On a turbocharged vehicle, the turbo compressor's job is to pressurize the air from the car's intake and force-feed it into the engine. This pressurized air is normally ingested into the engine and burned with fuel to make power. However, when you take your foot off the gas and the throttle body closes, a pressure spike occurs from the built up air in the charge piping. This pressure spike must be vented or the turbo will be damaged from compressor surge.

Volvo turbos have a Compressor Bypass Valve located directly on the turbocharger. The CBV takes the pressurized air and releases it back into the fresh air intake system. Generally the CBV works perfectly fine. When the CBV does not work however, the consequences are not so fine.

1. As the CBV ages, the rubber diaphragm inside tears causing boost leaks and a loss of power. This is an extremely common problem and is one of the main reasons for boost (power) loss. If your turbo is older than 5-6 years old or 60k+ miles, chances are the diaphragm is tired and weak and may have pinholes or tears. And if your car has over 100k miles or 10+ years old it is almost guaranteed your diaphragm has numerous pinholes and tears. Finally, upgrading boost via ECU upgrades or boost controllers will accelerate the wear on the diaphragm and often be the 'straw that broke the camels back'.

2. The diaphragm spring inside the CBV was designed for stock boost levels. When you upgrade the turbo boost level via an ECU upgrade or boost controller, the CBV has difficulty holding the higher boost level. The result is that the CBV is pushed open prematurely by the higher boost level, and leaks/bleeds boost. You will make less boost and will lose power as a result. This isn't what you paid for when you bought that expensive aftermarket ECU upgrade!

Problem #1 can only be solved by replacing the worn diaphragm with a new one. The way to solve problem #2 is to raise the spring pressure of the CBV valve, allowing it to resist being pushed open by high boost levels. There is an old band-aid trick to raise the spring pressure by shimming the CBV spring using quarters, but by doing so you are solving one problem yet creating new problems:

• If your CBV is already torn and leaking, shimming the CBV temporarily allows you to hold more boost, but only because the CBV spring seat pressure has overcompensated for boost leaks caused by CBV diaphragm tears. The catch 22 is that increased boost will stress the CBV diaphragm even more, causing more tears. Likewise, if your CBV isn't torn yet but is fragile from old age, rest assured shimming the CBV will wear out what little life is left in the diaphragm in no time.
• While quarters are OK, you want something that fits well and works properly. Quarters are too thick, and the number you insert is usually a crude fitment for what you may or may not need. Using too many can cause turbo problems or even prevent the CBV spring from seating altogether, and using too few can be ineffective and still allow the CBV to leak and not hold boost.

Clearly a real solution was needed that addressed all of the issues. So we designed the only complete solution, allowing you to raise the CBV pressure the "right way" way the first time.

The QBM CBV Upgrade Kit includes:

• (1) brand new CBV diaphragm to replace your old or damaged stock diaphragm. This way, you can reliably shim your CBV to higher boost levels without worrying about tearing your worn out stock CBV diaphragm.
• (5) stainless steel shims for boost levels up to 20psi**. Forget band-aid quarters - our shims are custom stamped to our specifications specifically for our kit. The shims are very thin and held to extremely close tolerances. This allows them to be stackable by design, giving you the flexibility to tailor your boost in granular increments for the perfect setting (unlike quarters). They are also sized to fit precisely into the CBV housing, whereas quarters are much smaller in diameter allowing them to shift around.

Installation is easy using the included detailed installation instructions, and only requires a single 10mm wrench.

Fits all Mitsubishi TD04 family turbochargers (09B/12T/13G/14T/15G/16T/18T/19T/etc). Use our handy application chart to verify your vehicle's fitment.

** For boost levels above 20psi we recommend replacing the stock CBV with a blow off valve (BOV) and one of our CBV blanking plates.

CBV Upgrade Kit: $49