Below is a summary discussion I found regarding turbo upgrades, and I thought I'd post it since I've been seeing a lot of recent interest in turbo upgrades. It leads off by discussing the typical reasons for an upgrade, and goes on to talk about limitations of the stock turbo, etc... It's a little wordy, and yes it reads like the advertisement it is, but its got some good info, and I think it's worth at least a quick read by all who are considering an upgraged turbo.

Better towing performance... Maybe you bought your truck to tow that gooseneck for work, to get your 5th wheel to the next resort or the boat to the lake. It sure would be nice to get up to freeway speeds quickly and maintain highway speeds in hilly terrain. With the right upgrades, that can be done safely and efficiently.

Competition Use... More and more enthusiasts are interested in heavily modifying their vehicles for competition use. Some are weekend warriors that use their vehicles during the week for routine duty then go to the track on the weekends while others are building strictly race vehicles that give up streetability for the demands of the track.

More fun... For many, making modifications for increased performance is a way of personalizing the vehicle and to have a bit more fun with the daily drive. There is a satisfaction that comes from modifications that put you back into your seat a little harder when the light turns green. And, there are always the grudge matches at the local drag strip.

What do I need to know to choose the right diesel upgrade turbocharger?... The amount of power that a diesel engine makes is directly proportional to the amount of fuel injected into the cylinder and that fuel needs sufficient air for complete combustion. For smoke-free performance, the engine needs about 18 times more air (by mass) than fuel. So clearly, as more fuel is added, additional air needs to be added also. In most applications, the stock turbo has some additional capacity for increased power, but as the compressor reaches the choke limit (maximum flow), the turbo speed increases rapidly, the efficiency drops dramatically, and the compressor discharge temperature ramps up very quickly. This creates a "snowball" effect in that the higher discharge temps mean higher intake manifold temps and higher exhaust gas temps.

The lower efficiency means that more turbine power is required to reach the same boost causing higher back pressure in the exhaust manifold. This can usually be seen on an engine with a performance chip (at the highest power setting) and maybe an intake or exhaust upgrade. Under heavy acceleration, smoke is pouring from the tailpipe as the EGT's and turbo speeds are climbing into the danger zone requiring a prudent driver to back off the accelerator pedal early to keep from damaging the engine. Under these conditions, the stock turbo is running on borrowed time.

With an upgrade turbocharger selected to compliment the extra fuel, smoke is drastically reduced, EGT's are under control and, since the turbo is operating in a more efficient range, horsepower and drivability are enhanced. When the modifications get more serious, a bigger turbo is a must have to compliment even more fuel.

In order to decide on the appropriate turbocharger for your diesel engine, the very first thing that needs to be established is the power target. Since turbochargers are sized by how much air they can deliver and airflow is proportional to engine power, a realistic horsepower goal is critical to make the right choice. The concept of a realistic goal needs to be stressed in order to ensure maximum performance and satisfaction. Sure, everyone would like to have a mega-horsepower vehicle but past a reasonable limit, as the power goes up, the reliability, drivability and day-to-day utility is diminished. Things are more likely to go wrong, wear out and break down as the output climbs.