MK7 GTI/R Fueling: How it Works and How to Upgrade

The OEM fuel system of the MK7 becomes a limiting factor as you increase the power level of the cars. Choosing the best solution for your needs is important and the MK7 GTI and R are fortunate enough to have lots of solutions available. So let’s go over how the OEM system works, when you will need to upgrade, and how to choose the best solution for your application.

Please keep in mind that throughout this article the power numbers are in reference to our Mustang Dyno. Power output on different dynamometers may vary. Here’s a video of how a Golf R performs on our Mustang.

mk7-golf-rTo start let’s look into how the OEM MK7 fuel system works. First of all it must be understood that the car injects fuel that is proportional to the amount of air entering the engine in order to achieve a correct air-fuel ratio. The more power you make, the more air enters the motor.

In order to know how much fuel to inject, the ECU needs to know how much air is being consumed by the motor. The more power you make, the more fuel the engine will be consuming to achieve that power output.

Below is an image showing the MK7 with both the port and direct injection systems in place. In Europe the MK7 GTI/R has both port (blue) and direct injection (red) while in North America the car only came with direct injection. Port injection can be added to North American cars – but more on that later.

mk7-intake-manifold-edit-2To measure air entering the motor, the MK7 GTI/R use a speed density (pressure) style control system that does NOT contain a MAF sensor. Some of you may be familiar with these and the main difference is that when you use a MAF, you measure airflow directly while when you use pressure, you need to translate that pressure reading into aiflow.

In order to do this the ECU primarily relies on 2 intake pressure sensors, one pre-throttle (PUT) and one post throttle in the manifold (MAP). Along with compensations for air temperature and barometric pressure these pressure readings then go into a volumetric efficiency model to determine how much fuel is required to meet the target Air/Fuel ratio (AFR).

mk7-airflow-diagram-overview-2

Further to this, the car has an OEM wideband O2 feecback sensor and the ECU constantly adjusts the fueling (under part throttle as well as wide open) to reach the desired AFR. All in all, this is a fast and modern ECU and it controls fueling very well under all conditions.

wideband-sensor-diagramOn the delivery side on North American GTIs and Rs, we have 3 main components: Low pressure fuel pump (LPFP) (in the tank), high pressure pump driven by the exhaust camshaft (HPFP) and the high pressure DI injectors spraying right inside the combustion chamber. Under high load/boost the MK7 injects fuel with a pressure of around 2900psi.

mk7-fuel-system-overview

OEM Fuel System Limitations

As we talk about fuel system limitations keep a few things in mind:

1. Pump gas without ethanol or other alcohol added to the fuel gives you the most headroom in terms of how much mass the fuel system can deliver. However the engine will experience knock the earliest using this type of fuel limiting the power by reaching the knock limit. Running E30 fuel requires around 10% more fuel volume to be injected and running full E85 requires around 30% more fuel volume to be injected compared to ethanol free gas. As you raise the knock limit using ethanol blended fuels allowing you to add knock-free power, you run out of fuel system headroom. You can run a little leaner without knock on ethanol blended fuels that can recover some the fueling headroom – however on a Golf R with the IS38 or an upgraded turbo you will often run out of headroom on the stock system.

2. Ambient temperatures have a big effect on turbocharger efficiency and fuel requirements. A car will require significantly more fuel running the same boost in freezing weather than it will in the heat of summer. If we want a reliable setup, consider the requirements during both winter and summer and build your system for the peak demand you will experience.

OEM LPFP: Starting with the first component in the fuel delivery line we have the Low Pressure Fuel Pump (LPFP) – This in-tank transfer pump is controlled electronically by the OEM ECU via the tune. The OEM LPFP on the MK7 can provide fuel for up to around 400 WHP for the GTI and R.

oem-lpfp-pic

OEM HPFP: The line from the LPFP feeds into the inlet of the HPFP (High Pressure Fuel Pump). The HPFP is driven by the exhaust camshaft of the engine and pressure is controlled via a solenoid. A four-point cam lobe on the camshaft drives the HPFP. As the engine RPM increases, the HPFP’s ability to pump a greater volume of fuel per unit of time also increases. Because of this we see the HPFP start to suffer at peak torque. You can tell the OEM HPFP is struggling if you see pressure drops under high boost and this usually happens around 380-400 WTQ.

