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I doubt that it has any real advantage when used for boost pressures of around one bar. It might be needed for higher boost pressures. Perhaps it has a stiffer spring! So it depends on your application.
The description on their web site implies that the the HP valve will flow a bit faster when the set point pressure is reached. This implies that the wastegate will be opened with less delay once the sete point pressure is reached that will open the ball-spring valve. A longer spring could have a lower spring rate which would allow the 'check' valve to open more compared to a stock valve. This might indeed help with 'spiking', which is worse with slower reponse control systems.
Bleed valves anticipate the set point and start opening the wastegate before the boost seet point is reached, which causes slow boost rates. The ball-spring units do not open the wastegate soon enough which causes spikes. The ball-spring units get worse, spike wise with longer signal paths. IE long hoses. So beeding these from the manifold adds another delay creating a much worse situation. The shortest distance is to feed the MBC from the compressor housing hose barb, but this then only controls pressure at that location, and at hi rmps and high cfms the pressure drops in the IC and pipes reduces boost at the manifold and pressures and torque taper off.
So a good solution is not really at hand. There are intermediate pressure tap locations which are better compromises, but still a compromised situations. That is why I am working on a hose clamp installable pop off valve to eat the spikes. Alternatively, the wastegate adjustement can be eased off to make the wastegate actuator response faster. This has definate theoretical merit. I also drilled out the inlet restrictor in my TurboXS HP MBC to speed up the wastegate actuator slew rate once the ball-spring opens. One could also apply a needle valve bypass to the MBC either up stream or down stream of the vent orifice. This could apply a preload to the wastegate so that is would be able to react faster to the MBC opening. Due attention should be then also paid to reverse flow possibilties and check valves etc. Perhaps I could get my Hallman MBC out or retirement and put it in in parallel, also with a needle valve at a softer setting to 'prime' or stage the actuator for the TurboXS action. So you see that we are now seeking a behaviour somewhat intermediate to the bleed valves and ball-spring units.
So the main MBC tapped at the manifold with a staging MBC feed from the compressor housing. Hmmmm Turbo feed forward compensator. This might eliminate most spikes.. have to see, and it would provide the least boost taper of any arrangement, as that would be then the result solely of the turbo characteristic and IC and piping characteristic. Got to try that. The seconary MBC will need a needle valve to limit its flow so that it will only create a limited preload pressure. So adjustment could be tricky, as there will be two adjustement variables. Note that the Hallman unit has an inline vent orifice, and that this would not be used. If this works, then two stage integral units might be developed, but the optimal arrangement would still have two pressure feed sources. Perhaps the secondary unit would be better as a basic pressure regulator.
The secondary feed forward MBC would be set high and then backed off until it stated to reduce the boost pressures.
Alternatively, on a NG900 T5 one could instead or in conjuction with other things, add some resitance to the MAP sensor to provide more head room with the fuel cut pressure. But once one starts doing that I suspect there would be motivation to go to higher boost pressures and the orignal issues would come back to roost.
posted by 208.24.179...
, Fri, 25 Jan 2002 12:21:30
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