On my D-series engine, it kicks in at 4650 or so... and instead of the trumpet-like BWAAAAAAAAAH I used to get on my 92 GSR, it's a high-pitched metallic whir. I like it - it's subtle. In fact, I really like the SOHC engine in general - very smooth, and a nice sound. I loved the B-series also... in fact, I think I just love all Honda engines. Has anyone ever heard the 1.5L V12 Honda developed for F1 racing, up around 10-12K rpms? That is a MEAN sound... literally sounds like a human screaming at the top of their lungs. It's amazing - I'll try to find a sound byte somewhere and post it.