Bypass Valve Installation and Adjustment

[ I have added this section after receiving a few inquiries for installation help. ]

Installation

Installing the bypass plumbing itself is fairly simple and straight-forward. Be sure the ends fit tight since it will be under pressure from the turbo! Mount the plumbing tube so the bypass valve faces straight forward and the "adjustment screw" is in front--(see pictures). Tighten the hose clamps on both ends of the plumbing. Later you will learn how to adjust this screw so the bypass valve opens when you want.

With the plumbing in place, connect one end of the long, little vacuum hose to the front nipple on the bypass valve (there is a second nipple that should be left alone--on the HKS valve). The little vacuum hose is then run straight across in front of the manifold to the right from the bypass valve where you will splice it into the "boost gauge sensor tubing." The boost gauge sensor is a reddish circular unit that is mounted to the right side of the engine bay. There is a small vacuum hose that comes off the right front corner of the engine's manifold and runs over to this sensor--this conveys the manifold (or boost) pressure to the gauge sensor! The line from the bypass valve needs to be spliced into this line--you will know the right one if you read this well AND they are the same size!

If you have the Top End unit, they should have provided a "T-shaped" splicer (see right): put this on the end of the hose from the bypass valve so the bottom of the "T" is firmly in the hose; next you need to figure out where to splice it--I would recommend putting it about 1/3 the distance between the manifold and boost sensor, but it will work fine spliced anywhere on this line! Cut the boost gauge sensor hose and put the "T" piece in between the two cut ends and connect them firmly to the "T." With this done you will have a tube coming off the manifold that will then split and run both to the boost gauge AND to the bypass valve!

The Bypass Valve is a passive device. There is an adjustment screw on it which changes the triggering sensitivity. You can adjust it to only open under large boost changes, or you could adjust it so it opens almost everytime you shift. The bypass valve "senses" when you shift or chop the throttle by the DECREASE in manifold pressure. If this change is big enough to trigger the unit, a spring-loaded valve will immediately open and the excess boost pressure will fire out the bottom of the bypass valve. You will be rewarded with an audible "whooosh!!" as your boost is released.

Since the excess boost is dumped it can not backfire on the turbo's turbine and stall it and cause wear on the bearings!! This will keep the turbo spinning happily between shifts so that when you come back on throttle your boost will rise back up VERY quickly. After you get over the sound of the valve in action you will see the boost needle on the gauge jumping right back up after shifts!!

Now for how to adjust the valve

First remember that this valve will NOT harm your engine no matter how it is adjusted; so you have plenty of experimental time to get the valve adjusted the way you want. Simply undo the bottom set screw and then turn the end of the adjustment screw. Replace the bottom screw when done adjusting and give the car a test drive.

I'm not sure how your bypass valve will be factory-set but it will probably be somewhere in the middle of the adjustment range. If memory serves me right, turning the adjustment screw counter-clockwise makes the valve "more sensitive"--meaning it will open under smaller drops in the manifold pressure. Along this line, a "very sensitive" setting will cause the valve to open almost every time you shift. If you turn the screw clockwise, the bypass valve will become "less sensitive"--meaning there will have to be a larger drop in boost for the valve to trigger. Thus, if the screw is adjusted far clockwise, the valve will ONLY open under full boost drop.

The spring in the bypass valve usually changes its properties a bit as it gets "worn in." Thus you may notice the need to re-adjust the sensitivity after using the valve for some time. This should only happen once or twice.

Have fun with your new valve and let me know how you like it. You will be happy to have the added response of the boost between shifts, and you will hear the large amount of energy stored in the boost when it dumps---just think, this used to be backfiring thru your turbo trying to tear it apart!!

Scott Aguilar has a fix for a Bypass Valve with too stiff of a spring:

Last night, I did the switchover from the stock RED spring to the new BLUE spring.  (Also, on the tension screw of the bypass valve, I noticed the head had a Red Dot on it.  I think that's how HKS makes sure what spring is in the bypass valve)  Top End said all I needed to do was open up the bypass valve and swap the springs.  After removing the 3 hex screws from the face of the bypass valve, the first thing that I found was HKS used some sort of glue to hold the 2 halves together.  I had to use a very sharp edge to pry the halves apart.  Then I noticed that the bladder in the unit was glued to the front half.  After some careful prying, I got 1/2 of the bladder off (no reason to take the whole thing off since all you need to do it get the spring out and put the new one in).

I  pulled the red spring and placed the blue spring in its place.  I contemplated using gasket compound before closing it up.  I gave up on that idea since the 2 halves had a groove that held the bladder in place.  Since the pressures are not great, I felt there was no harm.  Plus, it was better to try it without any compound, then if it did not work, I could always put some on afterwards.  Closing up the unit was as easy as replacing the 3 hex screws.

The blue spring is rated for 7-14 psi.  So, I wondered if I should crank the tension screw down or leave it loose.  I opted to start tight and screw it down.  Time for the test drive.

The first thing I noticed was a greatly improved audible report from the bypass valve.  No more intense snorting (but some still remained).  I then stopped and set the tension screw to all the way open, then one full turn closed.  In theory, this should be around the 7-8 psi range.  This "should" cause me trouble since I know I am putting at least 12-13 psi through the intake.  Well, I was very, very pleasantly surprised.  The snort was completely gone except under 0.9bar+ conditions, and even then, it was 75% rushed air noise and then ended with a diminished snort.  Nothing like the constant snort that was present under the other spring.  (Also, I think the loose setting is working due to the metallurgical characteristics of springs.  It's stiff now.  As time goes on, I feel I will need to increase tension.  The Red spring did not leave such room.)

I know I am not leaking through the bypass valve as the turbo pressure characteristics have not changed.  Actually, the acceleration is better.  I think it's because the turbo is now free spinning when before the snort was slowing it down.

So, for $10-17, I strongly recommend getting the BLUE spring.  The total time to replace it was under 30 minutes.  The results will bring a smile to your face.

Happy Elaning, Doug