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Discussion in 'A3/S3/Sportback (8P Chassis)' started by khalil, Jul 7, 2006.
has anyone fitted a dump valve on a 2.0 tdi
there is'nt any benefit by fitting one to a diesel,i believe?,a dump valve is only beneficial,because on a petrol engine,when the throttle valve is closed(when changing gear),the pressure build up will slow the turbo down,the dump valve will release this pressure,and keep the turbo spinning,
a diesel does'nt have a throttle valve,it just sucks air straight in to the combustion chamber,so when changing gear there is nothing,(throttle valve) to slow the turbo down.
So where does the air go when you are changing gear - when it is not needed in the cylinder - but the turbo carries on spinning?
into the other cylinders,it will slow it down a bit,but,on the petrol the sudden closure of the throttle is what slows down the turbo,there is nothing on the diesel that closes abruptly,other than the valves,and there are 4 or 8 inlets (4 cylinder)so the build up isnt as great as there will always be 1 or 2 valves open at any given time,
im probably not explaining it very well,but thats roughly why a dump valve will not realy work on the diesel.
well,i may have to eat my words,i just did a google and found some diesel dump valves,http://www.dervdoctor.co.uk/ although they work electronicallly,via throttle position etc.
Whether or not they work is another matter though
They are purely there to make the Chav 'Woooosh' noise, they do nothing for the performance of the engine other than probably make it worse.
This is a bad thing.....
I stongly advise against, unless you want to sound like a Chav......
Hmm. marketed for Chavs too:
"Our kits are the loudest available or your money back!"
LOL...Thank god someone mentioned chav!
as i thought at the start,a waist of time on a diesel,although they probably come in burbry(is that how its spelt),or with a free burbry scarf and cap.
Having said all that, I've noticed there is a "TISSSSSHHH" noise when you change gear, suggesting that the excess pressure is being blown off somewhere.
I've only heard it because a couple of times during the recent hot weather I've driven off with all the windows down. If you go full throttle in 2nd or 3rd and change up, it's very noticeable.
Yep, I've heard the same (sounds quick cool for a diesel!) - and more so since I've had mine chipped.
The pressure generated by the turbo has to go somewhere if you're not using it. It can't see how it can go into the other cylinders, as your foot is off the throttle and there is no need for it. So where does it go?
when your foot is off the throttle,the valves are still working,so are the pistons,it just wont be injecting diesel,there will be some pressure,but not as much as a petrol,because of the lack of throttle valve,im sure someone with a bit more knowledge of this will explain?.
no one buys a Dump Valve to add performance :lol: take a look at the Scooby boys !!
So, is a dump valve superfluous? Would the engine work just as well without one?
ahh many a debate about this on the Scooby Forums,
Basicly its suposed to keep the turbo spinning, so enabling faster gear changes and instant power back on the throttle.
On a petrol car, the dump valve releases the pressure which would otherwise hinder the engine and turbo on closed throttle by stopping the turbo from spinning due to high back-pressure. It also allows you to slow down - if you didn't release the pressure, the differential between either side of the throttle butterfly would be so great that the gas would bleed through. This would mean that when you take your foot off the gas, the car wouldn't react straight away and you may plough into a tree!
The main advantage of aftermarket dump valves (recirc ones rather than chav atmos ones) is that they have a quicker reaction time than oem units which helps reduce lag when you go back on the gas by keeping the turbo spinning faster and longer.
The VAG turbodiesels do have a pressure relief valve to avoid back-pressure but it doesn't work in the same way as a dump valve. I believe it's controlled by the ECU on a solenoid type arrangement.
We need a Turbodiesel engineer in here.....