bnl107

Yes, yes... I have STFA. Just looking for some more in depth answers to some more specific questions than I found answers for. I'm planning on placing an order over the weekend and just want to make sure I have all the correct, relavant info to make a good decision.

1. What exactly is the difference between clearancing and zero-clearancing (other than about $800, lol)?

2. I understand the concept behind ceramic coating the turbing housing (keep heat in to assist in powering the turbine and to keep the engine bay cooler), however, I keep wondering if maybe it could be deterimental to the health of the turbos to keep too much heat in. Just seems as if it could be a bad thing. Am I thinking about this the wrong way?

3. Porting & Polishing, seems like a common sense thing to do, but are there any solid numbers showing a noticable benefit. Not doubting that it is a good thing to do, but just wondering if it has been quantified yet. (Also, what exactly is the point of porting the waste-gate?)

Thanks guys :-)

B5QShip

clearancing is done on the hotside. It increases the gap between the turbine and the housing. This decreases the shaft speed for a given flow through the turbine. People do this on RS6/K04 hybrids b/c the KO4 turbine is not well matched to an RS6 wheel in the K04 housing.

zero clearancing is done on the cold side. Its a coating that minimizes the gap between compressor wheel and the housing and thus increases efficiency.

bnl107

Oh, ok that makes sense. Thanks.

bnl107

No one else has any info or me???

Hal_TT::CBP

(1) Clearancing is to reduce TP on the hot side, you sacrifice some low end spool for higher end performance. Zero clearancing is on the compressor side to close the gap between the fan blades and intake housing(think more air efficient). Zero clearancing probably is the one I'd look at on a stock K04, if I thought it necessary(I don't).

(2)do the manis, skip the turbos imo

(3)doubtful, another skip for me

My $0.02

EdyJun

These can be found under Turbo on my site.

<a href="https://forums.audiworld.com/s4/msgs/2209795.phtml">Ceramic coating on hot side of turbo worth it?</a>

<a href="http://buehnengineering.com/forums/viewtopic.php?t=142&start=0&postdays=0&postorder=a sc&highlight=">Description of Options for K04's and K04/RS6's Turbo options - EH, CZ, and ect. </a>

<a href="https://forums.audiworld.com/s4/msgs/2178571.phtml">Alright tech-junkies: Extrude Hone vs. Port and Polishing, which has more benefits?</a>


I hope they help out....
Edy<ul><li><a href="http://homepage.mac.com/edyjun1/S4/index.htm">EdyJun's S4 Directory (FAQ, DIY, Info, Tips and Help)</a></li></ul>

SForked

Port/Polish Turbine Housing and Extrude Hone: This option is pretty self explanatory; it is the port/polishing of the turbine housing, mainly the inlet of the volute area where the exhaust gas enters the turbine housing. The purpose of this is to increase the velocity of the exhaust flow to the turbine wheel as well as smooth out any areas that may cause turbulence in the flow. Advantages to this include a decrease in spoolup time as well as an increase in upper end flow due to the slight increase in volume within the housing. The advantage that port/polish has over Extrude Hone is the ability to shape and form areas which need attention. Each casting is slightly different and so to achieve the shape we are looking for as well as match the two turbine housings to each other, doing the port/polish by hand is needed. Also, there is one area after the turbine wheel which needs special attention and can only be done by hand. Exturde Honing does have an advantage in that it can smooth the housing further into the volute area where doing it by hand cannot be reached. For maximum efficiency out of the turbine housing, port/polish and Extrude Hone combined would be optimum. For those doing the K04/RS6 hybrids I would recommend at least one of these options in conjunction with the clearanced turbine housings.

Ceramic Coating: Ceramic coating is a coating that is applied to the exterior of the turbine housing. It is used to stop heat from radiating out through the turbine housing walls. By keeping the heat inside the housing we are able to use it as energy to spin the turbine wheel faster. The reduction of heat radiation also significantly reduces underhood temps.

Clearanced Turbine Housing: This option is designed to reduce pressure within the turbine housing. As we begin to increase flow through the engine, that flow has to also exit through the turbine housing. If pressure within the turbine housing is too high it can lead to negative effects including a limit on horsepower as well as a tapering effect of boost as rpms increase. By clearancing the turbine housing we are able to allow more exhaust gas to bypass the turbine wheel, reducing pressure significantly inside the turbine housing. If you are going with K04/RS6 hybrids this option is HIGHLY recommended. Even with standard K04's this option is recommended if your looking to get a bit more out of your car than the normal stage 3 S4.

Clipped Turbine Wheel: This option is designed to do the same thing as the clearanced turbine housings it is just a more traditional way of doing it. If you are interested in doing clipped turbine wheels please email me and we can go over your setup to determine if clearancing or clipping is going to work better in your case.

Wastegate Porting: This option can only be done in conjunction with the port/polished turbine housing option. Another way to reduce pressure within the turbine housing is to allow more exhaust gas to escape through the wastegate passage when the actuators are open. Wastegate porting involves removing the wastegate flapper assembly so that extensive port/polishing can be done to increase the flow through the wastegate area in the turbine housing.

Zero Clearance: 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.

reefer_bob

IMHO, we do everything we can to aid in getting the exhaust out of the engine more efficiently.

On K-04 based turbos, it's generally accepted that TIP is an issue.

So... Why not do all you can (PnP and EH) to help aid both situations. Both are relatively inexpensive...

EdyJun

2nd IMO