AWE Exhaust Manifold Test Preparations

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:

Wagner Tuning Audi S4/RS4 Exhaust Manifolds
Wagner Tuning Audi S4/RS4 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!

AWE Tuning Exhaust Manifolds
AWE Tuning Exhaust Manifolds

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.

AWE-Tuning Audi B5 S4 Exhaust Manifold on Flowbench
AWE-Tuning Audi B5 S4 Exhaust Manifold on Flowbench

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


  • 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.

AWE Tubular Exhaust Manifold
AWE Tubular Exhaust Manifold – Passenger Side
AWE-Tuning Tubular Exhaust Manifold - Driver Side
AWE-Tuning Tubular Exhaust Manifold – Driver Side

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

K04 Summer Boost Data

With the BW K04’s back on the car I took some readings of boost pressure when going WOT at various engine speeds.  The data is being collected on an 85 degF day to compare with data I collected during colder ambient temperatures, along with allowing me to compare the variability of the K04’s to that of the TTE550’s and FT21’s.

BW K04 Boost Rise - Summer 85 degF
BW K04 Boost Rise – Summer 85 degF

The results show that the K04’s boost onset is slowed some with the warmer ambient temperatures.  Even though the K04’s are now boosting a little slower they are still more responsive than the TTE550’s and FT21’s were in colder temperatures.

I also made a validation run with the K04’s to double check the exhaust manifold back-pressure reading.  The first time I made these readings I was a bit ‘relaxed’ about the process and didn’t think much of the data that was produced since I didn’t have anything to compare it against.

After taking the same reading with the FT21 and TTE550 and seeing that they both showed appreciably higher exhaust manifold pressure, for a similar level of intake manifold pressure, I began to question if I had correctly assembled the measurement apparatus when I recorded the K04 data.  Since the only way to be sure was to install the K04’s again, I had to wait a little while and then pull the engine out to put the K04’s back so I could record data to confirm if the initial round of data logging had been done properly or not.

BorgWarner RS4 K04 Intake Manifold vs Exhaust Manifold Pressure
BorgWarner RS4 K04 Intake Manifold vs Exhaust Manifold Pressure

Looking at the readings that were taken today, B3 & E3, I was relieved to see that they matched well to the readings taken several months ago.  Although it meant I did an engine pull for minimal benefit, the consistent results are satisfying.

Here’s how the three sets of turbo’s compare:

Turbocharger Intake Manifold vs Exhaust Manifold (Pre-Turbine Housing) Pressures
Turbocharger Intake Manifold vs Exhaust Manifold (Pre-Turbine Housing) Pressures

My belief is that this chart represents one of the keys for improving the performance of K04 alternative turbochargers.

BorgWarner RS4 K04’s cause a fair amount LESS back-pressure in the exhaust manifold as compared to two popular hybrid turbochargers.  Less back-pressure should improve the engine volumetric efficiency.

I had a couple of requests to display the pressure data above in a different format.  Below are charts showing back pressure versus mass air flow, and the ratio of exhaust back pressure to intake manifold pressure versus engine speed.

F21 & K04 Pre-Turbo Exhaust Back Pressure vs MAF F21 - 42 degF / K04 - 75 degF Ambient Temperatures
F21 & K04 Pre-Turbo Exhaust Back Pressure vs MAF
F21 – 42 degF / K04 – 75 degF Ambient Temperatures
F21 and K04 Exhaust / Intake Pressure Ratio versus Engine Speed
F21 and K04 Exhaust / Intake Pressure Ratio versus Engine Speed

SRM Shroud Fitting

I’ve had a set of SRM IC shrouds sitting in the basement for quite a while waiting for some attention.  I have not used them because they don’t fit the SRM SMIC’s in their current state.  I knew it was going to take a visit from Mr. Dremel to begin hoping to make them fit – and today I finally decided to try and get started on this undertaking.

SRM Driver Side IC Shroud
SRM Driver Side IC Shroud

The primary problem with the driver’s side shroud is that the right portion of the shroud extended about an inch out past the mounting tabs, and also beyond the core itself.  This meant there was going to be a 1 inch gap along the right side of the core, and failing to secure the shroud to the core there was likely to leave additional large gaps elsewhere.

The best option I see is to cut the shroud in half, and then use rivets, or nuts & bolts, along with some epoxy adhesive, to reconnect the two halves in an overlapping manner that should eliminate the majority of the perimeter gaps.

The passenger side has an additional problem in addition to poor fitment.

SRM SMIC Passenger Side Shroud
SRM SMIC Passenger Side Shroud

The cutout for the tow hook was not present, it was a solid piece.  In the picture above the tow hook can be seen because I cut an opening for it to pass through.

On this side as well the shroud extends out past the mounting tabs leaving a gap along the edge of the IC core.  I’m going to cut this shroud in half similar to the driver’s side, but with a good bit more curvature along the lower half of the shroud reconnecting these two halves in a clean manner is likely to prove challenging.

On a more positive note, the S4 is back up running again and after a couple of brief periods having the engine running I have not detected any leaks.  My next endeavor will be to gather some K04 spool-up data in warmer temperature conditions and to log pre-turbine exhaust gas pressure.

605 vs K04

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.

2-11 Time: Big, Medium, and Small Turbochargers
2-11 Time: Big, Medium, and Small 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:

K04 and 605 Statistics
K04 and 605 Statistics

When put into a boxplot the results are:

K04 vs 605 Torque Dropoff
K04 vs 605 Torque Dropoff

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.

Engine Installed

Today I put the engine and transmission back in.  I’ve still got a bit to do before it is driving again, but from here on out things can be done piecemeal.


72# EV14’s are in place:


And the wires are ready to be reconnected.


Audi B5 S4