What is a dump valve for? Do I need one?
Discussion
I've heard Scoobies and the like making that hissing noise from the dump valve. Just been on Youtube and seen the procedure for fitting one to my car's Mazda 2.3 DISI engine. Apparenlty accorind got the vid my car has a plastic one - it doesn't make the hissing sound.
What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
They are there to stop compressor stall on turbos. There are 2 types ones that dump to atmospher (make the hissing noise) and those that recirculate the air into the engine (make no noise).
They both do the same job and do it just as well as each other. The only difference is one makes a noise the other does not. On a car like a Supra or Skyline where it has a large 6 pot engine the sound of a dump valve isnt missplaced however on a Golf GTI it is a bit chav IMO.
They both do the same job and do it just as well as each other. The only difference is one makes a noise the other does not. On a car like a Supra or Skyline where it has a large 6 pot engine the sound of a dump valve isnt missplaced however on a Golf GTI it is a bit chav IMO.
Also you really dont want to be fitting a vent to atmosphere one, the ones that make a loud hiss, if your car has a stock recirc one and it uses a MAF. All these idiots fit them to imprezas, and then wonder why they get running problems because the ecu thinks its missing air etc.
Personally i binned mine, fitted a blanking kit and with an induction kit get a nice chatter sound, and no more bloody running issues.
Personally i binned mine, fitted a blanking kit and with an induction kit get a nice chatter sound, and no more bloody running issues.
Very very few road cars generate the levels of boost which might cause damage to the turbo on a gear change that the standard recirc valve cant deal with. 99% of cars fitted with noisy aftermarket dump valves have them fitted because the owner likes the sound. I had them on my Cosworths. The term Chav didn't exist back then, however I'm sure that I would have been labelled as one if it had.
wildcat45 said:
How would a compressor stall? I guess some sort of back flow - Ie the wind going into the turbine blades the wrong way?
Dan
Yes. Imagine a turbo car at high revs and wide open throttle. The turbo is generating a lot of boost and loads of air is flowing into the engine. The owner now causes the engine to dramatically drop revs (e.g. lifts the throttle) where is all that air going to go? The turbo is still spinning at high revs, and can't slow down very quickly so is still generating a lot of boost but now that air can't get into the engine. With no dump valve all that air would start travelling back toward the turbo, causing it to stall. That would cause wear to the turbine blades and make the turbo slow down (so you'd get more turbo lag next time you put your foot down).Dan
I think that's right, anyway...i'm sure someone will correct me if I'm wrong.
wildcat45 said:
How would a compressor stall? I guess some sort of back flow - Ie the wind going into the turbine blades the wrong way?
Dan
Basically. The usual example is when you change up a gear - the turbo is spinning fast and producing high boost, and you suddenly shut the throttle plate. All that air has nowhere to go, so something has to give - a turbo will eventually stall, a centrifugal supercharger (which is coupled to the engine and can't stall) will see air flowing backwards through the compressor - called surge in that case IIRC. Dan
The valve vents off the high pressure air, allowing the compressor to keep spinning, so you don't have to wait for it to spin back up when you open the throttle again.
wildcat45 said:
Yes I was thinking it was a bit chav. So my car - being a turbo - will have one but its the silent type that recircs into the engine.
How would a compressor stall? I guess some sort of back flow - Ie the wind going into the turbine blades the wrong way?
Dan
Turbo stall or LAG is an often mistaken thing.How would a compressor stall? I guess some sort of back flow - Ie the wind going into the turbine blades the wrong way?
Dan
What it isn't is boost threashold. This is a point in the rpms were the turbo will make boost. In a petrol engine that could be 2000rpm or for a big turbo 3500rpm, sort of thing. This is not lag.
Lag comes after a stall period. 2 things contribute to it. In a petrol engine you have a throttle plate in the throttle body. When you lift off the gas this plate closes and essentially traps high pressure air between the TB and the turbo. This high pressure air will help to slow the rpm speed of the turbo impeller. When you accelerate again there is a lag before the turbo starts spinning fast enough to again make boost and a lag while it pressurises the system.
