A few days ago I swapped out my S4’s OEM exhaust manifolds for a set of the AWE-Tuning tubular exhaust manifolds.

After getting the remainder of the car put back together I began measuring some performance data with the AWE exhaust manifolds, operating in conjunction with BorgWarner RS4 K04 turbochargers.

The first question on my mind was how much, if any, affect the tubular manifolds would have on turbocharger response.  I have been using the time it takes for boost pressure to build from 2 to 11 psi as a metric for comparing the response of different engine configurations.

Shown below is a comparison of the K04 turbochargers utilizing the OEM S4 manifolds and the AWE-Tuning exhaust manifolds.  The K04 data spans several months, and encompasses various ambient temperatures, so I have tried to group the data by temperature conditions as this does have some affect on the turbocharger response.

Since I was preparing to take before and after measurements I was able to conduct a couple of data collection sessions in relatively similar temperature conditions, identified in the above chart as K04 (Summer) 85F and K04 (AWE Mani) 76F.

In general the slightly cooler ambient temperatures should reduce the time recorded with this metric if all other factors are equal.  The times recorded with the AWE-Tuning manifolds are slightly greater than those recorded with the OEM S4 manifolds.  These results indicate that the tubular manifolds decrease the turbochargers responsiveness under the procedures followed.

As a practical matter the magnitude of the slower response with the AWE product, as compared to the OEM product, may not be significant.  It’s likely that the vehicle operator would have difficulty discerning a time difference requiring measurement in hundredths of a second.

Looking at this data in a more familiar format it becomes hard to distinguish between the two data sets.

The solid lines are OEM S4 and the dashed lines are AWE-Tuning.

I was also interested in investigating how the different style exhaust manifolds impacted the Exhaust Gas Temperature.  I wondered if the AWE-Tubular manifolds would exhibit a generally lower EGT as a result of greater heat loss out of the manifold walls.

Looking at the exhaust gas temperatures recorded over several minutes of driving I do not see any significant difference in the trend of the EGT’s.

This initial data does not show any significant detrimental effects from the installation of the AWE-Tuning exhaust manifolds.  Later investigation will focus on potential benefits that the AWE-Tuning manifolds may provide.

 

 

 

While I have long wanted a set of the Wagner cast manifolds two things have kept me from purchasing a set.  One, the price is quite a bit for a set of exhaust manifolds, especially since the OEM products do a pretty fair job.  Two, they were produced with what I consider a design flaw, when installed on the engine they change the orientation of the turbo outlet such that the downpipes either need to be modified, or a set of Wagner DP’s, that have been built for this orientation, be purchased.  Modifying my existing downpipes would probably be cheaper, but that would also preclude me from using them with any other exhaust manifold if I chose to try a different set, not a desirable situation.

The Wagner Tuning exhaust manifolds:

The marketing for the Wagner exhaust manifolds sounds impressive:

“Our engineers have removed the OEM bottlenecks by using a 3 into 1 merged collector design allowing an unrestricted path from the engine to the turbochargers. This results in increased throttle response, quicker turbo spool-up, and higher top end power capabilities.”

Reading that certainly makes me wish I had a set of these exhaust manifolds on my S4, but the two negatives have kept me away.

I also like the idea of using a set of the AWE tubular manifolds, a product that when it was being sold weighed in at a jaw dropping $2,900.  The AWE product makes the $1,790 price of the Wagner’s look like a relative bargain!

A used set of the AWE manifolds came up for sale and as I was curious to see how the flow through them compared to stock and the SRM manifolds, I purchased the used AWE’s to give them a look.

After conducting the flow bench testing I began to consider putting the AWE’s on my car to see what differences they produced compared to the stock manifolds, and in the process of thinking that through I began comparing the specs of the AWE manifolds to those of the Wagners.

What I found was that they were reasonably comparable, there were a few dimensional differences, but overall they were quite similar.  To me they were similar enough that I believe the results produced by either would be fairly representative of what the other would produce.

These dimensions are shown below for comparison:

AWE Tuning:

• Primary runner: 37.3 -> 31.24 mm
• Secondary runner: 41.12 -> 37.9 mm

Wagner Tuning

• Primary runner: 38 -> 32 mm
• Secondary runner: 42 mm

Stock

• Primary runner: 31.7 -> 27.14 mm
• Secondary runner: 26.87 -> 40.5 mm

A downside to the AWE manifolds, and upside for going with the Wagners, is the long term reliability.  The AWE tubular manifolds, and generally most tubular manifolds, have a history of not holding up over time, with cracks developing at joints.  In fact the used set I obtained have already had some repairs made to them.  Proof that this style exhaust manifold will eventually have issues, but good for me that it’s already been repaired so they should last a while longer, at least long enough for my needs.

Today I set about the task of removing the engine to make the swap over to the AWE Exhaust Manifolds.

The stock manifolds came off relatively easily and I was happy to be able to leave the turbocharger in place.

Both sets of manifolds have the Swaintech White Lightning ceramic coating.

Attaching the AWE exhaust manifold proved to be a good deal more time consuming than it was to remove the stock exhaust manifold.  The location of the nuts that secure it to the head are behind some of the runners, and with the turbocharger still in place it was a bit tricky to get a wrench on some of the nuts.  Tightening the nut down a tenth of a turn at a time took a little while.

The passenger side had some challenges as well.  Again the stock manifold came off quickly.  But to get the AWE manifold in place I had to reposition the aftermarket oil supply line slightly rearward.  I also had to spend some time trying to reposition the turbo slightly in order to get some of the bolts that attach the manifold to the turbo to line up.  Eventually it all worked out.

A while later the engine is back in place now equipped with the AWE exhaust manifolds.

I still have some more buttoning up to do before I will begin measuring with these exhaust manifolds.

Recent discussion of K04 vs larger (i.e. 605) turbochargers prompted me to pull up some data I’ve logged, 2-11 time for several turbochargers, and dyno plots from a number of cars with these turbo’s.

The 605 2-11 time data is from my S4, which utilized the 605.1 turbochargers, on stock S4 heads.  It spanned a number of months, and thus encompassed temperatures ranging from a low of 33 degF to a high of about 95 degF.  The spread in the 605 data is indicative of the affect that ambient temperatures had on these turbochargers. There is a similar spread with other turbochargers, but in the low airflow (engine speed) regime the 605’s appear to be more sensitive than the smaller turbochargers.

It is apparent that all three turbochargers generate boost pressure more rapidly as the engine speed (airflow) increases.

Another aspect of relative performance that I looked at was Torque Drop Off.  One of the claimed benefits of larger turbochargers is that the torque does not “fall off” like the smaller K04 turbo’s.  To assess how much less drop off there is, if any, from the larger turbocharger, I reviewed dyno charts from a number of S4’s equipped with TiAL 605 turbochargers and BorgWarner K04 turbochargers.

For this comparison I noted the peak torque reading and the torque value at 6500 rpm.  The difference was then calculated.  The result is a percentage change expressed as a negative value, which I made a positive number for ease of conversion into a boxplot chart.

The summary statistics are contained in the table below:

When put into a boxplot the results are:

The chart confirms that the larger 605 turbochargers do not suffer as much torque loss from peak as the engine speed increases to 6500 rpm.

The median torque loss for the 605’s is approximately 21% while the torque loss for the K04’s is approximately 26%.

I suspect the difference is not too substantial due to the source of the torque loss.  While the larger turbocharger is able to supply more airflow at higher engine speed, I believe the drop in engine volumetric efficiency as engine speed increases is causing the torque dropoff.