Hi all, I was browsing through the tinterweb 'tother day, and stumbled across a thread talking about the benefits of running without a dump valve, basically saying it's smoother....

haven't a clue if this is the case, has/does anyone on here run without one, and can give an opinion....

probably covered before, apologies if thats the case....

If you call turbo stall smoother?

Complete rubbish..

I thought so......cheers!

There have been many many many many arguments debates on the subject of running without a dumpvalve.

The only "improvement" I have heard about is the pidgeon noise if you like that kind of thing

Otherwise as the knowledgeable Sam says, it creates turbo stall, which I can't possibly see making anything smoother.

Some interesting reading on it here from Guy Croft, basically his opinion is that running with no dump valve risks creating turbo lag and damaging the turbo itself.

Having said that, last time I advised on running a dump valve on this forum I got some stiff disagreement so there's certainly those who think differently...

Personally I agree with Guy Croft and Fiat that a dump valve should be used.

Gareth

My experience concurs with Guy Croft's findings on lag...

The turbo spins at upwards of 100,000rpm so it is not stalling as the boost is running back through it, although I'm sure it does slow it down though. This would explain the slight jerky-ness I experience betwen gear changes. It is definitely not smoother than with a DV installed.

I've been running with no DV for about 20k and my standard turbo is fine (and on 115k). Since my OE one was broken I removed it and never got round to replacing it. Can't really comment on the lag, it may be worse than with a DV, however without a DV my turbo is on full boost by 2,500rpm. If you were slow upshifting from WOT to WOT the turbo would need to recover the speed lost, that said it does do it rather quickly as you tend to drop back into high revs if you are going for it.

It is on my to do list of things to do but I've just not got around to it, other things keep coming up!

Not been running one on my 16vt for all the time I've had it and it's been totally fine and on the stock turbo on 115k and not a breath of smoke or oil anywhere! (touches wood)

Dump valves, in my opinion sound chavtastic, (apart from the HKS jobbies) and create just as much lag as running without one.

As Vas says here - http://www.fiatcoupeclub.org/forum/ubbthreads.php?ubb=showflat&Main=37959&Number=470320#Post470320

"did around 150K km in four years without a DV (both pipes blocked) turbo is still fine, no play, no smoke, worked flawlessly.
Surge sound is so

I think it's one of these urban myths tbh..."

It sounds great, drives fine and is up to you whether you fancy running without one or not.

There will always be stories of people running with no dump valve and having no problems whatsoever, the same as there are stories of people running decat on a standard turbo with no problems alongside stories of people killing their standard turbo within a week of decatting.

In my view what's important is that people are informed of the risks (from forums like these) so they can make an informed choice and take the risk if they choose. What's scary is people (not on this forum) swearing blind there will never be any problems with running no dump valve and pretending manufacturers just fit them for fun...

Gareth

In theory, the action of turbo stall should lead to shaft play and, eventually, it does BUT the life of a turbo without a dump valve is not *that* much shorter than that of one with.

You'd be surprised how quickly a turbo spins down when the revs are off, even from full chat so stalling it isn't quite as bad as you'd imagine.

By keeping the boost pressure in the system, lag is reduced. A BOV will vent that pressure, increasing lag and sometimes causing fuelling issues. A re-circulating dump valve should both keep the turbo spinning and help retain some of the boost pressure but it's still not ideal.

That's my view anyway, afterall, when's the last time you heard a turbocharged car in motorsport use a dump valve - it doesn't happen.

By Jingo, I'd never thought about it really!
But listen to that chatter!

And I must admit I've been through lots of videos of rallying and can only hear pidgeon chatter.
But then motorsport turbos probably get rebuilt quite alot anyway

Yeah when cars are driven like on that video I think blue smoke on startup after 120k miles is the least of their worries

Never ran a DV for over two years on T34 No problems DV's are shiny things for kids and magpies IMO.

