After picking up 33 horsepower in the last installment (December 2016), we’re back at it with our ’03 Jetta TDI project. We’re once again chasing horsepower, adding reliability, and even looking for an uptick in fuel economy. To reach our goals this time, we needed to pick the perfect injector upgrade and install all the right supporting modifications. For that, we contacted our friends at Kerma TDI and came up with a sound game plan. Two days later, a set of the company’s DLC 520 injectors arrived at our door and a revised ECU calibration was sitting in our inbox.

Opting to tackle the clutch install fi rst, Jake Bosie of Flynn’s Shop got started by removing the items from the engine bay that would allow him plenty of access to the top of the 02J fi vespeed transmission. With the airbox, battery, and battery box out of the way, reaching the top bell housing bolts and disconnecting the shift linkages and linkage base was possible.
After the top starter mounting bolt was removed, the slave cylinder was broken free from the transmission (shown). Once that was complete, the top driver-side motor mount bolts were loosened (the bottom fasteners were removed after the driver side CV axle was out of the way). We would eventually be replacing the factory driver-side mount with one of Kerma TDI’s Street Density 034 Motorsports units when everything went back together.
Next, the car was hoisted into the air via two-post lift and the front wheels were removed, followed by the car’s aftermarket skid plate (i.e., panzer plate). Removal of these items made it possible to pull the starter (shown) and get to work removing the axle shafts.
It’s not possible to drop the transmission without removing both axle shafts from the car. A triple-square socket is needed to break them loose and Bosie used a 17mm socket to hammer them out. Now is the opportune time to inspect (and even replace) the axle shafts, if required. A torn boot, which allows debris to enter the CV joint, is usually the culprit behind most failures. Complete CV joint assemblies and CV boot kits can be purchased online, at your local VW dealer, or through Kerma TDI. Ours checked out OK at this time.
An engine hoist was employed to ease the process of pulling the transmission. The ability to tilt the driver side of the engine downward makes a world of difference when removing (and installing) the transmission. Once the hoist was in place, the dogbone motor mount was removed from under the car.
Here you can see that the factory clutch still had some life left in it (left). While it’s possible to get by with a stock clutch and Kerma TDI’s DLC 520 injectors, its ability to handle regular inputs of 200 lb-ft of torque or more can kill it in relatively short order. For this reason, we opted to rule out the weak link altogether and go straight to the Stage 2 Daily Clutch from South Bend (right).
More than doubling the holding power of the stock unit, the South Bend Stage 2 Daily Clutch utilizes an organic clutch disc material. A heavy-duty pressure plate provides vastly increased clamping force without sacrificing the stock pedal feel, and a 22-pound, solid-mass flywheel replaces the factory dual-mass unit. This clutch is well known for its quiet operation (no rattle), durability, and is conservatively rated to handle 325 lb-ft of torque.
Bosie made quick work of installing the single-mass flywheel (and we’ll note that its bolt pattern only allows it to be installed one way). Each of the supplied flywheel bolts’ threads were hit with a coat of Loctite prior to being installed, and then the 10mm fasteners were torqued to 65 ft-lb.
Using the alignment tool South Bend supplied with its clutch, the clutch disc and pressure plate were set in place behind the flywheel. Bosie then torqued all pressure plate bolts to 20 ft-lb.
Turning his attention toward the transmission, Bosie pulled the release lever clip out of the factory release lever and then slid the release lever off the input shaft. Because the clutch release lever can bend, the ball pin can wear on the release lever, and the clip that holds the release lever to the ball pin can bend, we heeded Kerma TDI’s advice and replaced all three items.
Once the ball pin, clip, release lever, and throw-out bearing were in place, the input shaft was hit with a liberal coating of grease, as this is where the throw-out bearing rides. Then the transmission was hoisted up (by hand) and bolted to the engine.