A dump valve or blow of valve (BOV) as some call them releases this high pressure air when you close the throttle. A "to atmosphere" BOV makes the loud noise. Recirculating ones are a lot quieter or silent, although run enough boost they will become noiser. These recirc ones direct the high pressure air back into the intake but on the other side of the turbo. Some claim this helps to spool the turbo faster, but I suspect most likely not, partly due to losing the pressure in doing this and how long you may have the throttle closed for.
On high boost application most people run to atmosphere setups. Not exactly sure why, thing its easier to mange, safer and better to tune.
Other causes of LAG and stall are the reduction of exhaust gas flow. When you let off the gas the exhaust gas flow rate drops rapidly, this means it doesn't spin the turbo as fast and when you open the throttle again you get the lack of the gas flow increase, spool to generate boost from the turbo and lag to pressurise the system.
Diesel engines don't have a throttle body or throttle plate, these don't suffer the trapped high pressure intake air that petrol engines do. So dump valves don't work on a diesel and have no use if someone bodges on onto a diesel engine.
I believe LAG is primarily caused by reduce exhaust gas flow. ALS (anti lag systems) like the "bang bang" used by WRC cars target this area.
Lastly, don't confuse "wastegates" on a turbo. Many like Clarkson get these muddled up with dump valves. A wastegate bleeds exhaust gas on the hot side of the turbo to control the amount of boost the turbo makes and to prevent overboosting.
Rotary Madness said:
Personally i binned mine, fitted a blanking kit and with an induction kit get a nice chatter sound, and no more bloody running issues.
Which is the sound of pressurised air forcing its way back past the compressor wheel - the whole point of a recirc valve in the first place.300bhp/ton said:
[On high boost application most people run to atmosphere setups. Not exactly sure why, thing its easier to mange, safer and better to tune.
Partly because you're venting the compressed ( hot ) air out of the inlet tract. That hotter compressed air would have to be cooled even more than normal so it avoids a heat build-up Shropshiremike said:
300bhp/ton said:
[On high boost application most people run to atmosphere setups. Not exactly sure why, thing its easier to mange, safer and better to tune.
Partly because you're venting the compressed ( hot ) air out of the inlet tract. That hotter compressed air would have to be cooled even more than normal so it avoids a heat build-up http://www.youtube.com/watch?v=VbNxugO-uf0
wildcat45 said:
I've heard Scoobies and the like making that hissing noise from the dump valve. Just been on Youtube and seen the procedure for fitting one to my car's Mazda 2.3 DISI engine. Apparenlty accorind got the vid my car has a plastic one - it doesn't make the hissing sound.
What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
No you do not need a dump valve ,they`re for DICKS only .What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
hot metal said:
wildcat45 said:
I've heard Scoobies and the like making that hissing noise from the dump valve. Just been on Youtube and seen the procedure for fitting one to my car's Mazda 2.3 DISI engine. Apparenlty accorind got the vid my car has a plastic one - it doesn't make the hissing sound.
What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
No you do not need a dump valve ,they`re for DICKS only .What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
hot metal said:
wildcat45 said:
I've heard Scoobies and the like making that hissing noise from the dump valve. Just been on Youtube and seen the procedure for fitting one to my car's Mazda 2.3 DISI engine. Apparenlty accorind got the vid my car has a plastic one - it doesn't make the hissing sound.
What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
No you do not need a dump valve ,they`re for DICKS only .What are they for? Whats the advantage? Surely that hissing noise is escaping pressure which could be better used being converted into power.
Or is it just a chav thing that is of no use.
If anyone could explain, I'd be grateful.
Cheers
Dan
wildcat45 said:
Cheers for the replies guys. The Mazda's staying stock then.
Dan
Good plan as far as the dump valve goes. If you want more poke from the 2.3 get a bit more air going in with a decent Cold Air Intake and get the gasses coming out a bit quicker with a freer flowing exhaust. These two things will give you 20bhp-ish on 98ron fuel. Add a mild remap and they easily put out 330bhp. It will also sound much nicer! Dan
These guys do some very nice mods for my MPS 6 so I am sure their tuning stuff for the CX-7 is just as good:
http://www.corksport.com/07-cx7/cx7-intake-exhaust...
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