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Performance Mods

Disclaimer: Nearly every modification on this page has the potential to harm your engine if done incorrectly.
I assume NO responsibility for lost warranties or damage caused by owners who duplicate my efforts.

Improved Airflow

                of engine bay with PD intake... Like most tuners, I began with my intake. Despite the fact that dyno runs on MY CAR proved only a 1-hp difference between a paper filter in the stock box and no filter/box at all, I still experimented with cones, "cold-air intakes," and other "improvements." Fast-forward several years and I found myself tired of the boy-racer soundtrack and seeking a quieter solution, not to mention one which didn't require cleaning/replacing every 10,000 miles. The stock airbox is known to flow over 170-hp, even with the accordian pipe. And there's no doubt the stock filter has more surface area than just about any other filter available. So I returned to the stock airbox and filter after years of messing around with alternatives. It helps maintain a relatively stock appearance and, let's face it, does't hurt a thing to be there. Save yourself some time and money by leaving this part of the engine alone. There's almost nothing to be gained by replacing it until after profound upgrades have been made elsewhere.

I also installed an intake manifold from a European PD130 Passat TDI. This manifold is identical to the PD150's, but with driver's side inlet. Some say this intake isn't the best improvement for the intake manifold. But everyone agrees it's far better than stock and is known to flow over 200-hp.

New Engine Programming

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                ECU, or Engine Control Unit. Changing the engine programming provides the most dramatic increase in performance of any single modification. It should be anyone's first move. You can count on a reliable 20-30% increase in power and torque from most programs without the risk of damaging your engine. More aggressive tuning is available for appropriate hardware upgrades (keep reading for examples). Naturally, the driving experience is greatly enhanced. I've used Upsolute, Rocketchip, Alligator, and MaloneTuning programs (in that order).   I believe Rocketchip and Malone provide the best flexibility in tuning for cars modified beyond a simple chip upgrade. MaloneTuning is more accessible. I've read good things about TDTuning.com, too. Plenty of folks like "tuning boxes," too. They have their merit with the older TDIs. But I'm biased toward changing the program itself since a proper tune operates the car in truth instead of via sensor deception. The choice of tuner is yours and should depend upon your location and timeframe. My current program is a mildly-aggressive MALONE TUNING program. My ECU also has a 3-bar MAP sensor for greater boost control at higher pressures.

More Fuel

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                fuel injectors... My next power upgrade was to replace the fuel injector nozzles with larger units for more fuel flow. I use PowerPlus performance diesel injection nozzles by Fratelli Bosio of Italy. They provide a better spray pattern and flow more fuel than the stock nozzles. The result is a 10-20% increase in power and torque, depending on your choice of nozzle. My current set of PowerPlus nozzles are PP502s. The ALH guys with large VNT turbos love them. But the smoke is a bit obnoxious in wastegated 1Z/AHU applications on stock turbos. I think PP520s are a better choice, maybe PP357s, even though they'll make less power. I'll try some PP764s when I move to a larger turbo. BTW, always have the injector pop pressures balanced when replacing the nozzles.

Additional Fueling Upgrades

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                pump and fuel cooler... I installed a PD-100 TDI in-tank "lift pump" to supply my injection pump (IP) with fuel pressurized to six psi. This, combined with a modification to the injection pump's case pressure relief valve known as the "Keystone Mod" (pictured), makes the car a tad more responsive and keeps my timing spot-on all the way beyond redline for improved top end power. CAUTION: This pump is powered via relay triggered by N109 so pumping is stopped in the event of an airbag deployment. DO NOT wire it to the ignition! FYI, I do not recommend the use of most economical external fuel pumps, a popular alternative to the more expensive OEM lift pump. Some work well, but you need to be careful with your selection. READ HERE for an explanation. Another benefit of the OEM lift pump is the reservoir surrounding the pump. It was likely intended to keep the pump submersed in fuel for cooling. But I've learned through experience that it also ensures the engine cannot be starved of fuel during aggressive manuevering (competitive driving)  when fuel is sloshing around in a nearly empty tank. The addition of a fuel cooler is an optional fueling upgrade. Cooler fuel makes more power and helps cool the fuel pump(s). Since the injection pump creates a lot of heat when pushing more than stock levels of fuel, it's not a bad idea to cool the fuel before returning it to the tank. The newer, more powerful TDI's have them; so they must serve a purpose. I use a four-pass transmission cooler to cool my fuel.

Turbo Upgrades

Turbo swaps are a serious investment in time, money, patience, and managing expectations. I've experimented with a T3 (laggy),  two different K03/K04 hybrids and a GT-15/20 hybrid (similar to K03/K04).   Generally speaking, larger turbos flow more air and deliver more top end power while smaller turbos spool faster and deliver more low end torque (better drivability).   So far, the K03/K04 hybrid is my favorite turbo. It flows slightly more air than the stock unit and provides a modest gain of ~9 whp and 12 lb/ft in the middle of the band. I'm currently using a one-of-a-kind K03/K04 hybrid which features a K04 compressor in a modified K03 housing as well as a K04 turbine stuffed into a modified K03 exhaust housing ("regular" K03/K04 hybrid uses a K03 turbine).   It gives up a tiny bit of torque in exchange for some top end power. Unfortunately, the top end yield isn't enough to make this turbo a worthwhile replacement for the K03/K04 readily available at BORA PARTS. But I believe an unexpected side effect of the larger exhaust opening is improved fuel economy when driving sanely. The K03/K04 hybrid is a direct replacement for the stock turbo.

