Boost Bypass Mod
What's the boost bypass device:
The boost bypass valve is a valve that controls when air is allowed to be pressurized in the intake manifold by the supercharger. During normal operation, the bypass valve remains open to allow pressure to bleed through the open valve and back into the intake system before the supercharger rotors. This increases gas mileage at low to mid throttle application but hampers performance by not allowing boost pressure to develop until heavy throttle application.
Give me the technical on how the bypass valve operates:
The valve consists of a butterfly inside the supercharger housing. Its position is determined by an external valve (a black canister on the front right side of the housing) that is operated off of engine vaccum. The valve inside is a rubber diaphram which lifts up a lever system to open the valve, at rest it is in a down and closed position. A vaccum source from a 3 way T ontop of the supercharger creates a vaccum on this diaphram to open the valve on startup. Once the throttle blade is opened and the supercharger starts to move more air into the intake manifold, this vaccum encounters a counter force. Running off the same vaccum line that fees the MAP sensor and fuel pressure regulator, this build of pressure in the intake manifold will feed into the top of the bypass valve from the opposite side. Upon a certain pressure off the intake manifold, an equilibrium will be created with the vaccum from the supercharger inlet that had held the bypass valve open. Upon this equilibrium, this bypass valve will close, and eventually a positive pressure will be created to keep the bypass valve closed. At this point, the intake manifold is sealed, free of major vaccum leaks and a positive pressure can be created by the supercharger aka boost.
Benefit of this mod:
The benefit of this mod is to decrease the amount of pressure from the intake manifold (created by increased throttle opening and thus increased intake cfm) needed to bring the bypass valve pressures into equilibrium, this is created from a shorter valve travel distance to its closed position. In essence, the bypass valve will close with less throttle opening thus the engine will start to build boost at an earlier stage of throttle opening. This will result in increased mid throttle response, especially in acceleration from a roll. A downside to this mod will be a slight decrease in mileage, undetectable to most, due to the increased air and fuel through the engine at part throttle. This mod should be noticeable and beneficial with any pulley size.
*Note: There is NO full throttle gains from this mod, so don't mash the gas and claim there's no performance increase other than the boost coming in quicker at part throttle or I'll say DUH
Tools needed:
10mm offset ring wrench
13mm socket to loosen the engine cover nut if needed
Time Needed to perform the mod: 5 minutes
Modification proceedure:
This modification is very easy and will be done in only a few minutes. First open the hood and remove the top engine cover if it is still present; to do this, remove the 13mm nut atop the cover, remove the oil filler neck by grabbing the neck below the cap and twisting counterclockwise, and remove the cover from where it secures against the back metal brace.
The bypass valve is the black canister to the driver's front side of the supercharger. It mounts to the supercharger with two bolts beneath its body, the holes under which it mounts are slotted to allow the valve to be adjusted. Using the 10mm ring wrench, undo the bolts until they are loose and the valve moves freely up and down with minimal force. Now push down on the valve with your fingers and hold it down completely while you use the 10mm wrench to retighten the bolts snug, after which you can let go of the valve.
Reinstall the engine cover if necessary, securing it to the back bracket, then reinstalling the oil filler neck before finally reinstalling the top retaining nut. You may now test drive the car, and notice the boost dial filling up sooner in 2nd gear and on the highway. Enjoy!
Want even more?
If you want your boost to come on even sooner, there's more you can do. Go to your local Home Depot or Canadian Tire and find the plumbing section, you're looking for brass compression fittings. You want to pick up size ____ and you only need one if you can buy them individually.
Now back at home, you want to access the boost bypass valve once again. The rubber line running from the fitting ontop of the supercharger to the top of the bypass, you'll want to pop this off; it can be stubborn and the end fittings are both plastic and can break if really forced on hard so some care must be exercised if it won't pop off easily. If yours is stubborn, use some WD40 on one of the ends, I recommend the bypass valve end. Now lightly grip the hose with some pliers and twist it on the fitting to free it up. Then you may use a flatblade screwdriver and your hands to pop the hose off.
You'll now likely have to reach for your trusty dielectric grease or some WD40 may work too, lightly lube up the inside of the hose. Now take your brass fitting and push it inside the hose, use a little screwdriver if needed, and get it in there about an inch or so. Now you can slide the tube back over its fitting and you're done.
What you've just accomplished is choke the vaccum source which opens the bypass valve. It should now take less positive pressure from the other hose to balance the pressures and close the valve.
Disclaimer: While the author uses this modification on his own vehicle with success and would recommend it to others, he cannot be held responsible for any mishaps that may occur on other vehicles the result of following this tutorial. You perform this modification at your own risk.
