Before You Buy A Used Turbo Car With Modifications, Make Sure The Turbocharger Isn't On Its Last Legs
Most car enthusiasts love turbocharged engines. Compared to their naturally-aspirated counterparts, turbo engines respond exceptionally well to power modifications. With a simple ECU tune you can increase the turbocharger's boost output, modify the engine's fuel maps, and drastically increase horsepower output in the process.
The only issue is that increasing the boost pressure puts a lot of extra stress on the turbocharger. Too much boost can cause the turbo to overheat, leak, and ultimately fail entirely unless proper maintenance procedures are followed. Before you make the plunge and buy a modified turbo car, it's a good idea to thoroughly inspect the turbocharger to ensure it isn't on its last legs.
Locating the Turbo
Different makes and models have drastically different engine layouts, so you should look up an engine diagram of the specific model you are considering before you check it out. However, turbochargers are driven by exhaust gas as it leaves the engine, so the turbocharger will always be mounted in the exhaust system. Generally, the turbocharger will be connected directly to the exhaust manifold on the side of the engine.
Since turbos produce a lot of heat, there is usually a metal heat shield concealing the unit. Wait for the engine to cool down, then remove the heat shield so you can access the turbocharger. You also have to unbolt the intake tube from the turbo's inlet so you can access the turbocharger's internal components.
Once you have a clear view of the turbo, carefully inspect the entire unit. Heat stress can cause cracks to form in the turbine housing over time, so make sure there are no fractures throughout the housing. Shine a flashlight down into the center housing located in the middle of the unit and look for oil residue. The center housing is home to the turbo's oil inlets and outlets, so oil residue is a sign that one or more of the internal gaskets has failed.
After you've removed the intake tube, shine your flashlight into the turbocharger inlet so you can see the compressor wheel. Look for dings or bends in the compressor blades, which are often caused by debris getting into the turbocharger.
Grab the end of the compressor wheel and try to wiggle it back and forth. The wheel should have almost no shaft play whatsoever if the turbocharger is in optimal condition. If you can easily wiggle the wheel up and down, that's a sign that the turbocharger's bearings are beginning to fail. Turbos can still be fully functional with a tiny bit of shaft play, but you should replace the bearings as soon as possible to keep the unit from failing altogether in the future.
To Buy or Not to Buy?
It's a good idea to have an automotive repair budget set aside when buying any used turbo car with engine modifications. However, if the turbocharger passes your thorough inspection, you can rest assured that it wasn't abused with excessive levels of boost pressure. Even if the unit exhibits minor signs of shaft play and oil leakage, a reputable repair shop can replace the internal seals and bearings to get the turbo back up to snuff. If those repairs are within your budget, simply use the turbocharger's issues as a bargaining chip to get the seller to potentially lower the price of the vehicle.