recirculating dump? or run without?

29th July 2011, 11:16

never looked into this but say on a boosted application you didn't want the poo valve going off and making that sound what would you use or do to keep it quiet?

also another thought if running low boost ie 8psi or so dv or no dv?

29th July 2011, 11:20

Most oe valves are recirculating. Still noisy at times though. You want to stop the noise completely?

29th July 2011, 11:24

wouldn't say completely craig but less obvious as to whats going on

29th July 2011, 11:29

Can you not buy closed loop valves off the shelf? That would be a better option than a dump valve. Would also hold boost higher and for longer

29th July 2011, 11:31

interesting it will be something I look into then

29th July 2011, 22:32

a recirc one puts the dumped boost back in to the inlet before the turbo

or either take off the DV or dont connect the vacumn line to it so it wont open when the throttle shuts

29th July 2011, 22:37

Quote:

Originally Posted by tweeqd

a recirc one puts the dumped boost back in to the inlet before the turbo

or either take off the DV or dont connect the vacumn line to it so it wont open when the throttle shuts

wont that cause turbo stall with no dump valve. i.e bad for turbo :s

30th July 2011, 20:47

only if your running lots of boost

30th July 2011, 21:01

I wouldnt recommend that martin, although it wont do any immediate damage, it will reduce the service life of the turbo considerably.

OEM's fit them for a reason. You can still hear them (my OEM ibiza was still noticable), but they are better than nothing

5th August 2011, 13:16

been thinking low boost application 8psi max dv or no dv?

5th August 2011, 13:51

no dv will mean slightly slower re-spool through the gears (probably unnoticeable on 8psi) and wastegate chatter which I personally like the sound of. Depending on the turbo, 8psi and no dump valve will probably do no harm whatsoever, depending on it's thrust bearing design.

Fitting a recirculating dv is probably your best option - you can keep it fairly quiet that way, and benefit from keeping spool times as low as possible (have the recirc outlet as close to the compressor housing as possible).

I've never seen a turbo fail (or heard of a turbo failing) as a direct consequence of having no dump valve fitted.

5th August 2011, 14:06

interesting Ross tbh with the spec in mind its going to be pretty much like steveo1600 diy setup using the stainless ebay mani t2 turbo etc etc just pricing everything up for local guy wanting to do it but he wants to keep it quiet. But still good to know it won't kill the turbo

btw hows yours coming along now after the valve incident?

5th August 2011, 14:14

Quote:

Originally Posted by Sophia_Bush

interesting Ross tbh with the spec in mind its going to be pretty much like steveo1600 diy setup using the stainless ebay mani t2 turbo etc etc just pricing everything up for local guy wanting to do it but he wants to keep it quiet. But still good to know it won't kill the turbo

btw hows yours coming along now after the valve incident?

Yeah I dislike the dumpvalve sound now completely - when I had the R5 15-16 years ago, 30psi through a forge dumpvalve was all I lived for

But tbh it's got really tiring and too chav for me. I recirc now and wish I didn't have to run one at all, but with such a large intercooler and high boost it's a necessary evil else the turbo would be stalled the whole time.

Car's doing well thanks - we've had a lot of grief with that bloody valve and the knock-on effects of it. Head's been off twice since then to try and rectify a problem with the valve seat we thought we had fixed. Bloody thing. Mapping is on Friday where we should see a reasonable gain in power as we're not binding the valve springs this time...

5th August 2011, 15:47

aye agree with your spec you will need one well over 350 now ain't it, Mauritius blue is such a nice colour on a gti. Ah good luck on the mapping hopefully see some nice figures and curves, anyway I think such low spec thats being talked about this will be sans dv

5th August 2011, 15:50

Thanks again for the compliments. It was at 403 last session. Should be somewhere around that (410-420) this time I hope.

excellent choice to go sans dv.

5th August 2011, 15:58

My engine still has the original turbo with standard built in recirculating valve. When I blocked the valve I noticed car became a bit more laggy

5th August 2011, 16:08

A recirc DV can increase intake temps, since your putting the same air through the turbo multiple times. Recirc DV's are needed if you are measuring the mass of air using either an AFM or MAF sensor. MAP and TPS and AIR TEMP doesn't need that.

You can get quiet DV's can't you?

No DV will make spool up slow and annoying

5th August 2011, 18:39

My dads old sierras cosworth never dumped, the car became uncontrollable on the road and shut the ignition off on the first touch of the throttle. That was years ago, but interesting story non the less

11th August 2011, 19:07

interesting will see how this pans out and report back with finidngs

11th August 2011, 20:43

just box the DV off to deaden the sound in an old open filter full of exhaust packing or cotton wool

seen it done a few times, its quite effective!

