Stupid dump valve question

Can or worms, opened!

Essentially the point of the dump valve is to improve turbo life. Snapping the throttle stuck can cause a pressure spike in the intake, which then tries to back flow through the compressor housing. This puts a large amount of stress on the shaft and bearings of the turbo. Some turbos are strong enough to deal with this surging and some aren't. Generally after market turbos are stronger than factory fit turbos.

The other thing, slightly more debatable, is that a well set-up dump valve can improve throttle response on quick gear changes. The theory is that by releasing just the right amount of pressure you keep the turbo itself spinning fast and so it spools quicker when you snap the throttle back open.

Not sure about petrols, but pretty confident most turbo diesels have dump valves as standard. Can hear the chatter on my Audi and the missus' daily Dub tdis.

Lol, sooooooo much mystery and intrigue, fact and misinformation on this one subject, you could probably open an entire new internetz just on this alone ;D

Short answer is no, modern turbo build quality being what it is, you don't need to run a dump valve. Nothing will break because you don't, though wear might, and I emphasize might, be accelerated on turbo bearings by a minuscule amount. It'll take so long that they'll have banned internal combustion engines before you really notice.

Most cars do indeed run some sort of recirculating valve as standard, generally plumbed back into the airbox somewhere. If you need dump valve whooshing noises in your life you can usually just vent the factory one to atmosphere instead of muffling it with the induction system, so long as it doesn't give your ECU mutant boost leak head****s


The "chatter" often mistakenly called "wastegate chatter" is in fact nothing of the sort. A wastegate's basically like a massive poppet valve; in no way does it chatter. It's either open or shut. What the fluttering noise is, is in fact a momentary stall or backwash of air in the compressor housing of the turbo being chopped up by the vanes of the compressor wheel as they continue turning. There's no proven evidence that this really affects the turbo's longevity or performance in any way, as the OP noted, many modified cars don't use them and most rally teams don't bother with dump valves and that stuff at all and run monster boost without their turbos grenading every five minutes.

Bottom line is if you like the noise, fit one because it'll do no harm at all. If you don't or prefer the flutter noise, don't fit one because it'll errrr... almost certainly do no harm at all. If performance of the turbo is paramount, think about more free-flowing manifolds or wastegate housings, especially if the wastegate is a restrictive internal one. Boost creep will kill more than just the turbo quick as anything...



Fortunately, on my FD the turbo is a ported shroud one so it flutters, whistles and makes more bizarre noises than a whole herd of R2 units, plus I still get dumpvalve whoosh too I just wish I could hear it above the exhaust


EDITED FOR PITIFULLY BAD SPELING

Win win ..

that audi looks the tits!! ive had tonnes of turbos and never had one and never had a problem, always 20psi plus boost

Don't think of NEEDING one think every little helps

.. if your turbo stalls you get lag as it takes time to start spinning back up .. this helps the turbo spin freely when the throttle is closed ready for when you stamp on the gas the turbo is already to go .. less lag between gear changes ...

So I'm guessing the main reason then is protecting the turbo rather than increasing performance significantly. I was thinking it also give the risk of boost leaks.

excellent replies luckyseven - you've said the exact same things I would!

And another little titbit.. NO diesels have dumpvalves. Recirc, Venting,or otherwise. Besides some more modern dervs, which have a throttle that partially closes to improve EGR gas flow, they generally have NO throttle at all.

They always run with an excess of air, and when you take your foot off the throttle, it's merely injecting less fuel (not restricting airflow like on a petrol) Running a dumpvalve on a derv, is just going to hurt throttle response

Gib> When I said Saab I was thinking of my battered old 9000. If the engine was to a really high state of tune I might get away with it, but not as it is. I'd look like someone that wished they had an Impretzle and only bought the Saab because it had a turbo.

The 99 is a whole different kettle of fish, I love the things. You can definitely get away with it in that because it looks like some mad old monster from the 80's.