This article outlines the differences between two seemingly similar turbochargers—the Garrett VNT17 and the Borg-Warner KP39–for TDIs made between 2004-2006 with an engine code of BEW (Golf, Jetta, and New Beetle).
Before you go crazy and start buying turbos, see our article How to Tell If Your Turbocharger Has Failed (and possibly a mechanic) to determine if you actually need a new turbo. If your car’s turbo is in fact dead, the choice between a VNT-17 and KP39 can be a complicated one. In this article I’ll outline the differences between the two so you can decide which turbo best fits your needs.
Why are there two replacement turbos available? When VW released the BEW cars in 2004, they came stock with a KP39 turbo, whereas previous TDI engines came with a Garrett VNT15. However, KP39s weren’t released to the aftermarket yet (they eventually were released in 2011), and Garrett saw an opportunity to adapt the VNT-17, which was used on PD 130 and PD 150 cars in Europe, to these North American cars and exploit the gap in the market. They did so by lowering the EGR pipes and sourcing actuators in North America.
The main difference between the two turbos is their size and how much fuel they can provide to the engine. The VNT-17 is larger, and can thus compress more air. It has a 49 millimeter compressor wheel, which is considerably larger than the wheel on the KP39. Fully modified TDIs with a VNT-17 can dyno at around 180+ HP/350+ft/lbs of torque, while with a perfect tune a KP39 would be doing extremely well if it dynoed at around 150 HP/240 ft/lbs.In order to take full advantage of the VNT17’s power, however, you might have to spend some serious coin.
Another point to consider about the VNT-17 is that, because it’s larger, there’s more lag time between acceleration and boost. Comparatively, the KP39 is more responsive.Tuning your car can eliminate this lag, plus improve performance.
While the KP39 might be easier on your wallet and have good response, it can struggle and fail at high altitudes. The turbo needs to work harder to compress the thin air, and therefore produces less power or might overspeed and fail. The VNT-17, because it’s bigger, has less trouble.
A second downside to the KP39 is that replacement actuators are unavailable. If your actuator breaks, you need a whole new turbo. Replacement actuators are available for the VNT-17.
In summary, if you’re running a stock TDI, consider the KP39 your best option. However, if your car is modified to take advantage of a larger turbo, or you live in a high altitude area, the VNT-17 is your best bet.