..as well of course as being easy and cheap

12th August 2011, 11:06

Rubber chicken over the outlet so it quaaaaaaaaaccckkss instead of psssssstttt

I had to ditch the HKS BOV on the MR2 due to the air not being measured correctly and causing it to run silly rich, so am now back on recirc one and I prefer my old Quuuuuaaaaaaaaakkkk

12th August 2011, 11:15

Just to add my 2 pence worth...

I dont run a dump valve, purely to get that sexy turbo chatter noise. And so far I havent had a problem with turbo faliure or lag. My mates astra doesnt run any sort of dump valve either and he hasnt had any problems with over 2bar through a GT30.

12th August 2011, 16:36

used to have a starlet gt only running standard boost 0.65 bar and messed about with the dump valve set up loads.
removing the standard bov and blocking it off made it pretty much silent.
but then fitted an air filter and it would chatter. none of which made any difference in spool time and caused no damage to the turbo.

Then refitted the standard dump valve with the air filter still fitted and it would dump louder than with a normal aftermarket bov on.

So basically i think u should just see what your set up is at the time and have a play.

19th August 2011, 09:41

take it off. tests have been done and with dump valve you end up with atmospheric pressure in inlet tract, without dump valve you still have positive pressure in inlet. and it wont instantly kill the turbo. dont think norris designs use one on their 1000hp evo so i wouldnt worry about it on a 200hp engine.

19th August 2011, 09:43

Quote:

Originally Posted by loudandproud205

Rubber chicken over the outlet so it quaaaaaaaaaccckkss instead of psssssstttt

I had to ditch the HKS BOV on the MR2 due to the air not being measured correctly and causing it to run silly rich, so am now back on recirc one and I prefer my old Quuuuuaaaaaaaaakkkk

that can only cause it to run rich on closed throttle with the engine slowing. as thats the only time the DV is open, which is the only time the air entering the engine is different to air passing the MAF.

19th August 2011, 10:15

Quote:

Originally Posted by williamsvts

take it off. tests have been done and with dump valve you end up with atmospheric pressure in inlet tract, without dump valve you still have positive pressure in inlet. and it wont instantly kill the turbo. dont think norris designs use one on their 1000hp evo so i wouldnt worry about it on a 200hp engine.

I totally disagree.

A dump valve is there to prevent compressor surge. Running low boost this isn't so much of a problem, but higher boost will harm the turbo quickly. Not only that, with a stalled compressor wheel, you're introducing more lag as the turbo has to spin up "from scratch" again.

19th August 2011, 11:13

compressors dont stall. i got the informantion from an engineer at garret that done a test on a 2l engine running 1.8 bar, when he shut the throttle with DV pressure went to 0 psi, when he done the same test without DV pressure only dropped to 7 psi. he also said that if a turbo is designd to last 100,000 mile. running without a DV MAY shorten that to 90,000 mile. he said it hasnt been proven that no DV CAUSES turbo failure.

its not my opinion, its what ive been told by someone in the turbo industry.

also on newer ball bearing trubos the load is spread more equal compared to the old journal bearings.

19th August 2011, 12:18

I still disagree completely I'm afraid.

My information comes from Alan Allard's book on Turbo and Supercharging. He specifically mentions compressor stall. http://www.allardturbosport.co.uk/

General opinion is compressors do stall. Frequently. I've certainly heard it on every car i've had when I've run with an incorrectly setup dump valve, or no dump valve at all. And the effects are obvious when driving. MUCH more lag between gearchanges.

Wikipedia - http://en.wikipedia.org/wiki/Blowoff_valve

99% of all modern turbo cars as standard are fitted with dump valves for this very reason. Your engineer seems to have a different opinion to everyone else, including some very respectable sources (Such as Alan above).

For example: Graham Goode - http://www.grahamgoode.com/dump.htm:

Quote:

Why do manufacturers fit a dump valve?

It is for a number of reasons. Without a dump valve, when the throttle was closed, the build up of boost pressure would be immense, very similar to closing a quickly flowing water tap. This excess of pressure, (which could be over five times the running boost pressure), would put the components of the system under a great strain. It would try to burst the intercooler and pipework. More significantly, it would put a large strain on the turbocharger itself, firstly stalling the compressor shaft, then trying to force the compressor wheel out of the turbo, against its bearings.
So, the dump valve prevents mechanical damage to the intercooler & turbo pipework, prolongs turbocharger life, and prevents excessive turbo - lag that would be caused by the compressor shaft stalling.

Turbo Technics - http://www.turbotechnics.com/turbo/faq.htm

Quote:

What is a dump valve ?

A valve which relieves back-pressure between the compressor outlet and engine as the throttle is closed. Only sometimes required on engines producing in excess of 14psi boost pressure.

HKS - http://www.hksusa.com/categories/?id=1062

Quote:

Blow-Off & Bypass Valves have one goal, prevent compressor surge. Compressor surge occurs when the throttle plate of a turbocharged engine closes and the pressurized air is forced back into the turbocharger’s compressor housing causing the turbo to slow down. Compressor surge not only decreases the spool of a turbo but can also damage its center cartridge.

