Compressor surge, Is it really that harmful ???

[BlitzBoy]

Carl Recirc valves still lose you boost on the stock setup, the other main use of recirc valves was to eliminate noise of the dumped air by feeding it back into the Air filter Air box on the stock setup, therefore eliminating the Tsccchhh noise as you would get from normal DVs, Mazda couldnt release a car which make weird and wonderful noises of strange plumbing lol, thats why Manufacturers sell cars with recirc valves and not atmos DV on turbo cars, they are a noise surpressant device (recirc valves) as well

[SiH]

On a car with an AFM rather than a MAF sensor, a recirculating valve helps the car run a lot better than a BOV as well. Obviously, this isn\'t relevant to most on here, but with a MAFif air is dumped out of the inlet tract after the MAF has metered it, then the car is supplying fuel for air that isn\'t there - hence momentary richness. This can make the car stumble between gear changes, as well as damping unburnt fuel down the exhaust.
My S14a ran soo much smoother with the stock recirc valve than it did with no valve at all, or with a vent to air valve.

On my FD I\'m going to be running an HKS SSQV in VTA mode. For two main reasosn: 1, it was free, and 2, it neatens up some of the pipework in the bay.

[Ricco_04]

Actually its more to do with Shaft failure (Imagen the amount of Exhaust gases does not change but on the other side of the turbo the Throttles are now shut,simply the pressure will build on the colds side until both sides are the same then the compressor stalls, all this happens in hundredths of second) the bearings will let go if you run higher boost levels, 360\'s help with that, the surge is renown for snapping shafts. Thats why the bigger turbo\'s handle it better (T series turbo\'s hard thicker shafts which made them stronger but also heavier)

If that made sense...

Yes makes sence - understand better now! :Thumbs-up

Also if dump valves were not needed then manufacturesrs would not put them onto production cars as it would save them money,and we all know that if they think a corner can be cut then they will cut it.
Regards
Carl

Could be wrong (again :o ) but I thought the main reason they used recirc valves was so they could get rid of the compressor surge noise, as in having a quieter/more refined car?

[BlitzBoy]

Yes makes sence - understand better now! :Thumbs-up



Could be wrong (again :o ) but I thought the main reason they used recirc valves was so they could get rid of the compressor surge noise, as in having a quieter/more refined car?

you are correct , exactly my point on recirc valves I made earlier, haha this debate will live forever lol

[Carl]

Carl Recirc valves still lose you boost on the stock setup, the other main use of recirc valves was to eliminate noise of the dumped air by feeding it back into the Air filter Air box on the stock setup, therefore eliminating the Tsccchhh noise as you would get from normal DVs, Mazda couldnt release a car which make weird and wonderful noises of strange plumbing lol, thats why Manufacturers sell cars with recirc valves and not atmos DV on turbo cars, they are a noise surpressant device (recirc valves) as well

You are quite right Mark,my bad,
I did get this all wrong.
I was getting muddled up with the setup that is often used on a supercharger where it is driven by the engine\'s rotation.
Regards
Carl

[MikeLMR]

vented to air dump valves are also an issue with emmissions. due to possible oil carry over from the turbo bearings and then venting to atmosphere.
So there is another reason why they are used on OEM turbo applications.

[Prof]

I think the main issue with vent to air valves is that the charge air, which will have been metered in a stock system will have a measure of fuel added per whatever tables the ECU is working from.
 
When you shut the throttles and the BOV let\'s the air out, the fuel is still in the system, but the air isn\'t there anymore, so you get a pop/flame and emissions will be richer as a result.  The recirc keeps the air in the system because it feeds back into the inlet, but it\'s recirculated after the Air flow meter.
 
Obviously most of you single tubby guys have dispensed with the MAF / AFM anyway so it\'s not relevant

[RemarkLima]

I think the main issue with vent to air valves is that the charge air, which will have been metered in a stock system will have a measure of fuel added per whatever tables the ECU is working from.
 
When you shut the throttles and the BOV let\'s the air out, the fuel is still in the system, but the air isn\'t there anymore, so you get a pop/flame and emissions will be richer as a result.  The recirc keeps the air in the system because it feeds back into the inlet, but it\'s recirculated after the Air flow meter.
 
Obviously most of you single tubby guys have dispensed with the MAF / AFM anyway so it\'s not relevant

I thought this was only the case with a AFM, as it\'s been measured how much air has passed, while the MAP sensors are after the throttle body hence unaffected by this (hence, Manifold Absolute Pressure).

But I know this was a huge issure on MR2 Tubbies as they had a AFM, so you\'d dump this metered ait to atmos, it\'s spike to being very rich, the lamda sensor would report this and the ECU would wet itself and cut a load of fuel just as you\'re giving it some beans and you\'d get very lean and a load of detonation

Sorry, just reread and saw you\'re saying a MAF sensor, when I\'m sure the FD runs a MAP sensor.

[marco]

prof, thats the thing, recircing back into the inlet would only work if the air could not escape through the airfilter. as it is you have around 1bar differential pressure across a very low resistance foam/mesh filter, and so it is going to equalize very quickly. the net result is that the air from the BOV is going to return to atmospheric pressure by exhausting the excess out through the filter- a net out flow of air. the only way to recirc would be to have a one way valve between the airfilter and inlet tract.

[BlitzBoy]

I think the main issue with vent to air valves is that the charge air, which will have been metered in a stock system will have a measure of fuel added per whatever tables the ECU is working from.
 
When you shut the throttles and the BOV let\'s the air out, the fuel is still in the system, but the air isn\'t there anymore, so you get a pop/flame and emissions will be richer as a result.  The recirc keeps the air in the system because it feeds back into the inlet, but it\'s recirculated after the Air flow meter.
 
Obviously most of you single tubby guys have dispensed with the MAF / AFM anyway so it\'s not relevant

Prof on a FD a MAF/AFM sensor is NOT used (the FC is different), a MAP sensor with an air signal of the Plenum is used. The recirc valves used on the FD is mainly used as a noise suppressant.


edit oops someone beat me to it lol

[Prof]

Prof on a FD a MAF/AFM sensor is NOT used (the FC is different), a MAP sensor with an air signal of the Plenum is used. The recirc valves used on the FD is mainly used as a noise suppressant.
 
 
edit oops someone beat me to it lol

I keep forgetting that... :rolleyes:  So apart from the noise issue, there really is no difference going for recirc or atmospheric, apart from possibly recircing air warmed by the compressor and turbo back into the system with a recirc, where a BOV would vent it off into the engine bay  (in most cases - to be sucked back in through the air filter, as most folk, myself included do not provide a direct cold air feed or shroud the filter in a cold air box :Laugh ) - so no difference then...

[BlitzBoy]

all depends if you prefer dump valve noises or not or real mans noise of compressor surge ala Rally style lol, some big single turbos have anti-surge compressor housings which get rid some of the surge noise