What is a dump valve ?

[stephearak]

What is exactly a dump valve?It is a good idea to make one?It is hard to do the montage?
Thanks for explain me everything you can about this and perhaps with pictures.

Thanks a lot.

[John_W]

Steph,
please see the following references which should give you an explanation:
http://www.lotuselancentral.com/lec/bypass.htm
http://www.lotuselancentral.com/lec/bvrouting.htm
http://www.lotuselancentral.com/lec/bva ... tm#install

There's also a lot of discussion on the Forum if you search on "dump valve" or "BOV".

Basically the valve's function is to vent the boost quickly in situations where the throttle is suddenly closed (e.g. when changing gear). The theory is that when you are accelerating nicely and the turbo is spinning fast and doing its stuff, it suddenly gets a rude interruption because you've reached the time to change gear and all of a sudden closed the throttle just when the turbo thought it was getting into its stride. The turbo can't suddenly stop just because you've decided to change gear and the boost it's generating suddenly has nowhere to go as you've shut off its normal path (into the engine).

This situation causes the turbo to try to continue to push compressed air into a closed pipe and it tends to stall (and extra stress is put on it). Some people say that they can hear a fluttering noise while changing gears which is the turbo struggling in this situation.

The dump valve is used as a cure for this, as it is designed to open when the throttle vacuum lessens (when you close the throttle to change gear). It opens quickly and vents the high pressure to atmosphere. Boy racers like the "whoosh" noise that this makes, whereas others like to attach a pipe to re-circulate this air back to the air cleaner (which makes the venting silent).

Proponents of the dump valve say that it reduces stress on the turbo (so protecting it and making it last longer) and also gives the advantage of faster pick-up of boost after changing gear because the turbo is allowed to keep spinning instead of the back-pressure forcing it to slow down.

Of course other people say that this is a load of cobblers and you don't need a dump valve because none of this actually happens in practice, and all you do by adding a dump valve is add a piece of kit which can leak and loose boost when you don't want it to.

Have a read of some of the threads on the Forum and make up your own mind.

If you decide to fit one, they are easily available, cost about £100 for all the parts and take about half an hour to fit neatly.

John

[stephearak]

Thanks for all there information
There is a specific dumb valve for the Elan or a standard one can be ok ?

[John_W]

Steph,
I have a Bailey DV30 (piston-type) recirculating dump valve and it works OK. (http://www.baileymotorsport.co.uk/baile ... ort/1.html) Other people have fitted a Bosch (Saab) diaphragm-type and some (eg Stevo) say it's OK and some (eg Dave) say it's rubbish.

Have a look at the comments here :
http://www.lotuselancentral.com/forum/v ... valve#3298
http://www.lotuselancentral.com/forum/v ... valve#4180
http://www.lotuselancentral.com/forum/v ... valve#3008

You will also need to buy a T-shaped piece of metal pipe to fit it into the inlet pipe, a short bit of 1" hose to connect the valve to the T-piece, a hose to go from the valve to the air cleaner (for recirculation) and about 3 ft of thin vacuum hose to operate the valve.

http://www.demon-tweeks.co.uk/products/ ... de=BAIFK10

John