The Bailey has to go As mentioned in another thread, it does not like the underbonnet temps out here, and is prone to sticking after a certain amount of time. Coupled to that, the sound it makes sound like enormous amounts of compressor surge to me, which considering how "sticky" the valve is, is no real surprise.

On the basis that expensive things are better, I'll probably go for the SSQV. But what will I need to fit it ? Does it come with all the bits - a bit of Googling doesn't really clear it up.

Rog - you run one of these, don't you ? Can you help ?

What is this compressor surge sound? Is it the sound it makes like when you have not much gas applied and then release? Mine makes a funny sound also I have never figured out what it is/was... I guess this is a bad thing?

Compressor surge is when you lift off the throttle and the boost pressure you are releasing is not strong enough for the dump valve to actuate. Say the dump valve opens at 1.0 bar, and you lift off with 0.9 bar pressure.

As you lift off the throttle, the closed throttle butterfly effectively blocks the induction route, whilst compressed air is being pumped in by the turbo. This should be released by the dump valve, but as (in this case) the pressure buildup is not enough, the compressed air has nowhere to go but back the way it came - i.e over the compressor blades of the turbo.

The noise is a sort of fluttery ffff-ffff-ffff-ffff-ffff noise, which I'll admit sounds cool - but it causes the compressor to virtually stop dead in its tracks, i.e goes from say 100k rpm to next to nothing in a fraction of a second.

You can imagine how good this is for the turbo And with my Bailey sticking, this is now happening at higher and higher boost pressures. Having taken the DV26 apart, I have to say I am not at all impressed with the quality of this piece Plastic piston which has worn badly down the sides, making the whole movement very "gritty".

i had same problem with my bailey too.

Aye, rubbish aren't they. How's the Forge ? Better made ? They're all-metal construction, no ? Maybe I should just get a Forge one, but the HKS does sound like the daddy - the separate low boost release / high boost release sounding like the ideal solution to protect the turbo, or is this just marketing spiel ?

Argh, i have been having this sound since i switched to an atmos valve...I thought it was a cool sound, but i guess this is quite bad, is it down to the dump valve being crap then?

Well, to be honest this is just assumptions I am making, based on the fact I know the valve is sticking - when I drive off after, say, 5 mins in traffic, for the first couple of gearchanges I only get say, half the normal amount of boost, then it unsticks and is "fine" again - i.e is not stuck open. However, after this, the compressor surge ffff-ffff-ffff-ffff-ffff seems even more pronounced than usual, so I'm guessing its now sticking closed.

Anyone ?

I must admit I didn't realise the SSQV was quite so much, I might just get a Forge

Ok but sticking close means you are also seeing big amounts of boost is this the case? Perhaps I am just way off here
I think might be time for yet another dump valve hmmm

Well the boost is controlled independently (wastegate / boost controller), so no problems there. Its more that, when the valve sticks, the boost pressure release is not the psssssssssssssttttttttttttttchhhhhhhhhhhhhh that is should be, but the compressor surge noise which sounds more like the compressor blades pushing the air out of the air filter

Blow off valves:

What is a blow off valve and how does it work?


A blow off valve goes under many different names such as dump, bypass, recirc (short for recirculation), diverter, and pop off valves. No one term is correct, the lingo just tends to change in different regions and countries. Basically these valves are all designed to the same job, and we will refer to all types as blow-off valves to save confusion.

What it does: The only job a blow-off valve is supposed to perform is to relieve excess turbo pressure that results from shutting the throttle rapidly under boost conditions. This then answers one of the questions we get asked a lot – yes you need a turbo to fit a blow-off valve! Otherwise you will have a rather expensive paper-weight. It is necessary to release this pressure because it will try to find a way out of the system, and the only way is back out through the turbo. This produces a fluttering noise as the air passes backwards through the turbo, which is often unwanted. There is also a school of thought that a blow-off valve can improve turbocharger longevity or, in extreme cases, prevent damage to the turbo.

There are two ways in which the majority of blow-off valves work. Most aftermarket and many factory types use two pressure signals to determine when the valve should open. The other type uses only one pressure signal to open. We will discuss the former type first.