With the transmission bellhousing bolts in place, the driver-side Street Density 034 Motorsports motor mount was installed. The Street Density 034 Motorsports mounts offer offer 25 percent more stiffness than the stock units, are fluid-free, and don’t increase vibrations felt inside the car. Once the new motor mount was secured, the shift linkages, starter, and CV axles were reinstalled.
After lowering the car back down and removing the engine hoist, Bosie began replacing the factory injectors with the DLC 520 units from Kerma TDI. He got started by first breaking all injection lines loose and then removing them.
To limit leakage, Bosie capped off the fuel ports in the injection pump. From there, all fuel return lines were pulled, followed by loosening each injector hold-down bolt (shown). We’ll note that Kerma TDI conveniently supplied all new return lines with its DLC 520 injectors.
Kerma TDI set our injectors up as a Stage 1 version of its DLC 520 units and equipped them with brandnew Bosio nozzles. A unique feature on the DLC 520 injectors is that the needle and all of its sliding surfaces receive a diamond-like carbon (DLC) coating to reduce friction and increase the hydrodynamic support that the needle utilizes to remain centered in the nozzle bore. According to Kerma TDI, the DLC coating provides an impressive 50 percent increase in component life. Our injectors were rebuilt, pop tested, and balanced as a complete set before leaving Kerma TDI’s facility.
Along with supplying new return lines, Kerma TDI also loaned us an injector puller tool. It simply threads onto the top of the injector and acts as a slide hammer to dislodge it from its respective bore in the head. Once each injector had been pulled, Bosie hit the injector bores with compressed air to ensure they were free of any debris prior to installing the DLC 520 units.
The Bosio DLC 520 nozzles fitted to our injectors are the same units found on the 110hp AFN/ASV European engine. They’re known to provide an approximate 20hp gain over the stock injectors used in the ALH engine. Their spray pattern is said to optimize horsepower, improve fuel economy, enhance throttle response, and lower smoke levels.
On ALH code injectors, it’s important to note that the number three unit is different from units one, two, and four. It’s still a Bosch VE unit, but it’s taller and equipped with the needle lift sensor that allows the ECU to monitor injection timing.
In addition, the number three injector is either equipped with a square-style plug or a D-shaped plug from the factory. For this reason, it’s important to determine which type your car has before you order a complete set of aftermarket injectors.
Prior to installing the DLC 520 injectors, Bosie swapped the factory return tee onto the new number three injector, and then seated each injector in its bore. Once all injector hold-downs were tight, they were taken back to snug, and then torqued to 20 ft-lb (for proper seating). After that, the new return lines were installed, followed by the injection lines (with their respective flare nuts being torqued to 18 ft-lb).
Naturally, with larger nozzles in the mix, the ECU tuning had to be tweaked to get the most out of them. Once again, we left this up to the guys at Kerma TDI, and after receiving a modified file via email we loaded it onto our Q-Loader programmer and immediately reflashed the Jetta’s ECU.
To make an apples-to-apples comparison, we stuck to the same dyno and ran the car in fourth gear from 40 mph to 90 mph. If you recall from the December ’16 article, we were able to clear 105 hp on stock injectors thanks to the Q-Loader programmer. Our new best of 120 hp puts the car right in line with what you can expect with a small nozzle upgrade and revised ECU tuning. Perhaps most impressive is that the car makes less smoke, yet makesmore power. And thanks to Kerma TDI’s refined ECU calibrating, throttle input remains linear—just the way we like it. To date, our Jetta has been the beneficiary of a 65 percent increase in horsepower, and there’s still more to come. Stay tuned.

But before we got busy adding power, we had to address the Jetta’s weakest link: the factory clutch. While it was holding the added horsepower and torque from the programmer just fine, we knew the larger injectors would inevitably push it over the edge. To avoid the frustrating conundrum of having more power yet not being able to use it, we promptly gave South Bend Clutch a call and ordered one of the company’s Stage 2 Daily units, which is rated for 325 lb-ft of torque. Read on for a full recap of the install, our new dyno numbers, and a detailed mileage log.DW

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