We recently published an article on how blow off valves (BOV) work, and these are extremely important devices for boosted applications. In the early days, diesels didn’t need them because the boost pressure that diesels used to produce was relatively low compared to what we see today. Because of that, turbo surge was not a huge concern.

This means that the displacement of the engine could handle enough volume to reduce the intake pressure down to atmospheric before the turbocharger would surge. Turbo surge is usually caused by a sudden reduction in load (i.e. the throttle pedal is quickly released and the boost pressure in the system has nowhere to go but back through the turbocharger). This reverse in flow is called surge and it is extremely hard on bearings. Typically, a “chuw chuw chuw” sound is heard during this event. Today, on the other hand, many things have changed and surge is becoming more and more prevalent. Not only are more trucks with aftermarket modifications experiencing surge, but factory trucks are starting to experience it as well.

Turbo Surge: What Has Changed

Over the past couple of decades or so, there have been major advancements in aerodynamics that not only make our turbochargers produce more boost but, also, produce that boost much quicker. These aerodynamic advancements have come through OEM needs for increased air flow at all engine RPM. This increase through the spectrum means that all of the aerodynamics have had to go through an extensive redesign and retooling.

On the compressor side, it is becoming more common for compressor wheels to be designed using lighter materials. Forged, and billet wheels are becoming increasingly common. A billet wheel is stronger than a cast or even a forged wheel. The increased strength of the wheel means it can handle more load.

On the exhaust side, not only have the aerodynamics been analyzed and redesigned, but the turbine housings themselves have gone through a huge transformation. There are still traditional turbine housings but more area over radius (A/R) have been introduced with a wider range of wheel configurations possible. In addition, new turbine housing designs have been introduced. On OEM trucks, it is common for there to be veins inside the turbine housing that are controlled by the computer (either mechanically or pneumatically). These veins can greatly affect when the boost pressure comes on and how much boost can be produced at a given RPM.

These advancements are great, as they allow our trucks to produce more torque lower in the RPM range, have much greater top-end power, reduce emissions, and increase fuel economy. What has been happening recently as emissions regulations have changed is that companies are trying to get more air into the engines much lower in the RPM range. To a certain degree, the leaner an engine can run, the lower its emissions. The downside to this increase in low-end performance is the phenomenon of turbo surge.

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(Top) Notice the scaring on this 360 degree bearing. This is caused from high thrust loads from either excessive drive pressure or surge. (lower left) While this bearing isn’t in extremely bad shape, the scratches indicate a high load on the bearing. (lower right) There are quite a few things wrong with this turbine wheel. The blades are broken, indicating impact on the turbine housing, the rear bearing surface has excessive scaring and discoloration from excessive heat, and the front surface shows light scaring.

To help eliminate turbo surge, many performance-oriented trucks utilize a blow-off valve (BOV). There are many different styles of BOVs available. Turbosmart has designed many of its BOVs for diesel applications. “The BOVs are very high flowing to evacuate the maximum amount of air and also durable enough to survive 100+psi of boost pressures,” says Marty Staggs of Turbosmart.

Turbo Surge: Identifying the enemy

As mentioned above, turbo surge is usually caused by a sudden reduction in load. This sudden reduction is usually the result of coming off the accelerator pedal quickly. On the road, people drive unpredictably, and many times our driving is more reactive than planned. On the track, ending a hard run or when something happens, coming off the pedal quickly is very common. A simple wave from the flagman means to come off the throttle because the run is done. For those who drive trucks with manual transmissions, coming off the throttle quickly is a matter of changing gears. Either way, all of the extra volume of air at the elevated pressure needs to go somewhere.

At lower boost pressures, the air simply enters the cylinders and all is well. At higher pressures/volumes there isn’t enough cylinder volume to reduce the pressure fast enough and the flow of air will find its next easiest place to equalize at — back through the compressor. Turbo surge can increase the wear on bearings exponentially. One way to prevent this is by adding a BOV.

“Everything we manufacture is based on consumer demand,” says Staggs. “We kept getting calls from performance diesel guys that were destroying turbos. They would have a turbo expire every event or every other event. They would beat the hell out of the thrust bearings and kill it and/or just completely break the shafts. They continue to install larger turbos, and when you let off the throttle that air has to go somewhere. So the turbos were being heavily overdriven and you know the air would back up in the system and just hammer the turbo. So, we kept getting asked for a solution.”

The Solution For Turbo Surge

The blow-off valve is the solution. By venting the compressed air into the atmosphere, there is no pressure left in the system to put unnecessary stress on the turbo. But how do you adapt it to a diesel application that doesn’t produce a vacuum to open the gate like a gas engine does?

“When we started developing it, there were other companies that had similar devices with varying degrees of success. But we worked with performance guys to figure out the best route to take. We developed an electronic blow-off valve that followed the throttle position. Once we got onto that and refined the circuitry and the response of the software and system, we were able to get a device that would react and work in almost every application. We started putting it on a few street vehicles and what have you. We worked on it for probably two and a half years before we released it to the public. Just refining it and getting it to work exactly how it should work to provide a true benefit,” continued Staggs.