How it works: The usual arrangement is to have the pressure side of the valve attached to the pipe between the turbo and the throttle, and a vacuum hose on the top of the valve hooked up to the inlet manifold after the throttle body. A spring holds the valve shut. When you are on the throttle, the pressure in the turbo piping and the inlet manifold is equal, meaning that the pressure on each side of the valve is the same and therefore cancels itself out, leaving the spring holding the valve shut. When you lift off the throttle, you have high pressure in the turbo piping, and a vacuum in the inlet manifold. The pressure on the bottom of the valve and the vacuum on the top combine to lift the valve open and release the pressure in the turbo piping, since it can no longer go into the engine.

Blow-off valve myth #1: One of the biggest misconceptions about blow-off valves is that you need to tighten the spring to run higher boost. This is totally incorrect (at least, for a GFB valve anyway), as you can see from the last paragraph, at full throttle, the pressure on the top and bottom of the valve is equal, therefore cancelling itself out. So no matter what boost pressure you run, the valve will stay shut.

Leaking factory valves: Having said that, some factory valves have systems designed into them to crack open at high boost, in order to protect the engine from boost spikes. They do this by designing the pressure to be unequal on the top an bottom of the valve, thereby overcoming the spring at a certain pressure.

If you are intentionally raising the boost level, this is bad news as the valve will begin to leak pressure. Examples of factory valves which exhibit this behaviour are the Subaru WRX MY95-98, and MY01-04, Mitsubishi Lancer GSR, and Nissan 200SX to name a few. Replacing these valves when increasing the boost is a good idea.

Blow-off valve myth #2: The fluttering sound is usually believed to be the blow-off valve. In reality, it is caused by a blow-off valve, but does not come from the blow-off valve. If the spring pre-load is adjusted too tight, this will cause compressor surge, which as described above is the sound of air exiting the turbo.

Compressor surge: You can think or surge as the point at which the compressor blades begin to “slip” in the air, losing their pumping ability, much like an aircraft wing loses its lift when it stalls. In a turbo, this happens in a series of bursts, as the blades slip, then bite, slip then bite. This sets up a pulsing wave in the turbo piping and explains why the sound has that characteristic “flutter”.

The interesting thing about compressor surge is that it occurs much more readily at low turbo shaft speeds. At these low shaft speeds, on road cars this is generally between 2000 and 3000 RPM, compressor surge is not much of a problem, as the loads generated by the surge are miniscule compared to what the turbo encounters at high boost. However, if surge occurs at high RPM and boost, it is possible to reduce the turbo life and/or damage the compressor.

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I get that 'fluttering' noise when I go through the gearbox.

I only got the sound after changing to the Apexi
Open Pod. I'm not sure whether it was always there but
couldn't be heard with the standard Fiat AirBox , or was
a result of the open-pod conversion.

whatever it is , I am really hesitant to call it compressor
surge.

why would you think that the fluttering is surge ?

cheers.

i ve got 18x b o v s coming on friday for sale let me know if interested

The Basics of How A Turbo System Works.

Ok, air comes in through the filter, then through the AFM (which measures the amount of air coming in so the ECU can calculate the amount of fuel required).
The air is then sucked into the turbo, where the compressor wheel increases its pressure and sends it to the engine. On the way there's an intercooler to lower the air temp, because a by product of the turbo is quite a lot of heat.
Before the air gets into the engine it passes through the throttle body, which is what your accelerator pedal is connected to.
The throttle valve restricts airflow into the engine so that you can vary the power it makes.
When it's open the engine tries to produce maximum power, and when it's closed (almost closed) the engine will be at idle.

So the path of air is: filter -> AFM -> compresor (turbo) -> intercooler -> throttle -> engine.

The exhaust gas flow from the engine is roughly proportional to the amount of power it's making, and that flow is what spins the turbo's turbine, which in turn drives the compressor.
So, the more air going in, the more power, and hence more exhaust coming out, which means more boost, which means more air, hence even more power. It's a feedback loop which is kept under control by the throttle input from the driver.

To keep the maximum boost at a safe level there's the wastegate, which is just a valve allowing exhaust to bypass the turbo, and therefore not spin the turbine any faster, or create more boost.
It works in a very simple way. The valve is held closed (all gas goes through the turbine) by a spring, until it is forced open by a diaphragm driven by boost pressure.
When the appropriate boost is reached the wastegate starts to open, and the turbo will stay at the set boost level while the exhaust flow can still increase as the engine revs rise.

