View Full Version : Difference between and re-circ dump valve and a free to air?
Hi,
Please could someone tell me the difference between a re-circulating dump valve and a free to air - I know its obvious from the name - but is there a performance difference between the two or is it just extra noise from the free to air version?
Thanks
Jack
arjunior45
23-05-07, 13:00
many use the 'free to air' just for the noise. Cannot tell for sure if there is any gain of power.
're-cycling' one gives you better-lower gas emission {I believe}.
Nick
Dump valves are a way of trying to avoid back pressure to the turbo (caused by the throttle closing suddenly) from stalling the turbo, which causes turbo lag as it speeds up again.
Atmo dump valves release the excess pressure to the air creating the whoosh noise but which leaves raw excess fuel through into the exhaust causing potential explosions / flames. Atmo dump valves tend to allow the turbo speed to be maintained and hence less lag.
Recirculating valves dump the excess pressure back into the exhaust side of the turbo thereby weaking the potentially explosive gases but with a downside that turbo spin speed can be impacted.
Under most road uses a recirculating valve is ideal as acceleration generally is smooth and emissions are important. In performance cars, eg. rally cars lots of on / off acceleration is more prevalent and emissions matters very little but minimising lag is critical.
Regardless of the type of valve, an after market performance unit will perform better than the cheap plastic device fitted to the Q4.
Well that's how it was explained to a non-techie like me.
Recirculating valves dump the excess pressure back into the exhaust side of the turbo thereby weaking the potentially explosive gases but with a downside that turbo spin speed can be impacted.
I have read this before too, but AFAIK, and willing to be corrected, the the excess pressure is actually dumped in to the pipe that connects from the air box to the side of the turbo - not the exhaust :? :?
I will have to go and do some more reading then. Since putting a atmo dump valve I do flames out of the exhaust which I didn't before. Fortunately with only 1 box and no cats there is little likelihood of damage.
cuore_sportivo_155
23-05-07, 18:15
Recirculating valves dump the excess pressure back into the exhaust side of the turbo thereby weaking the potentially explosive gases but with a downside that turbo spin speed can be impacted.
I have read this before too, but AFAIK, and willing to be corrected, the the excess pressure is actually dumped in to the pipe that connects from the air box to the side of the turbo - not the exhaust :? :?
Q4fatboy is correct, that's how it should be. But that doesn't necessarily mean it always is though...
cuore_sportivo_155
23-05-07, 18:15
Recirculating valves dump the excess pressure back into the exhaust side of the turbo thereby weaking the potentially explosive gases but with a downside that turbo spin speed can be impacted.
I have read this before too, but AFAIK, and willing to be corrected, the the excess pressure is actually dumped in to the pipe that connects from the air box to the side of the turbo - not the exhaust :? :?
Q4fatboy is correct, that's how it should be. But that doesn't necessarily mean it always is though...
Recirculating valves dump the excess pressure back into the exhaust side of the turbo thereby weaking the potentially explosive gases but with a downside that turbo spin speed can be impacted.
I have read this before too, but AFAIK, and willing to be corrected, the the excess pressure is actually dumped in to the pipe that connects from the air box to the side of the turbo - not the exhaust :? :?
Q4fatboy is correct, that's how it should be. But that doesn't necessarily mean it always is though...
No, He is not correct. Recirculating dump never contact exhaust side. Recirculating dump push air back in inlet side of turbo. Warm air.
When you use antilag system like rally cars do. Then your engine pushing air fuel mixture to turbo and it explodes there and turbo keep spinning all the time and you donīt lose any power, when you are shifting up (or down). They are two different system.
arjunior45
23-05-07, 21:12
No, He is not correct. Recirculating dump never contact exhaust side. Recirculating dump push air back in inlet side of turbo. Warm air.
When you use antilag system like rally cars do. Then your engine pushing air fuel mixture to turbo and it explodes there and turbo keep spinning all the time and you donīt lose any power, when you are shifting up (or down). They are two different system.
I agry, ALS {antilag or bang-bang system} is a different system from the recirculating valve. Has to do with the maps {in the eprom} in decelaration.
Any way, what AlfaJack asked was if there is a performance difference between "re-circulating dump valve" and a "free to air" one I believe not in a race car. Does anyone has the experience with the "free to air" valve? Was there any gain in power?
In my opinionit makes no difference.
Release the pressure out in the open or back in to the air inlet.
The only difference is the sound.
And because the after market blow of valves are way much better than the originale crappy Bosch valve..... you want to replace this ;)
Besides this, if you buy the correct blow of valve, you van adjust the reaction of the valve with different pressure springs.
Greetings,
Marc
Thanks all, im tempted by a free to air one now just for a bit more noise :D
Thanks all, im tempted by a free to air one now just for a bit more noise :D
It's fun ;) You wil get response from people in your surrounding 8)
It's fun to play with :D
Groetjes,
Marc
Juan AR155Q4
24-05-07, 00:03
In my opinionit makes no difference.
Release the pressure out in the open or back in to the air inlet.
The only difference is the sound.
And because the after market blow of valves are way much better than the originale crappy Bosch valve..... you want to replace this ;)
Besides this, if you buy the correct blow of valve, you van adjust the reaction of the valve with different pressure springs.
Greetings,
Marc
This is correct, I have the original one free air, and itīs just a pshhhh of difference. No gain or lose of performance.
Makes difference in cars with MAF, not with MAP.
cuore_sportivo_155
24-05-07, 13:19
No, He is not correct. Recirculating dump never contact exhaust side. Recirculating dump push air back in inlet side of turbo. Warm air.
I stand corrected. The Dump valve is on the compressor side of the turbo, bypassing the turbine there...
cuore_sportivo_155
24-05-07, 13:23
Hmm, got an error while posting so tried again...
Technical NUMBSKULL !
I will repeat 100 times as punishment.
What I do know, is after swapping to an Atmo dump valvle I would not change back. I love the sound it makes and it can be really fun to watch pedestrians jump as it dumps the air out !!!
Mucho fun
Im with fatboy, PUT the noisey one on,,, you know you want to :D
155'Ringman
11-06-07, 13:09
Think I'm gonna blank off the other pipe and turn the re-circ thru 90 degrees to try it as an atmo for a while.... (Mine's already a Bailey aftermarket valve) :P
:) its all the same if the standard unit can take the presure your turbo generates( dosent leak) lave it be. In rally cars whit ilne 4 engines(mitsu ,toyota) you blank it off , at subaru engines you tend to leave it be because it ''airs'' the IC and it cools it down. Regardin stock cars it makes no difference ,engine makes flames because there is to rich mixture whit the lack of the air that should be forced in normal operation . Hope you understand my shitty engilsh.
I have now taken out my Tas re-circ valve and replaced with this : http://static.marktplaza.nl/images/1/25/2639225.jpg
Much nicer noise - me happy - and it was only ?30 froma friend, It used to be on his Cosworth - but its the wrong colour for his new engine bay :D
...any chance of some pics Jack, to show me what mine should look like when I get my arse in gear and fit it! ;)
wrinx
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions Inc. All rights reserved.