Blow of valve's
Rotor Head
Joined: Jan 2002
Posts: 1,966
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From: British Columbia
The point of a blow off valve is to release air that is trapped between the compressor wheel of the turbo and the throttle plates, the blow off valve lets air out when the throttle plates close to prevent compressor surge (the wheel stopping) and having to re spool when you open the plates up, its thats simple!
Thread Starter
Junior Member
Joined: Aug 2007
Posts: 22
Likes: 0
From: Asheville, NC
The point of a blow off valve is to release air that is trapped between the compressor wheel of the turbo and the throttle plates, the blow off valve lets air out when the throttle plates close to prevent compressor surge (the wheel stopping) and having to re spool when you open the plates up, its thats simple!
Yea, from the sound of it my best option, and probobly the sound I am going to like the most, is going to be from the stock one, by just re-routing it.
I think I mentioned this somwhere earlier in the thread, but is it heard to re-route it? Do I need to get somone at a shop to do it, or is it simple enough that I could do it?
I think I mentioned this somwhere earlier in the thread, but is it heard to re-route it? Do I need to get somone at a shop to do it, or is it simple enough that I could do it?
To be honest, I don't think the stock turbos last long enough to demonstrate what the effects of not running a BOV would be. 
Big Daddy!!!
Joined: Jul 2002
Posts: 1,194
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From: Edmonton, Alberta, Canada
R.K.
^^ that's true. you can stick a small filter for the BOV to help that... or just clean it every once in a while... :P
either way there's good and bad. keeping it the way it is recycles quite a bit of hot air back into ur intake. but since we run a IC, hot intake air doesn't matter all that much..
i can't imagin having the bearing spinning both ways won't shorten its lifespan. Not to mention throttle response. yes, no BOV sounds cool, but constantly spinning ur turbos back and forth at high boost can't be good.
not to mention if u have some small grain of dirt getting in grinding w/ ur bearings back and forth.. ... >.< *shivers*
either way there's good and bad. keeping it the way it is recycles quite a bit of hot air back into ur intake. but since we run a IC, hot intake air doesn't matter all that much..
i can't imagin having the bearing spinning both ways won't shorten its lifespan. Not to mention throttle response. yes, no BOV sounds cool, but constantly spinning ur turbos back and forth at high boost can't be good.
not to mention if u have some small grain of dirt getting in grinding w/ ur bearings back and forth.. ... >.< *shivers*
development
Joined: Aug 2002
Posts: 5,714
Likes: 7
From: Lafayette, LA
I can barely hear it...or I barely notice it now. My exhaust is very quiet as well. Here are some clips from one of the crazy Aussies Mahjik speaks of...
http://mugenpower.net/rx7c/ricesp.mpg
Originally Posted by RICE RACING
BOV's are only fitted as OEM noise reduction device when fitted in plumb back mode.
BOV's casue charge loss in piping and circuit cars can and have gone slower when fitted with a dump valve due to needing to fill back up charge piping upon re throttle application.
I eliminate BOV's on every car I own or work on be it Mazda rotaries or big hp 2JZ supra's, I have never had a turbocharger fail due to not running a BOV. On the other hand have had lots of techincal problems with cars fitted with BOV's and also general losses of performance
Have data logs ranging back 7 years on every format from Autronic to Motec to stand alone loggers that show no performance gains when running one of these stupid devices on a motor vehicle. Its one of the biggest single cons on the aftermarket performance sectors ever.
BTW F1 never used BOV's, even when allot of the engine suppliers had OEM road cars running with them........ The truth is they do very little if anything measureable for perfomance and they do absolutley nothing for increasing turbocharger life, in fact they do the exact opposite if they do fail or leak they can cause turbocharger overspeeding, probably why they were never used in F1
Fuel engergy is what keeps turbines spining either that or working in a complete or partial vacum, we dont and cant achieve partial vacumes but we do introduce fuel into the turbine section,once this is shut (on closed throttle) off the compressor slows dramaticaly BOV or not.
