Here's How Much Horsepower Volkswagens Lose From Their Diesel Defeat Device

Illustration for article titled Here's How Much Horsepower Volkswagens Lose From Their Diesel Defeat Device

Volkswagen’s up the creek with their Dieselgate fiasco. They created a “cheat” calibration meant to trick the EPA into thinking their cars are cleaner than they really are. But there might be a quick fix. Question is: how much will this fix cost you in performance?

We’ve already told you that Volkswagen’s “fix” for their smog-inducing diesels will cost you performance, but how much performance are we talkin’ here?

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We can’t tell you exactly how much, but TFL Car put on its nerdy scientist hat and ran a quick and dirty experiment. They strapped a 2011 Jetta TDI to a dyno and produced power curves with only the front wheels spinning and then again with all four wheels spinning.

Why did they do this? Well, we’ve shown you the basics on how the “dyno calibration” works. One input VW uses to determine if the car is on a dyno being emissions tested is the wheel speed sensors. If all four wheels are spinning, the ECU will read the sensors and think the car is probably on the road. If the rear wheels are stationary while the fronts are spinning, chances are the car is on a dyno, and that’s when Volkswagen activates cheater mode.

By that logic, when tested on a four-wheel drive dyno with the rears spinning, the car should run normally and produce good power numbers, while on a two-wheel drive dyno with the rear wheels sitting still, there should be a performance degradation as the car activates its dubious “defeat mode.”

TFL Car’s results show exactly that. Peak power between both sets of data looks about the same, but the real difference is low and mid-range torque. The biggest torque disparity occurs at about 2700 RPM, where the “non-cheater” data with all four wheels rolling showed a whopping 32 lb-ft more torque. The biggest difference in horsepower occurred at 2800 RPM— the uninhibited car made 15 more ponies.

We don’t know how many tests TFL Car ran or if they truly were able to produce “apples-to-apples” torque curves, but if so, their numbers could indicate about how much power Volkswagen’s software fix is going to cost VW TDI owners.

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DISCUSSION

I watched this last night and came to the conclusion these guys barely know what they are doing.

Shomegrown on VWVortex was able to explain in greater detail why these results are largely incomplete and therefore meaningless.

“These guys have no idea what they are doing.

  • They fail to understand the difference between WHP and the flywheel outputs a manufacturer will provide.
  • They make a big deal about disabling the traction control/ESP. The 2011 Jetta they tested doesn’t even have a button to do this (which is precisely why the dash lit up and the car reduced power).
  • They fail to consider that the higher loading of running the dyno in 4-wheel mode can have a significant effect on torque output, especially torque ramp up. The same effect can be seen by dynoing in different gears.


TL;DR - they tested some stuff, saw some differences, had little understanding of why there were differences, and applied some heavy-duty conclusion jumping to make it fit their preconceived narrative. Poor journalism at its finest.”