K04 to the bench

April 17, 2015 Jeffrey Jones

A theory I’ve be thinking about lately is that the turbine side of the K04 hybrid turbochargers is the limiting factor in the amount of power these turbo’s can produce.

This theory has been accepted for some time, and seems quite reasonable given the results obtained with K04 and RS6 style turbochargers. I started thinking more about the subject when it occurred to me that continuing to upsize compressor wheels, or incorporate more advanced designs, would not be a particularly worthwhile pursuit if no matter the improvement to the compressor the turbine side put a ceiling on the power capable of being developed.

The dilemma of this situation became more clearer to me when I began to compare boost profiles of FrankenTurbo F21 turbochargers against the results I had recorded with the FrankenTurbo F4H turbo. The trend with the F21 has been to operate with boost pressure around 24-25 psi. The F4H turbo, with a slightly smaller compressor wheel could achieve similar results, but with noticeably quicker spool up.

It seemed that the larger compressor wheel was slowing boost onset but apparently not resulting in any more top end power. Maybe the turbine ceiling had been reached?

Flow testing turbines is not something commonly done outside of rebuilding Variable Nozzle Turbochargers (VNT) but I did find a research study done as part of a thesis at Ohio State University that incorporated a flow bench into turbine testing.

With a few ideas in mind about what I might do to check my own turbochargers I built an adapter sized like the bell-mouth entry to the downpipe to attach my BorgWarner K04 turbochargers to the flow bench.

BorgWarner K04 Turbocharger on Flow Bench

I then fixed the compressor wheel so that it and the turbine would not spin. I left the wastegate closed and ran the flow bench from zero up to 30 inches of H20 depression recording airflow through the turbine at several points along the way.

By itself the information shown above doesn’t say a whole lot. Shortly I’ll have my K03’s back from being rebuilt and at that time I will put them on the bench to gain a comparison dataset. At some point in the future I may get my hands on an RS6 hotside to be able to measure how much of a difference there is at these low airflows.

This post has some follow on testing with the wastegate door open.

FrankenTurbo, Testing

FrankenTurbo F4H Boost Data

April 5, 2015 Jeffrey Jones

After starting this to evaluate the effect of putting turbo blankets over BorgWarner K03 turbochargers I decided to keep the effort going by adding logs that I have of my car with K04 turbos, and some other K04 equipped cars, and then my F4H data logs. F21 data hasn’t been as easy to come by but I have a couple data points.

Turbocharger Boost Response Time versus Engine Speed

I’m a bit surprised to find that the short lived FrankenTurbo F4H spools as well as the K04.

Next I’ll be adding TiAL 605 v1 data to the chart.

Upgrade Work

Even more perplexed

April 5, 2015 Jeffrey Jones

To recap: I began by doing some pulls to check out a new software tune and verify the calibration on some pressure sensors was correct. During a third gear pull something went wrong and the wastegate duty cycle dropped to zero and the tone of the vehicle changed.

I found a wideband O2 sensor plug had come out of the downpipe changing the tone but I still couldn’t figure out why the boost had dropped so suddenly:

I was able to determine that the sensors were generally within 1 psi of the vehicle map sensor – shown above.

I disconnected the compressor signal lines from the N75, separated the individual lines from the tee, and attached a sensor to each line to monitor the pressure in the housings independently. Those results were not good, one K03 was boosting to almost 25 psi and the other not at all.

I started the disassembly process to try and find the source of the problem. After looking in the charge pipe and exhaust pipe I moved onto taking the motor out to inspect the turbocharger. After taking it off I cannot find anything wrong with it.

I’m thinking of having it rebuilt just for the sake of it, ‘while I’m in there’, and if I do will send this ones partner along with it for the service as well.

Audi B5 S4 Information and Testing