I'm pretty certain that manufacturers fit recirc valves primarily for noise suppression.

I've read up a huge number of threads on different forums (because I'm sad and get obsessed with car stuff) and you'll never find anyone who says "I ran without a DV and my turbo blew up." It just doesn't happen.



Now if you were running THIS at 30 psi, MAYBE you might wanna think about a recirc valve...

i have a whoosh type on mine and hate it would rather have a recirc or maybe none but if it is not needed why would the manufacturer fit it?

Why would someone who calls themselves lewoosh, hate the woosh sound

Recirculating all day long, ticks the most boxes. Best performance choice and no silly noise.

Yep if you're old and boring which I can imagine you must be lol!

rally cars CANT use them as they run anti lag,doesnt work.and dump valves were fitted by manufacturers as a noise suppression device as normal people running turbo cars would repeatedly bring cars back to dealers complaining of a strange noise.
and as for the performance related issue,ive never started blowing up a baloon,then if i need another breath leave the air to escape again before i blow again.i always pinch the bottom of the baloon between breaths,makes it a bit quicker.

THIS is chatter: http://www.youtube.com/watch?v=hEK7POxpVeE

...and also the best combination of sounds ever

Haha I like what you said there GS_Racing and so true lol!

Oh and Nedge the Group B Quattro is PORN and makes the perfect sound!!!

Mid thirties, is that old? sometimes feels it.

I could definately bore you on the engine fitted to your car as you don't like to listen I can tell.

Oh I like to listen to the noises my car makes you see. Mid thirties, well that's 10 years on me. Perhaps I'll want it quieter then?

[quote=DidCoop) Perhaps I'll want it quieter then? [/quote]

If you value performance over sounds by then you'll have proper engine noise and won't need the silly pishswishstallshxt.

the benefits of introducing heated air into the inlet of a turbo must be staggering.please do not belittle his choice on the grounds of performance,you would be hard pressed to see real life results.

lmao i called myself lewoosh when i was all excited about getting another turbo car but had a woosh one on my r5 and always wanted a recirc but already had a decent woosh one on so till i sort everything else out its last on the list but i do love the explaination of the balloon and yes why would you let air out each time you take a breath ha ha best explaination ever SO if i take mine off what sorta noise do i get i love the rally car sound how doi get it

And Lewoosh you have just shown a good example of a young guy with a turbocharged car. Oh dear oh dear oh dear.

The only reason mine is blocked off is due to the fact my Bosch device doesn't like 1.3 bar. I'll get a HKS SSQV when I can afford 1.

GS you're totally right about results. Perhaps when I get my HKS device I'll put it on the rollers before and after so we can see what performance different (if any) it makes.

As you say the brief moment of heated air being put back into the inlet to be diluted by the fresh incoming would take a bit of seeing in real life were it not for the fact that it's a higher mass than atmo being fed straight back in. Response can only benifit. If the recycling bothers you vent to atmo and live with the noise, I hate it. To not provide a vent of any kind is what makes no sense at all, that can only stall the compressor which makes it job harder. When you blow your balloon you pause to take breath, since when does a turbo stop spinning and pause for breath? wishpishstall

touche lol agreed turbo does not stop i will wait till i can afford a decent recirc untill then im happy to be a chav lmao

Chavtastic!

You ALL Wrong!!!!!

You should go out and get one of these

http://cgi.ebay.co.uk/Saber-EDV-V3-Fake-...=item23073b113c

ha ha think technicaly im too old to be a chav but if thats my label ill start wearing a dappy hat and shouting nai nai nai lmao

Ooooh nai nai naiiiii!

Get me Sabre Valve on my Saxo init init.

http://www.youtube.com/watch?v=u1jpJppnseI

mate that is so sh*t at least my chav valve is real

A stall isn't relating to the speed of the turbo (although that is a secondary product of the action).

