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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?
 

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The Librarian
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13,116 Posts
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.
http://www.focusfanatics.com/forum/showthread.php?t=176217
^^^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:
http://www.focusfanatics.com/forum/showthread.php?p=2395889#post2395889
^^^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.
 

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I.S.A.I.K.I.
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5,413 Posts
^^^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:
http://www.focusfanatics.com/forum/showthread.php?p=2395889#post2395889
^^^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.
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.

It has been clarified peeps. Thanks.
 

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The Librarian
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13,116 Posts
^^^Cool.
I will surely take some blame for not mentioning anything in the other thread last week when I saw the mistake.

At this point though, I didn't want to see the same mis-statement propagate throughout both threads.
Cause you know, before you know it, everyone's going to be talking about when their VCT kicks in...LOL!
 

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Registered
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11,906 Posts
Right...

on the older versions of the Factory tune (RLAx series) the DSI opened up at 6000 rpm... if you went in and had the new flash done (YRF0) it would open up at 5200rpm.
 

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Titular Wit Here
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5,205 Posts
I have to confess after nearly six years of owning mine, I really can't tell when the runners change over. [:I] I used to have a Mk.I MR2 that had a similar system, you could really tell when the runners changed, I dunno on the Focus I can't hear it even with the CAI to make the intake noises louder. I can, however, tell immediately if I have hit the rev limiter. [:D]
 
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