7 years and probaly 100 000km and up to 36psi boost speaking here across a plethora of vehicles. My SP FD RX7 only runs 16psi of boost but I have not had one issue at all in 8000km of driving and testing since removing BOV's infact only thign thats changed is that the car is more responsive and faster as a result.
BOV's casue charge loss in piping and circuit cars can and have gone slower when fitted with a dump valve due to needing to fill back up charge piping upon re throttle application.
I eliminate BOV's on every car I own or work on be it Mazda rotaries or big hp 2JZ supra's, I have never had a turbocharger fail due to not running a BOV. On the other hand have had lots of techincal problems with cars fitted with BOV's and also general losses of performance
Have data logs ranging back 7 years on every format from Autronic to Motec to stand alone loggers that show no performance gains when running one of these stupid devices on a motor vehicle. Its one of the biggest single cons on the aftermarket performance sectors ever.
BTW F1 never used BOV's, even when allot of the engine suppliers had OEM road cars running with them........ The truth is they do very little if anything measureable for perfomance and they do absolutley nothing for increasing turbocharger life, in fact they do the exact opposite if they do fail or leak they can cause turbocharger overspeeding, probably why they were never used in F1
Fuel engergy is what keeps turbines spining either that or working in a complete or partial vacum, we dont and cant achieve partial vacumes but we do introduce fuel into the turbine section,once this is shut (on closed throttle) off the compressor slows dramaticaly BOV or not.
7 years and probaly 100 000km and up to 36psi boost speaking here across a plethora of vehicles. My SP FD RX7 only runs 16psi of boost but I have not had one issue at all in 8000km of driving and testing since removing BOV's infact only thign thats changed is that the car is more responsive and faster as a result.
Originally Posted by RICE RACING
The fuel energy comment is not anti lag, it was not meant to read that way it was more meant that the only "normal" thing that gives a turbocharger energy is heat form combustion (temperature) and flow rate of gases over the turbine wheel. When you eliminate both these things (I.E. closed throttle and decel injector cut) amazingly the turbo slows down amazingly quickly with or without a BOV it makes no damn difference.
The admission of atomspheric particles or atmosphere slows any turbine system down very dramaticaly, the ONLY thing that can keep it sustained at any rate worth mentioning (aside form normal combustion on WOT) is running in a vacum and that my friends does not happen on anything but a lab type vacume system using in industry or a university. We rebuild turbo molecular pumps and I have seen this first hand
What does happen though in a negative way is that when running a BOV you dump all that hard work that was done by the compressor and loose all volume of compressed particles in the charge plumbing and charge cooler and this is a negative aspect since you have a lag to build this pressure back up on a re opening throttle. Turbine speed has greatly diminished since there is nothing to drive it since you lifted off anyway and the presence of atmospheric air pressure on the inlet of the turbocharger massively slows down the turbine/compressor anyway BOV equipped or not so its a net loss. This is why they were never used in serious competition at the top level.
The next biggest falicy is turbo failure, well I single handidly have proved that to be utter garbage but you dont need to take my word for it simple research will prove to you that turbochargers did not fail any sooner before the mass marketing of BOV's and they have not yet shown one scrap of evidence to prove what physics there is to back up their claims of increased reliability, they do however have a ton of scare tactics and adhominem argument to back up a baseless case though.
So far as practical fact I have no BOV's on my FD and it loves it I am constantly on 1.06kg/cm boost and have experienced no one single issue with many thousands of miles of hard driving and testing so far, car definatley has more pull between gear changes but so has every car that I have removed BOV's from.
