Increasing Boost With Wastegate Control Valves (WCV)

[ Read This! | Modifying The POV | Single WCV | Multi-Stage WCV ]


This has become the most popular method if boost control (more than bleeds), and is safe if done properly.  There are many options here, so read through them all.  Most of these modifications are entirely Gus's design.  Most of these designs are well documented on Dempsey Bowling's Turbo Performance Upgrades page and I will not repeat his (or Gus's) efforts here.  I will organize his pages here and give my personal comments on them based on experience.  If you're not sure how the turbo and wastegate work, read my Turbocharger Concepts page.  For some basic information about the parts used to install bleeds, see Dempsey's General Information Page.

A Word About WCVs

These setups differ from wastegate control bleeds (WCB), because they use a pop-off valve (or "Grainger" valve) instead of a bleed to control the wastegate.  They have proven to be much more effective and exact than WCBs and if installed well, they will prevent boost spikes almost entirely.  This gives you control over what level of boost the turbo will reach and how fast it will get there, while allowing the ECU to handle the details of keeping the engine running properly.  The only limitation this presents is that you cannot bleed beyond the overboost shutdown point of you engine (usually around 14.0psi to 14.7psi).

The logic module (whether stock or performance) is designed to bring up boost levels at a slow rate by opening the wastegate at about 3-4 psi.  This is to make the engine response more smooth and managable to the common driver.  As you probably know, the high torque of the engine tends to "kick in" at a certain rpm range.  If the logic module didn't suppress the boost inrease, the engine would "kick" even harder.  This also prevents the boost level from peaking, which is when it momentarily goes over the desired limit.

Taking control of the wastegate does not take away to ECU's ability to safely operate the engine.  If the boost climbs too high (past the overboost shutdown point), the ECU will shut the engine down.  If the engine is knocking, it will retard the timing.  You should retard the base timing some (to about 10 degrees, advanced) and use higher-octane gas, since the logic module would normally reduce boost if the engine was knocking badly.  Since the boost level is not allowed to exceed the shutdown point, the logic module always knows how much air is going into it and therefore will never let the engine run lean (unless you have a weak fuel system - see Diagnosing Your Fuel System).  The Engine Information page describes this further.  You can check the status of your engine during boost by installing an A/F guage, or connecting a volt meter to your oxygen sensor output line.  If the voltage is above 0.8V (8 lights), then you are OK.  Above 0.9V (9 lights) is preferred.

Modifying The POV

The sections below give details about how to install a WCV using the Grainger pressure-relief, or pop-off valves (POVs).  This section also give a quick overview of how to modify them.  You can purchase one or more of these pop-off valves made by Grainger through McMaster-Carr Supply Company.  They can be ordered right online and delivered to your door.  The McMaster-Carr part number is 48935K25.  These are well made valves with all-brass bodies and stainless steel ball and spring.  They are rated for 0 - 30inHg of vacuum or 0 - 20psi of pressure.

If you are not going to drill into the valve, there is no reason to switch the valve and spring inside.  however, since all of the other documentation on the web shows the ball and spring switched, this page conforms to this as well.  So when you get the valve, you need to unscrew the knob completely, remove the ball and spring, put the ball into the valve body first, and then the spring.  Once this is done, your valve will be configured like this:

Rather than using plastic and glue, I opted to solder on brass hose barbs for a more secure design.  I used two 3/16" hose barb to 1/8" pipe thread adapters.  I machined the threaded side off leaving about 3/16" of the hex body remaining.  I then machined about 1/16" of the remaining body down to a 0.285" lip, which fits perfectly into the bore of the valve.  I then soldered one on each side of the valve.  Be sure to sand the soldering surface of the valve before soldering it.

Gus's design requires drilling into the valve and using epoxy to glue in plastic hose barbs.  The diameter of the hole to dril depends of the hose barbs you get.  Measure twice, cut once.  The barbs can be cut off of a plastic 5/32" I.D. vacuum hose "T" fitting.  This method seems to work just fine, though you need to be careful not to drill all the way through the valve body or you will destory the ball valve seat.  Also in this case, you have to switch the ball and spring around as shown in the above diagram because you have to drill completely through the knob to secure the plastic host barb well.  Be sure not to allow the barb on the knob to protrude into the valve and try to keep the epoxy out of the valve and barb.  Using this method, the valve will be configured like this:

The Single WCV

This design is the simplest setup, but it has short comings.  The main disadvantage to this setup is that it causes very fast turbo spool-up.  This can make take-offs rather tricky in first gear, and impossible in slippery conditions.  The way to prevent this is to go to 2 or more stages.  Another problem is that in order to prevent spikes, the pressure relief bleed that is required to close the wastegate has to be kept small.  However when this bleed gets too small, it causes the wastegate to stay open.  So during fast shifts, you will not get good spool-up between shifts because the wastegate is still lingering open.  This is especially apparent with smaller turbos (which are also more prone to boost peaking).  The way to prevent this problem is with a WCV Quick Pressure Release.  Here is the link to Gus's procedure on his site, which includes all of the multi-stage setups:

Boost Controller, by Gus Mahon

Dempsey also has a page on it, which you should check out:

Using A Grainger Valve To Control Boost, by Dempsey Bowling

To learn about the WCV Quick Pressure Release, see my page on it:

WCV Quick Pressure Release, by Russ W. Knize

Multi-Stage WCVs Using The EEPC

By taking Gus's multi-stage WCV designs and adding additional stages along with a Electronic Engine Performance Controllers, you can give yourself even more precise control over boost and have better take-offs.  The multi-stage boost allows you to have a boost level for each gear or for different throttle positions, while incorperating the quick pressure release.  Here is my design, based on Gus's initial design, for the multi-stage WCVs:

Multi-Stage WCV Using The EEPC, by Russ W. Knize
Return to the Mini-Mopar Turbo Performance page


This page is maintained by Russell W. Knize and was last updated 04/20/99. Comments? Questions? Email

Copyright © 1996-2003 Russ W. Knize