TurboSmart - http://www.turbosmartonline.com/index.php?id=624

Quote:

When a gear change occurs, the throttle which allows air to flow into the engine is closed.

This results in a large pressure spike as the turbocharger is still trying to flow air due to the inertia of the compressor and turbine but there is nowhere for the air to go as the throttle is closed. The pressure within the intercooler piping continues to increase until the compressor reaches its pressure limit. When it reaches this limit, it cannot flow the air any more and the built up air pressure inside the intercooler and pipe begins to flow backwards through the compressor which is trying to flow air forwards.

The result of this reversal flow of air is the immediate deceleration of the turbocharger and a high load on the bearings which support the compressor/turbine shaft. At low turbo speeds and low pressures, the deceleration of the turbo and the load on the bearings is low, i.e. a small amount of fluttering at low engine speeds and throttle movements is negligible.

At high turbo speeds and high pressures, compressor surge during a gear change can be damaging to the bearings of the turbocharger as the deceleration rate of the turbocharger is high and the reversal airflow through the compressor is high.

Greddy - http://www.greddy.com/products/turbo...ow-off-valves/

Quote:

[GReddy] Blow Off Valves [are easily adjustable to] eliminate compressor surge and preventing premature boost leakage, while increasing boost response between shifts.

And finally, Garrett themselves - http://www.turbobygarrett.com/turbob...o_tech101.html

Quote:

The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it.

With respect, your engineer at garrett has it wrong.

19th August 2011, 15:27

ive never noticed a difference in lag with and without a DV. all cars without a DV make the noise of compressor surge.

that wasnt his opinion, it was the results from a test he had done.

modern cars are fitted with recircs to keep the noise down.

i will continue to run without a DV untill i see tests that show quicker pickup with one than without.

theres also a few of my mates that dont use them and have never had a problem either.

i dnt see how you can notice loads of lag without, as without you already have boost pressure ready when you open the throttle, without it you need to build all the pressure up from atmospheric.

19th August 2011, 15:39

i was looking into this as i want my new engine build to be perfect.
what he said about 'compressor stall'

Stall has nothing to do with turbo speed, its aerodynamic stall i.e. flow separates from the blades creating transient surge (fluttering noise). Unless you're going to run 3bar+ of boost pressure this shouldn't kill the turbo excessively quickly, put the BOV in the bin and be done with it.

so it seems the shaft/blades dont stop spinning.

19th August 2011, 15:42

trying to find the email about the tests.

19th August 2011, 15:54

When I did tests running with an without a DV logging the boost before the intercooler, car running 1.8bar

With DV, close throttle, pressure drops to atmospheric immediatley, re-open throttle boost build from 0 back to 1.8bar

Without DV, close throttle, pressure drops slowly, change gear and re-open throttle but pressure still at 0.7bar. Boost then builds back to 1.8bar bar at the same rate but from a higher starting point.

My car was pretty low lag and it saved about 0.2s. This is something only the logs showed as on the road you could barely feel the difference.

with what im spending on my new engine/turbo build i dont want to kill it, so if i had getting and information to say that not using a DV will kill it i would be using one.

19th August 2011, 16:13

I never used any form of dump valve on the saxo at 9.5psi and never had an issue with it. As ross said though, it really doesn't matter at mild boost.

My s14a had a re-circ when i bought it and running 22psi you don't hear anything on shut off. I removed the re-circ didn't have any issues apart from it would let a few flames and bangs out when you lift off but this was due to it being afm so it chucked extra fuel in expecting air to be going in with it as it normally would with a re-circ.

There is a lot of debates about it damaging the turbo or not, personally I never use a dump valve of any description as I enjoy listening to the chatter. A good friend of mine works at a well reputed engine tuner and he is dead against it and therefore always runs a re-circ on his gtr. On the flip side though, a guy who's in the same circle of mates has a sierra cosworth running 30psi on a gt30 and he runs no dump valve, so far no problems.

19th August 2011, 16:46

Quote:

Originally Posted by williamsvts

i dnt see how you can notice loads of lag without, as without you already have boost pressure ready when you open the throttle, without it you need to build all the pressure up from atmospheric.

The reason is simple physics. When you come off throttle, the boost that's in that pipework tries to take the path or least resistance. During transient throttle positions, that path is into the engine (the engine draws air in, whilst there is pressure from the turbo pushing more air out). When the throttle body is closed, that air still wants to take the path of least resistance - it cannot pass the (closed) TB, so attempts to go back out the turbo compressor, trying to vent to atmosphere via your air filter. The turbo stalls because the air in the intake pipes is fighting the rotational force of the exhaust gasses still coming out of the exhaust and subsequent centripetal forces of the shaft.

The noise you hear (the flutter) is the air being forced across the compressor blades the wrong way.

