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?