wastegates and dumpvalves

[Jon.L]

can someone explain the difference, and how a wastegate is fitted etc?

Cheers

 

[Andrew Cooke]

A wastegate is in the exhaust, and bypasses the turbine to control the boost.

A dumpvalve is in the inlet and make a moo noise when you let off the throttle

 

[Jon.L]

A wastegate is in the exhaust, and bypasses the turbine to control the boost.

A dumpvalve is in the inlet and make a moo noise when you let off the throttle

yer im familuar with dump valves but i love the sound of waste gates and with me a few months away from buying focus st i want a wastegate! how easy are they to fit? as i no the dumpvalves are a doddle

 

[cat171]

The ST is likely to have a dump valve on it already, it'll have a re -circ one most probs (it'll be silent) One that dumps to air makes the ptshhhh noise. I hate the sodding things tbh & find them proper chavvy.

 

[Andrew Cooke]

yer im familuar with dump valves but i love the sound of waste gates and with me a few months away from buying focus st i want a wastegate! how easy are they to fit? as i no the dumpvalves are a doddle

if it's a turbo it already has a wastegate, but unless you're running an open pipe on it you're unlikely to hear it.

 

[DannyR]

You literally just remove the DV and block up all the pipes, you'll also need an open filter for full effect!

Loved the sound my Punto used to make!

 

[Andrew Cooke]

You literally just remove the DV and block up all the pipes, you'll also need an open filter for full effect!

Loved the sound my Punto used to make!

and that does what?

 

[Mark One]

Turbos must have wastegates so that the amount of boost pressure delivered can be controlled. If the wastegate is open it allows exhaust gas to bypass the turbine (hot side of the turbo) thus reducing the turbo speed.
There are internal wastegates (built into turbo with an external actuator) and external wastegates (which often give better boost control).
There are pretty nasty consequences for having a wastegate that cannot handle the boost.

A dump valve releases excess pressure in the boost pipes when you back off the throttle. Without one you get a pressure wave that bounces off the throttle butterfly and reverses up the boost pipes and rushes back through the compressor side of the turbo. This makes the "chatter noise" (and btw it's nothing to do with the wastegate).
Two basic types of DV are atmospheric and recirculating. Atmospheric dumps to atmosphere (classic tsssh noise) recirc will dump into the inlet side of the compressor (this is what OEM turbo engines do to reduce noise).

 

[Jon.L]

maybe ill just get a forge or bailey dv then, this wastegate sounds like a mish do love the sound though!

 

[Mark One]

Wastegates never really make any noise. The "chatter" thing you can hear happens as a result of having no DV.

Without one you get a pressure wave that bounces off the throttle butterfly and reverses up the boost pipes and rushes back through the compressor side of the turbo. This makes the "chatter noise" (and btw it's nothing to do with the wastegate).

 

[Icarus]

Turbos must have wastegates so that the amount of boost pressure delivered can be controlled. If the wastegate is open it allows exhaust gas to bypass the turbine (hot side of the turbo) thus reducing the turbo speed.
There are internal wastegates (built into turbo with an external actuator) and external wastegates (which often give better boost control).
There are pretty nasty consequences for having a wastegate that cannot handle the boost.

A dump valve releases excess pressure in the boost pipes when you back off the throttle. Without one you get a pressure wave that bounces off the throttle butterfly and reverses up the boost pipes and rushes back through the compressor side of the turbo. This makes the "chatter noise" (and btw it's nothing to do with the wastegate).
Two basic types of DV are atmospheric and recirculating. Atmospheric dumps to atmosphere (classic tsssh noise) recirc will dump into the inlet side of the compressor (this is what OEM turbo engines do to reduce noise).

A turbo doesn't neccesarily need a wastegate if it is sized to reach peak turbo speed at peak engine speed. This system has been used by Saab on a production engine with the V6 Asymetricaly turbo charged engine used in the 9-5. The downside to this is that there is no way effectively ramp up turbo speed to increase delivered airmass at low engine speeds.

Also modern VNT/VGT turbos do not use wastegates and instead use pneumatic or electric actuators to control the size/shape of the nozzle or delivery vane position to control turbo speed.

If a conventional wastegate is too small to flow sufficent exhaust gas to maintain a set boost pressure then the effect is boost creep, which will result in an increase in turbospeed above the desired level. This isn't neccesarily a bad thing if the resulting turbo speed is within limits and fueled for.

Cheers
M

 

[sideways danny]

Wastegates never really make any noise. The "chatter" thing you can hear happens as a result of having no DV.

^^ Truth

It's compressor stall you're talking about

External wastegates do make a monsterous noise when vented out of the the exhaust, but that's a fairly involved bit of work, with no discernable gains to you in this case

 

[Jon.L]

sweeet thanks for the info