Understanding Dump Vales and springs

[HTC]

When the throttle closes the pathway of air into the engine is blocked. Thus the need to release pressure via the DV.

The "back pressure" is the force of air back onto the compressor. You'll know it it's occuring as you'll hear the chatter noise which is the blade chopping through the air. Some rally cars used to run without a DV along side an antilag device.

Take a look at this video for a sample of the noise.
http://www.youtube.com/watch?v=m5jZluytOOo

If you have a roller bearing turbo (such as an IHI vf34) or a 360° thrust bearing turbo it shouldn't be a problem.

Forge used to recommend running their DV in reverse with boost acting on the bottom of the piston. Orientatated this way would require a spring matched to your intended boost. I couldn't say if the pressure on the small hose pushing against the top of the piston would balance against the underside of it without measuring the surface areas. Run in normal orientation the spring doesn't matter as mentioned. It just depends on how quick you want it to open and close and the amount of noise whilst dumping. I run 22psi with my vf34 and use the green spring with no issues.

I suppose forge added the adjustability so you can run it either way round and dial in the speed of the piston.

 

[Skorchio]

Very informative, thanks

That Scooby sounds nice!

 

[Alps Pacino]

The DV debate has been done to death both the argument for and against.

My understanding of a dump vlave is that car manufacturers use them to quieten the noise down not as a safety device for the turbo or as a performance aid. I have read loads of articles and imo still cant make my mind up as to weather there needed or not as i have ran cars both with and without before without issue but did notice lag was decreased when i removed a dump valve on 1 of my cars.