Quote:
Originally Posted by dtm
Sorry....
The dump/re-circulation valves are operated by vacuum, not boost, so that doesn't make all that much sense. On the other hand those valves might not be venting enough of the backed up air, and can cause some turbulence, hence the flutter sometimes felt.
The location of the DV (for me and the way I understand this engines) is not all that important. That being said, it is a strange place to put one. I will try to explain myself.
The main purpose of the DV is to vent air that as been cut of from the engine and doesn't have anywhere else to go, this is, your one the gas putting pressure on the engine, and then your of the gas, and the engine does not need/receive that pressure, so it has to be redirected either back to the inlet port of the turbo or to the atmosphere.
That lift of the gas pedal creates vacuum that opens the DV. It should work any where in the circuit between the turbo and the inlet manifold, because it is releasing pressure of the system, and that is it's purpose.
My t4 is running between 16 and 21 PSI (pick boost) and still haven't had any problems with the original re-circulation valve. Mine does not drop boost climbing through the revs, but gets boost in the higher gears.
Losing boost above certain RPM is strange, but could have something to do with the way the BCS is setup by the remap. There is a sure way you can test that, but you will need to ask someone for a MBC and set it up for 1.1BAR and see how it handles the boost above 4500rpm.
Good luck
Daniel
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I don`t know who you aimed your post at as you don`t say but i will answer!!
Standard Dump/Recirculating Valve
Yes, the standard dump/recirculating valve is operated by vacuum, but what does it operate??
It operates the diaphragm type valve + a spring that shuts it again, within the dump valve to let boost escape that the turbo does not need as the vacuum caused to operate it is because the throttle has been closed.
Because our cars are 12 to 15 yrs old the spring which shuts the valve gets weak because of the temperatures involved on the turbo and the diaphragm gets worn and can split or wear all this can let the boost past the valve especially when one has a re-map or adjusts the wastegate to put up the boost to a degree well above standard. This is why the boost will shoot up to near max. what you set it at but then will quickly get less because the worn valve cannot hold the extra boost which is nothing to do with the vacuum which operates the valve. Although the boost will go down the vacuum hose from the inlet manifold to help keep shut the valve the size of hose is overcome by the size of the large orifice inside the turbo valve directly against the diaphragm.
I expect you know this already but know you can understand why owners replace these items and also why Forge make them.....the replacement Forge one is piston operated and not by diaphragm so can hold the high boost more easily with virtually nothing to wear.
When getting a turbo motor all pipes and hose and also valves and actuators should be checked for good operation so that you get the boost when you want it and of course all of it.
The TCV/BCS adjusts boost as the revs. go up so looking after the engine, so this has to be in good order also the actuator valve works similar to the recirculating valve but with a boost hose going to it, it still has the spring and rubber diaphragm inside which once again get weaker and wear with the amount of heat the turbo generates and also being 12 to 15 yrs old become unreliable boost waves all over the place.
This is the main reason an MBC should not be used until the actuator is giving it`s best. Fitting an MBC to an actuator that gives you boost fluctuating so much will only increase the chances of damage to the engine through large uncontrolable spikes as the ECU is not connected to do otherwise.
You may be lucky with your turbo being replaced or whatever but these things must be checked to get a reliable boosting and safe motor.
You see all the time on here boost problems of many descriptions which all mainly come down to the same thing the owner justs gets in his cheap years old T4 and expects it to go well, but sadly it doesn`t.