Wiki article summarizing VW TDI emissions cheating so far, click here. Anyone logged in can edit it by clicking the "edit" button on the upper right of the page. It's a reference so please post any comments or questions in the forum. It's a work in progress so feel free to update it!
Basic performance upgrades for light diesel engine
How to increase power in a light diesel engine: basic performance upgrades
It's easy to get more power out of a turbo diesel engine for a few reasons. An engine is basically an air pump and the turbos on all modern diesel cars can increase the efficiency of this pump over OEM levels. For more details on turbocharging systems and exhausts for turbos, please read: 1000q: turbocharging. A diesel engine can also run well in a wider range of air/fuel ratio (AF) compared to a gasoline engine. A gasoline engine must stay in a small AF range to run well but by adding a little more fuel to your diesel engine it can safely get more power and still run well. Lastly, diesel engines are all computer controlled so a simple chip tune can increase power significantly without even getting your hands dirty!
One you pass the point of diminishing returns with a chip you must upgrade other parts of the engine like the intercooler, turbo, and piping to be able to efficiently burn more fuel. Too much fuel in a diesel will result in some unburned fuel or fuel which hasn't finished burning which goes out the exhaust as black smoke. A little extra fuel from a chip will only create a small puff of smoke in cars without a DPF (no smoke in cars with a DPF) but a chip and fuel injectors that are too large for your setup might kill all the mosquitoes in the neighborhood from the massive smoke screen! An acceptable level of smoke is highly subjective from owner to owner and even varies from model to model. DPF (diesel particulate filters) will block excess soot from existing the tailpipe because they're filtered out. See the DPF FAQ for more details on these systems. Excess smoke from unburned fuel is also a sign that fuel is being wasted. If you use the available power often or see lots of smoke, it will lower fuel economy.
Overfueling will raise exhaust exhaust gas temperature (EGT). Way too much fuel will cause damaging EGT and even more fuel could cause engine meltdown! This is the opposite of a gasoline engine where running a little rich may lower exhaust gas temperatures.
The basic upgrades on this page will not significantly affect engine reliability or lifespan if they are properly designed and used on a car in working order. See 1000q: advanced and extreme performance upgrades for advanced performance upgrades such as intercoolers and upgraded turbos. Some performance upgrades may cause the clutch to slip. Before you do any power mods, make sure your car is in good running condition and all maintenance is up to date!
Some people complain about TDIs are very slow or that their TDI feels slower than it when it was new. If this is the case, read 1000q: constant low power or can't rev and 1000q: limp mode solutions because there is probably a sensor or other problem causing low power or power cutting out. Your car must be in good shape before adding power mods because adding power won't mask existing problems.
Chip and software upgrades for the VW TDI or Audi TDI engine
The first recommended modification would be a chip tune. This is a modification to the stock programs on the car's computer. Some older TDI required soldering a physical chip to the car's computer, the ECU/ECM. All newer TDI don't require soldering as the modification is done to the programming.
For a daily driver, this is an excellent first step since it preserves and improves stock drivability and won't significantly reduce fuel economy as long as you don't have a lead foot! I do not recommend chips for non-turbo or non supercharged or non diesel cars because the cost benefit ratio isn't there. You could pay hundreds of dollars for a small power increase, often only noticeable at high rpm near redline. With a turbo or supercharged car chip you could gain 20-50 peak horsepower (depending on the car) with a much better power curve due to the properties of turbocharging and diesels. Some chip vendors for the TDI will also reflash/upgrade their chip software for the original owner for free or at a discount so that as your modifications change you don't have to worry as much about the cost of adjusting the software.
Some chip tuners who specialize on TDI engines are at KermaTDI. They also do chip tuning for the newest CRD 2.0L TDI engines 2009 and newer models.
Why you can't just raise the boost
If you're new to turbo car tuning, you may have heard that you can get more power just by turning up the boost. More boost (air) only equals more power if fuel is also increased. In some gasoline cars, the fuel maps or injectors, etc., may not support increased boost. You must do research on each different gasoline or diesel car before modifying since turning up the boost can cause engine damage.
In the TDI, the car's computer controlled fueling will not increase fueling solely in response to increased boost. Unlike most gasoline turbo car's open loop/closed loop control, all TDI before 2009 are closed loop controlled fueling only. There is no o2 sensor to meter fueling and after the injection pump - there is no further metering of fuel by the car's computer. (2009 and newer TDI use a new emissions control system which does effect fueling.) With a diesel, you should be thinking about adding more fuel and adding enough air to control smoke, keep EGT down, etc.
2009+ Jetta, Golf, and Audi A3 TDI chip tuning
These engine all use the 2.0L CBEA-CJAA engine. Chip tuning has been tested on these models with great results. While high altitude, build variation, and dyno variables will cause small variations in actual and measured power, your average engine will make about 170 hp and 320 lb-ft torque after a chip flash.
The big difference vs. 2006 and earlier TDI is the diesel particulate filter. See 1000q: DPF FAQ for VW and Audi for more details on this system. If you have a DSG transmission it can limit the torque from a chip tune. For best results, a DSG transmission software flash will raise these limits. Note: always comply with all emissions laws where you live/operate the car.
