Category Archives: Turbo Selection

TiAL 605’s Return

With an eye toward checking out some of the larger turbocharger options, and to see how they stack up against the RS4 K04 based turbo’s I have already tried, I’ve picked up a set of the TiAL 605 version 1 turbochargers along with the various install hoses and fittings.

TiAL 605 v1 Turbochargers
TiAL 605 v1 Turbochargers

They’ll be in line behind the BorgWarner RS6 turbo’s that I have on the shelf, and a set of the current FrankenTurbo F21 design K04 hybrid that is being assembled at FrankenTurbo, so it may be some time before I get these TiAL 605’s installed.

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.

Temperature Rise Comparison

In the last post about the Turbo Concepts turbochargers I mentioned that the temperature rise across the compressor was looking a bit better than what I recorded with some other turbochargers.  To try to simplify the process of making a comparison I’ve chosen to assess the products in the following way.

I chose 5500 rpm as the engine speed at which to compare the temperature rise.  As the chart below illustrates, the rise in temperature is reasonably linear past 4000 rpm, yes there is some slight curvature to the data, but for my purposes this assumption of linearity with engine speed isn’t something that I feel will change the outcome of the comparison.  If I took the reading at 6000 or 6500 rpm the relative differences between products would still be like that made at 5500 rpm.

It is clear that the temperature delta at the start will exist throughout, though the magnitude does decrease some in the example below.  I have chosen some datasets, from many, that have starting deltas in the same ballpark, around 20-30 degF, and by using at least four samples and then averaging them I hope to show a ‘typical’ case comparison.

Below is how the BW K04’s, FT F21’s, TTE 550’s and TC Stg1 turbochargers compare.  Again, this is the rise in the temperature through the turbochargers compressor when the turbo’s boost profile is approximately the same and with approximately similar starting delta’s.  The conditions are not exactly the same in each case, which is why there are 4 to 5 samples taken and then averaged for each turbocharger, to give a general idea of how the products compare in this regard.

K04’s and Hybrids Compared

It’s clear that three of the products perform about the same as one another, and one, the Turbo Concepts, performs differently.  The Turbo Concepts turbocharger produces a lower temperature output from the compressor versus the other turbochargers.

This lower temperature produced by the TC turbo’s is a good thing, but as I discussed in the earlier post, the intercooler and water-methanol injection come into play before the charge air reaches the engine, resulting in an intake air temperature that is not much different between these products.