All of this works quite simply under constant acceleration:
Air comes in, is compressed to the set boost level, intercooled, used by the engine, and the exhaust keeps the turbo spinning.

It becomes more complex when you start changing throttle settings.
If the throttle is wide open, and you're at full boost accelerating, then close the throttle (for a gear change, or back off) suddenly the turbo is pushing against a closed throttle, and at the same time the engine has stopped producing exhaust gas, so the turbo starts to slow down.

Now that there's a whole intake system full of compressed air with nowhere to go, and the compressor is not being driven by the turbine - so it can't hold the same air pressure that it did while spinning flat out. The air will start to flow the other way, which means going backwards through the still spinning compressor.
This is where compressor surge comes into play. The compressor is still trying to pump air, but at the speed it's going it can't provide as much pressure as there already is in the pipe.

This causes the compressor to "stall". Stall is a misleading turn used here, because it doesn't mean stall as in to stop spinning. It's the aerodynamic stall, like a plane that's tried to climb too steeply, or has slowed down too much to maintain lift.

The smooth air flow through the compressor blades is broken up, and some of the air will flow back out through the compressor, making a hissing noise.
Centrifugal compressors work on a "squared" relationship for speed vs flow / pressure, so if the turbo slows down to half speed it will only be able to hold a quarter of the boost pressure.

The "chopping" or "fluttering" sound is caused by the accoustic effects in the intake system, determined by the size and length of the piping / cooler.
Rather than air constantly flowing back out of the turbo it tends to come out in bursts, triggered by pressure waves in the piping hitting the compressor.

Generally though the flutter is the sound of the pressure wave cause by the throttle closing bouncing back and forth between the turbo and the throttle plate (the longer the pipes the slower the flutter).
Every time the wave hits the turbo it causes the compressor to cavitate, which makes the noise.

It's not the blades chopping the air making the flutter. Since the blades are spinning at 80000+rpm you wouldn't be able to hear the individual "chops"

If you listen closely you'll actually hear a more constant hiss sound at higher boost levels and rpm when backing off. (ie, a "whooosh" rather than a "chop chop chop")

The loudest flutter tends to occur at lower rpm and boost levels of only slightly above atmospheric pressure (0psi). This is partly because the sound is "chopped" up more noticeably, and partly because the rest of the car is making less noise at lower speeds. This is also where it's least damaging.

Car manufacturers don't like weird noises from the intake system, so they use restrictive airboxes designed to muffle the sound, and more recently (SR20 onwards) used a Blow Off Valve.
The blow off valve provides a new path for air to get out past the compressor. Instead of forcing its way back through the spinning blades it is piped out of the intercooler piping and back into the intake piping before the turbo.

Obviously it could be vented straight out to the atmosphere, but the AFM has already measured that air coming in, and if it doesn't reach the engine the ECU will be injecting too much fuel in its absence.
(Also, venting to atmosphere makes a bit much noise for conservative owners and manufacturers)

The BOV works a bit like the wastegate, in that it's held closed by a spring, and controlled by a pressure operated diaphragm.
This time though the boost pressure helps keep it shut rather than open it.
The control air pressure for the BOV comes from the plenum, which is the chamber between the throttle and the engine.
When the throttle closes the engine creates a vacuum (negative pressure) in the manifold / plenum as it tries to suck air past the closed throttle.
The vacuum is used to "pull" open the BOV, to vent the excess air in the intake system, preventing "flutter" and other noises.

A BOV is a compromise device because, to eliminate all fluttering it will have to open at very low boost levels, and very quickly - which means that it must have a very weak spring. This can cause some leaking of boost due to the valve not staying sealed properly, and also means that every time you back off the throttle, all the pressure in the intake system is vented. When you open the throttle again the turbo will have to build up all that pressure again, whereas if there was no BOV there'd be more pressure remaining as it's a lot harder to get out through the compressor.

