recirculating dump? or run without?
 

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?

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

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

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 :D

interesting it will be something I look into then

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

only if your running lots of boost

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

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

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.

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 :p 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... :oops:

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

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. :D

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

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 :)

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 :)

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

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

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 :p

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.

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.

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.

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.

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.

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.

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:
Turbo Technics - http://www.turbotechnics.com/turbo/faq.htm
HKS - http://www.hksusa.com/categories/?id=1062
TurboSmart - http://www.turbosmartonline.com/index.php?id=624
Greddy - http://www.greddy.com/products/turbo...ow-off-valves/
And finally, Garrett themselves - http://www.turbobygarrett.com/turbob...o_tech101.html
With respect, your engineer at garrett has it wrong.

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.

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.

trying to find the email about the tests.

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.

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.

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. :)

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.

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 ;)

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.

You understand what compressor stall is... right?

http://en.wikipedia.org/wiki/Compressor_stall
Given the above...

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

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
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 :)

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.

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