APR is a leading innovator in aftermarket tuning solutions for popular Volkswagen, Audi, Porsche and other European performance platforms. The company’s esteemed reputation springs from blending drivability, league-leading power production, and stone-cold reliability into its software upgrades. APR’s engineering process is the driving force behind the potency of its products so we decide to probe the mindset of Product Director Arin Ahnell and outline how APR brings cutting-edge software tuning and turbo system to market.

Setting Limits, Looking Forward

APR's development process begins by pulling the vehicle into the workshop, where the engine is often removed for a thorough inspection. Engineers analyze components to identify potential failure points,” says Ahnell. “This consists of assessing material limitations such as where’s the plastic, where’s the metal, and what does that mean from a durability standpoint.” The team then installs various sensors to collect critical performance data.

For instance, a sensor is added to the turbocharger to monitor shaft speed, ensuring that the turbo does not exceed safe rotational limits. Additional sensors are placed in the exhaust and turbine housings to measure pressure and temperature levels, providing insights into exhaust flow and thermal conditions. Monitoring the discharge pressure and temperature at the turbocharger outlet is particularly important to prevent excessive heat buildup that could compromise plastic components.

With these data points in play, the APR engineering team moves to the dynamometer for calibration. Power output is incrementally increased while system performance is carefully analyzed. When working with a new engine platform, this testing phase may take up to six months to ensure comprehensive data collection and validation before offering the product to customers.

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Throughout the process, engineers assess whether the turbocharger is operating within safe limits and whether the desired power levels are being achieved. “Are we overspinning the turbocharger? Is anything in the system getting too hot? And if something is,” quips Ahnell, “what can we do to bring the temperature back into check? We’re constantly monitoring and adjusting various operating conditions. By adding more fuel we’re able to cool things down, so long as the fueling system has the necessary headroom. If it doesn’t we reduce load by limiting boost pressure or throttle angle, for example. Some of this is done by enabling new protection routines within the ECU that are not enabled from the factory, or coding our own. But the end goal is simple – ensure the engine produces tons of power, but don’t let it eat itself by getting too hot!”

Power Left On The Table

Part of power tuning involves tapping into the unrealized potential of a given engine. This can go beyond the OEM safety margins that everyone talks about, it’s also about the way in which OEM’s offer and package the same engines. “A great example of this,” relates Ahnell, “ is the 4.0-liter Audi RS6 engine. It's also in vehicles like the Cayenne GTS, and the RS6 gets somewhere around like 620 horsepower on the performance model, somewhere around 590 on the non-performance model. But then if you look at the Porsche, it's all the way down to like 450 horses. They leave a ton of room in there—so we exploit that headroom.”

The OEM safety margins are typically fuel quality related, meaning the engine is tuned to the lowest common denominator which is diametrically opposed to horsepower generation. “Let's take the Mk8 GTI as a case in point. From the factory the GTI is tuned for 87 octane, which in the rest of the world is somewhere around 91 RON—a very, very low fuel grade. So most of our customers in the United States will run either 91 octane or 93 octane which allows for far more tuning potential—that’s a lot of untapped potential there which is why we see such dramatic gains in our Mk8 tunes.”

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The Nitty Gritty Of Power Tuning

Developing a tune is a long and winding road with a multitude of factors to consider, calculate, and control. The key is having resolution detailed enough so you can see when you’ve come to the end of said road.

Managing peak cylinder pressures at the engine speeds where peak torque is generated is crucial, especially when ramping in timing and increasing boost. Carefully controlling these factors is essential to prevent exceeding the engine’s limits and compromising reliability. “So our team looks at it like this,” explains Ahnell, “ignition timing is especially important. We have to make sure it's not going to overheat the exhaust or cause issues by running too little ignition timing, or knock by running too much. We're also increasing boost pressure, but at the same time, we're considering other factors. For example, we ensure that if someone is at a very low speed and suddenly mashes the throttle, the system isn’t trying to do everything at once—which could cause low-speed pre-ignition (LSPI). We've seen LSPI issues on some small-displacement, high-boost, direct-injected platforms right out of the gate. The factory may not be pushing them as hard as we are, so when we do, we have to be extremely mindful of this scenario.

“To better understand how LSPI occurs, we invested in an engine dyno and purchased an in-cylinder pressure transducer. This allows us to ramp up boost and ignition timing while directly observing LSPI events. Otherwise, we'd have to rely solely on a knock sensor, which only provides part of the equation rather than showing us exactly what’s happening. Our team relies heavily on these advanced engineering tools to determine how aggressively we can push the system without introducing unnecessary risk.”

Reaching OE Hardware Limits

Ahnell says sooner or later the turbo will be maxed out, pushed beyond its efficiency range or to the point of failure. This is where software calibration ends and the operation transitions into staged performance packages that feature a better-flowing turbocharger. “The goal of this is to try and lower backpressure coming out of the out of the turbo. We've upgraded the wheels and A/R so they're much larger, which allows us to make more boost pressure at optimized wheel speeds and efficiency. Then the calibration continues to produce more power reliably.”

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Direct Injection Challenges

Direct injection systems can be a hurdle to clear for software tuners. Ahnell says not all direct injection system are troublesome. “Some of the direct injection cars are great, you can increase the pressure—you can increase the spray window of the injectors and everything's fine. But we’ve found there's a limit on the newer platforms. We can only put so much pressure behind those injectors before problems arise. And the same thing with the injection window—you can press those injectors only so far before they start overheating and they start to perform erratically. We've seen a lot of a lot of tuners having some problems with that because it's the old wisdom of how direct injection works. Strategies that worked maybe 10 or 15 years ago just don’t apply to some of the newer platforms.”

At APR, research and development is at the core of everything they do. The company doesn’t just push the limits—they redefine them through rigorous testing, cutting-edge engineering, and real-world validation using state-of-the-art tools, like engine dynos and in-cylinder pressure transducers. Whether it's turbo kits, software calibrations, or complete performance solutions, APR takes every detail seriously—because for them, excellence isn’t an option; it’s the standard.

Shop Stage 3 upgrade for 2022-up Mk8 Golf R here.