Recently it has seemed to me that a large percentage of dyno results that have been made public are developed on a DynoJet brand dynamometer.   I like the consistency that a DynoJet has with the measured wheel horsepower and this is the brand of dyno I seek out when I look for a place to have my S4 dyno’d.

The frequency that I have put my car on a DynoJet, along with the abundance of street logs that I have recorded, provides a good collection of results to use to compare the two methods for estimating vehicle wheel horsepower.

The summary below shows the setup that my S4 had and the DynoJet generated whp and the road acceleration derived whp.  The last column to the right shows the amount of change between the DynoJet and road measurement.

DynoJet vs Street

Comparison of Peak Wheel Horsepower Measurement by Method

Setup	DynoJet	Road	% Change
FT21-27	439	416	5.2%
FT21-25	418	398	4.8%
K04	405	385	4.9%
K04/AWE	399	373	6.5%
K03 Stk	237	216	8.9%
K03 Nef	283	258	8.8%
FT F4H	384	363	5.5%

From these seven data points the average change from DynoJet to street is about 6%.

Another source of wheel horsepower also derived from street data is the calculation made by the ECUxPlot program.  The application appears to take into account similar variables, but I suspect something may have been left out, or is assumed to have less influence, as compared to the assumptions I make in my calculations.

Shown below is a series of pulls made by my car with the calculated wheel horsepower displayed:

These same logs when evaluated using my calculations produce the following:

It may not be immediately clear, but the calculations I have made are greater than the results calculated by ECUxPlot.  Out of the four data points, ECUxPlot reports a peak wheel horsepower value about 4.5% less than my calculation.

So which is more accurate?  I’m not sure, I have found that my calculations more closely match the results that were recorded on a Mustang Dynamometer but who’s to say how accurate that dyno was.

An outcome of this comparison is, if it is assumed that the commonly used ECUxPlot is more accurate, the difference between DynoJet recorded wheel horsepower and that from ECUxPlot would be even greater than what I have calculated.

Using ECUxPlot’s calculations, the results are on average 9.2% less than that reported by the DynoJet.

Conclusion:

I am reasonably confident that the street measured results are more accurate than the DynoJet values.  The DynoJet would seem to read above truth by somewhere from 6% to 9.2%.

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.