Discussion
As I was walking to the station this morning, an MR2 went past and there was the familiar dump valve noise when he changed gear.
Then I got thinking that it'd been absolutely ages since I'd heard a car with one fitted. They used to be everywhere a few years ago.
Did they die out with the Max Power generation?
Then I got thinking that it'd been absolutely ages since I'd heard a car with one fitted. They used to be everywhere a few years ago.
Did they die out with the Max Power generation?
Blank off and the resultant compressor stall sounds better IMO.
But with all the diesel rep mobiles around, there is little point in having a dump valve because you don't have a throttle and aren't therefore in danger of closing off the inlet manifold suddenly at high boost pressures, and stalling the turbo.
But with all the diesel rep mobiles around, there is little point in having a dump valve because you don't have a throttle and aren't therefore in danger of closing off the inlet manifold suddenly at high boost pressures, and stalling the turbo.
I think it depends, as Toltec says. Some engine management systems can use atmospheric dump valves (gives you the whoosh/hiss) and some use recirculating ones (doesn't so much).
I know with Saabs, the Trionic 5 engine management system which was used up to the GM 9-3 could take an atmospheric DV, but the newer Trionic 7 system has to have a recirculating valve. More modern and efficient systems tend to use recirculating valves.
I know with Saabs, the Trionic 5 engine management system which was used up to the GM 9-3 could take an atmospheric DV, but the newer Trionic 7 system has to have a recirculating valve. More modern and efficient systems tend to use recirculating valves.
s p a c e m a n said:
They're just a brilliant way to give your car a boost leak.
Doesn't that depend on how clever the ECU and the Air mass meter are at knowing that some of the air in the system has been "lost" as such?I ran a G60 with no boost return pipe which effectively makes the throttle body a dump valve because at closed throttle a large opening on the side of the throttle is opened and excess boost is bled out of it - it was so loud since a supercharger makes far too much boost at low revs the opening is always partially opened
Hence it was a short lived experiment not to be repeated but my childish side still loves the noise of FI
aka_kerrly said:
Doesn't that depend on how clever the ECU and the Air mass meter are at knowing that some of the air in the system has been "lost" as such?
I guess that depends on whether the limiting factor in your engine's performance is the amount of boost the turbo can provide or something else. aka_kerrly said:
s p a c e m a n said:
They're just a brilliant way to give your car a boost leak.
Doesn't that depend on how clever the ECU and the Air mass meter are at knowing that some of the air in the system has been "lost" as such?
Fastdruid said:
neil1jnr said:
The recirculator valve in my Fiesta ST makes a fair bit of noise since getting the MP215 kit.
I can only hear mine (Mondeo 2.5T) with the windows open. 
However my Dad fitted a dump to atmosphere dump valve years ago on his old Impreza WRX which was promptly removed in a few weeks as it was leaking boost and ruining the performance, granted it was a cheapo dump valve so that's not surprise
Edited by Samjeev on Tuesday 5th August 13:48
MGZRod said:
My silvia has been 'pigeoned', blocked it off so no re-circ or dump valve. Makes silly noises and keeps me amused 
Compressor stall. So takes longer to re spool everytime you close the throttle and you may be damaging the cold side turbine blades and the bearings by forcing it to try to rotate the opposite direction? For the sake of a silly noise.
(I have done the same before on my Impreza...)
Its true, very rarely hear them nowadays... a few reasons I think:
1. Many of the cars that had them fitted had carbs (R5 GT Turbo) or MAP based EFI with no mass airflow sensor (cossi) - so didn't cause a problem with fuel metering
2. Most cars now do have very sensitive mass air flow metering, thus will royally screw up the amount of fuel injected - unless you are looking at a racing car which will probably be MAP based rather than MAF and can run atmos valves no problem.
3. Fashion - they are still about but make a "tweet" noise not a "hiss" noise - HKS SSQ etc
Recirc vs Atmos
From a purely performance point of view, atmos is better, recirc are fitted to factory cars because of the noise and above fuel metering issues.
Why are they better? Why suck up a load of air that's already been heated once with the recirc? Better to compress some nice new cold air.
There is absolutely NO performance benefit to "blowing" the recirc outlet into the compressor inlet as suggested by some tuning companies "back in the day"
(of course a leaking valve is a leaking valve, recirc or atmos its going to cause the same problem, which probably wont be less boost pressure, but a harder working turbo to compensate for the leak - and hence, more heat and probably more lag).
1. Many of the cars that had them fitted had carbs (R5 GT Turbo) or MAP based EFI with no mass airflow sensor (cossi) - so didn't cause a problem with fuel metering
2. Most cars now do have very sensitive mass air flow metering, thus will royally screw up the amount of fuel injected - unless you are looking at a racing car which will probably be MAP based rather than MAF and can run atmos valves no problem.
3. Fashion - they are still about but make a "tweet" noise not a "hiss" noise - HKS SSQ etc
Recirc vs Atmos
From a purely performance point of view, atmos is better, recirc are fitted to factory cars because of the noise and above fuel metering issues.
Why are they better? Why suck up a load of air that's already been heated once with the recirc? Better to compress some nice new cold air.
There is absolutely NO performance benefit to "blowing" the recirc outlet into the compressor inlet as suggested by some tuning companies "back in the day"
(of course a leaking valve is a leaking valve, recirc or atmos its going to cause the same problem, which probably wont be less boost pressure, but a harder working turbo to compensate for the leak - and hence, more heat and probably more lag).
Edited by sl0wlane on Tuesday 5th August 14:13
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