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. 


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.


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.


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.


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.


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.
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)
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.
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.
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

So you got a bad tank of gas … now what?

It happens. You are travelling, you don’t use your regular gas station, they change the fuel quality in your area. So now you are stuck with a bad tank of gas (and what I mean by this is fuel with lower actual octane than what you usually use) in your pride and joy and your heart sinks at the thought. Here’s what that looks like, means, and how to address it.

First of all, keep in mind that your car has modern reactive knock sensors and these will pick up the knock from the poorer gas and pull back timing to keep the engine safe. This applies to all modern vehicle platforms. On an Ecoboost for example, the car will LEARN the fuel octane you are using. The OAR (octane adjust ratio) parameter is used to do this. It will adjust closer to positive 1 and timing will be pulled preemptively from the tune to prevent the knock from occurring.

The engine won’t all of a sudden explode because of knock from a bad tank of gas if the tune is setup to make use of these safety features. It is not ideal, and if the fuel quality in your area has permanently changed you should have the tune adjusted. However, this NON-LSPI poor fuel quality knock can be handled quite well by the knock sensors to ensure engine safety.

Keeping an eye on your datalogs and live monitors will tell you if something is out of the norm. Here’s how our 3rd gear pull corrections look like with a bad tank of gas.

focus-rs-bad-gas-knockYou can see that the timing additions in this 3rd gear pull stop after adding about 1.5* and then drop due to knock ending up in the -2.5* region.

Here’s how our usual “good gas” behaves. These pulls are taken on the same road, same modifications, and same temperatures but with better fuel.


Notice that there are much fewer “drops” as the ECU is adding timing during the pull. Most cylinders are adding 1.5-2* near the end of the pull instead of pulling -2.5*.

Aside from the engine safety concern, this loss of timing advance does hurt performance. How much? In the case of our Focus RS the timing difference is worth a solid 16whp and 10 ftlb of torque. A ballpark figure is that 1* of timing accounts for around 3whp on the Ecoboost 2.0 and 2.3 engines.


So what can be done if you run into bad gas? Here are some tips:

  • Wait it out if you know it’s a poor tank. Unless the gas is VERY bad the car will rely on its sensors to adjust timing dynamically. If you are seeing consistent corrections take it a bit easier until the tank runs out.
  • Run a low boost map – we include this with all of our tunes.
  • Add some octane booster to the tank. A bottle of the over the counter stuff will make a 2-4* timing advance difference. More expensive Race Gas or Boostane brands will have a bigger impact but they can’t be found everywhere.
  • Add 1-2 gallons of E85 to the tank and top up with premium. Adding a splash of E85 increase the octane enough to ride a bad tank out and does not require a tune change.
  • If you are consistently seeing “bad gas” in your area, consider having the tune adjusted.

Understanding your PCV system, upgrades, and catch cans

Upgrading the PCV system on turbocharged cars is common among the enthusiast community. This has historical roots with older vehicles that had sub-par PCV systems and looser piston sealing tolerances that NEEDED modification to vent effectively. Modern cars have much better designed systems that actually include catch cans (catch and release actually) right from the factory. More on this later.

First of all we have to know what we’re working with. This means delving into what the PCV system is and what it does. The PCV system serves 2 purposes:

1. It maintains a low crankcase pressure. Every piston engine will have some level of blowby which is caused by combustion gasses that move past the piston rings during the power stroke due to the high in-cylinder pressure. The looser the tolerances on the motor, the more of these gases will escape below the pistons. If you don’t vent them from the crankcase they can cause issues such as a decrease in power and will push oil out of the crankcase. This can mean dipsticks popping out, seals leaking oil, and turbos smoking from the oil drain being backed up and not draining. We often seen turbo seals misdiagnosed due to the poor crankcase ventilation.

2. Excessive crankcase pressure used to be vented directly to the atmosphere. However this does pollute and now it is being recirculated back into the intake tract. While this does bring some oil into the intake tract, pulling it back in HELPS in reducing crankcase pressure which is a good thing for performance.

On turbocharged cars you need to vent crankcase pressure under 2 distinct conditions: boost as well as under vacuum. This is why you will see 2 PCV pathways on modern turbo cars.

