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Most of the time, small updates are made to articles without notice but these were totally unrelated to previous content. From the turbocharging article, notes on DIY turbocharging. The turbocharging article and other useful FAQ are located at the top of the forum. Here are the additions. They are not applicable to the TDI but something to be aware of if you plan on adding a turbo to a car.

With modern traction control and stability controls, the car can also restrict power if it senses the car moving faster than it was designed to. As an extreme example, with the stock engine, even under the most favorable conditions, your car may accelerate to 0-60 in 7 seconds. If the car's computer sees your car accelerating to 0-60 in 3 seconds, it knows that something is wrong or assumes that the tires are spinning on ice, and reduces power, applies traction control, applies the brakes to regain control, etc. This is not a problem with VW or VW TDI cars, but this obstacle is starting to appear on some German cars.


A final (or first, depending on your view) consideration for DIY turbocharging is emissions and emissions testing. Catalytic converters need to heat up from the exhaust before they start to work well. Modern cars are so clean and catalytic converters so good that the majority of emissions are during cold engine starts. Adding a turbocharger between the engine and catalytic converter will result in much greater emissions during cold engine starts because a heavy cast iron lump absorbs heat energy instead of warming up the catalytic converter. It also takes away energy to spin the turbine wheel. Factory turbocharged cars are engineered from the factory to meet emissions and adding a turbo will result in significantly greater emissions during cold starts and the possible failure of emissions testing. A gasoline car with a DIY turbo that is warmed up, in good working order, and is tuned well, with catalytic converters, should pass emissions. If the car is cold and had to wait in line at the emissions testing facility, or is poorly tuned, it will probably fail. Without catalytic converters, there's no way it will pass emissions. Modern passenger car diesels are all turbocharged and many states don't have diesel emission testing, so this is more of a problem for gasoline cars.
 

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Interesting stuff. I read in Road and Track that the nature of car tuning in general is changing. It started with dropping an engine in and that was it. Then you had to chip it. Now you have to have a degree in rocket science to decode encrypted ECUs to be able to tune a car without having it throw codes left and right.
 

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Interesting stuff. I read in Road and Track that the nature of car tuning in general is changing. It started with dropping an engine in and that was it. Then you had to chip it. Now you have to have a degree in rocket science to decode encrypted ECUs to be able to tune a car without having it throw codes left and right.
Somewhat, before the mechanic could do everything. They plugged in an engine. Now, he plugs in an electronic box that someone else took care of and does the other stuff that can be handled at the local level. There's always someone out there who can crack the ECU and do the tuning. And in the case of mild chip tuning and piggybacks, all you have to do is plug in a box - no mechanic's skill needed.

It's starting to go the other direction though, with BMW's ECU that knows if it's been ever chipped, that will really mess with a warranty. Then again, most people don't really mod their car until after the warranty is expired.
 
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Tuning is also a big part of wether a turbo car passes emissions. Too rich and a cat won't help. Some states just do plug in, some do dyno and sniffers. It varies by state, some don't even have emissions.
 

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You can remove the cat in a TDI and still pass emissions if it's just a visual check, most guys dont get under the car and inspect everything or you can put a dummy shield to make it look like there's a car there.
 

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IMO, leave the cat alone. Power gains are not that much but it makes the car much dirtier. Emissions are much worse and you won't notice the difference in the small gains.
 
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