School me on blow off valves...
Thread Starter
Joined: Nov 2001
Posts: 10,813
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From: Doylestown PA
School me on blow off valves... I did search, and there's no threads dedicated to talking about BOV selection and which ones sound better or perform better.
Currently, I'm running the ATI, ProFlo, which is working well. I have a filter on the end of it, and it's mounted in front of the driver's side tire, just after the intercooler. I think it might be at the end of it's abilities though. I'm pushing north of 17psi, and I'm not sure it's sealing well enough. I'm not getting flutter, which is good, as you can hear in this dyno video...
My complaint is I want to move it from where it's at because right now with the windows up, it's weird, I hear the air blowing in my left ear, like it's behind my head at the B-pillar. So I want to move it towards the passenger side pre-intercooler, but I'm also looking for a better 'blow-off' sound if that makes sense. I love the way the supras sound when they shift, not to sound like a ricer or anything, but I've always liked that sound, but I don't want the air to be obnoxiously loud either.
So is a poppet style valve better?
Currently, I'm running the ATI, ProFlo, which is working well. I have a filter on the end of it, and it's mounted in front of the driver's side tire, just after the intercooler. I think it might be at the end of it's abilities though. I'm pushing north of 17psi, and I'm not sure it's sealing well enough. I'm not getting flutter, which is good, as you can hear in this dyno video...
My complaint is I want to move it from where it's at because right now with the windows up, it's weird, I hear the air blowing in my left ear, like it's behind my head at the B-pillar. So I want to move it towards the passenger side pre-intercooler, but I'm also looking for a better 'blow-off' sound if that makes sense. I love the way the supras sound when they shift, not to sound like a ricer or anything, but I've always liked that sound, but I don't want the air to be obnoxiously loud either.
So is a poppet style valve better?
Bypass valves that are used for blowers are generally held open at idle and slam shut during boost. Have you tried looking into Vortech Mondo? They have a fitting to plumb them wherever you want.
Superchargers use surge valves.
Turbos use blow off valves.
In "STREET" applications I like to use two Tial QR valves in higher boost applications. They seem to be the quietest yet they're also a 50mm valve.
I use ONE with a 2# Spring which works as a Surge Valve and stays open until vacuum drops and boost begins.
The other I use a 10# Spring which works as a Blow Off Valve. This valve stays shut until engine reaches 18"hg. which is typically during engine deceleration or after you're in boost and let off throttle.
This is the quietest setup I've found which will still allow for plenty of boost to escape and not allow boost to leak when closed.
It will also give you the in between shifts sound you're looking for.
Turbos use blow off valves.
In "STREET" applications I like to use two Tial QR valves in higher boost applications. They seem to be the quietest yet they're also a 50mm valve.
I use ONE with a 2# Spring which works as a Surge Valve and stays open until vacuum drops and boost begins.
The other I use a 10# Spring which works as a Blow Off Valve. This valve stays shut until engine reaches 18"hg. which is typically during engine deceleration or after you're in boost and let off throttle.
This is the quietest setup I've found which will still allow for plenty of boost to escape and not allow boost to leak when closed.
It will also give you the in between shifts sound you're looking for.
Last edited by Firehawk441; Dec 22, 2013 at 02:56 PM.
Thread Starter
Joined: Nov 2001
Posts: 10,813
Likes: 15
From: Doylestown PA
Thanks for the responses guys. I'm going to keep reading and doing research.
I"m a little confused at to why you would have to run two of those Tial valves. Wouldn't one be enough considering the proflo valve is smaller in flow diameter and I'm not getting surging.
I'm not arguing, I'm trying to understand. At $250, they're not expensive, but they're not cheap either.
I"m a little confused at to why you would have to run two of those Tial valves. Wouldn't one be enough considering the proflo valve is smaller in flow diameter and I'm not getting surging.
I'm not arguing, I'm trying to understand. At $250, they're not expensive, but they're not cheap either.
Last edited by The Alchemist; Dec 22, 2013 at 03:23 PM.
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From: Norn Iron
One Big Red will do anything you need and vent plenty of air.
Some say it is loud ? Really....my Mondo was far louder than the Big Red. The Mondo made an annoying whistle that could be heard inside and outside the car.
The Big Red by comparison, inside the car I barely hear it. Outside I guess yes it could be considered sort of loud.
If you dont want an open valve, get the enclosed one so you can attach a hose and route it somewhere less audible.
There is no sensible reason to buy two valves when one will do the job.
Some say it is loud ? Really....my Mondo was far louder than the Big Red. The Mondo made an annoying whistle that could be heard inside and outside the car.
The Big Red by comparison, inside the car I barely hear it. Outside I guess yes it could be considered sort of loud.
If you dont want an open valve, get the enclosed one so you can attach a hose and route it somewhere less audible.
There is no sensible reason to buy two valves when one will do the job.
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I use 2 QR's to keep the noise down. I'm uncertain if one will allow enough boost out fast enough compared to a single Tial Q which is an open version.