The admission of atomspheric particles or atmosphere slows any turbine system down very dramaticaly, the ONLY thing that can keep it sustained at any rate worth mentioning (aside form normal combustion on WOT) is running in a vacum and that my friends does not happen on anything but a lab type vacume system using in industry or a university. We rebuild turbo molecular pumps and I have seen this first hand
What does happen though in a negative way is that when running a BOV you dump all that hard work that was done by the compressor and loose all volume of compressed particles in the charge plumbing and charge cooler and this is a negative aspect since you have a lag to build this pressure back up on a re opening throttle. Turbine speed has greatly diminished since there is nothing to drive it since you lifted off anyway and the presence of atmospheric air pressure on the inlet of the turbocharger massively slows down the turbine/compressor anyway BOV equipped or not so its a net loss. This is why they were never used in serious competition at the top level.
The next biggest falicy is turbo failure, well I single handidly have proved that to be utter garbage but you dont need to take my word for it simple research will prove to you that turbochargers did not fail any sooner before the mass marketing of BOV's and they have not yet shown one scrap of evidence to prove what physics there is to back up their claims of increased reliability, they do however have a ton of scare tactics and adhominem argument to back up a baseless case though.
So far as practical fact I have no BOV's on my FD and it loves it I am constantly on 1.06kg/cm boost and have experienced no one single issue with many thousands of miles of hard driving and testing so far, car definatley has more pull between gear changes but so has every car that I have removed BOV's from.
Thread Starter
Junior Member
Joined: Aug 2007
Posts: 22
Likes: 0
From: Asheville, NC
I am running close to stock, with a HKS SSQV (super sequential blow-off-valve) and it is simply amazing... people stare all the time... and Im sure the 16 yr old kids wet themselves :P
You can buy it as a kit for the FD... its cheap on ebay, be sure to get the real thing
You can buy it as a kit for the FD... its cheap on ebay, be sure to get the real thing
anybody know of a site besides youtube and **** that has specific BOV's and the noises they make? i like my stock woosh sound from venting it... and i wanna know what aftermarket sounds kinda like that
Rotary Enthusiast
Joined: Apr 2006
Posts: 849
Likes: 0
From: Grovetown, Ga
dunno if it's been said yet, but...
generally, blow-off valves (BOV's) vent to the atmosphere and bypass valves (BPV's) recirculate.
on the stock setup, the BPV recirculates the vented air back to the airbox. this keeps the air inside the system so there is more air readily available when you do lay into throttle again. the air is dumped into the airbox post-filter, so it won't have to go through the restriction of the filter. it's not a big difference, but it's still there.
another thing to consider is that some (if not most) stock cars are tuned to expect the air to be recirculated. so if the air isn't there the car will run a touch rich. this is especially true between shifts, when the process of on-off-on throttle is happening quickly enough to give the results of recirc vs venting a more pronounced effect.
if you're just looking for the sound, you'll get it with the stock BPV by opening up the intake. personally, i like the sound of a wastegate. open up the exhaust and enjoy that fluttery goodness.
edit: btw, i had an HKS SSQV BOV on an '02 WRX that i used to have and it sounded great.
generally, blow-off valves (BOV's) vent to the atmosphere and bypass valves (BPV's) recirculate.
on the stock setup, the BPV recirculates the vented air back to the airbox. this keeps the air inside the system so there is more air readily available when you do lay into throttle again. the air is dumped into the airbox post-filter, so it won't have to go through the restriction of the filter. it's not a big difference, but it's still there.
another thing to consider is that some (if not most) stock cars are tuned to expect the air to be recirculated. so if the air isn't there the car will run a touch rich. this is especially true between shifts, when the process of on-off-on throttle is happening quickly enough to give the results of recirc vs venting a more pronounced effect.
if you're just looking for the sound, you'll get it with the stock BPV by opening up the intake. personally, i like the sound of a wastegate. open up the exhaust and enjoy that fluttery goodness.
edit: btw, i had an HKS SSQV BOV on an '02 WRX that i used to have and it sounded great.
I vented mine to atmosphere to see what kind of sound you guys are talking aout, and to see if i liked it, and i didnt get any form of classic BOV noise. actually all i heard was the noise from the intake box hole i forgot to plug! lol. but when shifting under boost(what little im making right now,5-6psi) i hear nothing? what gives? not enough boost?
