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.

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.

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:

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.