It's taken me a while to finally write this novel of a thread, but I hope it encourages discussion and it helps other 2.5L owners.
In February/March of this year, I came across some (what I felt) really good deals on a gently used Magnaflow exhaust and a never-used Eurojet header.
I’d owned my 6-speed automatic 2008 Rabbit for a little over three years and wanted to begin modifying it beyond aesthetics. (I didn't want to delve into turbocharging the car for a number of reasons.) But I wanted to “do it right,” so I read up on exhaust headers and eventually even went and had it ceramically coated (to encourage heat resistance) before installation.
In addition, I was going to get Unitronic’s Stage 2 software installed simultaneous to the exhaust and header. I thought that doing all three of these upgrades would make a respectable, but not enormous, difference in the power my car was creating. Since there hadn’t been too many other 2.5L owners that had done such modifications, I was going to document the transition though dyno’ing the car after each mod.
After all, Magnaflow posted a Dynojet graph declaring a “10HP & 10LB•TQ Gain!” from the exhaust on a 2007 Rabbit.
(Granted this was the year where the engine was rated at 150HP, not 170HP like 2008+ years.)
Eurojet was claiming “Dyno-proven HP gains,” on every retailer’s website, without any dyno graphs.
Unitronic suggests a “15HP & 13LB•TQ” gain, albeit also without any dyno graphs.
Now granted, Unitronic’s numbers are going to be at the engine, not the wheels, for horsepower and torque gains. Which is why, quite honestly, I’d be more inclined to believe Unitronic’s claimed numbers out of all three manufacturers, because they do the testing with just the engine outside of the car. As we all (hopefully) know, there is approximately a 15% drivetrain loss, so let’s assume for the sake of argument that Unitronic’s software actually puts out around 12HP and 10LB•TQ. If you’ve been paying attention, the hyperlink above was to Unitronic’s Stage 1+ software, not Stage 2 - I’ll get back to that in a few paragraphs.
I brought my car to Mobile One in late April of this year. Aforementioned, I wanted to “document” the progression from stock to modified by dyno’ing the car after each installation. Mobile One has a Dyno Dynamics dynamometer, which have been known to be brutally honest about the power your car is delivering to the wheels. I don’t care to argue about Dyno Dynamics VS. Mustang Dyno VS. Dynojet.
The first dyno graph revealed almost exactly what I was expecting - about a 15% loss in the horsepower and torque figures that Volkswagen suggested for that year - 170HP & 177LB•TQ x 15% (loss) ≈ 144HP & 150LB•TQ:
The shop then installed the header and exhaust, and dyno’d the car a second time. The posted dyno results from Magnaflow of 10HP & 10LB•TQ from their exhaust - in addition to Eurojet’s claim of “Dyno-proven HP gains,” I was expecting a result of maybe 15HP & 15LB•TQ. Two runs in, the results show a gain of almost 14HP and 5LB•TQ:
After searching the databases and eventually calling Unitronic, Mobile One couldn’t find the Stage 2 software for my Rabbit’s engine/transmission combination, so they flashed my ECU with Stage 1+. The owner of the shop (Jason) even called Unitronic’s headquarters to escalate the problem and explained that he’d notify me once Unitronic notified him of the release of Stage 2 for my drivetrain combination. He also mentioned to them that I had a Eurojet header and a Magnaflow exhaust installed, so maybe they could further tune it for me. After Stage 1+ was flashed, the shop dyno’d the car a third time, but the results were interesting. To our surprise, we saw a decrease of about 6HP when this software was installed:
Mobile One kept in contact with both Unitronic and myself on the status of my Stage 2 file until July. After nearly five months of testing, Unitronic adamantly concluded that the Eurojet header that I have installed, actually lost power when tested by them on their engine dyno with my specific engine/exhaust/header combination. The shop and myself were surprised, and not quite sure how it's possible. Obviously they are not going to spend any time making a file for a piece of hardware that produces negative results.
I plan to remove the Eurojet header and replace it with the stock header, then dyno the car again to see the results.
It’ll be interesting to see what the outcome is.
If something positive has come out of all the work that’s been done thus far is how gnarly and unique my exhaust note is.
Really laying into the throttle brings a smile to my face. My girlfriend has a 2010 Jetta with the same engine/transmission combination and in comparison, the Rabbit is undoubtedly quicker. It's difficult to describe, but the car pulls away smoother and it's a lot more fun to drive.
I went into this blindly, not knowing what to expect. If there's one thing I've learned, it's to patiently wait for the proven numbers by a manufacturer. A lot of us 2.5L owners are holding on to our money, waiting for new and improved performance parts to arrive. Keep waiting, there's a lot of stuff on the horizon and I have a feeling 2012 will be a good year for us.
I'd still recommend Unitronic software and the Magnaflow exhaust to any 2.5L owner. Unitronic put in the hard work behind the scenes to finally reach an (unexpected) outcome. I also highly recommend Jason and the team at Mobile One in Glenview, IL.
I plan to continue updating this post.
In a way, it’s my build thread.
PERFORMANCE MODIFICATIONS (as of 12/6/11)
•Eurojet Stainless Steel Exhaust Header
•Magnaflow Stainless Steel Cat-Back Exhaust
•Unitronic Stage 1+ Software
•Black Forest Industries Stage 2 Transmission Mount
•Black Forest Industries Stage 2 Torque Arm Insert