This is a topic that is very active among automotive enthusiasts and is also relevant to the work we do in the Stratified office. If you do not already know this from experience then you must know: Knock (also known as pinging or incorrectly referred to as pre-ignition/pre-detonation) is a major limiting factor to safely increasing the power output of your motor. Knock occurs after the spark event begins combustion and is the spontaneous combustion of the remaining combustion mixture. Ideally once spark has occurred the intake charge will burn in a smooth manner outwards from the spark plug until the flame front is finally quenched by the cool cylinder walls. When knock occurs your engine experiences a sharp rise in pressure and temperature. If severe knock is occurring at high loads, it may lead to engine damage. Due to this we are limited in how much boost and timing we can safely run. An in depth analysis of knock is a topic for another discussion but it is important that you know of it’s existence and the limitation it imposes on performance. Every motor will eventually knock (with enough compression, timing, boost, etc), however, the goal is to use a fuel that safely and consistently supports your desired power output.

So knock is bad, what can we do about it?

Aside from cooling your intake charge via a bigger intercooler, water-meth injection, or a cold air intake, increasing your fuel’s octane rating is the best way to push your motor’s knock threshold up. High octane fuels are less likely to auto-ignite which is what makes them better for high performance applications. E85 has an octane rating that is much higher than the 93 octane most premium gasoline fuels provide. The octane increase benefits from E85 are applicable to any motor. Running 100% E85 is possible in vehicles where the fuel systems are built for E85 (Flex-Fuel vehicles) and where the fuel system can deliver larger volumes of fuel than what is needed with regular gasoline fuels. This is due to E85’s increased oxygen content and lower energy density. On the Mazdaspeed DISI as well as the Ford EcoBoost motors we do not readily have larger direct injection injectors and the fuel pumps are not designed to handle straight E85. Because of this we blend E85 with premium pump gasoline to achieve a mixture that is both compatible with the OEM fuel system while delivering higher octane. We have seen excellent results from an overall mixture of E30. This mixture is accomplished by mixing premium fuel (which usually contains 10% E85) with E85. The mixture should be 25% E85 by volume to net an overall mixture of around E30 (this is due to the premium fuel’s ethanol content).

Okay, ethanol is great, what kind of gains does it provide?

The gains we see from running ethanol blends in the EcoBoost and DISI motors will vary from case to case, however, they are always significant. The performance gains from an ethanol blended fuel will change depending on the base fuel used and modifications installed. For vehicles running the OEM turbo (K03 Ford, K04 Mazda) the average gains are on the order of 25 WHP and 25 WTQ for the Mazdaspeed DISI motors and 20 WHP and 20 WTQ in the Ford EcoBoost motors when going from a pump gas to E85 tune. If your vehicle has a bigger turbo then it will really shine with an E85 tune. As the airflow increases and temperatures start to climb the added ethanol really works to bring down cylinder temperatures and help keep knock away. Below are a few graphs which highlight the differences between E85 and gasoline tunes.The gains we see in these graphs come from the increased timing and boost we can push thanks to ethanol’s higher octane and increased cooling properties. In order to see these types of gains it is necessary to get a tune which is designed for ethanol blends.

The graph below is a comparison performed in warm weather on a stock Focus ST. The blue line is a pull using straight 91 pump gas and the red is a pull with an overall E30 mixture. Although the gains in the graph below are more extreme than what we normally see due to the high temperatures and poor 91 octane fuel, they do show the increased potential of E85.

Image 1: Stratified 91 Vs Stratified E85 Tune on a Hot Day

Here is another comparison; this time performed on our shop Focus ST while it was bone stock aside from a tune. The difference here (ignore the big torque peak at the beginning) is that the base fuel was of high quality and the pulls were performed in cooler weather (both things are advantageous to the straight gas tune).

Image 2: Stratified 92 Octane Tune VS Stratified E85 Tune On a Cool Day

Finally, here is a comparison on a Mazdaspeed3 vehicle. Again we are comparing 91 octane to an E30 mixture. The results here are quite typical of E85 blends on a strong running Mazdaspeed3.

Image 3: Mazdaspeed3 91 Octane Vs E85 Blend

So how do I get tuned for an E85 blend? 