1.The vent under vacuum. The image below shows what it looks like on an Ecoboost or Mazda DISI engine but all manufacturers have a similar version of this idea. It is made of an air to oil separator (an OEM catch can), a valve that closes under boost, and a hose directly to the manifold. This side of the PCV system pulls crankcase pressure out when there is vacuum in the intake manifold such as at idle and during cruising. It separates the oil film and gases through the OEM separator, returns the oil to the crankcase and pulls the gases through the manifold. Under boost the PCV valve closes and prevents boost pressure from entering the crankcase so this side of the system does not flow at all under boost.



2. The vent under boost. When the PCV valve is closed and the car is under boost as well as to a lesser extent under vacuum when it works together with the first system, this is where crankcase pressure is pulled from. The intake before the turbo has a vacuum effect from the turbo pulling in air through the intake tube and gases are PULLED from the top of the valve cover. The valve cover itself acts as an air to oil separator (a second OEM catch can which is also baffled) and returns the separated oil to the crankcase where it belongs.



Now, let’s talk about improvements to these systems. Most people try to improve a few things:

1. The PCV system flow. If you have a motor that is pretty loose (a more race oriented built engine with forged internals) you will need to pull more crankcase gases because the engine does not seal as well especially when cold. Combine that with very high boost and you may need to vent more. The RS motor for example has larger PCV openings versus the ST motor in the Fords. In order to improve flow, you need to add more passages or enlarge air passages. However keep in mind that the OEM PCV system is well designed for the OEM motor. If you are getting a lot of blowby with the OEM motor, you probably need to address why there is so much blowby from the pistons rather than a better flowing PCV system. Also keep in mind that any obstruction you add to the PCV system (ie extra catch cans) can impede flow and therefore can cause issues such as higher oil consumption, leaking, and smoking turbos.

2. Keeping oil out of the manifold/engine. This is a big one for DI (direct injection) cars and turbo cars in general as oil coats the intake valves and can cause knock if a lot of it enters the air stream. This is the intent when installing ADDITIONAL oil to air separators such as catch cans. The additional catch can DOES help in the separation BUT the effectiveness is difficult to measure. It can look like they are doing a lot when emptied but the fluid pulled out is in large part condensation that is a normal occurrence as motors come up to temperature after a cold start. Below are some of our observations regarding installing additional air to oil separators on top of the OEM ones already there.


A. They do not stop carbon buildup on the back of valves in DI (direct injected cars). We have seen this time and time again and this is because some oil film still makes its way past the catch cans just like it does past the OEM catch cans. Further, flow reversion during engine operation still brings in oil over the valves. The most effective methods at preventing carbon buildup are: 1. Using high quality oils (some are being designed for DI operation specifically), 2. changing the oil often, 3. driving the cars hard to maintain high valve temperatures (yes having fun!) 4. and if possible running secondary injection across the intake valves which washes them clean and which more and more OEMs are starting to use.

B. They can cause PCV flow issues and should be monitored. If they overflow or freeze during the winter (which they do; remember the content of these is mostly water) they can block the system altogether. Similar issue if the fittings leak.

C. The most common location people install them is on the manifold to crankcase connection. This connection is not flowing any gases while the car is under boost. Remember there are 2 PCV systems.

D. They will not solve mechanical issues such as smoking turbos, excessive oil consumption, etc.; they can exacerbate these issues. Make sure you fully investigate the root causes of such issues.

The options to eliminate oil completely from the intake have their caveats. One is to vent the gases to the atmosphere which we don’t recommend. This is not as effective flow wise because there is no vacuum draw from the turbo or manifold and to top it off these gases smell and get pulled into the cabin air vents. Another option is to use the exhaust system to pull gases out using a venturi. This does require a good amount of customization to the exhaust system. Finally, you can have a separate pump to pull crankcase pressure out which is a bit extreme for a street driven vehicle.

