Category Archives: Turbo Selection

Turbo Selection

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.

Go to top

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.

Go to top

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
Turbo Concepts, Turbo Selection

Turbo Concepts – Another option?

Several weeks ago someone posed a question about the Turbo Concepts brand of turbochargers for the Audi B5 S4.  I’d never heard of them before, so I checked out their website to try and learn some more about this company and their product line for the 2.7T engine.

I was happy to see that they provide some information about the products that they sell, that’s not always they case when it comes to aftermarket turbocharger suppliers.  Three products are available for the 2.7T engine, described as Stage 1, 2, and 3.  The Stage 1 product looks to be a replacement for the K04 with a bit more potential, and the Stage 2 & 3 are in the RS6 hybrid category.

As indicated in my quest for the best stock motor turbo, a K04 replacement is what I’m mostly interested in – a turbocharger that can retain K04-like spool yet delivers a bit more power towards the top end, the Turbo Concepts DZX-271 is the product in their lineup that is most closely aligned with what I am after.

Turbo Concepts DZX-271 Audi B5 S4 Turbochargers
Turbo Concepts DZX-271

Looking more closely at the information available it’s not clear if the Stage 1 turbo will differentiate itself from the other turbo’s that I have driven, or am planning to evaluate.   There is a claim of it being capable of flowing 28 lbs/min, but at what pressure ratio?  Even then, claimed flow rate numbers for a compressor don’t necessarily translate to vehicle performance.

For the time being I’ll wait to see if any user data is published that gives more indication of whether or not the Turbo Concepts product is something that will meet my criteria.

 

The Turbo Engineers, Turbo Selection, Turbocharger

More TTE550 Boost Onset Data

Taking advantage of some unseasonably cool weather I had the opportunity to record the boost onset characteristics of the TTE550 turbochargers under conditions more like those when the BW K04’s (and FT21’s) were logged.

Shown below is the 2-11 time for the BW K04’s and TTE550’s.  The 2-11 time represents how much time passes during boost buildup from when pressure reaches 2 psi and then builds to 11 psi.  This measurement is made beginning at a variety of engine speeds typical of my normal driving state.

Chart of BW K04 vs TTE550 2-11 time
BW K04 vs TTE550 2-11 time

While the TTE550 clearly trails the BW K04s at all engine speeds the difference becomes less pronounced with increasing engine speed.

Ambient temperature does come into play when measuring boost onset.  The chart below illustrates the response from the TTE550 under different ambient temperature conditions.

Chart of TTE550 2-11 time with ambient temperature represented
2-11 time with ambient temperature represented

The various measurements are grouped in range categories (degrees F) to make the presentation clearer.

This does obscure the fact that some of the differences in ambient temperature may be minor, or significant.  For example, a reading can be made at 48 degF and compared with another at 50 degF that resides in a different category despite there only being a 2 degF difference.  Also, within the same category one reading could be made at 50 degF and another at 59 degF.

Looking at this boost onset in a more familiar form, I have charted the boost onset at various starting engine speeds against engine speed.  This chart was made from measurements taken at an ambient temperature of 41 degF.

Chart of TTE550 Boost Onset
TTE550 Boost Onset

Impressively, at lower engine speeds the TTE550 is reaching approximately 17.5 psi at 3000 rpm.