We recently published an article on how blow off valves (BOV) work. These are extremely important devices on boosted applications. In the early days, diesels didn’t really need them because the boost pressure that diesels used to produce was relatively low compared to what we see today.
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. Surge is usually caused from a sudden reduction in load. The boost pressure in the system basically 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 and more trucks with aftermarket modifications experiencing surge, but factory trucks are starting to experience surge as well.
So, what has changed?
Over the past 15 years 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 lower rpm as well as higher rpms. This increase at both ends of 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 lighter, forged and billet wheels are becoming increasingly more common. A billet wheel is stronger than a cast or even a forged wheel. The increased strength of the wheel means the wheel 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 A/R’s have been introduced with a wider range of wheel configurations possible. In addition, new turbine housings 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.
When you let off the throttle that air has to go somewhere – Marty Staggs
Different Styles Of BOV's
There are quite a few different styles of BOV available. One cool aspect about Turbosmart is that they have designed many of their BOV’s for diesel applications. “The BOV’s are very high flowing so as to evacuate the maximum amount of air and also durable enough to survive 100 psi of boost pressures,” said Staggs.
As mentioned above, surge is usually caused from a sudden reduction in load. This sudden reduction in load is usually the result of coming off the accelerator pedal quickly. On the road, people drive unpredictable 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 that drive manual transmissions, coming off the throttle quickly is a matter of changing gears quickly. 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 a compressor. Surge can increase the wear on bearings exponentially. One way to prevent this is by adding a BOV.
The BOV offers a secondary option for the increased volume and pressure to go. By allowing the air a secondary means of equalization, the turbocharger is allowed to spin down at a more natural rate, reducing the load on the bearing.
“Everything we manufacturer is based on consumer demand,” said Marty Staggs, General Manager for Turbosmart USA. “We kept getting calls from performance diesel guys; racers, sled pullers, what have you, that were destroying their turbos. They would have turbos that would expire every event or every other event. They would beat the hell out of the thrust bearings and just kill it and/or just completely break the shafts. They could continue to put larger and larger turbos and when you let off the throttle that air has to go somewhere. And 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 blow off valve is the solution. By venting the compressed air to the atmosphere, there is not 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?
“So, we started developing it. The trick of it was, there are other companies that have had a similar device and it has had varying degrees of success. But we worked with performance guys to figure out what the best route was to take. And so we developed an electronic blow off valve that followed the throttle position. And once we got onto that and really refined the circuitry and the response of the software and system. We were able to get a device that would react and work in most every application to the level of response that these people were asking for. 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 straight forward. The system had boost pressure pushing up on the BOV, so they needed a way to provide a force to keep the valve closed, but also something that would vary to allow it to open also. 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. Then 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 basically no force keeping the valve shut, so the boost pressure opens the gate and vents. To operate the solenoid, they designed a very cleaver controller.
The controller works many different ways. The basic way it is designed to work, is by monitoring the throttle position sensor. The controller taps into the throttle position sensors (TPS) and monitors the speed in which the voltage changes. If the change is quick, then the controller sends power to the solenoid and the system is activated. So, 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 comes on and off, 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 sled track it won’t. 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 actually wire in a disable switch. “Some people dont 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).
One of the other neat aspects about the Turbosmart system, is that the controller and solenoid can be purchased independently of the valve. This means if you have a system currently 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 mentioned. “We took theses 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) all the way to full time drag race diesels.”
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 an 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 (studded, injectors, turbo upgrade, fuel system, EGR delete, etc). Due to all of this, Simmons’s truck regularly surges and he wants to extend the life of his newly purchased charger.
Mounting of the BOV
One of the first things Simmons did was roughly mark where he wanted to mount the BOV. He made sure that 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.
Once the elbow was on the bench, he re-marked 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.
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. There Joey McGrath welded 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.
Wiring and Plumbing
The wiring of the BOV is very straight forward 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 instrument panel just inside of 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 brakes 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.