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.