as the title says, someone please explain it to me. seen a few shiney ones for sale in various places and always wondered what they do?! cheers
it controls a DV/Wastegate/blowoff/whatever you want to call it usually. once the turbo has reached its set pressure the actuator will open a valve to keep the turbo set at its nominal pressure. for example, my saab is a low pressure turbo. its top boost is set to around 6.5psi even though the T25 its got is capable of much much more than that. so once it reaches 6.5 psi, the actuator opens the wastegate and lets all excess pressure out.
ah i geddit, in a modern say 20vt engine it opens the waste gate at pre set pressure back into the system so the turbo spools up again quicker. aye?
well if the wastegate is open, the turbo is already at nominal pressure set by the actuator.. its just recirculating the pressure instead of bleeding it to atmosphere.. i would think. but dont take anything i say for gospel.. i know feck all about turbo's i'm just good at theory..
on a 20vt the n75 valve which is controlled by the ecu uses vacuum to force the actuator which opens the wastegate venting excess pressure into the exhaust stream. The level in which the n75 valve tells the actuator to open the wastegate is pre determined in the "map" on the ecu. the blow off or diverter valve vents excess pressure between the turbo compressor and the throttle butterfly when the throttle closes so that the built up pressure doesnt stall the turbo which is still spinning. On the vag 20v lumps the diverter valve vents this pressure into the intake to the turbo to improve throttle response. on engines with a blow off valve this pressure is blown out to atmosphere instead of to the intake to the turbo. theres reported problems with using blow off valves on the vag 20v management as the ecu doesnt expect to see the lost pressure to atmosphere. so its best to stick with the diverter. hope that explains youre question a bit, just a basic overview.
The actuator controls the wastegate, either internal or external one. http://www.youtube.com/watch?v=q-cNZWworNo you can see it on this opening the wastegate to allow the turbo to spin at a constant rate once the boost has reached a set amount.
The only thing I would add to this comment is that you can still have a dump valve (a.k.a. blow off valve or "that thing that make syour car go psssssssshhht") if you us ethe Forge DV - this vents excess air into the atmosphere AND into the inlet pipe, so as to not confuse the ECU.
but at the same time still vents pressure to atmosphere, so you gain noise and lets face it its not as good as a decent bov, but still loses intake pressure so your throttle response will suffer. Everyone i know that has had a bov or one of the forge splitter valves has went back to a forge dv. they are the best for the job, and if you want some noise then fit a decent induction kit.
I agree with your comment, although you can adjust the Forge splitter valve. A lot of it depends on how much boost you're running. If you've got a stock 1.8T with the VAG ECU running up to around 180bhp, you don't need one - the stock or Forge recirc valve is fine. From experience, if you're running higher boost and a non VAG ECU which doesn't need the MAF sensor, you don't need a recirc valve at all. Venting the excess boost to the atmosphere does stop the turbo from "stalling" when you're running the engine flat out on track.
^^^^ agreed, but there is a reason theres so many splitr valves in classifieds and ebay, theyre not as good as dv on stock management.