The lag is caused by the turbo spinning to a STOP by these reverse forces - when the dump valve is introduced, the boost is lost, but the turbo is allowed to continue spinning, improving response.

I have listed many respected sources who have said that a dump valve should be used - including two separate turbo manufacturers (one of those being Garrett who you say your contact works for). Other than your posts, I'm yet to see anyone in a respected area of the industry vote against the dump valve.

In your last post you mention the guy had pressure without the dump valve remaining at 0.7 bar. Of course he did. There was no where for it to vent to. As it can't go down the TB, where do you think it's going to try and go? Reversing into the compressor wheel, stalling it.

I'm interested to see another perspective on the idea, but it's contrary to established and recognised industry practice - including the makers of the very components we're discussing. It's also something I've not come across in the 15+ years I've been modifying turbo cars.

19th August 2011, 20:05

the compressor does not stop or stall, its explained above.

thats my whole arguement, how can you have more lag when you have 0.7bar ready, as opposed to 0 bar. in his test it reached 1.8 bar 0.2 sec quicker without a DV, as posted above.

im posting what tests have shown.

and i will continue not to use them till i get proven otherwise.

19th August 2011, 20:13

Ok William, listen to him. Ignore everyone else

You've ignored the information I've given you - even your own counter-argument about this 0.7bar pressure proves my point - that's 0.7bar that's trying to escape out the compressor housing, via the compressor wheel. That's the reason you get flutter (noise) - you're stalling the compressor wheel.

You honestly want to argue the compressor wheel doesn't stall? Really? Even with all the links I've given you? Turbo Dynamics, Garrett etc? ALL saying it does??

Can you find a single argument by a reputable source, published on the internet backing up your perspective?

You've BEEN proven otherwise. By all the links I've posted. With respect, I think you're being a little blinkered on the subject by refusing to see another perspective. Even that of the turbo manufacturers. You're posting what you've heard from one person. the rest of the INDUSTRY has spoken, as I've highlighted to you.

As the saying goes, you can take a horse to water, but you can't make it drink

19th August 2011, 20:25

I haven't been proven wrong, the guy I was talking to explains its the air that stalls not the compressor. I have never see or heard of a turbo dying prematurely due to no DV and have never seen any proof to show that lag is reduced with a DV.

19th August 2011, 20:36

You understand what compressor stall is... right?

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

Quote:

Axi-symmetric stall, more commonly known as compressor surge; or pressure surge, is a complete breakdown in compression resulting in a reversal of flow and the violent expulsion of previously compressed air out through the engine intake, due to the compressor's inability to continue working against the already-compressed air behind it.

Given the above...

This is valid - http://www.turbobygarrett.com/turbob...o_tech101.html

Quote:

Blow-Off (Bypass) Valves
The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it.
Blow-Off valves use a combination of manifold pressure signal and spring force to detect when the throttle is closed. When the throttle is closed rapidly, the BOV vents boost in the intake tract to atmosphere to relieve the pressure; helping to eliminate the phenomenon of surge.

I really can not explain it any clearer than that. Now thats cleared up, lets address lag (although it should be self explanatory at this stage).

From here - http://www.turbosmartonline.com/index.php?id=497

Quote:

The secondary function of a BOV is to reduce the “turbo lag” effect between gear changes. Without a BOV, the compressor surge slows the turbine down, which then takes longer to spool up again when the throttle is opened. With a BOV, the excess boost pressure is released, keeping the turbine spinning and thus reducing the turbo lag effect.

TurboSmart even have a nice picture to explain:

Whilst they are singing their own praises (obviously) the principle they're talking about (the peaks and troughs of the boost cycle) are valid

19th August 2011, 21:28

the above explains that the airflow changes direction, not the the turbo stops spinning. what happens to the exhaust gasses then if the turbo stops spinning then?

i can understand how your point is valid that the turbo will be spinning faster using a DV than without, but the guy i spoke to about it used datalogging equipment in his engine and recorded a 0.2s quicker spool up, because of still having + pressure in the inlet tract.

even if the turbos life is shortend by about 10% its still not much.

you dont need to explain anything to me. ive got a good understanding of it all and im deciding not to use a DV on my new build.

19th August 2011, 21:33

Quote:

Originally Posted by williamsvts

the above explains that the airflow changes direction, not the the turbo stops spinning. what happens to the exhaust gasses then if the turbo stops spinning then?

http://www.turbosmartonline.com/index.php?id=497

Quote:

Without a BOV, upon shutting the throttle, the pressurised air caught between the free-spinning turbo and the shut throttle is forced back through the turbine blades, this, in turn, forces the turbine to slow down or stall. This phenomenon is often referred to as “compressor surge” or “cavitation” and it places undue load on the turbocharger bearings, significantly shortening the lifespan of the turbo or even causing serious damage.

