Dump Valves ..

[Borats Baby]

I've been over this a few times with different people and am still really none the wiser.

Put the chav factor aside for a few moments if you will.

Do aftermarket dump valves actually gain you anything ?

Weather it be in terms of performance, or fuel economy or whatever.

I was going to be specific with an engine, but sod it, across the board comments please .

 

[digitalfailure]

I've been over this a few times with different people and am still really none the wiser.

Put the chav factor aside for a few moments if you will.

Do aftermarket dump valves actually gain you anything ?

Weather it be in terms of performance, or fuel economy or whatever.

I was going to be specific with an engine, but sod it, across the board comments please .

A dump valve, would only be fitted to a pressure charged petrol engine, The speed in which the pressure between the compressor and the closed throttle plate is critical to prevent compressor stall and loading on the bearings, so uprated units can be an advantage, also some designs are prone to leaking in air, this would serve to weaken the air / fuel mix as the calculation for the air is done prior to the location of the dump valve.

A weak mixture takes longer to burn and can cause all manner of nasty things within the combustion chamber, turbo'd vehicles generally like to run rich as the excess fuel cools the combustion process.


There are several ways of dumping the pressure too, some designs are termed as recirculating, and they do exactly that...they loose the pressure in to the inlet before the compressor.....but while this is quieter, it has a negative effect on air temperature.

So.....wether it be recirculating, piston or poppet design they can be upgraded with better performing designs and even set to operate at different pressures.

As part of a complete engine performance package they can be valuable.......if poorly conceived they are a nightmare. The number of cars I've looked at with shiny alloy dump vales that are sticking or slow to react is shocking really considering the amounts people pay for them. :shrug:

 

[antonroland]

Hey, you petrolheads!

Take it elsewhere:rules:

 

[Jelster]

Mine doesn't need it, something to do with the way it's recirculated.

They do sound very naff though, like your motors caught a cold

Steve

 

[ppp]

http://en.wikipedia.org/wiki/Dump_valve

 

[Baz007]

It's already been covered but the basically keep the turbo from stalling. If i had a turbo car, I'd have one but I do like th e noise as well

 

[30psi]

The main reason to avoid the turbo stalling is to reduce the stress on the shaft. It spins at over 100,000rpm and can be brought to a halt in one or 2 seconds.

Unfortunately kids like the sound of the dump valve, and simply fit one for the sound, with no consideration to what its purpose it might provide. Which is normally minimal for the cheaper ones.

It's also something which is only really necessary for the high boost engines.

I've got a turbosmart recirc for my engine, on all my engines in the past I've never used one but this one is going to be running 2 bar of boost so its kind of a necessity. Luckily being recirc it won't make the sound often heard down southend on a saturday night lol

As digitalfailure explains if they're fitted to an engine with an airflow meter (eg nissans) then they can draw in unmetered air which won't help it idle well and could lead to an mot failure for being too lean.

Forgot to mention that dump valves also provide an arguable performance increase in the sense that they can reduce lag from one gear shift to the next. With no dump valve the compressor would stall so would have to pick up speed again, a dump valve will keep it spinning but may also remove too much compressed charge from the inlet tract and therefore would create lag in itself, so its a bit of a balancing act.

Quite a geeky subject really