October 26, 2021 Products

5 “Facts” About Blow-off Valves (BOV) That Are Wrong

The Blow off Valve (BOV)

Turbosmart was built upon the blow off valve (BOV ), also known as the diverter valve). It was the first product we ever made. Since then, we have been endlessly working to improve and perfect it. As a result, we’ve learnt a thing or two over the years, and we want to put some of the most common misconceptions to rest.

1. Cars Don’t Have Blow-off Valves From Factory, So I Don’t Need One

Cars not having blow-off valves may have been true back in the early days of turbo vehicles. At the time, most factory turbo cars did not come with a factory blow-off valve. However, these early turbo cars were also running relatively low boost levels.

Today, most modern turbocharged cars do have a blow off valve from the factory. However, it recirculates the vented air, so it doesn’t give the characteristic sound of a vent-to-atmosphere blow-off valve. Recirculating BOVs are sometimes called bypass valves (BPVs). Nevertheless, standard BOVs/BPVs are often very basic. Additionally, sometimes BOVs/BPVs are made of plastic, suffer from inadequate valve response, and do not cope well with increased boost levels.

However, it is essential to note that these cars run blow-off valves to prevent compressor surges, leading to the next misconception.

The Holden Commodore VL Turbo is an example of an early factory turbo car with no BOV. Modified VLs are known for their fluttering sound. However, they ran low boost pressures from the factory.

2. Turbo Flutter is Harmless

That fluttering noise that some turbocharged cars make when the throttle is suddenly closed, such as during gear changes, results from a compressor surge.

It’s a reasonably complex phenomenon which we explain in far more detail here. In short, flutter is the sound of a turbocharger trying to push air. However, failing due to closed throttle. Therefore, it dramatically increases the load on the bearings of the turbo.

If it occurs at higher engine loads or boost levels, it can cause premature wear to your turbo. To sum up, a BOV prevents turbo flutter by venting the air pressure that causes surge.

3. Blow-off valves only vent to the atmosphere

This misconception is likely because of the characteristic sound of a blow off valve, which is that a vent-to-atmosphere valve creates loud, sharp “Pssh”. Recirculating or plumb back valves exist and are very popular; however, you don’t hear them. As mentioned above, most modern factory turbo cars have a recirculating blow-off valve as standard.

Turbosmart manufactures high-performance aftermarket recirculating blow-off valves as well as the more noticeable vent-to-atmosphere versions.

Our Dual Port valves feature a split between recirculating and atmospheric operation. Therefore, Turbosmart Dual Ports provide quiet, computer-friendly operation on low boost. In contrast, that classic vent-to-atmosphere sound at a more significant boost. Our Type 5 Dual Port even lets you switch between fully vent-to-atmosphere, fully recirculating, or a mix of both as you wish. They are explained here in more depth.

A Turbosmart Type 5 Plumb Back BOV recirculates 100% of vented air back to the car’s intake.

4. A BOV is the Cause of a Boost Leak if it Leaks in a Smoke Test

Smoke tests attempt to diagnose boost leaks by pressurising the turbo system with smoke. Additionally, observing where the smoke is escaping. However, this test does not replicate actual driving conditions.

Typically in a smoke test, the plumb backport of a BOV is pressurised, which never happens when driving. Meaning, air leaks out of areas that do not have to be sealed under normal operating conditions.

Another form of test which is not an accurate means of testing a leaking BOV is the soap test. A soap test is similar to a smoke test, except soapy water is sprayed on the BOV and around the turbo system. The system is also pressurised with air, and bubbles will form in the soapy mixture where the air is escaping.

No piston style valve does not show some leakage in these tests. They all do, and for a perfect reason. Like a piston within an engine, there needs to be a small amount of clearance to allow the BOV’s piston to move. There is a minimal amount of clearance between the bore of the BOV and the piston so it can move freely.

This does NOT cause any boost leaks, and the amount of air getting through is negligible and would not cause any boost drop in the real world.

5. A Blow off Valve Needs an O-ring to Seal

Some aftermarket blow-off valves require a rubber O-ring to seal the piston with the valve body. It is further preventing leakage, which will perish or become displaced over time. That means the valve will have to be disassembled and that tiny O-ring replaced to ensure it continues operating as it should. Turbosmart’s blow-off valves are precision machined to mere fractions of a millimetre to ensure they seal without the need for a delicate rubber O-ring. This makes them much more durable.

Turbosmart Blow Off Valves - Race Port Range
Turbosmart Blow Off Valves - Race Port Range

Here is a handy self-help guide to helping you with your Turbosmart install and answers to some of the most frequently asked questions we get here. Turbosmart recommends that you get your products fitted and tuned by a qualified technician. If you choose to install the product yourself, ensure you have all the necessary tools and technical knowledge required to perform this task.

Thank you for picking up the latest Turbosmart catalogue. As we look back on 22 fantastic years of innovation and growth, we continue to look towards the future as we release some revolutionary new products that will cement our reputation as innovators and market leaders.

Please contact us here and fill out a quick form so that our team can efficiently help you!

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The last few years have been a little crazy for everyone, and we’re not immune - but we have managed to expand our product range as well as our manufacturing and distribution footprint. We’ve continued to innovate and keep our team and their families safe in uncertain times.

Turbosmart products are all manufactured in-house in our Sydney, Australia Head Office. We’ve been able to support our customers throughout these challenging times seamlessly. Despite the challenges of distance, we always continued to keep the demands and expectations of our customers our top priority, making sure our solutions are in stock & well supported where & when our customers need them!
Nic Cooper Ceo & Founder
Nic Cooper
CEO & Founder

ProPort Features & Benefits

Engineered to Win!

ProPort by Turbosmart is a 54mm (2.13in) Blow Off Valve with a tiny footprint and massive flow. 

Turbosmart BOV Range

Engineered to Win!

Turbosmart has manufactured the Blow-off Valve (BOV) Range with a focus on performance and reliability.

About Turbosmart

From our humble beginnings to establishing ourselves as a global brand, Turbosmart is well on track to lead the future in turbo technology.

Our engineers build and track test all products in-house. Therefore, we ensure we’re continuously producing the highest quality blow-off valves, wastegates, boost controllers, gauges, pressure regulators, and hoses. Furthermore, our products are designed and built for both track and street applications.

How to Adjust Your BOV or BPV?

Engineered to Win!

Each Blow Off Valve (BOV) or Bypass Valve (BPV) needs to be adjusted to suit the vehicle it is mounted on.

BOV5 Range Features & Benefits

Engineered to Win!

Designed for high flow and performance. The BOV5 from Turbosmart is well suited for both street and race vehicles.

BOV Range Rubber O-ring

Engineered to Win!

Designed for high flow and performance. The BOV5 from Turbosmart is well suited for both street and race vehicles.

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