OEM DI Injectors: The high-pressure fuel is delivered to the high-pressure fuel injectors These injectors sit on the intake side of the engine under the intake manifold. These injectors are pulsed for a maximum of half the engine cycle (so only around 50% duty cycle) because you can’t inject during the power and exhaust strokes unlike a port injected car. The fuel injector pulse windows shrinks as the engine speed increases and if the HPFP pressure drops, they have to open for longer still to compensate for the lower pressure. Because of this you can see OEM injectors become limited at both peak torque (due to the HPFP dropping pressure) and peak horsepower in the upper RPM due to the limited opening time. They too generally run out of headroom around 400WHP and 400WTQ.

di-injection

How to Upgrade the OEM Fuel System

LPFP Upgrade – With nothing else added this can get you about 20-30 WHP at the top end. The 450 LPH (liter per hour) pumps can supply enough fuel for around 550WHP and most are E85 compatible. If you are looking to push above this there are 525 LPH LPFP as well. Upgrading the LPFP requires tuning changes or running an external controller to prevent the OEM ECU controller from overheating. We recommend tuning for any fuel upgrades with something like a Cobb Accessport and custom tune.

lpfp upgrade

HPFP Upgrade – This upgraded replaces the internals of the HPFP with a larger bore pump. An HPFP upgrade increases the amount of fuel delivered per stroke and can prevent the pressure from dropping at peak torque. A HPFP on its own will give you an extra 20-30 Ft-lbs. of torque headroom in the mid-range and is E85 compatible.

hpfp-upgrade-pictureAfter you have replaced the HPFP and LPFP you have gained the capability to comfortably run E85 fuel on most IS38 bolted cars year-round and have fueling headroom for 420-430 WHP and WTQ.

However – there is a better way!

MPIMulti Port Injection. If your ECU and tuning solution support adding port injectors, you only need to add an MPI kit and an LPFP upgrade for a practically limitless fueling solution.

With some mild modifications to your manifold, adding MPI allows you to add 4 injectors to the manifold of the MK7 GTI and R to provide port injection.

mpi-upgrade

In addition to providing additional fueling, an MPI system will have the added benefit of port cleaning and a low side fuel pressure sensor which allows you to both read how your LPFP is performing in real time and to control the LPFP pressure.

mpi-injector-diagram

How To Choose your Fueling Upgrades:

The stock fuel system of the MK7 will get you up to the 400 WHP and 380-400 WTQ range.

If you are looking to just hit around or just above 400WHP/WTQ range, you can achieve that with just the HPFP upgrade.The HPFP upgrade alone is good to run on E30-E50 IS38 setups year round and full E85 IS20 setups.

HPFP and LPFP upgraded together will be sufficiency for full E85 setups on IS38 cars. 

Beyond that it is recommended to get the MPI kit with an LPFP (You can leave the OEM HPFP in place).

When sizing your MPI port injection kit – 700WHP can be reached with 980cc injectors and up to 1000WHP with the 1300cc injectors.

For the LPFP the 450 LPH LPFP will support up to 550WHP or there is the 525 LPH option if more is needed. Most cars over 600+whp may consider surge tanks and upgraded lines.

mk7-r-engine-with-mpiWe recommend running MPI with an LPFP upgrade if you want to run hybrid or larger turbochargers on E50+ ethanol mixtures. MPI also keeps your intake valves clean AND gives you the low pressure side readings and control over pressure in real time. This makes this setup the most robust and with the most features.

Below we break down the relative power potential of the different permutations.

fueling-upgrades-comparissonBelow you can see an example of a car that is we tuned using the COBB Accessport with a bigger turbo, upgraded low side fuel pump and a MPI kit making 500+whp.

mk7-r-mpi-big-turbo

Hope this helps you choose your fuel modification path and Happy Tuning. Get in touch if you have further questions.

The Stratified Team

*Pictures sourced from Volkswagen Service Training Manual for the 2.0L TSI Engine.

MK7 GTI Step Colder Spark Plugs and Compression Test

When turning up the power on a vehicle such as we are doing via the COBB Accessport, inevitably more heat is generated. With more heat in the combustion chamber, you may start to move outside the optimal heat range of the OEM plugs and thus have an increased risk of pre-ignition. For more in-depth spark plug tech check out our spark plug article here. Because of this our red development MK7 GTI is getting a fresh set of plugs.

Knock, Pre-Ignition and Heat Range

Do not confuse pre-ignition and detonation (or knock). Knock is what the knock sensor picks up and you can datalog this as ignition corrections during a pull. Knock is caused by multiple flame fronts starting AFTER the initial flame front was started by the spark plug. Replacing the spark plugs with a step colder will not prevent knock – knock is a result of fuel used, tune, and temperatures – and I mention this because we get asked all the time if replacing the plugs will reduce knock. It will not. However it will reduce the CHANCE for pre-ignition and pre-ignition is much more serious than knock and more damaging should it occur. The knock sensors can’t pick up pre-ignition because pre-ignition happens when the air-fuel mixtures ignites BEFORE the spark event and will usually result in a hole in a piston or broken rod. A colder spark plug helps this because it pulls more heat into the head of the engine from the combustion chamber and is less likely to act as a point of ignition before it is triggered by the ECU.