Compared to gasoline, ethanol has a richer oxygen content, different specific gravity, and other subtleties which do not work well with tunes which are based on gasoline fuels. Ethanol’s increased oxygen content requires a much richer stoichiometric air fuel ratio than gasoline. What this means is that you must put in more ethanol (by volume) per unit mass of air in order to reach a stoichiometric mixture (lambda = 1). In most instances (given an OEM or similar sized turbo) this increased flow is supported by the OEM fuel system (the MazdaSpeed does need upgraded HPFP internals). In big turbo cars where power levels are reaching the 400 WHP / 400 WTQ range fueling will become an issue in both the Mazdaspeed and Focus ST motors. When working near these power levels on bigger turbos, the E85 mixture has to be done carefully such that there is enough fueling headroom left to maximize power on the OEM fuel system. Remember that achieving the most performance requires the correct mix of boost, timing, and fueling. Once you have surpassed the capabilities of the OEM direct injection system, there are aftermarket options to increase fueling such as methanol injections systems, additional port injectors (5th / 6th port fuel injection) and hopefully larger DI fuel injectors in the future. Feel free to discuss these build options with us if you’re preparing for a big power build and tune.

Whether you drive a Mazda or Ford, we offer tunes that support ethanol blends for both cars. If you own a Ford, you can go for either a full custom tune or Stratified E85 Flash Tune for your ethanol tuning needs. For Mazdaspeed DISI motors we also offer both full custom tunes as well as Stratified E85 Flash Tunes which accommodate ethanol blended fuels. Regardless of the vehicle you drive the differences between gasoline and E85 make it necessary to get a tune designated for E85 blends. A lot of our customers opt to have maps for both gasoline pump fuel as well as E85 blends and switch/re-flash between these depending on the fuel they have in the tank.

We hope this clarifies a little bit more how E85 is used in these vehicles and its benefits. If you have further questions feel free to Contact Us!

The Stratified Team

We here at Stratified are often asked what are the best plugs to run in our modified cars. The answer to this question depends largely on the primary use of the vehicle, and the extent to which it has been modified.

TL;DR: Buy your NGK LTR7IX-11 plugs on our website HERE.

When changing spark plugs in your vehicle there are two things to consider:

1. The spark plug gap:

This is the easier of the two considerations; for the Ford Ecoboost engine found in the Focus / Fiesta ST as well as the DISI in the Mazdaspeed vehicles we always recommend a plug gap of 0.025 – 0.026″. It is important that the plug be properly gapped or else the car will miss fire under boost/load. A larger gap produces a larger, hotter, spark which helps increase combustion efficiency, however, the larger the gap the harder it is for the ignition system to send a spark across the gap. This is especially evident in the Ecoboost and Mazdaspeed motors which run high boost levels and sparking resistance increases with increased cylinder pressure. Conversely, if the plug gap is too small then the spark created may be too small/weak to properly ignite the combustion mixture.

Most plugs for the Ford ST and Mazdaspeed vehicles come with a gap that is larger than our recommended 0.025 – 0.026″, thus it is necessary to lessen the plug gap. When checking your gap it is important to use proper feeler gauges; you’ll know you’re at the right gap when the feeler passes through the gap with minimal resistance. When closing your plug gap it is important that you do not push up against the plug’s centre electrode as it is easy to damage. The recommended gaping procedure is to tap the ground electrode against a hard surface such as a vice or sturdy shop table several times and then to recheck the gap. You will quickly get the hang of this.

The proper tool to measure your plug gap:

Tap the ground strap down gently checking the remaining gap often:

When the feeler gauge passes through without catching you know you’re at the right gap:

The spark plug gap will generally widen as the spark plug is used. This is due to the erosion of the ground strap but also due to the strap experiencing heating and cooling cycles. If you start to experience misfires and it’s not time for a plug change yet, pull the plugs out to check and re-adjust the gap as necessary.

2. The spark plug heat range:

This is where your modifications, and primary use of the vehicle come into play. Cold plugs are better for highly modified engines, while hotter plugs are more reliable on a daily driven vehicle. If you primarily use your vehicle for low speed daily driving or allow it to idle for extended periods of time, then a cold plug may foul. If you race your vehicle or repeatedly expose your engine to sustained high loads then a hot plug may cause pre-ignition which often results in a melted piston.

