Category Archives: Turbocharger

Turbo Concepts Stage 1 vs BorgWarner K04

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.

Turbo Concepts DZX-271 Turbocharger Compressor Wheel
Turbo Concepts DZX-271 Turbocharger Compressor Wheel

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.


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.


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.


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.

Turbo Concepts DZX-271 Turbocharger Wastegate Canister
Turbo Concepts DZX-271 Turbocharger Wastegate Canister

TC Stg1

Functional Requirements Verification Matrix
NumberFunctional Requirement DescriptionVerification MethodPass / Fail
1Rapid acceleration at 2000-3000 rpm.DemonstrationPass
2Maintain strong acceleration from 5500-6500 rpm.DemonstrationPass
3Biturbo configuration.InspectionPass
4Does not require unique parts.InspectionPass
5Equal or exceed RS4 K04 performance.TestFail
6N75 DC <80% at 6800 rpmTestPass
7Wastegate modulation of boost at part throttle.TestPass

TC Stg1

Technical Requirements Verification Matrix
NumberTechnical RequirementVerification MethodPass / Fail
8Charge air temperature < 300 degFTestPass
9Exhaust back pressure:Manifold pressure ratio <= 1.5TestFail

TC Stg1

Supportability Requirements Verification Matrix
NumberSupportability RequirementVerification MethodPass / Fail
10Reputable vendor with good product supportDemonstrationFail
1112 month warrantyInspectionPass
12Cost competitive with alternativesInspectionPass
13Price not greater than 20% over RS4 K04 InspectionPass

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
NumberSpecification DescriptionVerification MethodPass / Fail
14Develop 20 psi of manifold pressure by 3100 rpmTestPass
152-11 psi time should be <= K04 time at all rpmTestFail
16Maintain >= 25 psi to 7000 rpmAnalysisPass
17<= 45 psi of exhaust back pressure at 6500 rpm and 25+ psi of manifold pressure.AnalysisFail
18Mass Airflow Rates >= 375 g/s at 6000 rpmTestPass
19FATS time <= 3.5 sec (Sea level, 60 degF)TestPass
20Torque >= 400 ft-lbsTestPass
21Wheel power >= 400 whpAnalysisPass
22MTBF >= 48 mo. or 50,000 milesAnalysisFail

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.

Turbo Concepts Exhaust Gas Temperatures

Further comparing the Turbo Concepts Stage 1 turbochargers to the Borg Warner K04’s, the chart below is an illustration of how the exhaust gas temperatures compare.

The pre-turbo temperature is recorded via the car’s Exhaust Gas Temperature sensors which are RS6 units.

Audi RS6 EGT sensors going into B5 S4
Audi RS6 EGT Sensors for B5 S4

Post turbo temperatures are recorded via a temperature probe located at a pre-catalytic converter bung that is also used with a wideband O2 sensor.

Auber Instruments K-type thermocouple
Auber Instruments K-type thermocouple

Temperature readings at about the same manifold boost pressure are shown below.

Turbo Concepts and BW K04 Exhaust Gas Temperatures compared

With the EGT’s starting slightly higher on the Turbo Concepts turbo’s the higher readings throughout are expected.

Nothing notable jumps out at me from these results, both turbo’s look to perform about the same under the conditions that these readings were made.

Low Boost Turbo Concepts Test

When I received the Turbo Concepts Stage 1 turbochargers I had inquired about what boost level to operate them at.  I was advised to aim for an initial ramp up to 18-20 psi then start tapering the boost off, try to reach 15 psi by 5000 rpm and down to 12 psi by redline. About what the blue lines on the chart below look like.

Turbo Concepts Stage 1 mild boost
Turbo Concepts Stage 1 mild boost

Initially after installing the TC turbo’s my intent was to record some basic performance data that I could compare with the other turbochargers that I have recorded.  That meant I had to operate the Turbo Concepts turbochargers at a boost level higher than  was recommended.

With the initial data collection behind me I’ve taken the opportunity to drop the boost and see what happens. The chart above is the result of the first revision to the tune.  The red boost lines are the Turbo Concepts turbochargers, the blue boost lines are the product of BorgWarner K03’s and the NVR Stage2+ tune.

Just by chance the NVR tune with the K03’s is a close boost profile to that recommended for the Turbo Concpets turbo’s – this provides an interesting case to look at for similarities and differences.

There are a couple of notable differences in the K03’s vs TC Stg1 results, first is that the TC turbo’s are being operated at a slightly higher boost level.  This was the first revision to the tune and I was taking a stab at the values for LDRXN that I thought would produce a boost curve close to what Turbo Concepts had recommended.  The second notable point is that the log with the K03’s was made during the summer time, with air temperatures of 70 degF.  The Turbo Concepts data was recorded in December with air temperatures of 20 degF.  The large gap between the Intake Air Temperatures is evidence of these different conditions.  The K03’s are the dashed lines and TC turbo’s the solid lines.

Given these two considerations, higher boost and colder air, one would expect higher mass airflow readings from the Turbo Concepts turbo’s, which is the case.  I would expect that if the conditions were more alike, similar boost and similar air temperature, the mass airflow would also be more similar.  This leads to an interesting conclusion, it’s likely that the engine would perform about the same with the TC Stg1 turbo’s as it would with the BW K03’s when operated at this boost profile.  I’ve found mass airflow to be a good predictor of wheel horsepower.

This leads to a question, how can the Turbo Concepts Stage 1 turbo’s reach the advertised 380 whp if they are being operated at the recommended boost level?  According to the results I’ve obtained the TC Stg1 should be making about 300-310 whp at the recommended boost level.

To get close to 380 whp the boost will need to be raised.  When I’ve operated the TC Stg1 at around 22 psi I am seeing close to 380 g/s towards the top end which should put the car close to 380 whp.

Turbo Concepts Stg1 24 psi taper to 22 psi

This leaves an unresolved issue, how to reach the advertised wheel horsepower at the boost level Turbo Concepts recommends operating these turbochargers at.