As of this writing, it's been almost a year since VersaTune first introduced support for tuning Mazda 2.2 l SkyActiv diesel powered vehicles with VersaTuner. During that time, we have worked relentlessly to improve the number of exposed tuning tables and the quality of the table descriptions in the VersaTuner Tune Editor. We have also worked with our tuning partners and customers worldwide to improve the power and driveability of our included base tune. The result is a reflashing/remapping solution that makes it easy and intuitive to tune your Mazda SkyActiv diesel and an included base tune that increases horsepower and torque substantially without compromise.
Now some background on the Mazda SkyActiv diesel engine. Mazda introduced the 2.2 l SkyActiv diesel engine in the 2012 model year CX-5 and 2013 model year Mazda3 and Mazda6 in markets outside of the US. Mazda recently announced that the SkyActiv diesel will be available in the 2017 CX-5 in the US.
Power specifications have not been published for the upcoming US version, but existing versions are available in two power levels 129 kW (175 hp) and 420 Nm (310 lb·ft) and 110kW (150 hp) and 380 Nm (280 lb·ft). The two versions are mechanically identical. The difference between them is less than 10 tables in the ECU. As a result, VersaTuner includes a low power to high power upgrade tune which remaps low power (150 hp) 2.2 l SkyActiv diesels to the high power (175 hp) factory tune.
To say that the SkyActiv diesel is a complicated beast is quite an understatement. Mazda has created an engineering masterpiece in this 2.2 liter two-stage turbocharged torque monster. With great fuel economy (thanks to the 14:1 compression ratio and lightweight internals) and 5200 RPM redline, this engine delivers power, driveability, and fuel economy without compromise.
How does the SkyActiv diesel make so much torque? In this case, two turbos are definitely better than one. There is a small turbo for off idle boost, and a larger turbo to handle the heavy breathing at higher RPMs. The result is a four cylinder that drives like a big V8. The transition from small to large turbo is handled by the ECU and starts at around 2600 RPM at full load. The ECU controls diverter valves in the intake and exhaust that change the flow path through the turbos based on driving conditions. Peak boost pressures of up to 1.65 bar (23.9 PSI) are produced with the factory tune. VersaTuner performance tune produces peak boost pressures up to 1.75 bar (25.3 PSI) and holds the boost longer to produce more torque and horsepower. Higher boost pressures are possible for even more tire shredding torque.
How does Mazda manage to get a diesel to spin to 5200 RPM? Reduced reciprocating weight thanks to the lower compression ratio helps a lot, but the precise control of ignition through the use of up to nine injections per combustion cycle is the key. The multi-hole piezo electric injectors are fed fuel at an incredible 197 MPa or 1970 bar (28,572 PSI)! This high pressure combined with high-tech injectors delivers a precision controlled ultra-fine spray of fuel which enables faster and cleaner combustion. VersaTuner gives you control of fuel pressure and injection timing to allow you to optimize your engine for your unique requirements if you choose to.
This all sounds great. Why can't we just turn the knob to 11 and make gobs more power? Making safe reliable power is never as easy as turning a single knob, although some unscrupulous tuners try to do just that. I have seen at least one tune that simply cranks up the boost and fuel while skewing the EGT (exhaust gas temperature) sensor scaling so that the ECU (or you for that matter) doesn't know that it is blasting the turbo and DPF (diesel particulate filter) with dangerously high exhaust gas temperatures. Without visibility into the actual tune, you would not know it because the skewing of the EGT sensor scaling would cause artificially lowered readings when you data log using the OBD-II port. If you choose to use a tuner that provides a locked tune, be sure to choose carefully and only use someone with a known good reputation. Ask them what EGTs the tune will produce.
The base tunes included with VersaTuner are fully open for you to inspect and modify for your specific needs. We have spent over three years analyzing the SkyActiv diesel ECU, developing VersaTuner for SkyActiv diesels, and developing a solid, reliable, high power performance reflash/remap tune with the factory EGT limits in place.
What are the challenges to making big power with the Mazda SkyActiv diesel? Mainly exhaust back pressure and exhaust gas temperature (EGT). As I mentioned earlier, the two-stage turbo configuration provides boost from off idle. I have seen 1 bar (14.7 PSI) boost as early as 1400 RPM and full boost by 1700 RPM on stock vehicles. The downside is the flow restrictions of the complex diverter valve system. The DPF also creates a major flow restriction. As a result, these engines become very inefficient at high load and RPM. The boost pressure has to increase to compensate for the increased exhaust manifold pressure which causes the turbo to operate outside of its efficiency range which in turn results in higher air charge temperatures. Higher charge air temperatures mean higher exhaust gas temperatures. Although turbocharger turbine wheels are made of exotic alloys, they do have their limits. We prefer to play it safe. Our base performance tune does not raise the EGT limit or skew the EGT sensor scaling. For those that are more adventurous, we have exposed the EGT limit tables and EGT sensor scaling so that you can squeeze every last bit of power from your engine at your own risk.
How can we address the exhaust pressure and EGT challenges? There are several options. Installing a larger intercooler or a water injection system will lower charge air temperature. Increasing exhaust flow by modifying the diverter valves or upgrading the turbos. Obviously, the latter choices are more technically challenging and costly. Some people remove or disable the DPF. We strongly advise against this for legal and public health reasons. VersaTuner will not allow you to pass an emissions inspection with a disabled or removed DPF.
In racing trim, Mazda is able to get 354 kW (475 hp) and nearly 813 Nm (600 lb·ft) from a stock block and head. This is with Garrett racing turbos running up to 4.8 bar (70 PSI) boost and EGTs below 870°C (1,600°F). This proves the robustness and potential of the Mazda SkyActiv diesel design. I look forward to continuing on the SkyActiv diesel tuning journey and seeing the full potential of the SkyActiv diesel engine on the street.
I hope you have found this history and overview of tuning SkyActiv diesels with VersaTuner informative. In the next installment, I will get into the details of boost and injection control.