CHUNKY.MONKEY.

i hear this pop up alot is it the same as a dump valve i was told they produce the chattering noise when you let off the throttle.
can you have one instead of a d.v. or are they the same?

BlooSooby

I've always assumed that Dump valve was another name for a wastegate??

A wastegate is a valve that joins the inlet and outlet sides of the turbo on the exhaust gas side. When you reach your preset maximum boost pressure the valve is opened by the air driven actuator on your turbo (this is driven by boosted air via the boost solenoid, which is operated by the ECU on a standard motor.). This prevents your engine from getting more boost than it's set up for by dumping the energy (in the form of exhaust gas pressure) from your turbo inlet.

Hope this helps mate.

GC8

A wastegate vents exhaust gas in order to prevent excess compression being created by the turbocharger, because ultimately it will generate more boost than the engine can use. A 'dump valve' (proper name air bypass valve) is a small valve in the pressurised part of the inlet tract, which lets pressurised air escape when the throttle is closed. OEM valves re-introduce this metered air back into the inlet tract. If this didnt happen then the turbocharger would quickly stall, dulling the vehicles performance.

The majority of turbochargers that youll come across have an integrated wastegate: some very large ones will use an external wastegate. Swapping the OEM re-circulating bypass valves for a 'VTA' type will affect the running of your vehicle negatively: at best all you will get is a pointless noise.

BlooSooby

Hmmmmm......correct me if I'm wrong but the compressor side of a turbocharger dumps air via a blow-off valve (re-circ valve as standard on a WRX/STi). This valve is normally fitted to the TMIC and dumps waste compressed air back into the inlet tract. A lot of turbocharged car owners replace this with an aftermarket BOV that dumps the air to atmosphere/inlet tract/combination of both dependant upon the BOV. If dumping to the atmosphere you will hear a 'Whoosh' sound when closing the throttle if the turbo is spooled up (boosting).

As stated above, the wastegate controls boost pressure by dumping exhaust gasses from the inlet side to the outlet side of the turbo turbine. As the wastegate opens and exhaust gasses by-pass the turbine, boost pressure will drop due to the kinetic energy being lost from the turbo. This will control boost pressure. All wastegate actuators are spring loaded to keep the wastegate closed below max boost pressure. The force of the spring will determine the 'default' boost setting of the turbo, i.e., if your boost solenoid fails and stays closed and doesn't dump pressure back to the inlet tract the boost pressure will be determined by the spring. A standard WRX will run at around 8 psi in this scenario. If, on the other hand, you disconnect the air pipe to the actuator and plug it to stop air being drawn into the inlet tract), no amount of boost pressure will open the wastegate. This will result in the boost pressure being limited only by the capacity of the turbo, normally resulting in a blown engine (if you drive it hard) Not a good idea.

So, my EJ257 has a wastegate and a re-circ valve (or BOV if i see fit to install one) bolted to the intercooler and an integrated wastegate in the turbo.

The only grey area for me is whether a dump valve is another name for a wastegate or a re-circ valve (or BOV). I assume it's another name for a wastegate because the turbo exhaust outlet pipe (or up-pipe) is sometimes referred to as the dump pipe.

Anyone else like to comment on this??????

bluenose172

iTrader: (2)

A wastegate is a wastegate, a dumpvalve is a dumpvalve. Both serve different purposes, you explain it above, I don't see why your confused?

Semper

Turbocharger - Wikipedia, the free encyclopedia Wiki is "sometimes" your friend.

CHUNKY.MONKEY.

thanks for the the answers people. i was confused because un like some people i wasnt born with an extensive know how on scooby and turbo engines bluenose 172

bluenose172

iTrader: (2)

My post wasn't aimed at you FFS!

CHUNKY.MONKEY.

missunderstood then
all hapy no probs

bluenose172

iTrader: (2)

Nae probs, it was just that BlooScooby explains it well then doesn't seem to be able to differentiate between a BOV and wastegate.

GC8

Consider yourself corrected.

bluenose172

iTrader: (2)

TBH mate, this aint correct either -

"A wastegate vents the excess compression created by the turbocharger...."

bluenose172

iTrader: (2)

It doesn't vent excess compression created by the turbo charger, it channels exhaust gasses away from the turbine, thus reducing it's ability to build boost/compression.

GC8

You might have me there...

bluenose172

iTrader: (2)

I only started to fully understand the boost sytem/turbochargers when I got my Spec C and started removing boost solenoids and actuators etc. This is a great article for anyone to read -

How Subaru's Factory Boost Control System Works v1[1] 01 - Fullscreen

GC8

Thats what comes of trying to be helpful at 2am: I tied myself up in knots,as you can see.

BlooSooby

No, as stated above, I KNOW the difference between a wastegate and a BOV and I know exactly what they do.

What I was unsure of was whether DUMP VALVE is and alternative name for a BOV or a WASTEGATE. I have since realised that a DUMP VALVE is in fact a pseudonym for a BOV, gottit????? Good.

bluenose172

iTrader: (2)

I could only go from what you posted -

"The only grey area for me is whether a dump valve is another name for a wastegate..."

BlooSooby

I you're going to quote me bluenose, I'd prefer you to quote the whole sentence instead of 'suitable clips'.

scooby L

Sorry Bloosooby, but I'm with Bluenose on that one, in your post you outline the 2 roles of the wastegate and the dumpvalve (or BOV), in a very knowledgible way, then finish by saying it's a grey area if they are in fact the same part?

mike h

iTrader: (10)

Wastegate chatter is actually a myth.
The noise is in fact the unused air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is stopped by the throttle plate closing and usually with the BOV or Recirc valve being removed.

The chattering sound is the air being "chopped" by the compressor blades.
Sounds louder aswell with an after market air filter.

So basically an internal wastegate can't chatter, it mearly opens or closes to direct exhaust gases to or away from the turbine.

BlooSooby

Errrrr...no, I said that I'd assumed that 'dump-valve' was another name for a wastegate because I was unsure whether it was another name for a wategate or a BOV.

If you read my post you'll see that I know what a BOV and wastegate do.

I now know that dump-valve is another name for a BOV, NOT a wastegate...........as I'm sure everyone else in this thread does.

GC8

Now Im going to be very careful, as its easy to make a mistake at 4am..... Youre going to get this just as it comes, because last time I re-wrote it all got mixed up.

A dump valve is a poor description, but its slang, rather than the correct name. The correct name is hardly ever used now, but it is an air bypass valve. Even that isnt the clearest of descriptive names.

That wastegate chatter is a myth is a myth. The only context in which it is used is a motorsport one (on the whole) and in those circumstances its common for an external wastegate to be fitted. The noise that people are usually referring to is indeed caused by the stalling compressor wheel, but it is erroneous to suggest that an external wastegate is silent.