I'm considering a GT-2052 wastegated turbo.  A benefit to sticking with a wastegated turbo is that I can continue to use my current programming and boost control. I'd need to do some parts fabrication to mate it to my exhaust manifold as well as to connect a custom downpipe. That's a bit of hold-up. But I've read a few reports to suggest it's worth the hassle. Another option is conversion to a variable-vane turbo (VNT)  similar to those found on newer TDIs. The VNT's strength is that it spools quickly like a smaller turbo yet flows well like a larger one. A drawback is the additional moving parts which can jam up with soot if not exercised with routine floggings. ;-) There is a bit more labor involved with a VNT conversion. Reasons I have not done it myself include the electrical/mechanical changes which need to be done and the car will fail the OBDII compliance test at inspection time. Sure, I'm currently exempt from emissions testing, along with many other states. But it's only a matter of time before full testing is performed on all cars 1996 and newer, including diesels. I plan to keep my car compliant until a workaround is found. If I do make a jump to a VNT, it'll likely be a VNT-17/22 HYBRID or a GTB1756VK. However, I really like the simplicity of keeping a wastegated system.


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                a mufflerectomy.  The main goal with exhaust system upgrades is to reduce exhaust back pressure and improve exhaust flow. This allows the engine to flow more air and improve turbo response. Many owners go with some sort of commercial 2.5" cat-back exhaust system. This usually costs over $800! Instead, one can get the same benefit by replacing the muffler and resonator with a straight pipe. The turbo and my 2.5 inch diesel catalytic converter by Magnaflow (#93006D)   do a pretty good job of muffling engine noise. The improved accelation and response was more than I expected. Eliminating the old cat likely removed a restriction and gave me some unexpected low end power and torque as well as improved EGTs. The new cat keeps me legal! I eventually took it just a step further and installed a custom 2.5" stainless steel downpipe by IDPARTS. Dyno testing of the larger downpipe and new cat showed a mild power increase of ~9 whp and 10 lb/ft; but the horsepower extends higher in the rpm band. I had also experimented with a resonator and eventually opted to put it in place of a muffler to pass a "visual inspection." Oh, since I know you're wondering, the new exhaust note is pretty appealing. An acquaintance who frequents Europe says my car sounds like the V6 TDI. Here's a small audio file (remember that I have a large, open exhaust).   :-)

"Chemical Intercooling" (Water Injection)

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                injection parts... Some Mk3 owners, gas and diesel alike, improve their intercooling via front-mounted intercooler (FMIC).   However, there's not a lot of space for installing one on a Mk3 without cutting two-thirds of the bumper rebar. Cutting the rebar reduces frame rigidity at the front end. This is undesirable and illegal on the autocross course where frame stiffness is paramount. Therefore, I went with "chemical intercooling" via water injection by SNOW PERFORMANCE.  I inject about 20% methanol (water-only in SCCA events)  and have not measured any significant gains. Instead, I'm likely maintaining initial power by slowing the rise of intake air temperature. Water injection's secondary benefit is reduced EGTs. I can still peg the EGT gauge, but it takes a lot longer to do so. I may also mist the intercooler since the plumbing is already in place. :-) Another alternative to a FMIC is an air-to-water intercooler (AWIC).   I had researched some systems by FROZENBOOST. However, there is now a LARGER FMIC available for the Mk3. Its exact benefits are unproven. But I'm sure it will delay heatsoak to the point where it would be almost impossible at jail-free speeds.

                of dynograph graph... I've measured most of my progress along the way. I chose to use a shop with a DYNAPACK chassis dynomometer. Measurements are taken directly from the hub and are VERY consistent and repeatable. My best dyno pull to date is 136 whp and 263 lb/ft. Using a popular Mk3 transmission loss of 17%, that calculates to ~163 hp and 316 lb/ft at the crank... or ~80% over advertized stock values. Check out my MY DYNO VIDEO (6 MB).  Oh, for the record, I do NOT recommend the use of lightweight flywheels in TDIs. TDIs normally do not rev high enough to make them practical; plus, TDIs run more smoothly with the stock flywheel. My experience with a lightweight flywheel was rather painful. Feel free to read MY REQUEST FOR HELP at TDIClub. In short, my lightweight flywheel took me on an adventure which saw the replacement of programming, injectors, the injection pump, and even the ECU before tracing my issues to the flywheel. The good news is I now have a lot of spare parts for my aging TDI. ;-)

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