Bypass Valve

Theory: The theory behind the Bypass Valve can be found on numerous websites regarding turbos and turbo cars. The Bypass Valve is installed onto the pipe which runs between the turbo and the intake manifold. It is a simple open/closed-type valve which sits closed in its resting state. When your foot comes off the gas pedal, as in shifting or decelerating, the throttle plate closes partly or completely. This causes the pressure in the intake manifold to drop. A small tube connects the Bypass Valve to the intake manifold (spliced into the boost gauge sensor line). The drop in manifold pressure sets off a spring-loaded mechanism to open the valve. When the valve opens it gives an audible sound as the turbo compressed air is vented out to the atmosphere. As the pressure equilibrates the valve is shut completely again.

   Without the bypass valve installed, each time you shift, the throttle plate closes and the compressed air slams into it and backs up. Having nowhere else to go, the pressure wave recoils back through the intake. This sends a pressure spike back through the turbo fan, stalling it and creating undue wear and tear on the turbo bearings. This can be heard in the stock Elan as a stuttering sound each time you shift. This sound is your boost pressure stalling your turbo and coming back out the air filter and duct pipe!

Type: I have had a Standard HKS Turbo Bypass Valve installed by Top End Performance since May 1998. There are many companies that offer a Turbo Bypass Valve for sale-also commonly known as a Blow-off Valve.

Cost: $375 from Top End Performance-this includes the mounting pipe as detailed below. Check online for prices from HKS directly and other companies too.

Installation: The Top End package includes the HKS Valve mounted to a custom-made metal pipe. This metal pipe replaces the lousy stock lumpy rubber hose that fits into the intake manifold and throttle plate. It is simple to install with merely a screwdriver. You must remove the old rubber pipe and then affix the new pipe with a screw clamp on each end. The Bypass Valve actuator tube is then spliced into the boost gauge sensor tube. It's that easy!! Should you choose to purchase a Bypass Valve somewhere else, you will need to find a way to mount it securely in place as it cannot be mounted to the stock rubber pipe!

Use: 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.

Review: The Bypass Valve is an excellent upgrade for the Elan or any turbo vehicle! There is actually a performance improvement from installing it. Since your turbo is not stalling between shifts, it continues to spin. Therefore, when you hit the gas again there is only minimal turbo lag. It is amazing to see the boost gauge needle drop from full boost down to zero when shifting, followed by it rebounding right back up to full boost as soon as you hit the gas!! This translates into better acceleration through the gears. You get better performance without changing anything on the turbo or engine-you are truly getting something for nothing (other than the cost).

     The Bypass Valve does make an audible sound as it dumps the boost (a "silencer" can be found for those annoyed by the sound). I found it truly impressive to actually hear all the energy stored in the boost as it is released! To think that all that energy was surging through the turbo backwards before I had the valve makes me very happy to have it now. I feel installing a Bypass Valve is IMPERATIVE if you raise the boost on your Elan. Without one you will be investing in a new or rebuilt turbo much sooner. Hearing the valve work has changed the way I drive as well. I now come off the gas more quickly each time I shift-this assures the valve opens and my turbo stays happy.