Everyone loves an underdog. At least we do, and we suspect it's one of the main reasons so many people hang onto older VWs and continue to drive them well after they can afford something more exotic. Sure they handle well, look cool and are economical, but at the end of the day it's just plain fun to line up against a more expensive car and blow its doors off.
Meet Dave Graf, owner of the Aberdeen, MD based VW/Audi shop New German Performance - better known as NGP Racing. He obviously feels the same as we do because as a long-term enthusiast whose first car was a Rabbit GTI when they were nearly new, he's the man behind the clean Mk5 Rabbit 2.5 five cylinder turbo you see here.
The idea wasn't just to champion the underdog, but to prove a hunch that the new VAG straight-five was a great motor for forced induction and not just an entry-level option.
"It has lots of torque and as far as I was concerned, the 2.5 had plenty of potential as long as the engine was built enough," he began.
He picked up the phone and dialed Chris Collier at C2 Motorsports, a company NGP has regularly worked with over the years, and discussed the possibility of working on the project together.
"We have a long term relationship with C2 and respect its ability to tune VAG cars," he continued. "We felt it would be better that they develop the basic kit, and then we'd go down the road of custom-building a higher horsepower version, because that's one of NGP's specialties."
The prototype parts were delivered a short time before last year's H2Oi, and they began the mad scramble to build the car for the show. Head technician Ron Weaver retained the exhaust manifold and T3/T4OE hybrid turbo from the stage 1 C2 turbo kit and custom fabricated the rest of the parts needed.
A modified Eurojet Racing side-mount intercooler from a Mk4 application was then chosen to both keep the front end clean and the competition guessing.
After a brief experiment with nitrous over the summer, Dave was aware that the stock pistons weren't suitable for the boost levels he had in mind.
"There were questions over the strength of the stock pistons at higher boost levels. It was up in the air; at this point you can run up to 13-15psi on the stock pistons, but above that would be an issue," he explained.
JE Pistons produced a forged set of pistons with 9:1 compression and a turbo-friendly ring design. They were matched to a set of forged Pauter rods before the 2.5 was buttoned up.
A large diameter intake draw pipe was fabricated and fitted with a K&N cone filter. They also manufactured a 3" stainless downpipe. A high-flow cat and 3" APR cat-back exhaust then finished off the system. One of the few headaches in the process involved squeezing all the parts into the tight engine bay, while keeping the bends smooth for adequate flow.
"It's a little tougher to accommodate the downpipe on the 2.5 because you have to make a 180 turn out of the turbo to get down the transmission tunnel," Dave said.
Jeff Atwood, the head programmer and co-owner at C2, created a custom program for the prototype stage 3+ kit based on what C2 had already learned with its test car. A set of "green giant" Bosch 415cc injectors replaced the puny stock parts, and ensure the engine won't run lean.
Unfortunately, a number of teething problems have kept the car off the dyno and from obtaining solid horsepower numbers, but it is estimated at over 300 to the wheels.
Based on the stage 1 numbers, this seems reasonable. However, a problem with over-boosting on the original internal wastegate design led to an external 38mm Tial wastegate. This improvement has also been incorporated into the production C2 stage 1 kit.