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Old 04-28-2012, 10:26 PM   #1
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Default Question regarding the VIC system on an NB1 head

Firstly, I didn't know where exactly to post this question, so I apologize if it's out of place.

I have read much info about what you need in order to make the vics work on an NA8 car. I know that in order to make the vics work with my 97 megasquirt, I'll need some sort of rpm switch. What I haven't found much info about is what that vacuum adjusted gate actually does.

I read somewhere else that 5250 rpms is the actuating point. Don't know whether that's true or not. What I do know is that when the intake is off of the car(out/off/disassembled), with negative pressure on the actuator linkage(me sucking on the actuator port to resemble a vacuum) the variable ports are closed. As vacuum minimizes to 0, the ports open up.

Since I don't exactly understand if the rpm switch is there to cutout the vacuum pressure or to engage it. My guess is that at idle the ports are closed, as throttle increases the ports open up allowing more airflow, until 5xxx rpms then the switch cuts out and allows vacuum to shut the ports, thus allowing the plenum of the intake to take over air flow at high rpm. The logic I see in this theory is; that in lower rpms if you want more go, you press the accelerator pedal down further to achieve greater speed. On a naturally aspirated engine this would create less vacuum on the vics ports allowing them to open up and give you increased airflow, until the engine reaches a certain point in it's top end rev range where the extra airflow in volume doesn't necessarily benefit you so now we apply vacuum back to the ports, shutting them closed, forcing the motor to pull any of it's air supply from the standard plenum and intake runners. (I think I read somewhere in an intake building thread that longer intake runners suggests you'll have better hp in top end as opposed to having shorter runners).

I'm looking for advice/comments on the above paragraph, and insight on how the vics ports would affect a turbo motor, if at all, because this NB1 head/intake will be used with a turbo setup.

Last edited by ttmiata; 04-28-2012 at 10:46 PM.
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Old 04-28-2012, 10:49 PM   #2
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I really wish I could read Keith Tanner's writeup on retrofitting an NB head on a NA 1.8 block. The google books preview only lets you see the first two pages of that chapter in the online preview. I have a feeling some of my answers may lie there.
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