turboaudi
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sounds ****** awesome , but the car idles like a sack of **** now, i take it you need the proper vag ones or is there something you can do to help it idle properly
fitted a baileys dump valve today
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Randomjim
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billybravo
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Because the float just bounces letting out too much air plus you will not pass a MOT with it either, how do I know I learnt the hard way.
turboaudi
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docurley said:Because the float just bounces letting out too much air plus you will not pass a MOT with it either, how do I know I learnt the hard way.
really? must be p1ss weak then, do you mean "bounce" as in when driving? surely it only affects compressor charge at lift off throttle, still don't see how that would affect idle.
At idle you have no boost therefore the valve would do nothing, unless it works in a completely different way or is fitted incorrectly.
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There will always be some pressure in the system even at idle and what you see is the piston moving up and down with that little pressure which fugs up the idle, hence you need a twin piston which keeps it shut.
docurley said:
Dont want to rain on your parade but there is no pressure in the intake system at idle, in fact there would be the exact opposite, vacuum. so the piston on the BOV would actually be pulled tighter closed at idle.
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Whilst on the subject, what is the best dv to have then. had a go faster bits blow off valve, and put the original back on. Lost to much power and kinda got fed up with the noise, sounded like air brakes on a bus lol. Gonna get one with my decat next month 
A4Quattro said:
The only vacuum a car creates at idle is in the inlet manifold due to the closed throttle butterfly, this vacuum opens the dump valve not closes it. Because you are then bleeding metered air into the atmosphere this causes the car to run rich and as docurly mentioned this causes emmisions problems
A vacuum in the rest of the intake system (outside the inlet manifold) would mean that the intake was blocked whish it isn't, its free flowing
Sorry but you are wrong!
There is only positive pressure in the intake manifold when the turbo is producing boost, which is does not do at idle.
A vacuum cleaner is free flowing but there is a vacuum at one end.
The engine is drawing in air and it does this by creating a lower pressure than is around it (1 atmosphere or 1 BAR or 15psi) all piston engines work in this manner whether they have a throttle flap or not, if you want proof find an old diesel cement mixer, they don't have turbos, and put your hand over the intake when its running, you'll soon experience the vacuum.
There is only positive pressure in the intake manifold when the turbo is producing boost, which is does not do at idle.
A vacuum cleaner is free flowing but there is a vacuum at one end.
The engine is drawing in air and it does this by creating a lower pressure than is around it (1 atmosphere or 1 BAR or 15psi) all piston engines work in this manner whether they have a throttle flap or not, if you want proof find an old diesel cement mixer, they don't have turbos, and put your hand over the intake when its running, you'll soon experience the vacuum.
a4singh
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what size as in psi is the standard turbo on a standard b5 a4. im not too sure like ive heard ppl say 10 pound turbos etc but i dotn have a clue what it all means.... anybody have an idea? sorry to post it here, but seen as though we are on the topic of turbos etc. thought it might be more approriate.
n sorry if im takling nonsense.
n sorry if im takling nonsense.
PhilR said that there is a vacum at idle i the inlet mani?
My boost gauge which is piped into a vacum hose on the inlet manifold only read negative boost on idle. Then only goes to positive boost when the turbo has kicked in.
My boost gauge which is piped into a vacum hose on the inlet manifold only read negative boost on idle. Then only goes to positive boost when the turbo has kicked in.
a4singh said:
Do you mean what Psi the turbo boosts too?
Mine runs about 0.5 bar, not sure of the conversion figures but for standard that is about right.
Obviously if the car is chipped then it will run at a higher level, same thing of a larger turbo is fitted it will prob run at higher Psi.
(PS god bless Google tool bars spell checker)
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Negative or positive flow, there is something there that is causing the DV piston to bounce when idle and it not doing it its self on a single piston DV.
A4Quattro said:
Yes i agree that there is a vacuum created on the induction stroke, but this vacuum is not experienced at any great (or useful) level within the intake system due to its unrestrictive nature
A vacuum cleaner works by restricting the airflow to the pump or motor (small diameter pipes or venturi effect) exactly the same way which a vacuum is created in the inlet, ie the engine wants more air than the flap will allow at idle
Small pipes and restrictors (other than throttle butterfly) are not found in an engine intake system so there is minimal vacuum produced in the intake pipework
In the cement mixer scenario, by placing your hand over the intake you are essentially doing the same thing as closing the throttle on a petrol engine.
Finally go and find a diesel which uses intake system vacuum pressure for the brake servo, they dont because due to the negligable vacuum produced they can't, you also cant have a conventional dump valve on a diesel for this reason as there is insufficient vacuum produced to open it
