Turbo Talk

[manback]

Hi,
im thinking about the whole MBC thing, but i just want some more information about the turbo in general. im bad with the abreiviations so it would be good if we could write the words to?




what are the 3 air line connectors on this picture.

i believe the bottom one is where the compressor housing pressure gets sent to the boost controller (BCS?)

The top connector is for the actuator which controls the wastegate.

These 2 connectors are used for the manual boost controller?

so whats the 3rd connector and where does the other end of the vacuum hose go to?


thanks.

[p fandango]

so whats the 3rd connector and where does the other end of the vacuum hose go to?

the 3rd one is the recirc valve, the other end of the pipe goes to the inlet manifold

[gmain1967]

If you are thinking of going down the MBC route, I can recommend it. I had been sceptical of them but after much reading, bought one and fitted it to my S70 T5 the other week. It made a massive difference, and is still running safe and consistent boost, with no spikes, and with the BCS still plugged in electrically, so as not to throw any warning lights.

[manback]

the 3rd one is the recirc valve, the other end of the pipe goes to the inlet manifold

And what's that for then?

[p fandango]

And what's that for then?

it does exactly the same thing as a dump valve. When you back off the throttle ie to change gear the turbo still continues to spin because of how well there balanced, the recirc valve opens & lets this unwanted boost out. A recirc valve puts it back into the system while a dump valve lets it out to the atmosphere

[Volvostorm]

And what's that for then?

It does the same job as a dump valve, it releases boost pressure when the throttle s closed, i.e changing gear.

It vents into the exhaust, while a dump valve vent to open, yes, you need it running a MBC

[manback]

It does the same job as a dump valve, it releases boost pressure when the throttle s closed, i.e changing gear.

It vents into the exhaust, while a dump valve vent to open, yes, you need it running a MBC

Now I'm confused. Mr. Fandango says it goes to the inlet manifold and you say it goes to the exhaust. Either way how does it know when to go off?

And surly its not going to the inlet
Manifold because that's where all the compressed air goes anyway.?

[Volvostorm]

Sorry, my mistake, that turbo does vent into the inlet,I was thinking of the wastgate

As for the valve, this might help explain things: http://en.wikipedia.org/wiki/Blowoff_valve

[p fandango]

how does it know when to go off?

the other end of the small pipe which connects to the recirc valve goes to the inlet manifold, when on power the positive manifold pressure pushes against the boost in the recirc valve keeping it closed. Once you let off the throttle the pressure drops in the manifold so there is nothing fighting the positive (wasted) boost pressure so it escapes

[nobananas]

I thought the recirc valve operated via vacuum pressure myself. When you close the throttle sharply (ie to change gear) the turbo is still spinning and producing boost but that boost is now hitting a closed throttle butterfly threatening to stall the turbo. When the throttle is closed you induce a vacuum in the intake manifold (caused by the engine effectively 'sucking' against a closed throttle butterfly). The recirc valve is connected to the inlet manifold by a rubber tube and the vacuum induced in the manifold at closed throttle pulls the diaphragm in the recirc valve back against it's pressure spring which uncovers a bypass port allowing the boost pressure to escape into the intake piping (the unpressurized pipe between the maf and the turbo inlet). All this happens in 10ths of a second of course.

[manback]

I thought the recirc valve operated via vacuum pressure myself. When you close the throttle sharply (ie to change gear) the turbo is still spinning and producing boost but that boost is now hitting a closed throttle butterfly threatening to stall the turbo. When the throttle is closed you induce a vacuum in the intake manifold (caused by the engine effectively 'sucking' against a closed throttle butterfly). The recirc valve is connected to the inlet manifold by a rubber tube and the vacuum induced in the manifold at closed throttle pulls the diaphragm in the recirc valve back against it's pressure spring which uncovers a bypass port allowing the boost pressure to escape into the intake piping (the unpressurized pipe between the maf and the turbo inlet). All this happens in 10ths of a second of course.

Good info.

If I remember right. There are 3 air pipes going to the unpressurised pipe. One at the top connects to the bcs. One connects to the oil breather system. I though the third one was the heated one that goes round the spark plugs on the engine cover/ rocker cover. And back to the pressure/vac tree between the idle contold valve and throttle body. So I don't see how pressure gets there unless it's always got a little bleed off!

[nobananas]

Good info.

If I remember right. There are 3 air pipes going to the unpressurised pipe. One at the top connects to the bcs. One connects to the oil breather system. I though the third one was the heated one that goes round the spark plugs on the engine cover/ rocker cover. And back to the pressure/vac tree between the idle contold valve and throttle body. So I don't see how pressure gets there unless it's always got a little bleed off!

I don't quite understand which ones you are talking about ! The boost control solonoid will have 3 pipes to it. One from the turbine housing (compressor side) to the BCS then one from the BCS to the wastegate. The third pipe from the BCS simply vents into the intake pipe. On simple systems (mainly diesels) the turbine housing pipe is connected directly to the wastegate so as the boost in the turbo rises to it's required level the wastegate begins to open, this allows the exhaust gases to partially bypass the exhaust turbine which prevents the turbo from spinning any faster and the boost level stabilizes. On older diesels this was all you needed and the boost level was set by the strength of the spring in the wastegate but on vehicles requiring more accurate control of boost levels a BCS is plumbed in between the turbine housing and the wastegate and is controled by the ecu and it's this that helps more accurately to control the boost levels. There was a useful diagram floating about on here for a while but I can't find it !

[nobananas]

Right found the diagram, don't know who first put this up but whoever it was ta muchly !

You can see the green pipe coming from the compressor turbine housing going to the BCS, then the yellow pipe going from the BCS to the wastegate, the blue pipe is the vent to the intake near the air filter. The red pipe goes to the re-circ valve which will be connected at the other end to the inlet manifold or vac tree.

[manback]

Hi again, MBC arrived today.

I fitted the big bit but am left with a smaller bit below.


I went for a test drive and the car felt much the same. So I turned it up abut and the boost never went above 5psi. So I turned it some more and it was avaunt just below 5psi. I don't suppose the mbcnworks the wrong way?

[claymore]

what you have there is a bleed valve (which is fine) you put the "T" into the pipe from the turbo to the wastegate (with the arrow pointing towards the wastegate) then a pipe ftom the other outlet on the "T" upto the bottom outlet on the bleed valve, leave the top outlet of the bleed valve open.
EDIT: just noticed it has an arrow on the bottom outlet of the bleed valve, so I'm actually not sure now

[manback]

So wha your saying is that the t piece should go In line between the Compressor housing and wastegate actuator. The 3rd conector should then go to the bleed valve. The 2nd conector on the bleed valve should be open to air. This would mean the more the valve is open the more air would vent and thus more presure would be required to open the wastegate????

[claymore]

Bingo