I received a FrankenTurbo Y-Pipe prototype to evaluate the flow characteristics of.  On hand I also have an RS4 y-pipe and stock S4 y-pipe as shown in the lineup below.

The FrankenTurbo prototype utilizes a stock size entry (80mm) and a larger outlet of 59mm, compared to the stock y-pipe outlet measuring 51.5mm.  For comparison, the RS4 y-pipe has 65mm outlets.

When put on the flow bench and tested at 10″ H2O the following results were obtained:

It was agreed that the results of the FrankenTurbo prototype were less than hoped for.  While the outlet diameter of the FrankenTurbo y-pipe were 15% larger in diameter than stock, the airflow had increased only 6% over the stock y-pipe.

By comparison, the RS4 y-pipe has an outlet diameter 26% greater than stock, and the airflow recording was 28% greater than stock.  Even the removal of the metal outlet pipes, leaving just the silicone portion of the y-pipe, with outlets measuring 62mm in diameter, failed to improve the airflow of the FrankenTurbo prototype.

My suspicion is that possibly the coefficient of friction between the FrankenTurbo’s silicone hose and air is greater than that with the aluminum wall of the RS4 y-pipe.

Next a set of FrankenTurbo turbo inlet pipes were provided to test in conjunction with the FrankenTurbo y-pipe and also when paired with the stock y-pipe.

These results are shown below along with similar configurations of the RS4 y-pipe and TiAL 2.25″ inlets.  Note, the TiAL inlets are the same diameter as the FrankenTurbo inlets.

The FrankenTurbo coupler cannot be used with the RS4 y-pipe due to the outlet of the RS4 y-pipe being larger than the FrankenTurbo y-pipe prototype outlet.

In the chart above I have highlighted a very unusual result of this testing.  The stock S4 y-pipe will flow approximately 385 CFM with nothing attached to it.  When the FrankenTurbo coupler hoses were attached to the y-pipe the airflow INCREASED, rising to 401 CFM, a 4% gain in airflow by attaching the coupler hose.

Unlike with the stock y-pipe, when the coupler is attached to the FrankenTurbo y-pipe the airflow drops, by about 6%.  The testing was repeated with the RS4 y-pipe and the coupler used to connect with the TiAL inlets, again a drop of approximately 6% was recorded for the airflow.

Additionally, when the stock K03 coupler hoses are attached to the stock y-pipe the airflow through the stock y-pipe decreases slightly.

My guess for why this is occurring is, the RS4 y-pipe and FrankenTurbo y-pipe prototype both constrict the airflow at the exit point, causing an increase in back pressure relative to how the y-pipe performs without the coupler in place.  The stock y-pipe does not see a similar constriction at the outlet when paired with the FrankenTurbo coupler.  That would seemingly be helpful, but one would expect that the airflow rate would be relatively unchanged whether the coupler was used or not, increasing the airflow through the y-pipe is an unexpected result.

Looking at the outlet area of the stock y-pipe it is apparent that there are two dimples on the lower side of the pipe, corresponding to protuberances on the exterior which provide a stop for the coupler hose.  This location of these dimples means that just prior to the outlet the piping is not smooth, promoting turbulence.  My theory is that the turbulence being created by these dimples enables a high pressure region to form just before the y-pipe outlet, adding to pressure losses through the pipe.

So why not also occur when the coupler is in place?  My theory is that the additional channel created by the coupler keeps the air stream in-line and prevents the formation of the high pressure zone.  The video below also shows what appears to be a strong vortex along the upper side of the coupler and this may also be helping with preventing the formation of a high pressure zone at the outlet.

* – Just to re-emphasize the explanation given above is just a theory and without some more sophisticated measuring devices this phenomena may remain a mystery.

 

[FMP width=”640″ height=”360″]https://myaudis4.com/wp-content/uploads/2012/12/flow_bench_qt.mov[/FMP]

 

Note: The flow visualization is being done using a fluorescent string and an ultraviolet flashlight.

 

As a follow up to the 80mm Throttle Body airflow test a good point was brought up about the detrimental affect that would be caused by having the bolt propping the throttle body valve open in the air stream.

My first idea for answering this question was to test the adapter plate alone and then place a bolt halfway across the opening to see what the affect was.  The hope was to get some idea about the scale of the change that could be caused by having the bolt in place.  As it turned out there was almost no measurable difference, while I suspect it did slightly impede airflow, it apparently was less than the naturally occurring variation in airflow through the bench.