Now you may be wondering to yourself “What does the heat range even represent?” A common misconception is that a hotter plug produces a hotter spark; this is not true. The heat range boils down to how much heat the plug dissipates into the cylinder head. The pictures below provide a good representation of the spark plug heat range:

As you will notice, the hotter plug has a much longer portion of the insulator nose exposed to the combustion chamber. This longer nose goes hand in hand with a reduced surface area for the heat transfer. Since hotter plugs leave less area for this heat transfer to occur the firing end will get much hotter. This reduced heat transfer is necessary when your vehicle is driven slowly or often idled for long periods of time as it helps keep the spark plug at optimal operating temperature (which prevents fouling).  However, if the plug chosen is too hot then the insulator tip may become overheated during spirited driving. Once the insulator tip reaches temperatures of around 800C (1470F) it can (will) act as a pre-ignition source (think of a glow plug on diesels) lighting the mixture long before the ECU initiates the ignition event. Pre-ignition is the silent killer of engines; once it occurs there is no sound (knock sensor does not become triggered), there is no warning, only melted pistons/plugs. Due to advancements in engine design pre-ignition is not very common in modern street vehicles.

On the other hand, if the plug selected is too cold then the insulator will never be able to reach its self-cleaning temperature of around 450C (840F) and carbon deposits will start to accumulate on the insulator nose, leading to a fouled plug. Fouled plugs will misfire causing a loss in power and fuel economy. Furthermore, the built up carbon on a fouled plug could start to ember as insulator tip temperatures begin to rise during spirited driving (for example going to a track day, or a canyon run). This embering carbon build up is again an ideal pre-ignition heat source. As you can see going both too cold and too hot can be detrimental.

Another consideration with the heat ranges is cold starting. A plug that is of a colder heat range may have a harder time starting your vehicle when the temperatures start to drop.

Keep in mind that if you are having any doubts about your spark plug health it is possible to “read” your plugs. The appearance of the firing end can tell you a lot about your plug’s operating temperatures as well as the health of your engine. Below is a graphic showing what it is you need to look for. If you are running a colder than OEM plug and it is carbon fouled then you should return to the OEM heat range. If you manage to overheat a plug and haven’t killed your engine then we recommend going at least a step colder.

Another way to check whether the plug’s heat range is correct for your motor is to check the annealing point on the ground strap. If the heat range is correct the annealing line should be around the beginning of the ground strap bend. If the annealing is occurring too close to the electrode then you know that your plug is too cold. If the annealing occurs far down the ground strap bend then the plug is too hot. Here are a couple of pictures of some healthy OEM plugs with around 3,000 miles on them from the Stratified Focus ST development car that were replaced with a step colder plug along with the downpipe, intercooler, and intake (and some tuning of course!). Notice how the colour of the ground strap starts to change right at the beginning of the bend; looks like Ford did their homework!

In conclusion, too cold or too hot of a plug is detrimental. There is a misconception that a plug will cause knock and this is generally not the case. If a plug is to do long term damage, it is pre-ignition and that is not picked up by any knock sensor but also dangerous and thankfully, fairly rare on both the MazdaSpeed and Focus ST/Ecoboost platforms.

For the DISI motors we recommend running a spark plug that is one step colder than OEM. Generally the Mazdaspeed motors do not like running plugs that are two steps colder than OEM unless very heavily modified. Cars that are running higher compression, large amounts of boost, or are often tracked / driven aggressively for extended periods of time may at times require a plug that is two steps colder than OEM (for example have an extra set of colder plugs for track days).

For the Ford Ecoboost we still recommend a plug that is one step colder than OEM for mildy bolted cars especially since 21+psi of boost is quite common. For highly modified cars that see a lot of heat it is advisable to try a plug which is two steps colder than OEM. The Ecoboost motors seem to be able to manage colder plugs better than the Mazdaspeed motors.

For both the MazdaSpeed DISI and Ford EcoBoost the recommended plugs are either the NGK LTR7IX-11 or Denso ITV-22.

Remember to not forget to change the plugs when worn and to not overtorque them when installing.

Happy Tuning,

The Stratified Team

Photo Credits:

Heat Ranges and plug conditions – NGK TECH 

Hot Vs Cold Plugs – Hot’N’Cold