TURBO FLUTTER and BLOW OFF VALVES explained in DETAIL - BOOST SCHOOL #8
1,454,750
Published 2021-08-01
GFB TMS Respons: gfb.com.au/products/blow-off-and-diverter-valves/r…
The BOV from this video: gfb.com.au/products/blow-off-and-diverter-valves/r…
Let's imagine a concrete scenario. You have your foot on the throttle and you're flooring it. The throttle plate is wide open and the engine is trying to make the most powerful combustions it can and as such it's also producing a lot of exhaust gasses very rapidly. These exhaust gasses drive the turbine wheel which then spins the compressor wheel as they're connected together with a common shaft. The more exhaust gasses are being sent into the turbo the faster the compressor wheel spins and the more it compresses the air.
So when the throttle plate is fully open we have both high airflow and high air pressure. We have high air flow because the throttle plate is fully open and there is no restriction to airflow. We have high air pressure because the turbo is working hard to compress the air and stuff more of it into the same space.
So what happens when we release the throttle? What happens is that we transition from a situation of high airflow and high pressure into a situation of low air flow and even higher pressure. The rapidly flowing pressurized air coming from the turbo suddenly hits a dead end and has nowhere to go. At the same time the turbo is still rapidly spinning and trying to keep stuffing the air into the engine which it can't do because the throttle plate is closed and this blockage further increases the pressure in the piping.
Now the blades of the compressor wheel are designed to „grab“ the air and push it onto the engine. In a situation where we have enough air pressure and enough airflow followed by a sudden closing of the throttle plate the dramatic drop in airflow and subsequent pressure spike can actually overpower the aerodynamic capabilities of the compressor wheel blades which results in them no longer being able to „grab“ onto the air causing compressor surge aka turbo flutter.
If you look at a compressor map of any turbocharger the left-most line is your surge line. Everything left of that line is the surge zone.
In the simplest of terms when compressor surge or turbo flutter occurs it means that there is too much air pressure and too little air flow for the compressor wheel to do it's job. When this happens the air has nowhere left to go and it carries so much pressure that it can actually force its way back through the turbo, past the compressor blades and out the intake. This wrong way out actually becomes the only exit path for the high pressure air. Compressor surge in a car engine is almost never powerful enough to stop a turbo from spinning and it can never cause a turbo to start spinning in reverse. But what it can definitely do is slow the turbo down and shorten the lifespan off the turbo as it exposes it to increased stress.
The sound of compressor surge or turbo flutter and is often voiced as stutututu or chu chu chu chu.....in fact each of those stu or chu is a small chunk of air separating from the blades and escaping past the compressor wheel out the intake. The first stu is going to be the loudest because it has the most pressure behind it and each subsequent stu will be less loud until all the excess air pressure is gone.
So how do we get rid of compressor surge or turbo flutter that occurs when we release the throttle? The answer is simple – instead of relieving pressure back out past the compressor wheel we relieve the pressure somewhere else.
And that's exactly what a BOV or a blow-off valve does. It gets rid of the excess air pressure in the piping when you suddenly release the throttle. By getting rid of the excess air pressure at a different location we do not subject the turbocharger o the increased stresses associated with turbo flutter.
A blow-off valve has a piston inside it. When the throttle is wide open both the top and the bottom of the piston see the same air pressure because the top of the blow-off valve piston references pressure from inside the intake manifold. But when the throttle plate closes the top of the BOV sees vacuum and the bottom boost pressure. This means that the boost pressure can easily overpower the spring on top of the piston and open a path for the pressurized air either to be vented to atmosphere (blow-off) or recirculated in front of the turbo inlet (re-circulation or diverter valve)
A special thank you to my patrons:
Daniel
Peter Della Flora
Daniel Morgan
William
Richard Caldwell
Pepe
Brian Durning
Brian Alvarez
D4A merch: d4a-store.creator-spring.com/...
Patreon: www.patreon.com/d4a
#d4a #boostschool #stutututu
00:00 What is turbo flutter (compressor surge)?
08:40 How a BOV prevents flutter
12:07 How a BOV works
13:55 Where to install a BOV
14:30 When a BOV can't help
All Comments (21)
-
Go Fast Bits: gfb.com.au/ GFB TMS Respons: gfb.com.au/products/blow-off-and-diverter-valves/r… The BOV from this video: gfb.com.au/products/blow-off-and-diverter-valves/r… Let's hang out: superpeer.com/driving4answers Support d4a: driving-4-answers-shop.fourthwall.com/
-
I can't believe he actually made a graph of the stututu sound. This guy is a legend!
-
the man literally got his shirt wet as hell trying to explain throttle position, i tip my hat to u sir, ur commitment to educating others has no limit
-
It takes a very smart person to explain complex subjects in a simple way for non-familiarized people to understand easily. Thanks once again for such an educative video. I enjoy absolutely each and every one of them !
-
Your water example was priceless 😂
-
The amount of information in the video is INSANE. Mad props to you sir. This video needs to go viral so people actually understand what’s going on to clear up the many misconceptions we have in the car community. You’ve gained a subscriber.
-
All this BOV talk reminds me of a system Ford came up with for their Focus WRC car in the late 90s/early 00s. World Rally Cars have intake restrictors to keep the power down. Ford created a 'tank' at the back of the car which would capture all the air that would otherwise be vented off by the BOV. When the driver was off throttle this tank would be filled up with compressed air, which would be available for the engine once the driver floored it again. Once the FIA found out about it (it took them a few rallys IIRC) they were quick to ban it because in their eyes it negated the purpose of the intake restrictor by allowing more air than what should be available for the engine, even if only for a brief period of time.
-
If every teacher had your approach of explaining things, 1 by 1 chronologically, where would be our limit...?!? Thank you for your effort!!! 🙏🏻🙏🏻🙏🏻
-
Twist the knob until it blows off... Interesting advice.
-
As a longtime mechanic, I would have to say that this is the best presented explanation as to why a bov is needed in a turbo circuit! Well done
-
another informative and entertaining episode of BOOST SCHOOL!!!!....Thanks again bro Saving it to my playlist on Turbos for future use!!!
-
Shorter name of the video would be HAPPINESS EXPLAINED IN DETAIL
-
Stuututuuuu is priceless, that's why I wanted a turbo in the first place 😁
-
These videos of yours are an important reference library for any gear-head. Thank you for your patience and good simple and sober approach to any of the subjects you cover. The humour in your diagrams is appreciated 🙂
-
You're telling me I can't make dope stututu sounds without hurting my turbo? Day ruined.
-
Just wanted to say thank you for your videos, I'm a trainee mechanic and have worked at a few different garages and it seems rare to find people who know what they're on about so I haven't learned as much as id liked about cars, and this channel has really helped me understand more about different parts of a car how they work what they do etc Fantastic content thank you
-
Wonderful explanation, good illustrations. You explained better than most profs, well done
-
This has got to be my most favorite automotive YouTube Channel. The videos are perfect for someone who is a visual learner. Also this channel goes to show that a video doesn’t need to be flashy and have a huge budget to be an amazing YouTube channel. Perfect Channel keep doing what you do best!
-
I know next to nothing about turbos and this is probably the best video on YouTube for explaining it to a newbie like me! Superb job!
-
I have seen several explanations of this, but yours is the clearest. Thanks.