A stall is when the air flow goes from being laminar to turbulent in the turbo. The compressor wheel and the turbine wheel are like lots of little wings attached to a centre point and thus laminar flow is critical to efficient operation.

Without a dump valve the pressure upstream of the compressor becomes too great when the thottle is closed on boost and this in turn causes the air to break away from the blades of the compressor and become turbulent.

This is a problem because suddenly there is high pressure where there should be low and low where they should be high on the compressor wheel.

As well as resulting in a slightly lower turbo speed, when you do get back on throttle the air has to "re-organise" itself and this is the lag that is felt.

Performance aside, the major problem is that the major localised pressure changes occurring in the compressor are akin to hitting it with a hammer.

So szkom are you saying running a D/V is better than running without one or that both are bad?

Running a D/V, re-circ or atmos, is better than none as without any, i.e blocked off, you run the risk of damage and increased lag.

I'm definitely going to test this theory on the dyno next week.

Be interesting to see. Fluid dynamics states the air will become turbulant, but the real world...

Will be good to see if there is any noticeable increase in lag

I'm genuinely interested to find out so will post my findings!

If you read the Guy Croft link I posted earlier in this thread you'll see a similar debate, that in theory the performance should be worse with no DV but on the rollers it's hard to prove. Doesn't mean that the performance isn't impaired by running no DV, just that it's hard to prove on rollers

As I mentioned earlier, the science of a DV makes sense to me and enough people more learned than myself seem to think the same so I'm all for them. Of course it's all personal preference, as long as people have the facts they can all make their own mind up

Gareth

You're not going to notice any difference on the Rolling road whatsoever. It'll just be slightly less responsive and the turbo will probably wear ever so slightly more without the DV.

Like was mentioned earlier....
Rally and race cars use anti lag systems. In old cars this involved having another injector firing fuel into the exhaust manifold to cause combustion to take place in the exhaust manifold and keep the turbo spinning at high RPM. Modern anti lag technology achieves the same goal by controlling ignition and injector timing, some even use a variable vane turbo.

When the throttle is closed it causes a restriction. Pressure rises between the compressor side of the turbo and the throttle body and it is this pressure that gives rise to the chatter noise you hear on cars without a dump valve.

On any car without an anti lag system the turbo is already slowing down on closed throttle, due to there being reduced exhaust gas. By forcing it to try and compress a closed vessel (The inlet system) you are in effect slowing the turbo even further

A dump valve is introduced to the system to release this inlet pressure build up. Whilst it is not an absolute requirement it does offer the benefits of cooler turbo temperatures, less stress on the turbo internals, better fuel economy and reduced turbo stall. It also needs to be understood that the Fiat Coupé engine management system was designed for an engine running a recalculating dump valve. The engine management (sensors etc) all expect that at closed throttle conditions the excess inlet pressure will be released back into the pre-turbo compression line.

Removal of the dump valve may have no immediate or long term effects but I see the only reason for doing so would be to make your Coupé sound like a rally car. To my mind the Coupé already sounds fantastic (Well the five cylinder version does)

Thing is though: All the maths and the science behind why you should run a DV is perfectly sound and no doubt correct. But in the REAL world, where things actually matter, has anybody ever proved they've taken 10ths off their quarter miles by running a DV? Do DV's add an extra five years' life to your turbo?

Nah.

On the other hand: Do faulty/incorrectly fitted DV's causing running problems? Are they an added expense and complexity that could be used somewhere else more effective.

Yep

Until the day when someone does some physical tests and comes up with the proof, no DV FTW.

Far too much 'desktop tuning' goes on on forums.

Do the maths, build it, test it, prove it. The end

Erm...Fiat did, that's why we don't have to

Here here!

Garrett




You did do the maths right?

The probable reason why Fiat fitted a recirc valve has already been mentioned. I don't hink Fiat care whether your turbo lasts ten years or eight years!



Read it years ago and unfortunately no proof. Just words. Shame really.

