Dumpvalve - warning (it would seem!)
14 January 2002, 03:32 PM
#31
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Hold on, I see what you mean now ...
You are thinking: does the air go back out (passed the MAF again) out of the airbox and then out of the filter into the open air ?
The turbo will still be spinning at say 50.000 RPM so it will probably still suck enough air in to prevent that.
I think
You are thinking: does the air go back out (passed the MAF again) out of the airbox and then out of the filter into the open air ?
The turbo will still be spinning at say 50.000 RPM so it will probably still suck enough air in to prevent that.
I think
14 January 2002, 03:40 PM
#32
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Yeah, but the air that is being sucked in is also being blown out of the same place, so I think that the net effect will be air going back out of the induction system.
I also think there may be anti-lag benefit by using a valve that does not just let go totally when there is vacuum. But rather keeping a bit of pressure in the intercooler etc. Although this could equally apply to well designed re-circ valves.
James
14 January 2002, 03:48 PM
#33
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My knowledge is fairly limited but I thought it dumped it through the engine... as the throttle is closing...
When I swapped from a dump to atmos to a re-circulating dump valve the from boost to closed throttle became smoother and less of a decelleration... it used to feel like you hit something if the throttle setting was in a particular place and on boost and you took your foot off as the decrease in the inlet went from high pressure to no pressure..
I believe that as the throttle closes which is reletively slow compared to engine rpm that the pressure of the air goes through the engine with the relevant mixture added etc... so the engine decreases slightly smoother... so Turbo spinning slows down in relation to the engine rpm etc..
I could be wrong mind...
When I swapped from a dump to atmos to a re-circulating dump valve the from boost to closed throttle became smoother and less of a decelleration... it used to feel like you hit something if the throttle setting was in a particular place and on boost and you took your foot off as the decrease in the inlet went from high pressure to no pressure..
I believe that as the throttle closes which is reletively slow compared to engine rpm that the pressure of the air goes through the engine with the relevant mixture added etc... so the engine decreases slightly smoother... so Turbo spinning slows down in relation to the engine rpm etc..
I could be wrong mind...
14 January 2002, 04:00 PM
#34
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OK, the air will recirculate, and possibly do a few "loops" 
It might even push a bit of air out, but the net effect will probably be that there's temporarily no airflow round the MAF sensor (I wonder now if the sensor is directional ...)
With a vent to atmo you will blow away that air, suck in some more (turbo keeps spinning) and blow that away as well (for as long as the throttle butterfly is shut).
The net effect must be that you loose more measured air than with the recirc system. The richness/flames/pops & flat spots have been noticed time and time again.
It might even push a bit of air out, but the net effect will probably be that there's temporarily no airflow round the MAF sensor (I wonder now if the sensor is directional ...)With a vent to atmo you will blow away that air, suck in some more (turbo keeps spinning) and blow that away as well (for as long as the throttle butterfly is shut).
The net effect must be that you loose more measured air than with the recirc system. The richness/flames/pops & flat spots have been noticed time and time again.
14 January 2002, 04:05 PM
#35
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Jolly, not through the engine, but through the rather thick black pipe coming out of the BOV which connects to the inlet just before the turbo.
The dumpvalve opens because of negative pressure in the inlet manifold as opposed to the positive pressure after the turbo/before throttle butterfly. It's that pressure difference that acts on the BOV.
Sure, the slower you release the throttle, the less "heavy" the blow off effect will be.
The gerkyness you feel with a lot of aftermarket BOV's is because they open on a higher pressure difference, so you have the worst of both worlds: not enough protection of your turbo bearings, but pressure loss nonetheless.
The dumpvalve opens because of negative pressure in the inlet manifold as opposed to the positive pressure after the turbo/before throttle butterfly. It's that pressure difference that acts on the BOV.
Sure, the slower you release the throttle, the less "heavy" the blow off effect will be.
The gerkyness you feel with a lot of aftermarket BOV's is because they open on a higher pressure difference, so you have the worst of both worlds: not enough protection of your turbo bearings, but pressure loss nonetheless.
01 June 2002, 10:55 PM
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What about the HKS Super Sequential, which claims to be forced shut while under boost, and release only when it receives a vacuum signal when the accelerator is released?? I would think that since there is no chance in it leaking, and it slams shut as soon as throttle is applied again, it wouldn't affect the ECU much? I'm looking at getting this particular valve, but now I'm curious...
[Edited by StingerSK - 1/6/2002 11:01:27 PM]
[Edited by StingerSK - 1/6/2002 11:01:27 PM]
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