It's called a surge valve because it's always open when not in boost.
Last edited by Firehawk441; Dec 22, 2013 at 04:04 PM.
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From: Norn Iron
Surge, BOV, whatever, make up whatever name you wish to call them., Their job is the same. To vent excess air that the engine cannot consume due to throttle position.
As for hearing a hurricane...maybe I must be deaf then, because I could certainly never hear such a thing.
If I drove with my head under the hood maybe I would, but that never happens.
As for hearing a hurricane...maybe I must be deaf then, because I could certainly never hear such a thing.
If I drove with my head under the hood maybe I would, but that never happens.
Thread Starter
Joined: Nov 2001
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From: Doylestown PA
I didn't mean to start a crap storm here... just looking to understand the function of them better. I understand that the blower puts out more air than the motor needs at idle, so you have to vent it somewhere. Same thing happens when you lift while in boost and the valve is closed, the valve must react quickly to open to allow all that excess boost to vent or else you have compressor surge, which hurts bearings, and a bunch of other parts.
Blow off valve isn't the same in a supercharged application compared to a turbo application. They operate completely different which is why PROCHARGER calls the Big Red Valves a surge valve and not a blow off valve
That is what I'm referring to.
That is what I'm referring to.
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From: Norn Iron
As long as you use one with adequate flow that is designed for the job in hand, all will be well.
Based on my own experience, the Mondo is too small at least for my own car, and a Mondo is louder than a Big Red.
Directing air as the Mondo and enclosed valves do, does create the potential for more noise as all the air is directed through a single passage. But at least that can then be routed somewhere or in such a manner as to dissipate any noise.
Based on my own experience, the Mondo is too small at least for my own car, and a Mondo is louder than a Big Red.
Directing air as the Mondo and enclosed valves do, does create the potential for more noise as all the air is directed through a single passage. But at least that can then be routed somewhere or in such a manner as to dissipate any noise.
I understand that the blower puts out more air than the motor needs at idle, so you have to vent it somewhere. Same thing happens when you lift while in boost and the valve is closed, the valve must react quickly to open to allow all that excess boost to vent or else you have compressor SURGE, which hurts bearings, and a bunch of other parts.
In a turbo application the valve doesn't have to be open at idle
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From: Norn Iron
They use spring+manifold pressure to hold them shut under boost, and vacuum will pull the valve open when the throttle is closed.
ALL such valves operate in the exact same way. The only major difference is typically units intended for SC applications have a larger diaphragm which means any pressure applied offers more force to open/close the valve so they tend to open much easier against the spring pressure
They can call them what they like, there seem to be more names for such valves in the US than the rest of the world added together. They still operate in the same way.
Users may choose to adjust them or muck about with them to achieve slightly different effects, but they're still doing the same thing.
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From: Houston
I run a Tial Q but I am also running turbo. Stays shut under vacuum and boost. It only opens when there is a certain amount of pressure. I do get a little bit of compressor surge under 5psi because it does not open under a light load. A bypass/surge valve will be open during part throttle to bleed off excess pressure since the boost is rpm dependent with a supercharger. Two different style valves for two different applications.
I only stated how to have adequate flow and cut the noise down considerably by using two 50mm bypass style valves.
I don't care for the wind noise and found a way to quiet it down considerably. That's all I was saying.
Last edited by Firehawk441; Dec 22, 2013 at 04:42 PM.
Thread Starter
Joined: Nov 2001
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From: Doylestown PA
I'm with you as well Firehawk, I am not a huge fan of the wind noise, which is why I want to move it and possibly change it.
From what I have read, you put a very light spring in the 'WHATEVER YOU WANT TO CALL IT valve', so that at low throttle positions, under vacum, the vacum is able to hold open the valve. Then when the pressure drops, the valve closes, and now you have the same amount of pressure pushing against the valve, plus the spring pressure holding it closed to build boost.
From what I have read, you put a very light spring in the 'WHATEVER YOU WANT TO CALL IT valve', so that at low throttle positions, under vacum, the vacum is able to hold open the valve. Then when the pressure drops, the valve closes, and now you have the same amount of pressure pushing against the valve, plus the spring pressure holding it closed to build boost.
From what I have read, you put a very light spring in the 'WHATEVER YOU WANT TO CALL IT valve', so that at low throttle positions, under vacum, the vacum is able to hold open the valve. Then when the VACUUM drops and Pressure Increases, the valve closes, and now you have the same amount of pressure pushing against the valve, plus the spring pressure holding it closed to build boost.
Correct.
The issue you may have with your current valve is under higher boost application it will have a difficult time staying closed allowing boost to escape which you already know.
The "Whatever you want to call it" valve is just like years ago when people used a GMC blower on a gas engine. On a diesel engine it was called a "BLOWER" and was used for scavenging. When used on a gas engine for making boost it was called a "SUPERCHARGER". Same device. Different name for different applications.
Last edited by Firehawk441; Dec 22, 2013 at 05:03 PM.