Actually the nearest I ever saw to any sort of proper test was one in Redline where they tested 0-60 times (or 1/4s??) With a particular car fitted first with a DV, then recirc, then blanked-off.
DV came last, blanked-off came second. To be fair there were 100ths of a second between all three results, IIRC.



2 years, and 3 track days, running 15 psi and now 18 psi. Turbo removed several times for various reasons and not a hint of wear.

So no, not really. I just built, and tested it, and might possibly be proving it.

How about you?

KJ I'm liking these replies lol!

Surge, do that maths if you can.

Appears to be some confusion over surge and stall which are two very different things.

I hear a lot about things like, 'why do I need this?'. I don't understand why folk are continually questioning accepted practice when it comes to turbocharging.

GC

While I don't really agree with the terms being used surge vs stall this is as I see it in this discussion, and Szkom knows a lot more than I about fluid dynamics, I hope this will help some reading this

It is easiest to see on any compressor map. Compressor surge (as per compressor maps) is the compressor flowing more air at a given pressure than an engine can consume at those given pressure and revs parameters and the compressor goes into surge - I use the below GT3076R map below for demonstration. At 3000rpm and 1.5bar on the map you can see a 2l engine (and yes there is a bit of maths to it) is below the surge line in this example ( the engine air use calculation is off the island to the left). Here the compressor would go into surge as at 1.5bar the minimum air the compressor wheel will pump is greater than the engine will consume at these revs (it's even called the surge line)

This happens when at a given pressure and revs the air off the compressor blades leaves the turbo for the engine but only say 80% of it can be used by the engine, due to volumetric efficiency, capacity etc for a given turbo/engine combo, So where does the other 20% go, it backs up in the inlet plumbing and tries to come back out the inlet pipe, back past the compressor blades. The compressor beings to chatter and surge as the air reaches it and basically tries to turn it backwards and flows backwards over it as it escapes -. However the exhaust is still wide open and receiving maximum airflow from the engine, so the compressor is still receiving positive "drive" from the exhaust turbine via the shaft - this is not good for turbos as the two ends (compressor and turbine) are working against each other and a broken turbo shaft can result.



In regards to BOV's or Dump valves what you are talking about is stalling the speed of the compressor (it still surges to some extent) and the air flowing over it, which can be spinning at circa 125,000rpm at WOT, with backed up air but unlike above in this example the turbine is not in positive drive (throttle plate is closed and exhaust gas flow is well down). If the compressor is pumping hard and you lift off to change gear and the throttle plate slams shut, not only do the exhaust gases slow (loss of positive turbine drive from above) but that compressed charge air needs somewhere to go, with no blow off value it can't so it quickly backs up and slows "stalls" the compressor, aslo as per szkom the air "falls off" the blades - as the air backs up and the compressor slows rapidly, without the positive drive of the turbine it doesn't surge in terms of this discussion but rather stalls, it is less harmful to the turbo i would say as the two ends are not working against each other so strongly - but in regards to the turbo shaft speed revs are being lost quickly, O.K. if you are flat shifting on a sequential box maybe not a problem but in the coupe world why would you want to stall the compressor speed and airflow - you wouldn't.

Antilag is a different ballgame, by introducing un-burnt fuel into the exhaust manifold you can keep the turbine spinning (positive drive to the turbine with the throttle plate closed) and the compressor surging with your foot off the gas, you actually create exhaust flow to drive the turbine, but these turbos are built to take it (WRC antilag units etc - seen the price !) - ever tried running antilag on a standard turbo, it would not be happy - again broken shaft can result not due to surge under throttle but rather surge caused by the antilag and positive turbine drive on a closed throttle position.

With a BOV of either type the air vents away, the turbo revs are higher after the closed throttle, the air stays on the blades, and boost response is improved.