There is reduced exhaust gasses because you've shut off the throttle (and therefore fuel and air) - the flutter you hear is the reversed airflow trying to turn the compressor the wrong way. It's a flutter because the compressor wheel and the turbine wheel are locked in battle to spin in opposite directions. Eventually the flutter stops - because the turbine wheel wins out once the pressure in the boost system is reduced to the point where the turbo can spin normally.

19th August 2011, 21:36

the compressed air goes back through the compressor between the blades and the housing, i kow theres not much room but thats where it goes.

we'll just agree to disagree. i'll not worry about your engine you dont worry about mine,

19th August 2011, 22:04

I'm not worried about your car (nor mine that much to be fair!) - I was replying originally because I don't like to see misinformation on a subject that could end up actually damaging someone's engine if heeded.

I'm still waiting for you to link to where lag is reduced by NOT running a dump valve.

22nd August 2011, 09:41

ive posted it about 5 times. the car made 1.8 bar after a gear change 0.2s quicker without a DV.

22nd August 2011, 09:48

According to one of your "mates" who you claim works at garrett. You've provided no link or documentation to back up this claim.

However, garrett disagree. As does the rest of the industry. As per the links I posted, I've backed up everything I've claimed with major players documentation.

I'm still waiting for your links.

22nd August 2011, 09:52

he isnt a mate, it was a private conversion so its pretty hard to provide a link to that,

22nd August 2011, 09:56

Quote:

Originally Posted by williamsvts

he isnt a mate, it was a private conversion so its pretty hard to provide a link to that,

So in essence, one guy you know said something to you that you've taken as gospel truth.

The entire turbo industry disagrees (with which I've backed up from all major players, garrett, turbo dynamics, turbosmart, hks, greddy, grahame goode etc).

Don't you think that's a little bizarre? "The whole world is wrong, and I'm right because one person told me something". Are you honestly that naive?

22nd August 2011, 09:57

only one of your qoutes say they reduce lag, turbo technics say they are SOMETIMES required on boost above 1 bar, and the rest explain what DV's do. i had come to that conlcusion before i spoke to this person. and from the test he done showed me it made boost quicker.

22nd August 2011, 10:00

i'll be honest. i got it all from max power mag.

22nd August 2011, 10:02

Just to clear this up one LAST time, here's what Garrett say on the subject:
http://www.turbobygarrett.com/turbob...r/faqs.html#t3

Quote:

What is compressor surge?
The surge region, located on the left-hand side of the compressor map (known as the surge line), is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur. When referencing a compressor map, the surge line is the line bordering the islands on their far left side.
Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain. This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall. In cases of extreme surge, the thrust bearings of the turbo can be destroyed, and will sometimes even lead to mechanical failure of the compressor wheel itself.

Common conditions that result in compressor surge on turbocharger gasoline engines are:

A compressor bypass valve is not integrated into the intake plumbing between the compressor outlet and throttle body

So - we've established NOT running a dump valve causes surge or compressor stall (dictated by the amount of pressure built up in the intake system).

Given that...

Quote:

What is Turbo Lag?
Turbo lag is the time delay of boost response after the throttle is opened when operating above the boost threshold engine speed. Turbo lag is determined by many factors, including turbo size relative to engine size, the state of tuning of the engine, the inertia of the turbo's rotating group, turbine efficiency, intake plumbing losses, exhaust backpressure, etc.

So - we can see a direct correlation between the compressor stalling and lag.

Is that clear enough?

22nd August 2011, 10:05

but you already have boost pressure built up in the intake. your starting with postive pressure as opposed to atmospheric.

22nd August 2011, 11:13

Quote:

Originally Posted by williamsvts

but you already have boost pressure built up in the intake. your starting with postive pressure as opposed to atmospheric.

Agreed. And that positive pressure is effectively trying to turn your compressor wheel the wrong way as the shut TB is forcing air to go back into the compressor housing it's just come out of.

Lets say the turbo is spinning at 50,000 rpm whilst making boost. In your example, the turbo is forced to slow to perhaps 5,000 rpm because of the back pressure on the compressor wheel trying to force the blades the wrong way as the air has to go somewhere - obviously it's losing inertia slowing down like this. With a dump valve, the boost is allowed to escape the intake system, meaning the compressor is NOT slowed down by the air being forced back on it, and it is allowed to continue spinning with it's own momentum, perhaps retaining 80% of it's inertia. The time taken to recover the RPM from this near stall is FAR higher than the time taken the recover from a 20% loss.
(I've plucked these numbers of of the air but just to highlight the examples).

