F21 First Logs

After puzzling over the results I was getting yesterday (shown directly below) I began thinking about what I could have done during the turbocharger swapping that may have messed with the F21 wastegates.  The tune was ruled out after conferring with Daz, (who is helping with my tuning efforts), that this initial tune should have been similar to the K04 boost profile and had a low wastegate duty cycle.


Preload checks were good after installing the engine.

The one other change I had made was to solder a wire to the N75 to enable the boost cutoff safety that the TorqByte WMI controller uses.  The perplexing part was that I hadn’t completed the wiring, I’d simply spliced into the wire going to the N75 and left the rest of the wire coiled on it’s spool and tucked under the Y-pipe.  Without anything else changing I decided to look at this wire as a possible cause of the problem.  Sure enough, when checking the continuity on the N75 connector it was getting a good check with the ground terminal on the battery – that shouldn’t be happening.  Upon closer inspection I found that the end of the wire inside the spool was bare and had managed to come into contact with the top of the intake manifold.  I wrapped the end in electrical tape and the problem went away.  Out for a check with the N75 disconnected, proving that the wastegates were functioning correctly and limiting boost to 13-14 psi.

N75 electrically disconnected
N75 electrically disconnected

Then I reconnected the N75 valve and made a few abbreviated pulls starting at different engine speeds to assess how the boost onset looked.

Chart of FrankenTurbo Mixed Flow F21 Boost Onset
FrankenTurbo Mixed Flow F21 Boost Onset

In a follow up I’ll be comparing these results with similar data from the BorgWarner K04’s.

I have discovered that I have oil dripping from the driver side turbocharger – doh!  I was hoping that it may have been coming from the oil return line, but after checking I found those bolts to be tight so I am now left with trying to check the oil supply line, which will entail taking the engine back out.

First Impression of FrankenTurbo F21

The first time I got on the accelerator with the F21’s my first thought was, where’s the boost?  It took a couple of moments before the turbochargers began to spool up, and when they did very quickly I was thinking ‘whoa too much’ as I was letting off the gas and my boost gauge needle swung up somewhere between 25-30 psi.

I thought that perhaps since this was the first time that I had got hard on the gas that the PID for the N75 had not had time to develop appropriate correction values for the wastegates on the F21’s that are set to a preload of 14 psi.

I also needed to temper my expectations as I had just come off driving for a several weeks with the Borg Warner K04’s, a turbocharger that I knew to be faster spooling than the F21.  I was also on the initial tune for these turbochargers and possibly the apparently slower boost onset was an intentional result of the first tune.

The second time that I got on the gas I did so at a slightly higher engine speed which shortened the time for the boost to build, not like the K04’s, but more quickly than the first time.  I also allowed the boost to build a bit longer, anticipating the N75 to kick in and taper the boost.  As my boost gauge pegged at 30 psi I quickly reconsidered the likelihood of the N75 kicking in and opted to let off the gas.

It was clear that the tune was not yet controlling the F21’s as needed so I stopped try to record any further boost data.

The first drive has been inconclusive.  I cannot tell if the perceived slow boost onset is attributable to the tune, a potential hardware problem, a bias from having just driven the car with K04’s, or is just a noticeable delay as compared to BW K04’s.

FrankenTurbo F21 First Run

Got the S4 out on the road today with the first version of the tune to shake down the parts and make sure the car is running properly. Got on the throttle briefly to see how the boost comes on.


My intent is to operate around the same boost profile as I had with the K04’s in order to gather some comparison pressure and temperature data, so this will need to be toned down a little.  Then I’ll start to up the boost level and see what comes of it.