Air Control Valve (ACV) Modification

From the advice of Gerald San Agustin, and some testing I ended up taking the ACV completely out of the picture. Gerald has done this to his twincharged MR2 and has success with this mod also. I did it mainly because I saw some boost leaking from the ACV into the elbow. It does feel like it pulls a bit stronger now, but how much is impossible to say without the use of a dyno, before the mod and after. The best part is that this mod is not only free, but has been proven by Gerald and myself to work safely. There is one other person who has done this but as far as I know he is still in another country right now. This isnít like the mod to the air flow meter or other sensitive mods. Itís quite simple and can be done by anybody who can turn a wrench.

The Air Control Valve system is designed to vent out fumes of oil and grease from the sc. To follow along please refer to the BGB. Begin on page SC-12 (at least in the 89 book) and look for the inspection/testing of the air control valve, they have a diagram with the acv.

The ACVís port A goes to the elbow right above the throttle. B goes towards the backside of the supercharger while C goes towards the front (y-pipe). They show with power there is airflow from a to b and c. This happens only when the SC is off and the engine is not at idle. When the SC is engaged power is dropped and the only airflow is between b and c. There is no valve or anything to stop airflow between b & c, itís a straight through shot.

I used one of the tubes (from A to the elbow) and jumped the 2 tubes on the SC, and of course put a cap over the elbows nipple. After over a month I have yet to see any change in the consumption of oil or any other bad effect. I believe it is running a little smoother power wise, but itís hard to tell without the use of a dyno. The important thing to remember this mod will NOT increase your max boost pressure, since that is determined by the ABV, which I do plan on testing and will try to modify to see what kind of pressure I can get out of it.

From my previous posted results I did get some pressure at A, which does not suppose to have any pressure at all when the SC is on. I donít see any other way the airflow from the SC could have "gone around" the acv into the pre throttle intake to create pressure, other then going through the acv. So it just shows that the acv is of weak design and is not doing its job, at least mine... Here are the test results:

Manifold pressure at boost: 7.5-9.5

ACV Results:

                Idle                         Cruising/50mph/4th               WOT (full boost)

A             0                              2inHg                                     .95PSI

B&C       18.75inHg              4inHg                                     1.5-4.5PSI


Advice: check your ACV with pressure applied at b/c as the valve may be opening, letting pressure escape.


All there is to do it is the following (its so simple you can memorize it):

- Move whatever components out of the way so that the bolts on the acv bracket are more accessible (I moved the water catch can, and that VSV on the rear wall)

- Disconnect the power connector

- Disconnect the 3 hoses from the acv

- Use a 10mm (might be 11-12mm) wrench to take the 2 bolts out of the bracket (it can be a pain but can be easily done, just remember to turn the bolt the correct way, clockwise as you look down on it from the top.)

- Using the longer hose (from the acv to the intake elbow) join the 2 tubes on the SC together

- Either tape up the power connector or seal it some how (make sure whatever method is used is reversible)

- Use a nipple to seal up the elbow's port

And thatís it. It takes a whole 5 minutes if that.


As mentioned above another mod I will look into deals with the Air Bypass Valve (ABV). In the past it was mentioned that it might be possible to change the peak boost pressure by adjusting a screw that is on top of the ABV. Since I could not find any more info on it, and no one has confessed in doing this mod already, Iím going to play around with it to see what I can get it to do. There is a sticker over the top of the valve, but if you gently push down on it you can feel a hole under it.