Off-the-shelf parts were non-existent, so it was the task of engineers to discover a different solution. "The existing pump is almost like a piston pump," he continued. "It compresses a finite volume of fuel and quickly reaches its limit. To overcome this we had to change the pump internals. We took a lot of calculations and remanufactured them to a different diameter size - the tolerances inside are crazy! It's literally microns that drastically changed how the fuel would flow and only a few places in the US can produce parts with this tolerance. Fuel flow is where most people are hitting the wall, so looking into the future we wanted something simple for the customer to do. The new parts needed to have repeatable results with customer-oriented design. The key to the whole thing is our experience and know-how in changing the variables of the ECU, and our understanding of how it affects the hardware. You can't just throw this pump on the car and go. You have to get the ECU to understand the data so it can make the car run properly."
The correct fueling allowed engineers to use a Garrett GT2871R turbo, sourced from APR's stage 3 kit for the 225hp Audi TT, but it was re-clocked and re-configured with a different wastegate.
Along with the big turbo, a new exhaust manifold was added. Because the factory manifold is incorporated into the turbo, APR reproduced it with more breathing room. The manifold is also manufactured from inconel to prevent the heat and energy dissipating.
A redesigned front-mount intercooler sits in the stock location. APR designed its own version with a similar length and height as stock, but it's 50% deeper for increased cooling. Silicone hoses were used to connect the end tanks to the turbo and throttle body.
Another key ingredient is the diverter valve. The 2.0T has an internal DV and an upgrade isn't needed with a factory turbo or K04 conversion, but the Garrett turbo made it necessary. "This DV is a diaphragm valve, similar to the factory one but with a cast bottom and machined top. It's stronger but has the same appearance."
"To aid air flow we designed an intake pipe with the factory MAF inside. We snaked a 3" carbon pipe to the front of the car where a filter sits." Chris continued. "Because the Mk5's airbox is part of the engine cover, retaining it would limit the flow, so we designed a flow straightener into the pipe for accurate air readings. Without the straightener, it gets really turbulent inside and disrupts the sensor readings."
APR already had a 2.0T exhaust with downpipe in production, but engineers opted to develop a 3" system featuring dual tips for this project.
While APR's 2.0T produces plenty of reliable power, it's important to note this particular GTI had forged connecting rods. "We fitted rods to ensure everything would stay together," Chris added. "It was done for SEMA and the GTI Challenge because we didn't want to push or break things before we'd done our real testing. It won't be something we're going to require for the production kit, though."
Track Tuned
In addition to the fuel and turbo upgrades, APR had to make sure the GTI would be fit for the track, so a Spec stage 3 clutch was installed, as well as a Quaife differential.
Tweaking the suspension was also crucial but there weren't many options available, so APR fitted Koni coilovers with custom-valved shocks and Eibach springs. An H&R rear sway bar corrected understeer and the combination handled exceptionally well during the GTI Challenge.
Brakes were next on the list and 14" Alcon slotted rotors with four piston calipers ensured ample stopping power.
Wheel and tire selection proved to be just as important and APR contacted BBS. "They had to make us wheels," explained Chris. "They didn't have the right offset for our brakes, so took a Porsche face and put it on a Mercedes barrel. They were reluctant to do it because BBS didn't want people thinking they offered wheels for this application. It's definitely not a wheel the public can get." Once the 19x8.5" RS-GT wheels were finished, APR painted the centers black and the lips red. Finally, 235/35-19 Michelin tires gave tremendous traction at the track.