Sure you can run without a BOV, is it ideal and best for performance and turbo life, i doubt it

@did the dyno will not show you any different you're not changing gear

Most excellent Paul, good writings. Not sure the effort will have much effect though. I only mentioned surge as maths was brought up, stall would need equipment as you'll know but is more the true description as said. Doesn't help to throw the turbo towards surge though does it.

http://autospeed.com.au/cms/A_1457/article.html - This article speaks volumes

1NRO what experience do you have with turbos then?

About 15 years running gralies on my own, designing and commissioning engine parts for the engine in your car with a large amount of DIY on certain parts with insatiable thirst for research. How about you?

I was merely asking and from what I've read I'm happy with the choice of how my car's setup!

I thought I was asking you what your experience is with turbo cars?

^^No work on actual turbochargers though?^^


That article that DidCoop linked makes for some reeeally interesting reading. Someone who truly has "Done the maths, tested it, and proved it" when it comes to turbos. And the ONLY person I've EVER heard mention using a turbo tacho (No, it's not Mexican fast-food). How the heck can anyone say what a compressor wheel is or isn't doing at any point without one.

I think it answers every question about the usefulness of dump valves and recirc valves once and for all.

It really is an interesting article and I strongly suggest everyone should read it for themselves. But here are few brief excerpts:

"The blow-off valve is designed as an emissions control device for OE manufacturers."

"Some people do think that at the absolute upper extremes of boost levels - about 30-plus pounds - the blow-off valve does, somewhat, save the compressor wheel and shaft from trying to rotate backwards. It doesn't actually rotate backwards at all..."

"We've tested one on a manual gearbox performance car run at Winton Raceway... it would lose 2 seconds a lap putting the [dump] valve on."

"...it was quicker through every timed section without a dump valve. You'll never hear a World Rally Car going pssshhht because they don't use a dump valve - you get the woof-woof-woof noise instead."

"The fact that people think that [dump valves] keep the turbo spinning is a problem. The people that suggest this have never had an engine on the dyno and never had a turbo tacho in their hands."



End of argument surely??

Emissions control device...losers

Simply one Internet article KJ, hardly worthy on being conclusive is it. As you said earlier, do the maths. Learn about air and how it behaves would be my advice.

Sure, loads of work on the turbo chargers on my cars over the years, they've numbered over 20 and all had turbo chargers. Just last week I stripped and rebuilt the turbo on my girl friends daily integrale, buckled and went and had it's balance checked just to be releived of £80 to be told it was fine and good to go. Why I'm justifying to you what I have and haven't done on whatever car part you might mention I'm not sure, take it from me I've spent most of my life doing ground up restorations, more work than the average person in a life time. What makes you tick then?

Question.....

Answer......
And follow up question......

----------- TUMBLEWEED MOMENT------------

Classic

I never get this I've done it for years so it must all be fine argument. Indeed I know plenty of people who smoke but have never had cancer........

Being old I also knew FAR TOO many people who are no longer with us due to smoking related cancers......

That webpage link makes far too many assuptions and appears to take little account of automotive engineering and physics principles

To be clear.....

On a Fiat Coupe (Designed to have a recirc dump valve)

As Standard = Reduced Turbo wear, cooler running, correct fueling.

BOV = As above, generally, but potential for overfueling & damage to CAT.

Blanked off = Increased stress on turbo, hotter running, greater possibility of ovefueling and even underfueling.

So all sensible advice would have to say keep the standard set up and modify at your own risk.

I am going a bit off topic - this thread is about BOV not surge so sorry for the hijack but further to my explanation of surge vs stall - this is surge - not cool but a good vid.

