Today I conducted a flow test comparison of a pair of RS4 MAF’s and an EPL MAF housing.
For some time I’ve wondered how much, if any, restriction the screen on the RS4 MAF housing causes. A parts car that came through the garage was equipped with a Bosch MAF housing that is the same size as the Bosch RS4 MAF but had a set of screens that are removable.
MAF housing lineup
I decided I would pull the RS4 MAF from my car along with the RS4 airbox top and stick them on the flowbench with the rest of the stock intake to see how the screen affected the airflow through the intake. I also decided I would retest the EPL MAF housing attached to the stock airbox top as that combination had out-flowed the RS4 MAF and RS4 airbox combination previously.
The results of the flow test are shown below:
Interestingly the removal of the screen from the RS4 MAF provided only a little benefit. The EPL MAF and stock airbox still provided a little more airflow than the screen-less RS4 MAF and RS4 Airbox top. All tests were conducted with a stock air filter, modified lower airbox (Darintake modification), and the snorkel attached.
I also have a large K&N cone filter available, so I attached the RS4 MAF to the K&N filter and retested using the RS4 MAF housings.
The results of this test are shown below:
The removal of the screen from the RS4 MAF housing produces a larger increase in airflow with the K&N filter versus the RS4 MAF with the screen in place.
More dramatically, the K&N filter allows for much higher airflow at the test depression of 10″ of H2O.
A couple of things should be noted, first is that a test depression of 10″ of H2O is not very much pressure. In these tests there is a substantial amount of airflow passing through the intake with minimal pressure drop. It’s common to test at 28″ of H2O, nearly three times the level this test was conducted at. This test was performed at 10″ due to a bench limitation of around 600 CFM.
From this test it would seem that the K&N cone filter would be a desired substitute for the stock intake. What this test does not account for is the potential disruption of airflow over the MAF sensor caused by the cone filter, which could lead to tune problems.
Nor does it show how engine compartment temperatures may alter intake air temperatures with the cone filter.
After loading a revised tune onto the car’s ECU I took a short drive and had a couple of alert lights come on the gauge cluster. I plugged in the XTool to see what the problem was and the device could not connect with the ECU.
I decided I should return home, but now the car would not start. I had to pull a MacGyver to get the bolts out of the ECU box, and then I disconnected the ECU, re-connected it, and then was able to start the engine to return home. Upon arrival I hooked up VCDS and received the following alerts:
18010 – Power Supply Terminal 30
P1602 – 35-00 – Voltage too Low 16985 – Internal Control Module P0601 – 35-00 – Memory Check Sum Error
The second one I had never seen before, but I immediately thought that maybe I hadn’t created a checksum on the latest bin that I had loaded on the ECU. Looking in the folder with the development tunes I saw the latest file name lacked a CS at the end of the name, my indicator that the (C)heck (S)um had been set. Doh!
It took unplugging the ECU for a while before I could get Nefmoto to connect to it, but finally it did and I was able to write a corrected file.
Lesson learned about staying vigilant when installing files on the ECU.
The Turbo Concepts Stage 1 turbocharger was a late entry in my effort to find what I thought would be the best stock motor turbocharger. When I ordered the stage 1 turbochargers it was with some expectation that the vendor’s claims for the product would be met, or at least would be close to being met. Those claims were to be capable of out-flowing an RS4 K04 by 20%, have a strong low-end response, and reach up to 450 wheel horsepower on pump gas.
After purchasing the turbochargers and while I was in process of installing them on my S4 the vendor revised the target horsepower downward substantially, to a new expected value of 380 whp. When I inquired about the boost level to run the turbochargers at the recommendation was a boost level similar to that of a conservative K04 tune. Based upon the vendor’s statements about the product the Turbo Concepts Stage 1 turbocharger is not going to be competitive in my search for the best stock motor turbocharger. It is more likely that the Turbo Concepts Stage 2 or 3 turbo would be a contender for the best stock motor title.
The TC Stage 1 turbocharger does present a good alternative to the BorgWarner K04, and that is what I am going to show some comparison data with.
