I installed the GDM down pipe and deleted the cat/flapper/resonator as well. Les at worked with me to get what I needed for the car and helped with cost, I am a disabled Veteran from the Vietnam era and driving my Jetta is one of my joys in life. The car is a 2012 Jetta TDI sedan with premium package and DSG trans. As a stock vehicle we averaged just over 43 MPG for the first 41 thousand miles (tracked on Fuelly.com). On the first trip after the install we got an amazing increase in mileage but thought it best to do some more testing before writing a report.
So here are the results from the last five fill-ups and trips. All trips are in 70 to 80 degree weather on roads in Arizona, trip three and trip five are the same exact route (except for our lunch stop place) and used the same station and pump. The car is always filled to “wet in the neck” a condition that has liquid diesel standing in the filler neck, not foam but actual liquid. All trips had the air conditioning on and were driven by me with the wife riding in the passenger seat. Tires are set at 45 PSI and a K&N air filter install when the car was new.
As a side benefit the tune cured all the low speed regen bucking and stumbling that the dealer said they could not replicate in their test drives. Also there is no turbo lag during idle to pulling out in traffic.
Trip 1. Casa Grande to Gila Bend to Ajo to Organ Pipe Cactus National Park back to Casa Grande via Indian 15. Total miles 270.3, gallons used 4.724 MPG 57.218. The trip is approximately 90% two lane roads with speeds of 55 to 60 MPH and 10% town roads with 35 to 45 MPH limits.
Trip 2. In town (Casa Grande) short stop and goes for several days. Total miles 140.3 gallons used 3.044, MPG 46.090. The trip was 95% town and 5% highway.
Trip 3. Casa Grande to Los Algodones Mexico back to Casa Grande via highway I 8. Total Miles were 379.9, gallons used 6.973 MPG 54.482. The trip was 95% highway and 5% in town roads. Speed on the highway was 65MPH using the throttle manually (no cruise control).
Trip 4. In town (Casa Grande) short stop and goes for several days. Total miles 119.2 gallons used 2.529, MPG 47.133. The trip was 95% town and 5% highway.
Trip 5. Casa Grande to Los Algodones Mexico back to Casa Grande via highway I 8. Total Miles were 374.5, gallons used 7.158 MPG 52.319. The trip was 95% highway and 5% in town roads. Speed on the highway was 65MPH using the cruise control, and very little manual throttle use.
As you can see the car responds well to the tune and pipe, better on the lower speeds as opposed to the constant highway speeds, and better with manual throttle than with cruise control. I think the better mileage in manual throttle control is due to being able to see hills and respond easier to accelerations and decelerations then the cruise controls more rapid responses. I can build up speeds for hills at an easy pace rather than the cruise controls instant response.
In summary, I am extremely pleased with the modifications to the car and will realize a payback in savings much sooner than I anticipated. So if you are on the fence about spending the money do not hesitate it is well worth the time and money to make the mods.