Generally speaking when starting to tune a car, we go for a step colder plug than factory to avoid pre-ignition. Going too cold can prevent the plug getting hot enough to burn off deposits in daily driving and can result in fouling and misfire – so a compromise must be struck for a street car. For the MK7 GTI we chose the popular Denso IKH24KT.mk7-gti-stratified-spark-plugs-compression-1The Install

Installing the spark plugs is fairly straightforward. You will need to remove the engine cover, the coil pack harness, and then pull each individual coil pack. 
mk7-gti-stratified-spark-plugs-compression-3

mk7-gti-stratified-spark-plugs-compression-4

Once the spark plugs have been pulled it’s a good time to give them a look-over. Our plugs were very clean with no speckles or excessive deposits. They were burning cleanly without obvious evidence or oil consumption or knock. The orange deposit is due to running some race fuel additive (and normal if doing so). You can see that the new step colder plugs have a slightly recessed tip which is a feature of colder plugs.

mk7-gti-stratified-spark-plugs-compression-14mk7-gti-stratified-spark-plugs-compression-9

Compression Test (while the plugs are out)

If you have a compression tester handy, this is a great time to perform a quick compression test of your GTI. Very little is required to do so. You simply plug the compression tester in each spark plug hole and crank the engine while holding the accelerator pedal to the floor. I crank until the compression tester needle stops rising and this is around 12-15 cranks per cylinder.

mk7-gti-stratified-spark-plugs-compression-15

What you are looking for in terms of the compression test results is consistency across all the cylinders. The absolute number will depend on the tester used and altitude above sea level. Our development vehicle was very healthy with a 190psi reading across all four cylinders.

mk7-gti-stratified-spark-plugs-compression-17

Before putting the new spark plugs in and torquing them down to 18-20ft/lb it is worth checking their gap using a feeler gauge. We recommend 0.024-0.026″ (0.60-0.66mm) to prevent misfiring under heavy load. The gap will naturally open up over time as they wear out and heat cycle. The new Densos did not require any adjustment of the gap.

mk7-gti-stratified-spark-plugs-compression-7

Once the plugs are back in along with the coil packs and harness, you’re done! You’ve now checked the health of your motor with a quick compression test, looked at how clean it is running via inspecting the old plugs, and freshened up the ignition system with new plugs that are more tolerant to tuned, higher performance driving.

The Stratified Team

Does a leaner Air-Fuel Ratio result in more power on the MK7 GTI?

Calibrating an engine revolves around solid data analysis and testing of any hypotheses. In the case of the MK7 GTI, the OEM ECU calibration commands a relatively lean air-fuel ratio (AFR) target during wide open throttle operation. For the majority of a pull, unless one of the temperature failsafe thresholds are triggered, the ECU will command a 14.7 AFR tapering to mid 13s by redline.
vw-gti-mk7-oem-air-fuel-ratios
It has to be understood that these targets are within the context of the OEM tune. The boost pressure targets, ignition timing targets, and variable timing targets are all taken into consideration when selecting the appropriate air fuel ratio. On top of this, economical operation is a strong requirement for the OEM.

 

When pushing the car beyond the factory setup in order extract maximum effort from the engine, all variables including the air-fuel ratio must be reconsidered and retested.
When commanding a higher output the engine requires more in-cylinder cooling in order to avoid detonation (knock) while maintaining maximum performance. This is the case with other internal combustion engines we have worked with but we had to put the hypothesis to the test for the EA888 Gen3 as well.

 

The COBB Accessport gives us a very powerful analysis and datalogging tool at a high sample rate of 12hz (that means we get 12 datapoints per second for each sensor or actuator signal we log)
vw-gti-mk7-cobb-accessport
We tested this hypothesis in a controlled environment where we only varied air-fuel ratios. We made sure that this was done on a hot day with 91 octane fuel that is knock prone. This was done such that we can clearly see the effect of the air-fuel ratio without any other variables interfering.
vw-gti-mk7-stratified-tune-dyno
Here you can see that the richer run did produce more power. The question now is why? We looked at the knock traces from both runs for to get an answer to this as boost and temperatures were identical. The graph below answers this question.
vw-gti-mk7-stratified-tune-dyno-knock
As you can see, the leaner AFRs do not offer the necessary in-cylinder cooling to prevent the engine from knocking. Yes, the engine knocks in both runs because we have setup the test as such to ensure we see a contrast between the two sets of data. However you can see that the richer air-fuel ratios result in a diminishing knock trend which in turn results in the engine making more power and staying safer!

