Observing the intermediate results of an in progress tune of an SRM RS6/K24 equipped S4 it was clear the car was developing boost much sooner than the typical S4 with these turbochargers.

In the chart below the lines are of the subject car and the colored dots are data from other S4’s.  It’s clear that the subject S4 is generating boost on average about 250 rpm sooner than past averages.

During discussion to try to discover what differences this car may have that could led to such a result, one possibility proposed linked the outcome to a higher than normal preload on the turbocharger wastegates.  The normal preload setting for these turbochargers is in the 14-16 psi range, in the case of the subject car the setting is 18 psi.

If this cause is correct it has some noteworthy ramifications.  To try and determine if raising preload more generally has a similar effect I looked to some data I collected with my S4 showing the boost onset with FrankenTurbo F4H turbochargers before and after the addition of helper springs to the BorgWarner K03 wastegates that I was using.

The solid lines of the chart above are for the unaided K03 wastegates and the dashed lines are with high spring rate helper springs.

It appears that the addition of the springs slightly improved the boost onset when boost levels reached double digits, but when accounting for the Intake Air Temperature, it is clear that the IAT’s were higher in the unaided case.  Higher intake air temperatures result in reduced spool up, thus the slight difference in boost onset can be explained by the difference in IAT.

In the case of my S4 with the F4H turbochargers, increasing the wastegate preload did not appreciably change the rate of boost onset.

A recent forum discussion brought up an old topic of billet, ceramic ball bearing, k04 turbochargers.  An outfit in Australia called Billet turbochargers is a vendor that advertises these k04 replacement chra’s.

The topic discussion had not gone anywhere but the idea of BB chra’s has been something I’ve been interested in so I decided to look into the Billet turbochargers a bit more closely.

The website where the product is advertised is not much to look at.  It has a design feel that matches the copyright date of the site, 2007.  Any business that hasn’t revised the copyright date on their website for a decade creates skepticism in my mind about how savvy the business is.

There is not much information on the site about the k04 suitable centers that is on their Hottest New Product page – this is surprising since the original post to the page was made 5 years ago.

I sent an email to the address given on the website and after a couple of weeks had not heard a reply back.  This was similar to what others had experienced years earlier, apparently the website was no longer actively being supported by the business.

I moved over to Facebook and was able to find a page that the business had established and which contained newer content, thought still quite limited in quantity.  There are seven reviews of the company and products over the past 3 years, another sign that the company is probably not setting the world on fire with its products.

I sent the company a message via Facebook not expecting to hear anything back, asking if they were still in business, to my surprise I did get a reply.  They said they were very busy with expanding here (Australia) and in the U.S.  I don’t think I believe that, but I was out for information about the product line so I started asking questions about the offerings for the 2.7T engine.

The phrase “like pulling teeth” comes to mind.  Slow and spotty responses came back to my questions.  I found out that they apparently offer replacement centers for the K04 series turbo’s and the cost per center is $1250 AUD, the same as what was quoted in the forum discussion 5 years earlier.  A series of questions over the next several days were sent to Billet Turbochargers, to include asking if FB messenger was the preferred way to communicate with them.  No response has been received.

I tried doing some research on forums where the product might be talked about and came across one thread where somebody said they had a Billet Turbocharger product on their VW.  Close enough and better than nothing.  Going and researching the guys discussion it was clear he was located in Australia and was using the turbo’s, but to my disappointment through the course of years worth of posts in a build thread there was not a single datalog, no dyno pulls, and the owner even mentioned that the car had not been dyno’d.  In other words there was zero data about these turbochargers from the owner.

Nothing about this product, other than what it claims to be, is encouraging.  There is an absence of user feedback, the company selling it provides little information or communication, and the turbo centers cost a heckuva lot.  I’ll be sticking with straight BorgWarner Turbo’s for now.

This was a surprise, receiving an envelope from Audi of America containing the following:

What a very nice gesture on the part of Audi of America’s Customer Experience team.