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Performance Mods

Disclaimer: Nearly every modification on this page will void your new car warranty!  My car was modified after its warranty expired.  
I assume NO responsibility for lost warranties or damage caused by owners who duplicate my efforts.  MODIFY AT YOUR OWN RISK!

Improved Airflow

Like most tuners, I began with my intake.  Since 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 stuck with paper for quite some time.  Later, AMSOIL introduced their new EA AIR FILTER which uses synthetic nanofiber technology by Donaldson.  In a nutshell, these filters flow like cotton gauze but trap dirt like paper.  Best of all, they do this WITHOUT OIL.  I adapted an airbox from a Ford Mustang to work in my car since the EA filter was not available for my application.  The result is an intake that'll flow more air than I'll ever need combined with a better air source (beneath the engine bay).  The elimination of the stock "accordian pipe" also reduces intake restrictions (a good idea for turbo upgrades).  I eventually installed an intake manifold from a European PD130 Passat TDI (similar design as the PD150s, but with driver's side inlet).

New Engine Programming

Changing the engine programming provides the most dramatic increase in engine performance of any single engine modification.  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 Rocketchip, Alligator, and Upsolute programming.  I believe Rocketchip and Alligator provide the best flexibility of tuning for cars modified beyond a simple chip upgrade; and Rocketchip has the most experience with TDIs old and new.  Plenty of folks like "tuning boxes," too.  They have their merit.  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 Rocketchip's RC6, an aggressive program which pulls all the way to 6000 rpm!

More Fuel

The next power upgrade is to replace the fuel injector nozzles with larger units for more fuel flow.  I prefer 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 nozzles are PP502s.  The ALH guys with large VNT turbos love them.  But the smoke is a bit obnoxious in 1Z/AHU applications.  I think PP520s are a better choice... maybe PP764s.        I installed a PD-100 TDI in-tank "lift pump" to supply my injection pump (IP)  with fuel pressurized to six psi.  This 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 a collision.  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.  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.

Turbo Upgrades

Turbo swaps are a serious investment in time, money, patience, and managing expectations.   I've experimented with a T3 (laggy),  a K03/K04 hybrid, and a GT-15/20 hybrid (similar to K03/K04).   Generally speaking, larger turbos flow more air and deliver more top end power; but smaller turbos spool faster and deliver more low end torque (better drivability).   So far, the K03/K04 hybrid is my turbo of choice.  It flows slightly more air and provides a modest gain of ~9 whp and 12 lb/ft in the middle of the band.  The K03/K04 hybrid is a direct replacement for the stock turbo.  However, 9 whp is not worth the SCCA class penalty at autocross events.  Therefore, I'll likely stay stock for more-level competition.  :-)  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.  Be forewarned there is a bit of labor involved with a VNT conversion.  Reasons I have not done it myself include the minor flaws which remain in the software (I don't think any tuner has it 100% correct at this time), some of the electrical/mechanical changes which need to be done, and (most importantly) 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.  But I may experiment with other wastegated turbos as time and $$$ allows.

"Mufflerectomy"

The main goal with exhaust system upgrades is to reduce exhaust back pressure.  This allows the engine to flow more air and improve turbo response.  Many owners go with some sort of commercial 2.5" 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.  The new cat keeps me legal!  Dyno testing showed a mild power increase of ~9 whp and 10 lb/ft; but the horsepower extends higher in the rpm band.  I took it just a step further and installed a custom 2.5" stainless steel downpipe by TDIPARTS.COM.  Oh, since I know you're wondering, the new exhaust note is pretty appealing.  A friend 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)

Some MkIII owners improve their intercooling via front-mounted intercooler (FMIC).   However, there's not a lot of space for installing one 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 water-only since that is what's legal in SCCA events.  I have not measured any significant gains.  Instead, I'm likely maintaining initial power by reducing the rise of intake air temperature.  Water injection's secondary benefit is reduced EGTs.  I can still peg the EGT gauge, but it takes longer to do so.  I may also mist the intercooler since the plumbing is already in place.   :-)

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 MkIII 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.com.  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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