They do not yet have larger fuel injectors available.
2006+ VW Touareg TDI and Audi Q7 TDI chip tune
The 2006-2008 VW Touareg TDI used a V10 with 550 lb-ft of torque. The engine's weak spots are the turbos and the transmission is the next weak spot if you raise power levels. There are chip tunes out there if you wish to proceed. The 2009+ VW Touareg TDI and Audi Q7 TDI use a V6 engine that is much more robust with more room to increase power. They also feature a DPF system but since they use Adblue diesel exhaust fluid, see 1000q: DPF-Adblue FAQ for more on their systems.
Fuel injectors or nozzles
Older VW TDI respond very well to larger fuel injectors or nozzles as a basic fuel upgrade. This delivers more fuel to the engine without changing the car's computer. Unlike gasoline cars which require a narrow AF ratio, diesel engines are variable ratio engines and running rich will produce more power. One advantage of changing fuel injectors vs. a chip is that it also increases the amount of fuel to the engine and maintains stock drivability. Another advantage is that all fuel injector nozzles will wear out over time so upgrading the fuel injectors/nozzles may prove to be a good value alternative to buying new nozzles in the same size. For detailed fuel injector information and technical details, see 1000q: fuel injector and nozzle TDI FAQ. For the updated detailed installation procedure, see 1000q: fuel injector / nozzle install.
For 1996-2006 VW TDI: You can use a VCDS tool by Ross Tech to change the ECU "adaptation" and fine tune fueling to reduce smoke and make very small changes to fuel consumption. Note: the automatic and manual transmission VW diesels have different sized fuel injectors and injection pumps! The automatic transmission uses smaller nozzles but a larger injection pump. Putting a larger injection pump on a manual transmission car is like putting larger nozzles on an automatic transmission car because they both increase fueling. More information is in the fuel injector FAQ linked in the above paragraph.
The newest nozzle designs use a diamond like coating (DLC) to increase durability and service life vs. the older nozzles with the use of ultra low sulfur diesel (ULSD) that is now sold in Europe and North America.
.184 injectors: stock on 90hp North American manual transmission diesels. This would be a mild upgrade for automatic transmission cars, although recalibrating with a VAG-COM is recommended for automatic cars because they have a larger injection pump, this will adjust smoke.
.205 injectors: stock on 110hp European manual diesels. Keep in mind that they also had a larger turbo and different ECU to supply more air to burn more fuel. Note that power gains from switching from .184 to .205 will be less than .184 injectors with a chip. For most car setups, this is a good choice.
.216 injectors: stock on the 150hp 5 cylinder VW t4 diesel vans. It is not recommended since a chip with .184 or .205 injectors would be more efficient at raising power safely, although it can be done. When combined with a chip, you should be adding larger turbos, intercooler, exhaust, and fueling supporting mods. See Extreme power modifications for more details.
The picture shows the location of the fuel injectors on a VW diesel (non pumpe duse) circled in blue. Cars with pumpe duse have the injectors located inside of the valve cover so it's harder to swap them out.
For 2005-2006 pumpe duse VW TDI injectors: replacement is slightly harder than earlier cars because they're underneath the valve cover and are replaced as whole units. If you have a pumpe duse, I would recommend getting a chip and seeing how you like it first before swapping injectors. You can always add injectors later and have the chip updated for the new injectors. If you still want injectors, kermatdi at http://www.kermatdi.com/ sells larger pumpe duse injectors. If you don't know if you have a pumpe duse, all VW diesels in North America model years 2004-2006 are pumpe duse. For more details, see 1000q: pumpe duse description. Since pumpe duse engines came with more power than earlier cars, getting a chip will give you more power than earlier cars that only have a mild chip and nozzles.
Here is a picture of PD fuel injectors. The injector rockers and fuel injector block bolts have to be removed.
Chip + fuel injectors
Using both an aftermarket chip and fuel injectors will also produce more power than one modification alone. However, since the ECU doesn't know if you have larger injectors or not, make sure you get a chip that is written for larger injectors. Otherwise you will have unnecessary levels of smoke and lower economy which a chip can adjust. Because of the higher power levels, your clutch could start to slip due to the higher torque. Turning off the EGR with VCDS is not recommended since it could set off a check engine light and the ECU may adapt which results in lower fuel economy.
If you have an automatic, keep in mind that they have a larger injection pump than manual cars so if you are using larger nozzles with a chip, the suggested upgrade is to use injectors that are 1 size larger: .184. Any larger than .184 with an automatic transmission and you could get smoke. .205 is the suggested maximum size you can use with a chip in manual transmission with no other supporting modifications. Again, each car, each software tune, each driver, and their tolerance for smoke is slightly different. Other mods may increase or decrease the amount of smoke and power you see. Clutch slip is more likely with chip + nozzles since using them together makes more power and torque. As a conservative recommendation, the mk4 TDI should use smaller nozzles and a light tune or only a chip or only nozzles to prevent clutch slip. Mk3 and Mk5 cars seem to be have stronger clutches.
