The process is tedious, to say the least.

It can even brick the ECU. As Harvey noted with a chuckle, APR ends up making a lot of “$1,800 lawn ornaments.” He also clarified that the company often holds on to them, as they could potentially be recovered and used for future R&D.

Sheer complexity

Mapping out a safe tune that preserves factory protections, such as fault codes, has always been hard work, but it has only become more challenging as technology has progressed.

This reflects the increasing complexity of modern fuel-injection systems. For the B5 Audi S4, there were only 10 to 15 things that needed adjustment, APR said. By contrast, the 2005 Volkswagen GTI required 90. “Current production stuff? We’re well-north of a couple hundred changes,” said Gorton—about 225 for the 2022 GTI and over 400 for the current Porsche 911 Carrera.

“We’re over 500 on the latest product that’s coming out,” Harvey added. As he explained, turning one knob can cause 50 others to react, so you have to find the sweet spot for each parameter to ensure everything works in harmony.

Factory ECU calibrations are also now global, meaning variables like fuel quality and operation environment must be accounted for in a single file. Tuners often don’t know which parts of the code correspond to their region, so APR says its software is designed to work no matter your location.

Then there are the surprising differences between models that share the same engine, like an 8V-generation Audi A3 and a Mk7-generation VW GTI. Each development team has its own philosophy for how the car should drive and perform.

Torque management is a prominent concern—should the model be tuned to err on the side of efficiency, or should it be more snappy and fun? Those differences make APR’s job harder because even with identical engines, “the two teams came at the same problem from opposite directions, and nothing lines up,” Gorton said.