 

Finally, we have to ensure the data is repeatable. For this we have two back to back runs of the richer tune. You can see that the data is repeatable within 2-3whp which gives us further confidence in the test results
vw-gti-mk7-stratified-tune-dyno-repeatableThe conclusion to all this – when calibrating a vehicle outside of the OEM parameters, all variables and hypotheses need testing in order to optimize the new set up.
Happy Tuning,
The Stratified Team

Upgrading the Volkswagen GTI FMIC

I will preface this with the fact that the OEM front mount intercooler (FMIC) on the VW GTI is very good for an OEM unit. Here’s a little comparison between the MK6 GTI and the OEM unit on a MK3 Focus ST. vw-gti-vs-focus-st-intercooler-efficiencyWhen you are looking at the performance of an intercooler you want to look at the difference in temperature between the beginning and end of a wide open throttle run. This change in temperature will tell you whether the FMIC is maintaining a cold air charge or whether it is struggling. The OEM Focus ST FMIC in this case is clearly struggling in comparison to the GTI and this comes down to the size. The GTI/Golf R FMIC is very large by comparison – having the same frontal area as the radiator!

Our COBB Tuned development GTI received its final piece to being fully bolted with the F23T turbo. The Golf R FMIC. The install is quite straightforward. There are a lot of screws to take out of the front end to get to the FMIC (bumper and crash bar must come out) as it is between the AC condenser and radiator so if you DIY this install make sure you keep track of these. Having a second pair of hands and a couple of floor jacks to support the cooling stack as you take out and put in the FMIC helps.

golf-gti-fmic-install

I really do like the design of the cooling stack. Lots of airflow in the front end of this car. The R FMIC has a core that is 5mm thicker and it has 31 rows versus the GTI 27 rows.

golf-gti-fmic-oem-thicknessgolf-r-fmic-thickness

Some data comparisons indicate that on a 4th gear pull the change in temperature from the beginning to the end has dropped from 17.5* F to 9.5* F with the R FMIC. A second advantage to the better flowing and larger R FMIC is a smaller pressure drop across its core. Due to the lower pressure drop and lower temperatures, at the same boost pressure the turbo is more efficient and we also gained around 4-5 g/s of airflow.

vw-golf-r-vs-vw-gti-intercooler-fmic-efficiency

I do recommend this upgrade for stock and upgraded turbos alike. The GTI FMIC is quite good but the R FMIC is a direct fit, relatively inexpensive, and will be worth around 5-10whp and be more resilient during multiple pulls.

VW GTI MK6 Cobb Turboback Installed

Last weekend we had the opportunity to install the COBB turboback exhaust on our Stratified Tuned MK6 GTI. This is a very nice piece of kit and it consists of a full 3″ exhaust from the turbo back replacing the OEM 2.4″ exhaust.

VW GTI exhaust tips COBB Stratified

This short video overviews the constructions of the exhaust and its features:

Now … what about performance? Before getting to the nitty-gritty; where is the performance gained with the turboback? There are two avenues actually.

The first is the drop in post turbine pressure. By replacing the two OEM catalytic converters with a single high flow unit and enlarging the piping diameter from 2.4″ to 3.0″ you are dropping the pressure right after the turbine of the turbo. This in turn increases the pressure DIFFERENTIAL between the exhaust gases before and after the turbo. The end result is that the turbine has more energy input and that in turn means faster spool and more air delivered to the engine via the compressor which is now spun faster throughout the entire rev range.

VW GTI downpipw COBB Stratified

The second area where performance is gained is a drop in pumping losses. The engine must pump exhaust out of its cylinders and that is energy that is wasted. By making the process easier, the engine doesn’t waste as much energy doing this and that translates into more power making its way to the wheels.

After verifying repeatability and ensuring that all other variables are kept consistent (temperature, 91 octane fuel) the downpipe and catback gained +13whp and +18wtq (red line). This is very much in line with our expectations. A catless downpipe will add a little more but at this point it’s the turbocharger that’s the biggest restriction in the exhaust stream. The car previously had a Stratified Tune via the COBB AP, COBB intake and diverter valve replaced with no other modifications
VW MK6 GTI Stg2 91 Dyno StratifiedThe exhaust sound is very much a personal preference … so I will another video do the talking.

What’s next? Time to get more consistent torque delivery with a look at DSG tuning. After this, revisiting E85, intercooling, AND and then moving onto a larger turbo! Stay tuned!