3. Turbo
The turbo is not necessarily an issue if it wasn’t for the known engine problems but there are 2 major features of this turbo that need consideration to avoid oil consumption.
The oil seals of the turbo are designed to hold the oil inside the turbo around the bearing rather than it leaking down the turbo shaft to the turbine and impeller (2 wheels at each end of the shaft). These are designed and balanced perfectly to take into account the forces applied on them in both directions. The internal force on the seal is made by the heat expansion inside the bearing and the oil pressure flowing through it. On the other side there is back pressure. On the intake side of the turbo it is the air hitting the wheel and the force of compressing the air to send to the intercooler. On the exhaust side it is the back pressure of the downpipe, catalytic converter, cat back pipe and silencers.
One rule of thumb with a turbo engine is that the best sort of exhaust is no exhaust at all; and no exhaust = no back pressure. Thus after market exhausts deliberately try and minimize back pressure, resulting in the oil seal losing the pressure balance it once had. On a normal car this is not usually too much of a
problem and the seal could potentially hold the oil in with minimal seepage, but together with the second feature of this turbo, it simply cannot.
The second issue is the internal pressure inside the turbo. These turbos, as confirmed by their manufacturer, are designed with internal pressures of 40-60psi in mind. When measuring the actual pressure through the turbo even with a new engine it was found that it could raise to 70psi. This is because of the under piston oil jet system, which coats the pistons in clean cooler oil before they raise up into the bores for the next stroke. There are a few other manufacturers that have had similar problems.
Now if you imagine the engine and pcv problems being present as discussed earlier with high internal pressures and no back pressures then it becomes a very serious issue.
There is no SEAT solution to this
problem as they don't want us to run sports exhausts to begin with, especially de-cat exhausts. I designed an oil restrictor bolt based on another VW variant. It has slightly smaller holes than the OEM one on the 1.4TSI and have I have logged the pressures at between 40-45psi. This results in a healthy internal pressure allowing a decat exhaust to be run safely with a healthy engine.
This is even more important to fit if you are using a hybrid turbo. The reason is the turbine wheel on the exhaust side is MUCH bigger and the housing has been bored out resulting in more flow but less back pressure. Thats great for performance but not good on the oil seal. For this reason, I have also had the oil seals strengthened in my hybrid turbo.
Solution:
Custom oil restrictor (if running decat)
Strengthened oil seals (as part of the turbo hybridization process)
NOTE: LOBA270 has normal oil seals, and is not suited to a de-cat exhaust, despite what they say!
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