As one of the leading purveyors of performance turbochargers to the racing and enthusiast community, Precision Turbo and its tech staff have a pretty good handle on what you can and can’t do when it comes to the care and feeding of your horsepower-producing snail. In this video, Technical Sales Rep Tristan Kimpel covers some of these specifics, along with how to avoid potential pitfalls which can affect the performance of your turbocharger.
Oil Coking: This is caused by hot shutdowns of the engine, where the oil has not had a chance to cool down before the engine is shut off. As the oil cools inside the super-hot turbo housing, it causes thermal breakdown of the oil, and is caused by one of four things: high temperatures in the turbo’s bearing housing, engine oil that is not designed for high-temperature use, engine oil with a wide viscosity range (as the additives in this type of oil are what causes coking in the first place) and infrequent engine oil changes. The engine oil acts as a coolant, so when you turn off the car without giving the turbo a minute or two to cool down, the oil simply cooks itself, and becomes hard and brittle. It can cause bearing damage to both the engine and turbocharger.
“Let the car idle for a couple of minutes. Just sitting there idling allows that oil to pass through the turbocharger and pull some of that heat away, helping to cool it down. It will really extend the life of your turbo,” says Kimpel.
Wastegate Placement:With often-cramped underhood areas—especially once a turbocharger and its associated plumbing are added—it can be difficult to fit all of the components to add forced induction to your vehicle, especially the wastegate. But it’s critical to get this right. Kimpel says that any external wastegate must be placed so that it has a priority flow (direct line of sight) to the exhaust flow, or you run the risk of the air flowing right on past the wastegate and into the turbocharger, which can cause overboosting issues. The company recommends that the gate is mounted at a 45-degree angle to the pipe.
“Make sure that your wastegates are placed properly, and sized properly. There are different sized gates for different applications,” he says.
Oil Feed:“Ninety percent of the time, you don’t want to use a restrictor [in the line],” says Kimpel. “Oil restrictors are typically only used in a ball-bearing system, and not in a journal bearing system. Journal bearings need the oil much more than the ball-bearing systems do,” says Kimpel.
The company has an additional video discussing the differences between ball-bearing and journal-bearing turbochargers here.
Perhaps just as important is the use of an oil drain. A faulty oil drain can cause smoking or oil leakage out of the turbo; flange size and line size are critical to prevent these issues from occurring. A 5/8-inch or -10 line is the minimum the company recommends, and he goes to extra lengths to explain that the hole in the flange must be large enough to uncover the drain in the CHRA or you run the risk of the oil backing up into the turbo.
Crankcase Ventilation: So you need your turbocharger to drain properly in order to keep itself cool, and you’re wondering why the crankcase needs to be ventilated properly in order for that to occur. The short answer is that without adequate ventilation, the pressure will build up in the oiling system and try to force itself out of the engine… which means that it’s quite likely that the oil supply will try to reverse itself up the drain line and back into the turbocharger, then out the exhaust side of the turbine housing. Nobody wants a leaky exhaust. He doesn’t recommend a baffled catch-can system as they can retain pressure, but a good breather system which is adequate.
Pipe Considerations: When aluminum or steel pipe is used to feed the turbocharger’s boost to the throttle body (or intercooler), Kimpel says you can run into an issue where the turbo is side-loaded. This occurs typically in situations where the turbo itself is also hard-mounted to the chassis. As the engine and turbocharger and chassis all flex differently, it can cause the compressor wheel to touch down and cause a turbocharger to fail. The solution is to use a coupler, traditionally on the turbo’s outlet, which can permit some flex in the system to relieve this pressure on the turbocharger housing. It can also be accomplished by mounting the turbocharger directly to the engine so they move as one unit, but space considerations often make this impossible.