I know there are many threads about improvements of the VTCS manifold being gutted, but less so on the VICS. Has anyone done this for an NA application and seen gains?

We are allowed to do this in Champcar so long as its done by hand and we currently are at 145-148RWHP with a JDM 99-00 motor a megasquirt, straight intake, and header. We would get points for the squaretop or any other aftermarket manifold, so we don't want to go that route.

We set our rev limit to 6950 and would hit a low RPM of 4700 in race conditions (lowest speed 3rd gear) and 5200RPM on our up shifts.

Any thoughts on someone who has done this, or ideally anyone who's dyno'ed this, your thoughts would be very much appreciated!

Thanks,
Lucky Kid
www.ruggedbadger.com

 

There was a lot of discussion about this back in the day. From what I recall it turned out to not work well at all. The big plenum volume was probably a good idea, but making the runners that much shorter was not, and the poorly shaped transition between the throttle and the plenum was still a problem.

Just buy a flat-top or a Skank2

 

This.

If you want to step up your manifold game, get a skunk or a flat top.

 

Thank you for the reply. Buying a new manifold isn't "worth" the points, which can be used on Aero or in other areas on the car. We would need to see ~10RWHP gain to justify the 25 points champcar charges for a manifold.

 

FM has a good dyno graph showing the comparison of a VICS, with working system, the Skunk 2, and flattop. It was on a turbo engine, but the results for the working VICS showed it had a flatter torque curve, and higher output up till 6K. I think the same is true in the NA application. Flattop and Skunk went up at the top of the revs, but IMO, having the more robust, flatter torque with the butterfly's working is the best choice. I'm in the middle of finding the missing bits to enable the BP4W I'm cleaning up, which will go in my '93 for that very reason.

 

I don't follow. Are you saying the VIC system changes the runner length?

 

No, but when you "gut" it, youre cutting out all the material inside, which shortens the runners by quite a bit.
The other way Ive seen it done was where they cut out the top of the resonance chamber so that it connects into the plenum, the idea being that it would be a variable length intake manifold. Im not sure if Ive ever seen a dyno comparison of that, but I know it has been done. My guess is that it would not work well.

EDIT:
Found this thread from back in '12
https://www.miataturbo.net/general-m...testing-66901/

This is the type of "gutting" that I described



but apparently it did seem to work, at least in VD on a turbo car

 

I see, I thought you were just referring to removing the shaft and butterfly. The effect of the VIC chamber in the oe form is to increase the manifold/plenum volume which will raise the resonant frequency. If I were only concerned about the output from 4700rpm+ I would remove the shaft and butterfly's.

 

There are no wholesale gains to be made from modifying the VICS manifold. Any gains that might be had up top come at the cost of midrange power.

If you can't do a square top, just make sure VICS is tuned properly and run it.

 

In the same boat as you (Champ Car, NA with a BP4W swap). When we first put the motor in, we made the mistake of blocking/damaging the vacuum chamber in the intake manifold. So our first tune was without working VICS. We added an external vacuum chamber to operate the butterflies after the first race. After a retune and playing with the VICS switch over point we picked up a bunch of mid range torque and the car drove much easier out of the corners.

The major guy posted above is going to do nothing but shorten your runner length and increase your plenum volume. Due to the low revving nature of the BP, you're not going to gain anything from the short runners. You might gain something from extrude honing the intake manifold. I haven't found anything on extrude honing the VICS though. Probably been done in secret.

If you still want to play with a gutted VICS, I have one sitting on my self. I'd let it go for cheap if you want.