A blow off valve will have no effect on this but watch the turbo move for the phyiscal effect of surge

http://www.youtube.com/watch?v=nCj6Spwl1CU&feature=player_embedded

Some people raised an intetresting point why WRC and other race cars don't run BOV's - good question and I wanted to know why myself so a bit of research it seems they do of sorts, plus as prevouisly discussed their IHI rx turbos are biuilt for it. Basically the excess intercooling plumbing pressure charge air rather than being plumbed into the turbo inlet (recirculated) or vented out to atmosphere is actually dumped straight into the exhaust manifold to assist in the antilag, you don't want to vent it off if you need it to drive the antilag

good explanation I found from wiki WRC, the point being the air doesn't back up in the intake but is used in the antilag, and the antilag computer can take care of it based on the fuel it adds.

Today's WRC cars also use anti-lag systems which feed air directly to the exhaust system. The reason is that these systems are more refined, more effective with advanced computer control, and also quieter. Today this kind of system has reached such a refinement that it’s even possible to use the system in a road car. A recent example is the Prodrive P2 prototype. The system works by bypassing charge air directly to the exhaust manifold which acts as a combustor when fuel rich exhaust from the engine meets up with the fresh air from the bypass. This will provide a continuous combustion limited to the exhaust manifold which significantly reduces the heat and pressure loads on the engine and turbocharger. With the latest anti-lag systems the bypass valve can not only be opened or closed but it can actually control the flow of air to the exhaust manifold very accurately. The turbocharger is fitted with a turbo speed sensor and the engine management system has a map based on throttle position and car speed which is used to find a suitable turbocharger speed and boost pressure for every condition. When the engine alone can’t provide enough exhaust energy to reach the turbo speed/boost demanded by the management system, the bypass valve opens and exhaust manifold combustion begins. This not only reduces turbo lag, but it also allows boost to be produced at very low engine speeds where boost was previously limited by compressor surge or exhaust energy. With relatively high boost at low speeds, this makes the low end torque superior even to large naturally aspirated engines. The system is quite loud and is banned on some rallies because of the noise it produces.

It's an interesting system and may explain the lack of BOV on other top end racers?

@Saint. Off topic, but Good info, and nice vid of proper compressor surge. ie. going over the left-hand side of the compressor map.

Yeah exactly. "I've run a dump valve for years and my turbo has never blown or got stomped on by elephants, therefore dump valves save turbos and act as elephant deterrents"



Glad to see your an automotive engineer. No offence to you (or anyone else for that matter) but you're missing my entire point - PROVE IT don't just tell us what they do/don't do, show us. A video, an anacdote, anything.

The Nispro guy in Didcoop's link said he used a turbo tach and found that the compressor slows rapidly, DV or no DV. He said he timed his racing cars and they went slower with a DV fitted. So, according to his anacdote, he proved it.

As pointed in DidCoop's link. recirc valves are fitted to cars with airflow meters as an emmissions control device. That's been established now and I think that's a perfectly good reason to fit one.

However cars with MAP sensors, such as the 16VT, won't be affected by those emissions/fuel metering problems at all. That means the recirc valve is there purely for noise suppression.

Being automotive engineer, you knew that already though, right?

And as for hotter running. Care to explain that?


Something we can agree on!

First off this thread is regarding dump valves on 20VT, so MAF & not MAP sensors

My comments in this section are being made to try and explain to the normal user there is absolutely no benefit in removing the dump valve or fitting a BOV. In reality it could actually cause problems that if you are not aware of could result in damage to components or internals.

This is not to say that for cars designed for drifting, drag or track racing and modified as such, running without a DV could offer some turbo performance advantage.



Yes the link does say that, but it is just not true!!
The link also tries to say that WRC cars do not use them and that is proof they are not needed. Again this is NOT true. Some turbo charged Rally cars have used them. Indeed the BOV Atmos type valves were becomming common and were banned by the FIA. Teams were forced into using recirc systems.

Come on KJ, answer my questions and provide some proof as you call it. It's you deviating from normal practice, you proove it.

Yep agreed! I can go with that.
Throughout this thread I think we've now established that recirc valves have a use on at least some MAF metered cars, and nobody can come up with any, even anecdotal, proof that running without a DV is harmful to a turbo.
I'm not just arguing here for the sake of it. Just sick of the baseless "your turbo's going blow up/tear a hole in space-time" mantra to DV questions.



