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.

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.

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.

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