pinch the short hose that runs down from the Rear Tee to the Rear Solenoid
Connect syringe to the Hose you just cut
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Apply vacuum by pulling syringe plunger and check for smooth movement of actuator rod and a metal to metal sound when the wastegate closes.
Once wastegate is closed it must remain closed and the force needed to hold the plunger steady must remain constant. If it gets easier to hold the plunger in place it means the hose and or actuator is leaking.
Repeat for front actuator connecting syringe to remaining 1” of OEM tube & pinching front line between Tee to Solenoid. The front actuator that is NOT visible from above engine. If you don’t have access to a borescope to watch the rod movement, listen closely to the sound and compare to the front. If you can’t see the actuation rod you will have to make the call (by listening) if it’s operating like the rear actuator.
Connect Tee and go to next step or plug the open end of the Tee if you are done.

Step 2c. Solenoid Functionality – Tools & Equipment
• Vacuum gauge
• 6’ of 5/32” vacuum hose
• 5/32” Tee ( if you didn’t take my advice in 2b)

Install 5/32” Tee into vacuum hose you cut in 2b.
Connect 6’ hose to Tee & gauge
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Route gauge thru drivers window & into car
Getter warmed up, cruse at about 60 mph in 3rd,
Go WOT, w/ a Tune the gauge should spike then hold at about 20” while under boost.

If the 30FF is not gone then there’s only 2 more options:
1. Wastegate rod adjustment back to OEM spec
2. New Turbos

534WHP 532WTQ – One-off set of custom turbos from Vargas – Race Gas + Meth – New N54 Stock Frame Turbos/Stock Motor Record? We think so..

Went back to the dyno this past Saturday. It was a lot hotter out than last time when the car did 523whp on pump+meth. With the same conditions as on the pump/meth runs it could’ve maybe done a touch better, maybe 540 even, maybe not. It shows just how close meth/pump numbers can be to a more expensive race gas+meth alternative when you’re already maxed on the turbo side of things. However, with race gas some additional timing managed to be had without knock through the top end helping power not drop off as quickly in the 6-7k rpm range.

These are the one-off set of stock frame upgraded turbos from Vargas. These will never see production and are not Stage 2 Batch 2 turbos. These have a one off housing that was used in the name of “science” to see the effects of a lot more machining work on the turbine housing when it comes to hp while preserving the OEM exhaust manifold in place.

This seems to be the new stock frame turbo stock N54 motor record, with a tune that was done in the most appropriate of ways possible (i.e. not testing hardware limits with bottom end boost or torque), even though its a hybrid of VTT/ASR hardware. The rpm/mph chart below the power/torque graphs is to show the RPM pickup cutting out Click here to enlarge dyno shop will need to sort that one out hopefully soon

GREEN line is pump/meth
RED/BLUE lines are race gas/meth

Both tunes run the same boost and wg duty cycles. Only thing remaining is to try maybe using an E85 blend with meth, possibly.

523WHP 520WTQ – BETA VTT Turbos – Pump gas and Methanol Injection

Had some fun with a set of BETA VTT Stage 2 turbos on Wednesday night and here are the numbers. The tune is running 21psi peak down low, 20psi at 6k rpm, 19psi at 6200rpm, 18psi at 6500rpm, 16.6psi at redline. Timing is in the range of 10.5 to 11.5deg peak without any hint of timing corrections all the way through.

This was on  pump 94 octane from Petro Canada (formerly Sunoco) running the Aquamist HFS-4 setup with two 1mm nozzles and 100% meth. According to short term trims the DME is pulling out 25% through trims with two 1mm nozzles so we could probably dial it in a bit better by dropping one of the two 1mm nozzles to a 0.9 or a .8mm instead.

Numbers look really nice and the most this car has ever made on pump and meth so far with this much timing and boost. Boost wise there isn’t any more to be had up top but we expect there’s possibly another 2-3 degrees left in there on race gas.

Design wise these turbos should be close to what the next Stage 2 Batch 2 setups end up looking like from Vargas Turbo Technologies. The actual Stage 2 Batch 2 dyno numbers will be published with our tuning once they’re ready and installed for testing on the the new VTT shop test car.