Next I decided to try and devise a less intrusive prop to keep the throttle body valve open.  The result is shown below:

A Harris Teeter VIC card cut down to the appropriate size was rigid enough to hold the throttle plate open, yet as shown below, was much narrower than the bolt that had previously been used.

The thickness of the card is very small so that it should not cause much impediment to the air flow through the throttle body.  Below is a picture of the throttle body being propped up with the card section.

The next step was to test the new prop out.  Actually the next step was to retest with the bolt in place to have a baseline reading for the days temperature and pressure conditions.

After the bolt was retested I tested with the card as shown above.  Note, when I have tested using the bolt I have placed it on the lower right hand side of the throttle body as viewed from above in the pictures.

I found that the card and bolt read within 6 CFM of each other, well within a reasonable margin of error for the readings.  As an aside, because the air flowing through the system is turbulent, especially just prior to the throttle body where two air streams collide, the airflow readings vary slightly as the air flow disturbances cause the pressure to rise and fall slightly.  For this reason I consider +/- 5 CFM to be a reasonable accuracy when reporting results.  To obtain a CFM value I observe the fluctuating reading  for several seconds and mentally estimate a center point, so the air flow value reported is not precise to a single digit value.

With the bolt and card reading very similar I was satisfied that the bolt was not causing an excessive amount of resistance.  I was puzzled by the fact that the narrower card had a lower airflow reading, no matter how small the difference.  So I placed the bolt on the top of the throttle body and retested.  This time the reading was about 17 CFM lower than the card in the same location.  Ah-ha, proof that the bolt causes more of an air flow drop than the card.

But I had not tested the card in the lower position, so I wondered if the placement lower in the throttle body made the difference, not the part.  I retested, this time with the card in the lower position, the results were 7 CFM less than with the card in the upper position.

Finally, I went and put the bolt back in the lower position and tested it again, recording a value only 3 CFM off from the first time, and well within my own margin for error, effectively reading the exact same as the first time.

All of this is illustrated below:

So, what does it all mean?  Swirling, turbulent air flow has a lot more going on with it than a simple commonsense observation can describe.  My suspicion is that with the way the air flow is coming out of the up-pipes the interaction with the card and bolt props is much more complicated than it would appear.

In the end I feel the similar results achieved by using the card and the bolt means that the comparison with the stock throttle body, that does not require such props, is valid and that any gains that might be had by not having and prop at all within the 80mm Throttle Body would be small.

 

Going to be testing this 80mm Throttle Body shortly, connected via the 034 throttle body adapter boot to a set of JHM/ARD/034 style up-pipes.

Upon receipt of the throttle body I discovered that the operating gears are not accessible like they on the S4 throttle body, so my procedure for holding open the throttle valve was not going to work on this part.  In needed to place something into the throat of the throttle body that would hold it open and also not become dislodged with airflow passing over it.  Something small and lightweight would have the potential to get sucked into the flowbench vacuum chamber and through a motor.  I ended up using a bolt as can be seen below.  It’s round shape should hopefully not impede the airflow much and due to the flat surfaces on either end it remains firmly in place.  In addition, it’s heavy enough to not be sucked up into the air if it were to fall out.

The Results

Attached the JHM/ARD/034 style (which I will refer to as typical aftermarket “TA” from here on) up-pipes to the throttle body boot and ran two tests, the first without the inlet hoses and the second with them.

I also retested the TA up-pipes with the stock throttle and also retested the APR bipipe with the stock throttle body.  Due to the rigid construction of the APR bipipe is cannot be used in conjunction with the larger throttle body.  A keen eye will notice that since the last airflow tests of the throttle bodies the values for the APR and TA pipes with stock throtte body are slightly lower, this is due to recalibrating the bench and revising the correction factor applied to the results.  The relative performance between the test articles remains consist when making changes to the correction factor, but the absolute airflow reading will shift upward or downward.

* – Already breaking my just established convention, the chart above refers to the JHM/ARD/034 style up-pipes as JHM versus TA.

Not unexpectedly the 80mm throttle body enables a higher airflow for the test pressure, roughly 17% greater than the stock throttle body.

Interestingly the APR bipipe when used with the stock throttle body makes up some of that difference.  The 80mm throttle body outflows the APR bipipe and stock throttle body combination by only 6%.  Previously I theorized that the shape of the APR bipipe is what allows it to outflow the TA style up-pipie.

If it were possible to combine an up-pipe with the shallow radius curvature of the APR bi-pipe with the 80mm throttle body the results would likely exceed all that have been recorded here.

Thanks to infinkc from Quattroworld/Audizine for loaning the 80mm throttle body and adapter boot for this testing.