Turbosmart’s approach was very straightforward. The system has boost pressure pushing up on the BOV, so they needed a way to provide a force to keep the valve closed but would allow it to also open. Their system sends the same boost pressure pushing up on the valve to a solenoid. That solenoid, when not energized, directs the boost pressure to the top of the BOV head. This counters the force pushing the valve open and the gate stays shut. When the solenoid is activated, the boost is no longer sent to the top of the BOV, but instead, the pressure in the BOV is vented into the atmosphere. This results in no force keeping the valve shut, so the boost pressure opens the gate and vents. To operate the solenoid, they designed a very clever controller.

The Controller

The basic way the controller is designed to work is by monitoring the throttle position sensor (TPS). The controller taps into the TPS and monitors the speed at which the voltage changes. If the change is quick, then the controller sends power to the solenoid, and the system is activated. But what about the trucks that don’t have TPS sensors? Well, don’t worry. Turbosmart has you covered too. There are two wires to accommodate the wiring of an external TPS sensor.

Are There Any Other Options?

If you are picky about when the BOV opens and closes, then you can wire in your own “on” switch. That way if you don’t want the BOV activating while you are having to “pedal” the truck down the track it won’t function. Just flip the switch when you end your run and all is well.

On the other end of that, occasionally you may want to be able to turn it off during certain situations. So, you can wire in a disable switch. “Some people don’t want it to be active when using cruise control so we made it very flexible,” says Staggs.

In addition to that, there are adjustments to adjust the sensitivity of the controller or how long the solenoid stays open (duration).

Another neat aspect of the Turbosmart system is the controller and solenoid can be purchased independently of the valve. This means if you currently have a BOV on the truck that doesn’t work properly, you can keep your existing BOV and connect the Turbosmart controller kit to it. This gives you the ability to choose which BOV you use. “We designed this system in response to numerous and continued requests from consumers over many years,” Staggs mentions. “We took these requests and feedback very seriously and designed a system that could meet everyone’s needs. The controller was designed to be very sensitive so it could work on completely stock vehicles that need help combating surge (Ford Power Stroke is one example) to full time drag race diesels.”

The Install

With all of these cool features, we had to test one out. As luck would have it, Jared Simmons, Diesel Technician at Diesel Dynamics was going to install one on his truck. Simmons has a ’01 Ford F-250 that is pretty unique. He converted the regular cab long bed truck into a short bed and swapped out the 7.3L for a 6.0L. The truck has the normal 6.0L modifications (head studs, larger injectors, turbo upgrade, fuel system, etc). Due to all of this, Simmons’ truck regularly surges and he wants to extend the life of his newly purchased charger.

Mounting The BOV

One of the first things Simmons did was roughly mark where he wanted to mount the BOV. He made sure the fittings that screw into the top of the BOV had room. From there, Simmons removed the silicone hose that connected the CAC (Charge Air Cooler) tube to the intake elbow. With the silicone hose removed, Simmons then removed the intake elbow.

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Once the elbow was on the bench, he remarked the mounting location. When the elbow was mounted on the engine, he could not get all around the BOV with a pen. The reason he wanted to make sure that he had the whole thing marked was to ensure that when they cut a hole into the elbow, they were not removing too much or too little material.

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Initially, they drilled a pilot hole in the center of the marked area and then came back with a hole saw. With the initial hole drilled, Simmons filed down the edge to ensure a smooth transition as well as removing any debris that could later fall into the engine.

The Sinister Diesel intake elbow is made out of some pretty thin-wall tubing. So, the elbow was taken over to the guys at Gear Heads Performance to have them TIG weld the flange on. Once the flange was welded on, Simmons just reversed the steps and reinstalled the elbow with the BOV mounted on the elbow.

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Wiring And Plumbing

The wiring of the BOV is very straightforward, and the Turbosmart directions have a great diagram to go by. Simmons mounted the solenoid on the passenger’s side fender and then used a “T” to tap into the boost line running to the MAP (Manifold Air Pressure) sensor. The new line was the supply line to the solenoid. Then he routed a line from the solenoid to the BOV.

The last stage of the plumbing was to route a vent line from the solenoid to the atmosphere. So, Simmons just used the remaining boost tubing and routed the line down the fender and under the battery.

To control the solenoid, the controller was mounted under the dash, just inside the kick fuel panel access panel. The controller is a simple four-wire install. The black wire went to the chassis for ground. The red wire was tied into a 12-volt battery power wire inside of the fuel panel, and the white wire is the TPS signal wire. After looking at a wiring diagram and probing a couple of wires, Simmons found the proper wire.

The last remaining item was to connect the output of the controller to the solenoid. Simmons ran a jumper wire from the solenoid to the yellow wire of the controller. In doing his final check of the system, he found that the BOV head had two threaded areas for inputs. Simmons plugged the second one and started the truck. He ensured that the wiring and hoses were out of the way of any moving parts and any heat. He then did a few power brake tests to verify the BOV would hold the boost and then release it when he let off. If he would have encountered problems then he would have needed to adjust the sensitivity or the duration. Being that everything worked like he wanted to right out of the box, he was done!

One cool thing to note, Turbosmart USA is now offering both aluminum and stainless steel flanges with each kit. No longer do you have to worry about ordering the right flange.