Will Blow Off Valves & Wastegates Work On Diesels?

By February 16, 2022Turbocharger

Blow off valves, and wastegates have and can be used on diesel engines but they are usually not used because diesels don’t have throttle plates that can be adjusted to regulate boost.

My personal observation is that wastegate and blow off valves work pretty well on diesel engines; however, it is a matter of what kind of diesel car. 

There are a lot of myths about blow-off valves and wastegates. While it is true that these parts are generally used in turbocharged engines, they can also be used in diesel engines as well.

Whether you have a turbocharged or supercharged engine, there will be excess pressure created by the turbocharger or supercharger. This is not ideal because too much pressure could cause damage to your engine’s pistons and other components. 

Blow off valves and wastegates are designed to release that extra pressure so that it doesn’t cause any damage to your engine.

In this article, I will talk about wastegates and blow off valves in detail when it comes to engines. This should be interesting to many – given how popular diesel trucks are! Especially in the US.

You can put a blow off valve on diesel, although it is not recommended for most applications. Blow off valves are designed for gasoline engines that have a turbocharger in the intake path. 

Diesel engines have a turbocharger in the exhaust path and do not compress air into the intake manifold, so it is not necessary to run an aftermarket blow off valve. 

The only case where an aftermarket blow off valve would be necessary is in high-performance diesel engines that employ massive turbochargers. These vehicles do not use the factory turbo but rather a completely different setup with its own wastegate, BOV, and other tuning parts required to achieve high boost levels.

The blow off valve, or BOV, is a part that’s been in use on gasoline-fueled cars for decades. It works by venting excess pressure from the intake system when you lift your foot off the accelerator. It makes that distinctive “pshhhhhh” noise and has become a favorite of street racers.

The main reason to have a BOV on a gasoline engine is that it doesn’t have a throttle plate to close off the intake when you let off the gas. So, when you lift off the pedal, there’s nothing to stop air from flowing in backward through the turbo and into the intake pipe. That causes compressor surge, which is what leads to that nice “pshhh” sound when you hear it venting air out of the BOV.

If you can’t wait to hear the satisfying, loud, and proud “Psh!” sound when you step on the pedal of your diesel car, then don’t worry—there are plenty of ways to make it happen! Let us share our practical knowledge with you. 

Here are three ways to make your diesel engine make a “psh” sound:

  1. Depress the accelerator pedal while pushing the clutch down completely. (Make sure the car is in neutral.) The noise should be similar to a “psh” when you do this.
  2. Push the gas pedal as far as it will go and release it quickly. You’ll hear a “psh” when you do this.
  3. Push the pedal and then depress it, then push it and depress it again quickly. Then hold your foot on the gas for about five seconds with the car in neutral, followed by another quick push and depression of the pedal.

Related Article: Blow Off Valves 101: Function, Horsepower, Tuning & Warranty

How Does a Blow Off Valve Work on a Diesel?

A blow off valve (BOV) performs the same function on a diesel engine as it does on a gasoline-powered vehicle: it releases pressure that builds up in the turbocharger when you’re not accelerating.

BOV on diesel is like the safety valve on a pressure cooker. The safety valve vents off too much pressure and stops the pressure cooker from exploding. 

The first place to start when you’re wondering how a blow off valve works on diesel is to understand what a blow off valve does.

A blow off valve, often called a BOV or diverter valve, is an essential component of turbocharged engines—both diesel and non-diesel. 

A turbocharger is mounted on the exhaust manifold of the engine, and turbochargers work by using the energy from exhaust gasses to compress air and force it into the engine. This extra air increases the amount of oxygen in the cylinders, which allows more fuel to burn—and therefore produces more power.

When you let off the gas pedal, all that excess air has to go somewhere since it’s not being used. If it’s not released properly, it can cause damage to your engine as well as annoying hisses and squeals. That’s where your blow off valve comes in! 

When you let up on the gas pedal, the blow off valve opens up and releases the extra pressure that was built up by your turbocharger. This prevents damage to your engine and saves you from having to deal with weird sounds coming from your car.

Why Most Diesels Don’t Use Blow Off Valves

In diesels, blow-off valves are not often used because they add extra weight and complexity to the engine and don’t improve fuel consumption. 

Diesels have no throttle plate that can be adjusted to regulate boost, as in gasoline engines. 

After digging some history, I came to know that blow-off valves were used on diesels in the first half of the 20th century. But they were discovered to be unnecessary: they didn’t do much, and they were fairly complicated to install and maintain. So, they were discontinued not too long after they came into use.

