where the dump valve ?

[norman lovie]

OK i,m baffled - where the blooming dump valve ? - or how does it dump the boost pressure when you lift off

[ashm]

Haha, unless the plumbing has been altered (or your hose clamps aren't done up tight enough :S ) it goes backwards through the compressor!
I believe that's the fluttery sound you can often hear when you lift off.
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[old yella]

I thought the dump valve was the 'add on'......such as the Bailey variety which gives you a loud woosh

[norman lovie]

Haha, unless the plumbing has been altered (or your hose clamps aren't done up tight enough :S ) it goes backwards through the compressor!
I believe that's the fluttery sound you can often hear when you lift off.
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thats exactly what it sounds like - always though this was nasty for a turbo: ok atleast I can stop trying to find it

[ashm]

In theory it's best avoided I think as it adds stress on the turbo, hence why a lot of turbo cars have a recirculating type valve installed at the factory.
There are a lot of people who've retrofitted one to their elans, it doesn't seem too complicated.
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[racerstev]

Funny thing is the Impulse RS with the same turbo and engine has one while the Elan dosn't.
I really don't see much of a differance between the drivability of the 2 cars either.

Steve

[tigerdog]

Use the search feature for "dump valve" or "blow off valve" and you'll find several different approaches people have made. The usual spot to install one is on the hose between the fender and the throttle body. In theory, you could even make a stealth installation on the hose connecting the turbo outlet and the intercooler inlet. In any case, it's a good idea to connect the output to the clean side of the air cleaner. This way, if you ever pull vacuum strong enough to open the valve while the engine is running, any reverse flow through the valve would be clean air, not dirty atmosphere.

[rip]

Plenty of answers for your first query, but none for the second so far:

There are 2 types of valve. A dump valve releases excess pressure above a certain value. This must be adjusted to above your max boost pressure or you'll throw away your turbo's boost. As soon as the boost reaches say 1bar, the valve opens (which will only happen when you close the throttle because the air has nowhere to go).
A most sophisticated configuration is a blow-off valve (BOV). This has an extra pipe which is connected at the other side of the throttle valve plate. When the throttle is open, there will be no pressure difference across the plate. With the throttle closed, there will be a postive pressure difference which will cause the valve to open & release the excess.

Each type can 'dump' or 'blow off' excess air either to the atmosphere (atmospheric) or to the air cleaner (re-circulating). The atmospheric type usually creates the whoosh sound but it can be made quiet by using a longer pipe & small filter.