What are blow off valves and can I put them on my normally aspirated car?
Questions from beginner car enthusiasts on where to get blow off valves for normally aspirated cars are not uncommon as they don’t know what blow off valves are for, and how they work. It is not possible for you to install a blow off valve onto a normally aspirated car, they are for forced inducted engines. No matter how much you like the sound. Hehe.
Normal engine operation.
Let’s ignore how turbochargers work and just assume it works since this post is not about turbochargers. The engine receives the turbocharged air through the intake. That’s assuming the throttle is open. Now what happens when you lift your foot off the pedal? The compressed turbocharged air has no where to go. It hits the closed throttle plate and goes back up the intake manifold the opposite direction. Back into the turbine. This high pressure air hitting the turbine blades from the wrong side of the turbo slows down the spinning turbine, thus reducing boost. When you press the accelerator pedal again, the turbo has to slowly spin up again to gain maximum boost. This is bad. Very bad. The reverse surge of turbocharged air could also damage the turbine. This is also bad. Very bad.
Air is released. Pardon the noobness of the diagram!
This is why blow off valves exist. It releases turbocharged air coming down the wrong direction of the intake manifold out to the atmosphere. You get longer turbocharger life, quicker spool, and better transient response. Of course, there is the issue of the stock standard ECU expecting air but not getting air, and pumping too much fuel in, but that’s a different issue. For cars with that problem (usually because of the usage of Mass Airflow Sensors) there is a different type of blow off valve that recirculates turbocharged air back into the intake instead of releasing it into the atmosphere. Sounds a lot less cooler though heheh.
Recirculating blow-off valves send air back into the intake
You can’t put a blow off valve on a naturally aspirated car because induction (the sucking of air into the engine) is done using vacuum. The engine itself sucks air in, instead of the turbine pushing compressed air in. When the throttle is closed, no air is being sucked in, and there is no boost bouncing back into a non-existent turbocharger turbine. There is nothing to “blow offâ€.
So that’s what blow off valves are for, and that is why you only put them on turbocharged cars. So if you want that cool sound that turbocharged cars have whenever they shift gears, you need a turbocharged car. Like a Perdana V6 Twin Turbo.
March 16, 2006 @ 11:14 pm
Biggest Turbo fan here but cant afford any car with Turbo. Any recommendation for cheapest high pressure turbo cars? I seriously mean cheap! Hehe.
March 16, 2006 @ 11:46 pm
Hi Paul…great website!i stil remember frst time i heard the sound of B.O.V, it was from an RX7 FD and Starlet GT.
March 16, 2006 @ 11:54 pm
wow,u just bought a perdana,sell already your satria ?
March 17, 2006 @ 12:02 am
Perdana twin turbo. Eterna engine ey? I understand got a bit of problems this one and not too powerful for the displacement. Nevertheless, hope you got a good one in your hands.
Jason: Cheap turbo? Go to the half cut shop and ask. every shop holds a different price. Cheap = high maintenence. Remember that.
Paul. I am curious of one thing. There are some variations of turbochargers which do not need blow off valves, eg, Ford’s Lynx RS does not include a BOV. So how come they don’t need it? Won’t it reduce the lifespan of the turbocharger? I think it’s a Garrett T93 (not too sure of the model number).
March 17, 2006 @ 12:03 am
Twin turbo? Is it Eterna?
March 17, 2006 @ 12:08 am
Yup. 6A12TT from the Eterna. Not bad lah, 220hp from a 2.0 V6 with quite low boost. Too much power is ridiculous anyway.
March 17, 2006 @ 1:19 am
Woohoo! 6A12TT! Can’t wait for ya AWD conversion!
Anyway, BOV is for Turbo or Supercharger ONLY.
Anyone asking whether it can be used on NA is PLAIN STUPID or simple IGNORANT!
Putting those NA BOV Sound Device is just asking for trouble n probably lose face after being chased by a real turbo car.
Get real. Get the real deal. Nothing beats a force-induction car. Drive one to feel it.
I did n although the fuel consumption is a little high… I don’t mind because I’m addicted to POWER!
March 17, 2006 @ 10:40 am
Wahlaueh…
had attended a valueble class.
Paul, do you have any info regard the boosting bar like the higher boost better or lower better??
March 17, 2006 @ 2:32 pm
karheng: simply because the manufacturer did not decide to include one. hehe.
March 17, 2006 @ 5:05 pm
paul, as far as i know la, sometime cars like volvo, saab or even stock cars got turbo but no bov because they got low or light pressure turbo. Other than that they wanna cut cost la i think.
anyway paul, the pic was really cool man, especially the one got pssshhhh.. hehehe simple but easy to understand.. but for the newbies, better go to howstuffworks first la.. hehehe
March 17, 2006 @ 5:46 pm
Nothing surprise la kawan our firebrigade also have turbo what? But still didn’t heard the kepishh one lei! lol…
March 18, 2006 @ 6:21 pm
hahha.. really?? fire engines are forced induced engines? hahaha.. new fact everyday i suppose..
congrats on your buy paul. don’t break the speed limit yeah?
March 19, 2006 @ 6:45 pm
So guys…. can a BOV installed in a diesel turbocharged engine?
March 19, 2006 @ 10:29 pm
can, but i think it’s a BOV if a different kind ler.. anyone care to share some light on this?
March 20, 2006 @ 10:35 pm
I wanted to know about By Pass Valve !! hehehe just bought an Audi A4 1.8T … very reliable car ! (Except the fact that people who doesn’t own one dont know anything about it and talk crap bout it….. ) hehe Paul ~~ what do you think? i remembered you thought of getting one right? Go Ahead ! great car !
August 3, 2007 @ 2:24 am
hi, i’m a complete novice and i’ve just bought a peugeot 306 xrdt. was wondering if i could fit a blow off valve onto it and how would i do it? help appreciated!! ta
March 19, 2008 @ 9:45 pm
can i install my HKS blow off valve without turbo?
March 19, 2008 @ 9:48 pm
can i install my blow off valve without a turbo kit?
March 19, 2008 @ 10:00 pm
how to kill a porsche with turbocharger,Greddy SSQV,and a special intake manifold…?