Cool. Interesting stuff. Any idea why they banned it? Noise regs?

Don't worry, 1NRO, I haven't forgotten you. Things to see, people to do...

What makes me tick? Engines, tuning, mapping, power, and more power!

Entirely self taught, I do all my own work, from full engine rebuilds, ecu mapping, fabrication - all the way to just changing a clutch.

Projects to date include:

Nova SR on twin Dellorto DHLA's, Corsa B, close-ratio gearbox, Mk 2 dash transplant, Astra GTE digital clocks (yeah, yeah it's a Nova. We've all gotta start somewhere right!)





The UK's only 100% homebuilt and tuned Clio 16V turbo conversion. Everything home fabricated - even the exhaust manifold and downpipe. Also mapped by myself. Dyno'd at just over 200bhp (Featured in PFC magazine if you're interested!)







My current 16VT. Again homebuilt and mapped by yours truly. Only making a measly 260 bhp / 289 lbs ft @ 17psi at the moment, but I'm working on it!

If you're wondering about the weird AFR, BTEC's WB lambda spazzed out halfway through the run!

Read the project page




All pretty modest IMHO. But I'm relatively young, and do the best with the money I have (Most of my projects were done whilst studying and bloody poor!).

I've spent hours and months and more months reading, building, rebuilding, trying things out, testing (especially with regards to mapping), and yes occasionally blowing [censored] up. Hey it happens - any tuner that tells they've never broken anything is a liar!

I'm by noooo means an expert and will never pretend to be (well, until I become one!). However I think it's fair to say I know more than most...

Proof? I gave you the best proof I could personally manage about two pages back.

What about you pall? Done any particularly interesting projects? Post 'em up I love a good read! (although in a new Thread somewhere I think. This thread is beginning to go off topic!)

Hats off for the engine mapping DIY, my weakest area by a margin is electonics.

Your just not looking hard enough for my work, there's plenty on the internet. I'd show you a ton of stuff that would be of interest to your current car but not feeling too sharing just at the minute, sorry. One thing I will say PALL?!!? is nothing I write is without careful consideration as to how sure I might be, I don't guess or believe anything without doing my homework, I'd rather admit I lack the knowledge.

P.S. That's not proof ;-)

MY POST HAS BEE EDITED

Please do not post personal insults, it is against the Forum Rules.......

what i dont get is 1 how would the dump valve lower or change emissions

Because metered air is getting dumped to atmosphere, which will affect the AFR.

It is based on what I talked about a page back, on a MAF sensored car (like the 20vt) with a recirc BOV from OE you are releasing the pressure between the turbo and the throotle plate and re-using this old pressurised charge air downstream of the MAF, so the air is only measured once and emmissions are "clean" when compared to dumping pressurised air, ie venting to atmo as when this happens more air is drawn through the MAF and measured hence more fuel is added by the ECU even though some air has "escaped" through the BOV and fuel is not needed for that measured air

Guys....

Can we please try and keep this thread civil. Please avoid personal insults and tadger wagling.

I would say that the Balance Motorsport website has a fine detailed description on this whole subject.

Like they state it is extremely difficult to prove that any turbo wear or failure could be directly attributed to running without a DV.

With an absence of any conclusive physical evidence one has to return to text books and science principles. It is obviously possible to predict precisely where any wear and eventual failure would take place but it would take a good deal of time and effort. I will keep searching to see if I can find anyone who has conducted such research.

My dump (have a Forge) hose came off on Spa and it does affect the lag a lot. Every gearchange was like starting over..
It doesn't feel good to get that massive pressure before the throttle either - although nothing came off or broke this time.

i start work at mml sport works rally team wednesday so ill see what the pro,s have to say lol

Oh dear, oh dear oh dear!