How Much Power Does the VW TDI Lose in “Cheater” Mode? [Video Report]

2011 VW Jetta TDI power loss dyno emissions test
2011 VW Jetta TDI

One of the unknowns in the Volkswagen diesel emissions cheating scandal “Dieselgate” is the potential power loss when an affected VW TDI car go into the “cheater” mode. Does it lose any power when being tested on the dyno? When Volkswagen releases a retrofit or fix for the emissions problem, will the corrected cars lose power in daily driving? If so, what power loss are we talking about? TFLcar wanted to find out, and this was the result.

We talked to the local Boulder Diesel Emissions testing station to verify the testing procedures. The Denver area counties that test for diesel emissions, only test for particulates. The Nitrous Oxides (NOx) emissions are not measured at all. This is strange, because it is the main point of contention in this scandal. EPA states that affected TDI cars emit 10 to 40 times more NOx in daily driving than the “cheater” mode during dyno testing.

The acceptable particulate level in Colorado emissions testing is 35% opacity. That means the smoke and particulates that are coming out of the exhaust pipe can block up to 35% of light and pass the test. This is a lot of smoke. Most TDIs we observed emit far less smoke. The red 2010 Jetta TDI emitted a maximum of 0.9% opacity, or 35 times better than the passing level.

Next is the actual dynamometer testing to simulate regular on road driving on an all-wheel-drive dyno, versus front wheel only emissions testing.

vw tdi power loss graph dyno emissions dieselgate
Solid Red: Test #1 WHP, Solid Blue: Test #1 Torque

The silver 2011 Jetta TDI put down 138.5 horsepower and 260.0 lb-ft of torque on the dyno with all four wheels spinning. This is the simulation of regular on road driving. We saw no warning lights or other indications from the test car with all four wheels spinning. (Two consecutive runs were performed with four wheels spinning. They were nearly identical.)

The same car registered 136.5 horsepower and 228.4 lb-ft of torque when the rear wheel were left stationary. The same dyno was used with the same dyno technician. And the tests were performed within several minutes of each other. (Two consecutive runs were performed with front wheels spinning only. They were nearly identical.)

The math shows a total loss of two horsepower at the peak, but if you look lower on the RPM curve the difference is significant. The car lost 15 horsepower around 2,800 RPM, and 32 lb-ft of torque near 2,700 rpm. In fact, there are power disparities between the tests going up to 3,800 rpm.

The bottom line is, we observed a power loss of approximately 10.5% when simulating the emissions testing procedure.

Get all the details in this video.