Blow-off valves are popping up on diesel-powered vehicles a lot as of late. Compared to their road-car counterparts, which have been used for ages by the racing community, diesel versions are still in their infancy. But there is one thing all BOVs have in common: they regulate pressure.

When a diesel engine operates at its optimal level, the valves that allow extra pressure to release are unnecessary. The compressed air is forced out of the exhaust valve and pushes the piston back into its natural position without any excess force. The valves are not needed to release extra pressure like they do in a gasoline engine.

The whole point of a diesel is that it doesn’t have valves. A diesel engine has no throttle plate and no intake valves or exhaust valves; it just has fuel injectors, intake ports, and exhaust ports. With all the air and fuel mixed together, the only way to control the amount of fuel is by controlling how long the injectors are open. It’s controlled by mechanical means, not hydraulic ones.

However, in diesel engines, blow-off valves can be used to prevent or stop pre-detonation (also known as detonation), which causes engines to knock—a rattling sound originating from when fuel ignites prematurely and causes engine damage.

Knocking isn’t usually an issue for gasoline engines, but it can be very damaging for diesels. I will discuss it another time.

Do Diesels Need a Wastegate?

Diesel trucks may benefit from wastegate only if it is heavily modified and has enough horsepower.  

Generally speaking, if your truck is stock or moderately modded (i.e., less than 350 horsepower), then no, you don’t need a wastegate. But if your truck is tuned for more than 350 horsepower at the wheels, then yes—you need one. 

Which muffler is your car right now?

If required, I recommend that you install one because of the performance gains you get from it. A wastegate allows you to more accurately control the boost pressure of your engine, which can give you better efficiency and power. For example, it can let you set the maximum boost pressure at 21 psi instead of 22 psi for better fuel economy or 25 psi for more power.

A wastegate is a valve in your engine that lets exhaust gasses flow out of the system when they’re not needed. For example, your engine needs extra power to push the car up if you’re driving uphill; this requires extra fuel, which creates more heat and pressure in your engine. 

So, with a wastegate, you can relieve some of this pressure by opening the valve and letting some of the exhaust gasses flow away before they exit through the tailpipe.

Wastegates are what keep diesel soot and particulates out of the air. They collect it before it can escape into the atmosphere. Otherwise, you’re breathing in something that’s more than two-thirds black carbon, which is related to asthma, lung cancer, and heart disease.

Do you want to live long enough to see your grandkids get married? Then keep yourself from developing lung cancer by investing in a wastegate for your diesel engine today!

So yes, diesels do need a wastegate; it’s just not always called that in cars. It’s called various things depending on the manufacturer, but it does the same thing: it relieves excess gasses when they aren’t needed. In the end, it is more of a matter of personal opinion and subjective to situations.

Blow-off Valves and Wastegates On Diesels: My Thought

So, do blow-off valves and wastegates work on diesels? As we’ve seen, the answer is a resounding “yes”! While some systems are more fine-tuned than others, these intuitively designed devices produce measurable results in terms of horsepower, torque, and reliability. 

With this kind of proven performance and widespread adoption by major manufacturers across the industry, it’s no wonder that diesel enthusiasts have been won over to the side of wastegates and blow-off valves. In fact, they might even be considered standard equipment on modern diesel engines.

Now that we know that Blow Off Valves and Wastegates work on diesels, the next question is, are these worth the extra power they can give your car?

The short answer is yes; they are—especially if you feel like your car needs a little extra kick. But if you feel that it’s working just fine as it is, there’s probably no need to invest in one. If you do decide to go for it, make sure you invest in a high-quality product and get it installed by a professional mechanic.

In the end, it’s up to you whether or not you want to add a blow off valve or wastegate to your diesel engine. There are pros and cons to each of them, and only you know what’s best for your vehicle, needs, and driving style. 

A little bit of research and even some tinkering will help you figure out if a blow off valve or wastegate is right for your car, so don’t be afraid to experiment!

Conclusion

So, if you’re like me and you’ve been struggling with using blow-off valves and wastegates on a diesel engine, I hope that you found this post to be helpful.

In the end, finding the right blow-off valve and wastegate by performance and price will depend on your shopping style. You should also consider what you’re installing it in, where it’s going, and any other factors that may influence your decision.

Many thanks to you for reading this far. If you have any questions about blow off valves or wastegates or any other product, don’t hesitate to get in touch with us.

Ifandi L.

Ifandi L.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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