Most aftermarket BOVs won't open until you reach 6psi or so of boost (because with an atmo venting BOV if it leaks boost you'll have major problems - whereas a slightly leaking plumb back type won't cause bad running, just a very slight loss of power)

When you start running well over stock boost, and have larger intercoolers / intake piping obviously there's a lot more air in the intake system, and it will be at higher pressure - so when you back off the throttle there's a lot of air trying to escape through the compressor. This means it will be slowed down quite quickly and violently, which puts large loads on the turbo bearings, wheels, and shaft. Repeated hammering by high boost backoffs can harm the turbo, and the amount of slowing each time causes a lag when the turbo spools back up after each backoff / gearchange.

The best compromise setup is to have a BOV which will open when you back off at over say 6 psi, and vent back into the intake to prevent the rich running problems of atmo BOVs. If it's too loose you'll lose boost response due to too much presure being lost on gearchanges, and if it's too tight you'll lose response due to the turbo being slowed down too much - and potentially damaged by the rapid deceleration.

Why does it flutter when my gauge isnt reading any boost?
The reason it flutters even when you can't see boost on the guage is that you're looking at the pressure in the plenum (after the throttle), but the turbo can actually be producing a bit of boost in the cooler and intake piping.

Noise reasons mainly Chang. I just don't see why it should be making such a ffff-ffff-ffff-ffff-ffff-ffff-ffff noise as it is all the time - the valve should open and release the pressure without so much fuss !!

But its more the sticking when its hot that is making me want to replace it. The Bailey really looks pretty cheaply made when you take it apart, so I guess I shouldn't be too surprised that it seems FUBARed

To fit a HKS SSQV you need the dump valve itself plus an adapter for your intake tract (plus the fitting kit which attaches the two bits together). The 'universal' adapter is a weld-on adapter which is only useful if you have some metal piping to weld it on to (they come in aluminium and steel). Then they also sell the SSQV as a kit for particular applications. Basically you need an adapter with a 25mm pipe so that you can fit it to your standard location. You can buy the adapters that fit the coupe separately which is usually cheaper than buying a car specific kit (some of the car-specific kits will fit the coupe but there is not one for the coupe)


BTW when people talk about compressor surge they are not usually talking about any context relating to dump valves at all. From a turbo builders' point of view compressor surge is a mismatch between the compressor and turbine wheels that cause the compressor to over accelerate if you like leading to a spike in the boost, followed by the boost dropping back when the turbine wheel cannot handle the extra speed. When a turbo has compressor surge you can see a see-saw effect on the boost where the boost controller (be it the standard peiburg EBV or an aftermarket controller) is unable to deal with the change in boost fast enough (related to the sample and reaction rate). Depending on the severity of the mismatch the turbo will either not visibly surge (i.e. the boost controller can handle what surge is there), surge only in high gears or surge in all gears (where the higher gears will have more of an effect).

When the turbo flutters between gearchanges on boost that is compressor stall. When you lift the throttle the turbo is still spinning and so making positive pressure, but that pressure has nowhere to go because the throttle butterfly is closed so the pressure built up stalls the turbo. Since the turbine side of the turbo is doing no work (there is little or no fuel being put in) there is no resistance to the stall. The function of a dump valve is to release the pressure build up before the compressor is stalled so when you are back on power the turbo is already spinning and so doesn't have to spool up again. The bigger the turbo the less time you have to change gear and keep the turbo spinning at a useful speed.

imo the forge is made a lot better than the bailey,iv got the forge recir dv which plumbs back in to my straight ind pipe, it still got that dumping sound as it dumps it through the cone filter. forge motor sport can also provide the dump vavle with different presure rated springs give um a call on 01452 380999

dont give them a call , just noticed ur location lol

LOL, I've had parts shipped here from a lot further away than Gloucester, believe me !

OK mate - the Apexi looks good so thats the first hurdle out of the way I'll wait for an update on Friday

James,
i told you that you will face the same problem even if you clean it!! anyway, i have a solution check my thread..

http://www.fiatcoupeclub.org/forum/showflat.php?Cat=0&Number=141679&an=0&page=0#Post141679

You did say it mate, and you were right !!

PS excellent post on the solution I'm no expert but even when I took the DV26 apart, I was surprised at how poor quality it was, especially with the size of the seal, and the plastic piston. Rubbish.

hi jayell, not in post this morning so probably monday/tuesday now dont worry your 1st to contact

Good price !! Game on

edit : would it come with all the bits needed (what are the bits needed, btw ?)

yes dont worry jayell ill make sure its a perfect fit for our car