Has anyone modified their RS2 by putting a dump valve in?
I took my car in yesterday (need the turbo serviced and the throttle pipe replaced...) and there was another RS2 (noggy blue) in the garage with a dump valve mod. I understand that the idea is to keep the turbo spinning when the throttle closes (ie gear changes), thus reducing lag. The mechanic didn't think it made much difference except for a impressive wooshing sound replacing the wastegate whistle, and the potential to take years off the life of the turbo.
Anyone done this, and with what effect?
Dump Valves
the RS2 uses a closed loop system. I.E. all air is kept inside the loop once passed the MAF. The DV which is fitted as standard is like a dump valve except instead of letting the air to atmosphere it put it back into the inlet of the turbo. This is potentially better for the turbo's spooling since the pressure that is built up by the turbo is shot back into the inlet of it momentarily helping to keep it spinning. As does the wastegate on gear changes because it bypass's exhaust gas past the turbo allowing it to keep spinning then exhaust gas gets redirected back thru the hot side when the wastegate spring closes again.
By fittin a dump valve you will get a woosh noise but potentially it will confuse the ECU and it will run richer since it will think there is more air in the engine that what there actually is.
Personally i would just replace the DV with a standard 710N item as used on alot of the newer turbo engines, this performs better than the original DV for the car and it is also about £15 cheaper from a dealer.
Greg
By fittin a dump valve you will get a woosh noise but potentially it will confuse the ECU and it will run richer since it will think there is more air in the engine that what there actually is.
Personally i would just replace the DV with a standard 710N item as used on alot of the newer turbo engines, this performs better than the original DV for the car and it is also about £15 cheaper from a dealer.
Greg
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quattroturbo
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Wastegates, Diverter Valves and Dump Valves are different items not to be confused with each other.
Wastegate regulates boost pressure but its duty cycle is controlled by the Wastegate Frequency Control Valve (the little brown plastic tee piece with a connector going to it next to DV). The spring does not control boost pressure unless Superchimps have fecked with it. Tightening the spring down will increase the point at which the wastegate cracks open, and hence increase boost pressure, but this is not clever. Tightening the spring down will mean that your ECU is unable to go into limp mode if it detects too much unmetered air entering the engine (boost leak). The turbo will damage itself if the boost leak is large because it will be working harder to generate the required boost pressure if the ECUs safety features can't intervene.
DV is an abbreviation which can stand for Dump Valve or Diverter Valve but they are both different articles although they operate by the same principle. When you close the throttle on gear changes a vacuum is created in the inlet manifold. It's this vacuuum that open the DV allowing it to do its job. DVs prevent compressor stall on gearchange as the throttle closes. Compressor stall is bad news for turbos too. DVs are passive devices which keep the turbo spining by either venting the bosted air or creating a closed loop of air.
Dump valves are 'vent to atmosphere' devices which give a loud woosh on gear change when it vents air from the inlet tract. Diverter valves are quieter because they keep the air in the inlet tract in a closed loop without venting it. I use a Forge DV006 diverter valve which is the recirculating variety. It is more relaible and easily serviceable than stock but as Greg states, the stock valves are cheap as chips. You should NOT use a 'vent to atmostphere' DV on a car with a MAF....
Changing DVs for aftermarket is not a performance modification. In most cases the aftermarket DVs have pistons inside. Stock DVs use a diaphragms which are prone to splitting. Split diaphragms are a result of the valve exercising and increased boost pressures are unlikely to cause them to fail quicker.
Lee
Wastegate regulates boost pressure but its duty cycle is controlled by the Wastegate Frequency Control Valve (the little brown plastic tee piece with a connector going to it next to DV). The spring does not control boost pressure unless Superchimps have fecked with it. Tightening the spring down will increase the point at which the wastegate cracks open, and hence increase boost pressure, but this is not clever. Tightening the spring down will mean that your ECU is unable to go into limp mode if it detects too much unmetered air entering the engine (boost leak). The turbo will damage itself if the boost leak is large because it will be working harder to generate the required boost pressure if the ECUs safety features can't intervene.
DV is an abbreviation which can stand for Dump Valve or Diverter Valve but they are both different articles although they operate by the same principle. When you close the throttle on gear changes a vacuum is created in the inlet manifold. It's this vacuuum that open the DV allowing it to do its job. DVs prevent compressor stall on gearchange as the throttle closes. Compressor stall is bad news for turbos too. DVs are passive devices which keep the turbo spining by either venting the bosted air or creating a closed loop of air.
Dump valves are 'vent to atmosphere' devices which give a loud woosh on gear change when it vents air from the inlet tract. Diverter valves are quieter because they keep the air in the inlet tract in a closed loop without venting it. I use a Forge DV006 diverter valve which is the recirculating variety. It is more relaible and easily serviceable than stock but as Greg states, the stock valves are cheap as chips. You should NOT use a 'vent to atmostphere' DV on a car with a MAF....
Changing DVs for aftermarket is not a performance modification. In most cases the aftermarket DVs have pistons inside. Stock DVs use a diaphragms which are prone to splitting. Split diaphragms are a result of the valve exercising and increased boost pressures are unlikely to cause them to fail quicker.
Lee
1995 S2 Avant with a few mods
Oh yeah, Wastegates do not 'whistle'. Turbos whistle when they are on the way out! Wastegates chatter on gear change whn you start pumping up the pressure.
The S2 and RS2 engine has a Diverter Valve as standard of the diaphragm variety.
A split diaphragm on a stock valve is effectively a boost leak which could cause your turbo to work harder. The splits are often not big enough to cause the ECUs 'limp mode' but they are damaging to the turbo. A split DV diaphragm will not be a great problem unless you are running high boost pressures (turbo model dependant). This was the main reason why I changed to a piston valve...it is less likely to leak and my car has been custom remapped.
Finally, my Forge Diverter valve does make a wooshing sound on gear changes which was more pronounced when I fitted a K&N. I only really hear it when I change gear at about 3.5k revs when my boost pressure is around 1.4bar. WOOOSH.....
The S2 and RS2 engine has a Diverter Valve as standard of the diaphragm variety.
A split diaphragm on a stock valve is effectively a boost leak which could cause your turbo to work harder. The splits are often not big enough to cause the ECUs 'limp mode' but they are damaging to the turbo. A split DV diaphragm will not be a great problem unless you are running high boost pressures (turbo model dependant). This was the main reason why I changed to a piston valve...it is less likely to leak and my car has been custom remapped.
Finally, my Forge Diverter valve does make a wooshing sound on gear changes which was more pronounced when I fitted a K&N. I only really hear it when I change gear at about 3.5k revs when my boost pressure is around 1.4bar. WOOOSH.....
1995 S2 Avant with a few mods
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