If we look on wikipedia for example:
http://en.wikipedia.org/wiki/Turboch...low_off_valves

Quote:

Turbocharged engines operating at wide open throttle and high rpm require a large volume of air to flow between the turbo and the inlet of the engine. When the throttle is closed compressed air will flow to the throttle valve without an exit (i.e. the air has nowhere to go).
This causes a surge which can raise the pressure of the air to a level which can damage the turbo. If the pressure rises high enough, a compressor stall will occur, where the stored pressurized air decompresses backwards across the impeller and out the inlet. The reverse flow back across the turbocharger causes the turbine shaft to reduce in speed more quickly than it would naturally, possibly damaging the turbocharger. In order to prevent this from happening, a valve is fitted between the turbo and inlet which vents off the excess air pressure. These are known as an anti-surge, diverter, bypass, blow-off valve (BOV) or dump valve. It is basically a pressure relief valve, and is normally operated by the vacuum in the intake manifold.
The primary use of this valve is to maintain the turbo spinning at a high speed.

Ever heard of Guy Croft? Engine building legend? Here's his personal take on it:

Quote:

The dump valve gets rid of surplus pressure when the throttle is closed thus preventing the compressor wheel from stalling. Repeated stall (or near stall) can fatigue the blades on the compressor wheel and a severe stall can burst it. Allowing the air to vent off keeps the compressor wheel spinning and thus enhances the turbocharger response when the throttle is re-opened.

I don't really recommend running a turbocharged unit without one, especially with boost pressures over 10psi or so.

22nd August 2011, 13:35

Don't mean to take away from your debate gents. To the OP, I have personally found that the Bosch brand valve is very quiet, nearly silent. Also, have you thought of going with a dual port valve? Best of both worlds, recirculating and atmospheric. Most of the dual ports you can convert to a full atmospheric or full bypass using a plug(which they supply). Just my 2 cents

22nd August 2011, 17:45

love it its like verbal tennis

22nd August 2011, 20:26

I'm just not sure how someone can continue to disagree in the face of total overwhelming evidence to the contrary. I've posted links from industry experts, engine builders, suppliers, tuners and even turbo manufacturers themselves, and yet here we are, still disagreeing. All because one person had a conversation about it. I don't understand. Hell - I hate being wrong, but when faced with the evidence as strong as this, even I would concede

22nd August 2011, 20:26

Loving the debate I personally don't know bugger all about turbo stall so I'll keep myself to myself. From reading most of the posts i feel like im getting more inteligent.

What I want to know is if I remove my dump valve. Will I get the famous flutter noise? If so, anyone want a Bailey dump valve lol.

22nd August 2011, 20:31

Quote:

Originally Posted by stevo1600

Loving the debate I personally don't know bugger all about turbo stall so I'll keep myself to myself. From reading most of the posts i feel like im getting more inteligent.

What I want to know is if I remove my dump valve. Will I get the famous flutter noise? If so, anyone want a Bailey dump valve lol.

Yes you will. And it costs nothing. Right up until your turbo fails

... You'll also loose response on gearchanges - exactly what the discussion is about

22nd August 2011, 20:34

hopefully will see something different come out of this in the next few weeks

22nd August 2011, 20:40

On 8psi though Ross? Will I notice any lag? Will it damage my turbo quickly?

Cheers for the help mate.

22nd August 2011, 20:40

So anyway - to clear this up, as William said he spoke to someone who worked at Garrett, I emailed Garrett this AM, and have now got a reply. Here's what they say when asked the direct question about damage and spool up time.

Here's my email to them:

Quote:

Guys

I hope you can quickly help clear up a discussion Im having with your opinion on the matter.

I understood that adding a dump valve in the intake system will reduce compressor stall and decrease lag. Someone else is claiming that running WITHOUT a dump valve actually improves response (less lag).

Would you be so kind as to clarify the situation for me?

Thanks very much!

And their reply:

Quote:

Hello Ross,

Im not sure what you mean by dump valve, so Ill address my best hypothesis which is that it is a blow off valve.

If this is what it means, then I highly recommend using one in order to reduce the occurrence of surge in the turbo and significantly increase the life of the turbo. Blow off valves should absolutely be used on gasoline engines.

I would tell the person with whom you seem to be having this discussion the same thing.

Regards,

Garrett Gearhead

I replied:

Quote:

From: Dagley-Cleworth, Ross [mailto:Ross.Dagley-Cleworth@somewhere.com]
Sent: Monday, August 22, 2011 8:49 AM
To: Garrett Gearhead
Subject: RE: Turbo lag / dump valve

Hi again

I was under the impression that transient lag was reduced (ie, between shifts) because of the buildup of pressure in the intake system forcing pressure back on the compressor wheel (stalling it).

Disregarding the damage that could be caused by not running a blow off valve, would you say the pickup of boost whilst shifting would be improved or worsened with a blow off valve?

Thanks very much for your thoughts thus far its good to get it from source!

Ross

and finally, their reply:

Quote:

Hello,

There will likely be some advantage between shifts to utilizing a blow off, or dump valve. It helps to keep air in the system, while preventing surging of the wheel. Your general argument is correct in that time that the wheel doesnt have to recover from surging it time that it can be working to produce useful boost.

