Can someone technically explain Zero Clearancing for me?

[Leif S4]

Pros/Cons, what is the process, why does it increase performance, why/how does it "wear off"?

[Imolavirus@BuehnEngineering]

Zero Clearance is a process that applies an abradable coating to the inside of the compressor housing where the compressor wheel rides. In the picture you can see the coating on the inside where the compressor wheel is.



There are basically two advantages that z/c gives that work in conjunction with each other. They both have to do with eliminating the space in between the edges of the compressor wheel fins and the housing.

In a non-z/c turbo, that space allows air to pass by the wheel and into the housing uncompressed; effectively lowering the PR(pressure ratio) in the given volume of the housing because the higher pressure from the compressed air is going to equal out with the uncompressed air that slipped by the wheel. Now, with the z/c housing, that air that previously would have by-passed the compressor wheel is being compressed by the compressor wheel. This is what leads to the faster spool-up and higher PR of a z/c vs non z/c turbo. At the same shaft speed the z/c turbo is able to create a higher PR. Lower shaft speeds create benefits as well.

The second advantage still has to do with the air that once bypassed the compressor wheel in the housing/wheel clearance. When circulating air is enclosed within a housing, like the compressor housing, the friction between the molecules creates heat. Heat is created by the air friction of the unused air circulating in-between the wheel and housing in a non-z/c turbo. By SIGNIFICANTLY reducing that unused air, you're going to lower the heat caused by friction.

These advantages can also been seen in some high quality ball bearing turbochargers. The clearances in ball bearing units can be tighter than a journal bearing turbo like our KKK units. This allows a tighter clearance in-between the compressor wheel and housing. The KKK units have to maintain a larger clearance from the factory to account for any variance in tolerances within the turbo. Each turbocharger housing is not machined to match the specs of the internals. While the specs on their internals are kept within very tight limits, they do maintain a certain "safety" clearance on the housings to eliminate any chance of wheel rub.

Now, with the z/c process we are able to apply and customize the coating thickness to match each individual turbocharger. This allows us to tighten up the clearances tighter than the factory. The fact that we use an abradable coating also ensures that any wheel rub on initial break in will not damage the turbocharger or the engine. Once the z/c has gone through its initial break in period the turbocharger will run without wearing off additional coating unless some type of external cause start to place abnormal wear on the bearings (oiling issues, FOD, ect...). I've had z/c on my car for about 50,000 miles now. The wear of the z/c is periodically checked and has not increased past the wear from initial break in.

The good ol' two week thing again on testing......but I actually do have plans to have back to back testing of z/c vs non-z/c done by the end of the month.

[BUFFALONOGAROpebFATS]

[Imolavirus@BuehnEngineering]

[BUFFALONOGAROpebFATS]

gonna be driving a ton............plus howard stern.......


why are you selling an xm one?

[SAC-CA-GTI]

think I may find out soon if I have to pull the engine to piece out the car. Damn other half is really gettin' shaky. And I'm going to be getting all my crap off that car! Or maybe I should just take a deep breath!

[SAC-CA-GTI]

Buy J's first though...he's cooler than I am.

[BUFFALONOGAROpebFATS]

[Nigel (no more S4)]

[Imolavirus@BuehnEngineering]

you have z/c in your car, yeah.