Overall, it is important to understand that the flow of the OEM PCV system in a modern car is well matched to the OEM motor. Excessive crankcase pressure means something is mechanically wrong – either a blocked PCV system or excessive cylinder leakage that should be addressed. On a looser race built engine, increasing that flow means adding additional pathways for crankcase venting as well as different air to oil separators to match the new system. This means an overhaul of the OEM system altogether with bigger or multiple tubes and new separators/catch cans. 

Hope this sheds some light on the the PCV system in your car. Happy Tuning!

The Stratified Team

Is your Ecoboost Tune on point? Here’s what to look for

We’ve had the opportunity to tune thousands of Ecoboost vehicles over the years and have developed a thorough understanding of the ECU and how it controls the engine. We also analyze A LOT of data from cars all over the world in all kinds of different configurations. Data analysis is a very important part of tuning the vehicle and making sure it is behaving and driving optimally.

As we refine and dial in the tunes, there are some key characteristics in the collected datalogs that indicate that the tune is well adjusted to the vehicle. In this article we go over tuning parameters you can check yourself by analyzing the logs from your own car.

The example vehicle used in this case is a Focus RS with an upgraded FMIC and catback and running 93 octane fuel. These key elements discussed in this article however apply to any Ecoboost powered car.

First things first – you have to valid data. Here are the parameters that we recommend datalogging for this exercise using your COBB Accessport (and here is how you set these up):


After you’ve setup your Accessport to datalog the correct parameters, it’s time to take some datalogs. There are two types of logs that we like to see because they highlight different aspects of how the engine is responding.

The first is a single, full gear pull. This can be done in 3rd or 4th gear. 4th gear will load the engine more and we prefer seeing this data ONLY if safe or possible. Press the logging button on the AP and wait for the numbers to start updating again on the screen. After this punch the throttle to the floor at 2500RPM and hold it there until the tach needle reaches the indicated redline.

The second type of pull is a multi gear pull. This is a demanding pull and it stress tests the tune and how it responds to fast changes. Good tunes behave predictably as you go through the gears. Here you start in 2nd and finish in 3rd (or 4th if safe). You once again punch the throttle and quick shift into the next gear near redline. No need to FFS, a fast shift is enough.

After the data is collected using a graphic software of your choice (Excel, Open Office, etc) to visually represent the data. Let’s start with the single gear pull.


Correct fueling is essential for performance and reliability. These cars come with full time closed loop wideband control. That means that the ECU will try and achieve the fuel targets in the tune at all times using the OEM wideband sensor.

How much fuel to inject is primarily calculated based on the manifold pressure sensor (MAP) as there is no MAF sensor on these vehicles. Deviations from safe fuel targets means that either the tune is not dialed in, fuel system can’t supply the needed fuel, or the wideband sensor is not working properly. The charts below show you what to look for in a single gear pull datalog.focus-rs-st-fuel-pressuresfocus-rs-st-air-fuel-ratios


A turbocharged car with poor boost control is both unpleasant and unpredictable to drive as well as unsafe for the engine. The Ecoboost controls torque and boost control via the wastegate and throttle. The wastegate is used to spool the turbo and adjust the turbo speed and boost level in the charge air system. The throttle is used to finely adjust and trim boost without having to slow down the turbo. This makes for a very responsive system when dialed in correctly.



The Ecoboost has a very responsive knock control system. It listens for knock at all times and reduces timing when it picks up knock-like noise. At WOT, it will add timing until it reaches the knock limit and also LEARN the octane quality via the OAR parameter. This is a very powerful system and if tuned well can exploit the full performance of the vehicle on the fuel it is using while keeping the engine safe from excessive knock. More about knock here.focus-rs-st-knock-control


Stress testing a tune is very important. This will tell you whether the tune is setup to take on daily driving tasks as well as track conditions. We don’t drive our cars in steady state WOT, we drive them in transient conditions (coming on and off the throttle at different RPMs all the time). Single gear pulls/sweeps don’t expose these areas and they are easy to miss especially if the tune is only done on a dyno.

If there are weaknesses in the tune you are likely to find them in a multi gear pull. Here’s what to look for in a multi gear pull above and beyond the single gear behavior found above.
Feel free to contact us with any questions, and enjoy data analysis and making sure your tune is on point!

The Stratified Team