Regards,

Garrett Gearhead

Hopefully that settles it

22nd August 2011, 20:53

dam you! I have to budget for a poo valve aswell now lol! oh well no harm done

22nd August 2011, 21:34

if you hate the noise and want it as quiet as possible, you'll need to recirc. Given that, and that you'll be running low boost, you could consider a cossie / vw standard recirc valve - I used to run one on my R5GTT. Almost silent (well, as quiet as you'll ever get).

http://www.ebay.co.uk/itm/SAAB-44418...c#ht_918wt_905

22nd August 2011, 21:55

nice!! now thats good know

22nd August 2011, 22:24

So this argument is basically a trade off of either:

keep the inlet pressurised but take a hit in turbine rpm - a la no DV
de pressurise inlet & maintain higher turbinerpm - a la DV

Would the individual turbo not also play a big part, larger slower spooling turbo would see more benefit to maintaining its rpm, compared to a turbo which can spool quickly & might lend itself more to maintaining pressure?

What about if you are at full boost/high rpm & just close the throttle to engine brake without a DV, surely that wouldn't be good?

22nd August 2011, 22:39

Quote:

Originally Posted by Mystic

So this argument is basically a trade off of either:

keep the inlet pressurised but take a hit in turbine rpm - a la no DV
de pressurise inlet & maintain higher turbinerpm - a la DV

Yes - but really there is no benefit from keeping pressure in the inlet. You risk damage to the turbo, and the very pressure you're trying to keep is working against you to slow the rotation of the compressor wheel.

Quote:

Originally Posted by Mystic

Would the individual turbo not also play a big part, larger slower spooling turbo would see more benefit to maintaining its rpm, compared to a turbo which can spool quickly & might lend itself more to maintaining pressure?

Absolutely. That's a very good thought.

However, remember that the larger turbo has more mass in it's rotating assembly (compressor and turbine wheels), and therefore more inertia - so the "bad" pressure on throttle closure has less effect on stalling the compressor wheel. I think it would even out somewhat, but it's something I didn't think about actually!

Quote:

Originally Posted by Mystic

What about if you are at full boost/high rpm & just close the throttle to engine brake without a DV, surely that wouldn't be good?

Yes - that's the worst case situation for the turbo - maximum boost pressure, maximum turbo rpm (perhaps 100,000 rpm+) and then TB closure. That would be the point where you'd have the most stress on the compressor wheel and front side bearing.

22nd August 2011, 23:00

Quote:

Originally Posted by RossDagley

Absolutely. That's a very good thought.

However, remember that the larger turbo has more mass in it's rotating assembly (compressor and turbine wheels), and therefore more inertia - so the "bad" pressure on throttle closure has less effect on stalling the compressor wheel. I think it would even out somewhat, but it's something I didn't think about actually!

Mmm, it may all just be relative actually, the larger turbo will probably be giving higher compression anyway so a greater force back onto the turbine, despite the larger inertia i imagine it would be somewhat similar to the small turbine/low boost.

Good food for though though, good thread!

22nd August 2011, 23:10

My dumps tend to recirculate, stinky ones too, tis annoying!

23rd August 2011, 10:16

Wow just seen all this. Ross bieng his typical self in that his way is the only way everyone else is wrong.

At the end of the day its down to personal preference, how you want the car to act and sound. There are way to many variables to simply say no DV-loads of lag, DV-no lag... I'd be much more bothered about the spec/build/map of the engine.

BUT what i can't stand is people banging on about it damaging your turbo, none of the big power cars round here run dump valves, I don't my mates 500bhp+ astra doesn't, a 700bhp scooby doesn't... All without problem. The internet breeds rumours like this and everyone gets scared.

23rd August 2011, 10:18

Quote:

Originally Posted by RossDagley

Yes - that's the worst case situation for the turbo - maximum boost pressure, maximum turbo rpm (perhaps 100,000 rpm+) and then TB closure. That would be the point where you'd have the most stress on the compressor wheel and front side bearing.

The worst that will happen there is damaging your inlet. I do this with 1.2-1.4 all the time and it has never caused me any problems, on a turbo with millions of miles on already.

23rd August 2011, 10:20

Quote:

Originally Posted by Jungle

Wow just seen all this. Ross bieng his typical self in that his way is the only way everyone else is wrong.

At the end of the day its down to personal preference, how you want the car to act and sound. There are way to many variables to simply say no DV-loads of lag, DV-no lag... I'd be much more bothered about the spec/build/map of the engine.

BUT what i can't stand is people banging on about it damaging your turbo, none of the big power cars round here run dump valves, I don't my mates 500bhp+ astra doesn't, a 700bhp scooby doesn't... All without problem. The internet breeds rumours like this and everyone gets scared.

Yeah. screw Garrett. What do they know.