Boost Onset
TC Stg1 vs BW K04 Boost Onset (2-11)
The TC Stg1 turbo’s response is close to the BorgWarner K04’s. It needs to be noted that I have not had the opportunity to log the TC turbo’s under warm weather conditions. Based on the slower response that comes with warmer weather I would expect the Turbo Concepts results to expand upward slightly if data were recorded during summer conditions.
Not withstanding the partial data shown above, the TC turbo’s are performing well. The difference in responsiveness between the TC’s and K04’s is quite small.
Airflow
BW K04 vs TC Stg1 (54F vs 48F)
I have not logged any meaningful increase in airflow from the Turbo Concept’s turbos as compared to K04’s operating under similar conditions. This is not surprising, the TC compressor wheel is only slightly larger than a K04 compressor.
Compressor Efficiency
K04’s and Hybrids Compared
The efficiency of the compressor wheel, estimated from the rise in the charge air temperature passing through the compressor housing, is better with the Turbo Concepts turbo. The charge air temperature exiting the compressor ends 60-70 degF cooler with the Turbo Concepts Stage 1 turbo’s.
Pre-Turbine Backpressure
TC vs BW Manifold and Pre-Turbine Pressure
For an equal intake manifold pressure (boost pressure) the Turbo Concepts turbos have a higher pre-turbine pressure in the exhaust manifold. Higher exhaust back-pressure in this situation is not desirable.
Exhaust Gas Temperature
Turbo Concepts and BW K04 Exhaust Gas Temperatures compared
Temperature of the exhaust gasses before and after the turbine are about equal between these two turbochargers.
Power
Lately I’ve skipped taking the S4 to the dyno to record data for turbocharger comparison purposes. With the variation that arises from shop temperatures and tuning the outcome is potentially less clear than measuring more ‘raw’ data.
On the street I am recording similar FATS times with the TC Stg1 turbo’s as I did with K04’s. Again though, environmental conditions and the tune come into play, but with quite a few pulls on each setup having been conducted I feel these two turbochargers produce similar FATS times.
Conclusion
Long term reliability will remain a question for some time, and determining a preferred boost profile is something that the vendor will want to give some attention to. Overall the Turbo Concepts Stage 1 turbocharger performs very well when compared with the BorgWarner K04 and is a cost-effective alternative that has delivered K04-like performance on my S4.
Exhaust back pressure:Manifold pressure ratio <= 1.5
Test
Fail
TC Stg1
Supportability Requirements Verification Matrix
Number
Supportability Requirement
Verification Method
Pass / Fail
10
Reputable vendor with good product support
Demonstration
Fail
11
12 month warranty
Inspection
Pass
12
Cost competitive with alternatives
Inspection
Pass
13
Price not greater than 20% over RS4 K04
Inspection
Pass
The TC Stg1 product Fails the reputable vendor requirement due to the short period of time that Turbo Concepts has been providing products for the B5 S4 platform, there is insufficient information available at this time to award a Pass.
TC Stg1
Performance Specifications
Number
Specification Description
Verification Method
Pass / Fail
14
Develop 20 psi of manifold pressure by 3100 rpm
Test
Pass
15
2-11 psi time should be <= K04 time at all rpm
Test
Fail
16
Maintain >= 25 psi to 7000 rpm
Analysis
Pass
17
<= 45 psi of exhaust back pressure at 6500 rpm and 25+ psi of manifold pressure.
Analysis
Fail
18
Mass Airflow Rates >= 375 g/s at 6000 rpm
Test
Pass
19
FATS time <= 3.5 sec (Sea level, 60 degF)
Test
Pass
20
Torque >= 400 ft-lbs
Test
Pass
21
Wheel power >= 400 whp
Analysis
Pass
22
MTBF >= 48 mo. or 50,000 miles
Analysis
Fail
The TC Stg1 turbo Fails the MTBF requirement due to the short period of time that the product has been available. There is insufficient user information available upon which to base awarding a Passing score.