Keep in mind that delivering extra fuel at the engine must be supported by extra fuel flow in the whole system. The fuel filter must be unclogged, the injection pump must be able to supply a sufficient amount of fuel. The automatic transmission VW diesels had a 11mm injection pump, the manual transmission had a 10mm injection pump. Basically, the maximum amount of fuel that the smaller manual injection pump made was offset by using larger fuel injectors. The diesel long block, the main engine itself, is the same in auto and manual transmission cars, but the auxiliary parts such as the flywheel, the injection pump, etc., are different. As a result, if you require a lot more fuel than what the injection pump can mechanically deliver, the ECU will sense a fault and can go into a safety mode.
1996-2003 TDI did not have any electric fuel pump because the injection pump sucked fuel from the fuel tank. Adding a "lift pump" from a 2004+ TDI, a low pressure in-tank electric fuel pump, will boost fuel pressure to the injection pump and support higher power levels at higher rpms. In the above picture, the injection pump is the rectangular metal pump below the left two fuel injectors.
Remember, adding more fuel must be accompanied by more air, otherwise you are just over fueling the engine, creating smoke, and unnecessarily raising the exhaust gas temperatures. Everything else being equal, you can't turn the boost up beyond safe limits without raising temperatures and stressing the turbo. See 1000q: turbocharging to understand more about turbocharging and read 1000q: advanced performance modifications for how to efficiently add more air. Unlike many cars, an aftermarket oiled high flow air filter is not recommended for the TDI because the mass air flow sensor (MAF) is failure prone, especially the mk4 generation. There is a noticeable link between aftermarket high flow oiled cotton air filters and MAF failure when used on a TDI. In addition, to save parts and inventory costs, VW used the same air filter on most mk4 TDI and the 240hp R32 Golf, and there is more than enough air filter capacity for all generations of TDI. See 1000q: MAF faq for more details on the MAF sensor.
The way advanced timing will increase power is by injecting fuel later as the engine piston is moving up and down. By adding fuel later in the stroke, you create greater pressure and energy. Note that this also increases stress and heat on the engine by a small amount. Fuel that is injected early has more time to burn and produce energy than fuel that is injected late. As long as you stay within the normal operating range of engine timing as found in your service manual, advancing the timing may result in more power, easier starting, and better fuel economy but hotter temperatures and engine stress. Note that there is an optimum point for timing. Anything other than this maximum point will decrease power and mileage, but this is impossible to know since there are too many variables involved. As long as you stay within the normal operating range of engine timing, you are safe. Slightly advanced timing will also result in easier cold starting.
Biodiesel also slightly advances the timing. It does not change the mechanical timing because that is set by the injection pump and ECU. Biodiesel should burn faster when injected because of the properties of biodiesel and higher cetane which effectively advances the timing.
Also note that there are two different ways to advance timing: physically adjusting the injection pump pulley or through VCDS adaptation. If you have an aftermarket chip, the chip maker has already adjusted the timing as necessary!
To adjust the injection pump timing, adjust the injection pump as shown in (for mk3 cars: 1000q: timing belt part 2) , OR (for mk4 ALH cars: 1000q: timing belt part 2). These are exclusive articles so please join our free community to view. Use a VCDS to make sure that you are staying within the normal operating boundaries and adjust the pump as necessary. mk4 pumpe duse cars (2004+) do not have mechanically adjustable injection timing.
More advanced power upgrades
You can still buy off the shelf performance upgrades to further increase your power but past this point, the value of dollar/horsepower in the upgrades is reduced and you may also experience more reductions in fuel economy. The most common advanced performance upgrade is a larger intercooler. However, only the VW Mk4 cars have off the shelf replacement intercoolers, so I have included this modification in advanced performance modifications. Mk5 and newer cars use a front mount intercooler so it's difficult to add one much larger due to space limitations unless you change the bumper as well. Mk7 cars use an air-water intercooler integrated into the intake manifold and at this time, there aren't any off the shelf upgrade kits.
Beyond this point, the likelihood of clutch slipping is greatly increased. Mk4 cars may get clutch slip with just a chip, so remember that if you want more power you need more clutch clamping force!
Performance tires are also recommended to get the most power to the ground. Sticky tires usually wear out faster and give less fuel economy than harder non performance tires, so take this into account when thinking about what your performance goals and intended use are.
Other advanced performance upgrades would include custom exhaust components, upgraded turbo systems, or custom made tuning chips. Keep in mind that one of the biggest advantages of 4 cylinder diesels is that they have enough power to serve as daily drivers and deliver nearly unbeatable fuel economy. The most common diesel passenger cars, VWs, are not very good sports cars when compared to true sports cars. They are light but the suspension setup is not that great, front wheel drive isn't good for a sports car, and you are limited by tire width (because suspension clearance of tires). None of these traits contribute to making a very good sports car out of the box.
A stock used corvette will always be a better sports car than a brand new TDI and for less money. A corvette doesn't have rear seats, but this article's focus is on power upgrades, not rear seating or fuel economy. In the end, the whole point of modifying your car is to suit your taste and preferences, so if you want to upgrade your existing car read on to 1000q: advanced performance upgrades