23rd August 2011, 10:20

Quote:

Originally Posted by stevo1600

On 8psi though Ross? Will I notice any lag? Will it damage my turbo quickly?

Cheers for the help mate.

On 8psi it shouldn't cause any lag at all. And it won't damage your turbo.

23rd August 2011, 10:24

Quote:

Originally Posted by RossDagley

Yeah. screw Garrett. What do they know.

They know nothing...

23rd August 2011, 10:29

Quite

23rd August 2011, 16:54

just realised you got same email. it says it doesnt effect lag to me though.

23rd August 2011, 16:56

stupid computer

23rd August 2011, 17:04

3 fooking posts!!

23rd August 2011, 17:06

you have missed the part off your email which says that it has NO effect on lag. edited perhaps?

23rd August 2011, 17:07

here is the unedited version

Subject: RE: dump Valve
Date: Mon, 22 Aug 2011 08:30:31 -0700
From: GarrettGearhead@Honeywell.com
To: williamsperformance@live.com

Hello Marc,

I’m not sure what you mean by “dump valve,” so I’ll address my best hypothesis which is that it is a blow off valve.

If this is what it means, then I highly recommend using one in order to reduce the occurrence of surge in the turbo and significantly increase the life of the turbo.

Neither of these greatly effects the lag of the turbo. Proper turbo matching, tuning and a host of other things does, but control devices such as blow off valves and wastegates aren’t going change the transient response that much and should absolutely be used on gasoline engines.

I will tell the person with whom you seem to be having this discussion the same thing.

Regards,

Garrett Gearhead

for people that want to see what garret actually replied.

is there a reason you edited this out your email? he must of said that to you as your email after that was regarding that paragraph about transient response?

23rd August 2011, 19:39

I did email them twice (as I posted). Did you specifically request they clarify the exact situation as I did? Thats why I got a second reply.

Well, lets put this to bed shall we! I suspect the debate will continue far longer than either of us care to worry about it - not just on this forum, but also elsewhere judging by how much discussion there is on the subject!

What we can take from this Marc is that the situation is unclear. I was very sure of my position (and still am obviously!), but your email from Garrett, although similar to mine, implies there is no difference in response. I apologise for being so strong-willed with my opinion.

What we can deduce from this is that it seems even those who should know the answer don't.

Unfortunately, we're still no clearer ourselves! Perhaps the way to settle this is to test it back-to-back on a dyno somehow. We should be able to perform a series of tests with a dump valve whilst logging data and see the results, then overlay the data from running without the dump valve. I would guess that's the only real way now!

Did you fancy organising something? I'll be next on the dyno on the 6th September. I can do some runs then if you'd like? You're welcome to come along. Or if you're on the dyno before then. I can come to you? Should make for an interesting time

Thanks for such a good debate Marc - it's still not settled, but at least we're clear that there IS no clear answer!

24th August 2011, 19:25

thats the only way to find out. thats what i have been trying to tell you though, the person i was talking to about it had already done the tests and showed it made full boost 0.2s quicker without DV.

mine wont be back on the road for a while so your best trying it with your car next month.

24th August 2011, 19:33

I'd love to see the results to see what sort of difference it made, with and without

24th August 2011, 19:37

lol, iv posted it numerous times. on an sr20det running 1.8bar with i think a 3071 turbo it made full boost 0.2s quicker without a DV.

24th August 2011, 20:14

well in that case, it's a deal. I'll make a concerted effort to talk to my mapper about it, and see if we can't do a couple of logged runs with, and then without

Hold please caller

24th August 2011, 20:39

be interested to see the results of this actually,

to be quite honest, there's alot these days that needs re testing and re clarifying, lots of stuff was thrown about and assumptions made back in the day, for stuff that was tested and tried and failed or broken etc

lots more info is widely available now then previous, and tuners and consumers know much more now then a few years ago, the advances made in mapping and engine management now is massively impacted all areas of engines and how they work

for exmaple, ppl say you cant turbo a non turbo car with out forged internals, and even those that can wont last long on 8psi and under

i know my car for one will die eventually, but for now im running 15psi and have been for abut 3 months, for 3-4 months before that i was running 10psi, im waiting it to blow up now lol, but for now its soldiering on, its had alot of hard driving, and untill last week was a daily driver aswell

jungle is running standard compression on his rallye turbo, he runs between 1.2 and 1.4 bar on his engine and has done for a long time

there are lots of other scenarios like this, ive yet to hear of a dp or atspeed on decomp engine that has died??

ppl need to get off the chinese whispers and try stuff, if ppl didnt try stuff back in the day tuning wouldnt be where it is now...

24th August 2011, 22:03

theres loads of stuff on the internet that need tested out. i dont like taking advice to be honest lol, even if i do make the wrong decisions sometimes, that goes for every area in my life though not just cars ha. if there is a hard way to learn something i tend to do it that way.