okay, i dont know about any other models, but on my SVT 03 focus, i will be accelerating and at 6000 rpms there is a sound difference. what is this sound and what is happening to make it?
^^^That's not correct, and I need to get to that other thread and explain it there as well.It is your intake runners switching over at 6000 rpms. This is why SVTs have such a nice midrange powerband.
I just went back and found a thread you should read that verifies that the VCT on our cars changed between years.
I meant to type that in, but I had the boss flying in circles around my dept. at work, so I left out some straight facts. My bad.^^^That's not correct, and I need to get to that other thread and explain it there as well.
The VCT did not change, it was the DSI switchover point that changed between years.
VCT and DSI (Dual Stage Intake) are completely different systems on these cars.
The linked thread is also misleading and gets the two systems mixed up.
JRODSVT's post has a great explanation of the VCT:
^^^IGNORE his first statement about switchover, as he was answering a question about the DSI, not the VCT.
That's where the mixup ensued.
VCT: Always active, you won't feel/hear it reacting.
Your VCT does not "kick in" at 5,000 rpm.
DSI: Activates at 5,000-6,000rpm (depending on year, and aftermarket tune).
The intake runners switch from long (matched for low-end to mid-range power),
to short (matched for top-end power) somewhere between the above listed rpm range.
You may (or may not) hear the switchover if you have a short ram or CAI,
but it won't nail you back in the seat or anything.
^^^It's relatively subtle.
In fact, if working (and tuned) properly you really shouldn't feel it,
as that would mean you had a dead spot in the power band,
if it all of a sudden picked up when it switched over.
I hope that clears some things up.