Can someonr please explain to me the value of fitting one of these things? I know they make a bit of noise on lift off of the throttle, but is that all? surely there must be more to it than that?!

Thanks.

 

Hi there,
The purpose of your dump valve (or blow off valve) is to expel the air circulating in your turbo when you lift off to change gear. When this happens it means your turbo can keep spinning at high speed. This is handy for when you engage your next gear and throttle up coz the turbo is already spinning at high speed meaning there is less turbo lag. Hope this helps.

Steve

 

As i understand it: the dump valve releases the charged air and dumps it to atmosphere or is recirculated. this keeps the turbo spinning. so when u put your foot down again. the turbo doesn't have to 'spin up' from the start so ur boosted a bit quicker?
im sure ill be corrected but thats my basic understanding. hope its right

 

hows ur luck!! we both posted at the same time

 

nice one one_lung. don't think you can be corrected coz you hit the nail on the head.

 

How Turbos Work

should help

 

I think the original question was actually why fit a VTA type?
Is noise the only benefit?
Col

 

Wow, that was quick! Thanks for the info guys, that leads me onto two secondary ones, where does the air in the reciculating type get dumped to, and then as Colin sayes, are the vent to air type any better, except for the noise?

 

The reciculating type dumps down the exhaust.
These are standard ie all turbo's have them.
Col

[Edited by Colin P - 2/19/2003 3:20:36 PM]

 

Ummm....the recirculating ones dumps between the MAF and the turbo....

/J

 

What are the real benefits of fitting after market D/V's apart from noise? aren't the OEM ones much cop?

sorry to butt in!

 

the dump to atmos must just be a noise thing. The advantage for race cars would be that you don't need extra connecting pipes and gubbins to recirculate. Saving weight and problems with reliability. People may argue that there is less back pressure dumping to atmos, but the difference is chuff all compared to the high pressure the charged gas is at.

I remember asking my dad what the mad chattering noise was when watching GT racers on the over-run as a kid, so i can see why people want to have them. Not my cup o tea though.

z

 

Supposedly the VTA version does cause over fuelling on gear changes as more air is detected so the engine dumps more fuel for it. On a decatted system with induction kit the major downside ( ) are flames out the back.

 

I thought that the re-circ type dumped the air upstream of the throttle butterfly. Then, when this is opened, [e.g. when you have changed up a gear], the high-pressure air is fed into the turbo and helps spool up.
Obviously, the BOV is to alleviate the backpressure that builds up between the Turbo and the throttle butterfly when you throttle off - as this slows the turbo vane.
I've been told that the VTAs can dump faster, thus giving faster inter-gear change times [these clearly DONT help spool up in the same way].. But I've not got one and think it's a much debated topic !

Mark

 

Mark,
From S.A.M's post

So you are correct

 

Even with unmodified turbocharged cars, an original equipment "dump valve" is usually there as a safety device for the engine. If for any reason the boost settings become out of adjustment, by accident or deliberately, there is serious risk of over-boosting without appropriate adjustment of fuelling etc. A glance at some of the queries on various scoobynet and other technical threads illustrate what can and does happen when things go wrong or are stretched too much. That valve is set to open at a predetermined pressure level and release this excess of boost. Tampering with turbo control settings can provide lots more power and/or lots more problems ... often expensive.

When you change up at high engine revs, the turbocharger is still spinning away and at very high revs too! Up to around 130,000rpm IIRC even on something like an MG Turbo, thus continuing to heavily pressurise the induction system at a time when the throttle is CLOSING sharply SHUT! ..... Where does that pressure go if there is NOT some release valve? Back pressure can and does cause broken turbo problems unless that valve "dumps" that excess which solves that problem with the bonus of allowing the turbo to continue to spin on freely without much harm that could be the case without that excess pressure being dumped.

Suspect those expensive, shiny aftermarket dumpvalves do little more than the original equipment except impress the punters with that much louder "WhooshTish" than that made by the standard fit valve ... Unless the car is seriously and competently modified of course .....