Subaru Wrx Dump valve
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Scooby Newbie
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From: Mauritius
Subaru Wrx Dump valve
I have a subaru impreza wrx with engine EJ20 on it.
I would like to ask you something, can i change my original recycling dump valve to an original HKS SSQV dump valve will it cause any problem? do i have to remap my ecu or something thanks..
I would like to ask you something, can i change my original recycling dump valve to an original HKS SSQV dump valve will it cause any problem? do i have to remap my ecu or something thanks..
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You may not notice any difference, you may notice rough running.
Either way, you WILL have overfuelling.
This can lead to a breakdown of any cats fitted, borewash, diluted oil, excess upper cylinder and valve stem wear, even exhaust valve and manifold damage.
None of which will be apparent until your engine lets go.....if it does. You could be lucky.
But this is what you have to ask yourself, do you FEEL lucky?
And all this for a silly chavvy noise...........
Either way, you WILL have overfuelling.
This can lead to a breakdown of any cats fitted, borewash, diluted oil, excess upper cylinder and valve stem wear, even exhaust valve and manifold damage.
None of which will be apparent until your engine lets go.....if it does. You could be lucky.
But this is what you have to ask yourself, do you FEEL lucky?
And all this for a silly chavvy noise...........
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Scooby Newbie
Joined: Dec 2011
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From: Mauritius
what you mean by rough running??
have you ever experience one ( changing the wrx recycling to HKS SSQV) ??
but if i output more power from the engine definitely i have to change the BOV?
Last edited by .:Subaru:.; Dec 9, 2011 at 02:14 PM.
As it says, the engine can feel rough due to over-fuelling, especially on gear changes.
The stock recirculating valve is good to 500bhp. Are you going to go higher?
Scooby Regular
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Don't want to turn this into an argument about 'dump valves are for chav's ect', but I can't see how it would make your car run rough. If someone can explain why I'll stand corrected. On idle and under load i.e when the BOV is shut there can be no difference to the airflow in the inlet as when the standard recirc valve is fitted (assuming its fitted properly). When the throttle is closed and the engine is at high rpm (as is the case during a gear change), as far as I'm aware no fuel is injected into the engine until it reaches near idle speed. I've ran several cars with and without BOV's and I can't say I've noticed much difference in the way the car drives. Surley if a BOV was going to give you any bother it would make the car run rich anyway? leaking and drawing in unmetered air ect? I'm not saying I'm right, but this was my understanding of the matter. I would welcome any opposing opinions.
The Subaru system on inlet relies on a MAF meter to measure the mass of incoming air after the filter. That air is then compressed by the turbo and the correct amount of fuel added.
Now, if you lift off the throttle suddenly, the excess pressure in the manifold is dealt with by the Dump Valve.
In a recirculating valve, the air is dumped back into the inlet, no longer under pressure and, mixed with the fuel that was measured for it, burns as normal.
However, if you use a VTA dumpvalve, the air is dumped to atmosphere, "lost" to the engine, so to speak. The FUEL however, which was measure for that air, is still in the system, and enters the cylinders with insufficient air, making the rich mixture.
Result: (all possible, none definite, but do you want to take the chance?):
borewash,
damage to cats if fitted,
dilution of oil,
lack of upper cylinder lubricant,
possible valve/manifold damage,
and, of course, due to the sudden excess of fuel, rough running.
If you doubt this last, get hold of an old type engine with a choke, let it warm up, then pull out the choke: rough enough for you?
Now, as I said, NONE of the above WILL DEFINITELY happen, but I've lost count of the number of people who have reported rough running after fitting a VTA valve, which has disappeared after going back to the recirc type.
They FAR outweigh those who say everything is OK.
And even though it MAY appear to run OK, do you WANT to take the chance?
Approximate cost of a rebuild if it does let go: £2000.
And for what? A daft noise? No power OR ANY OTHER gains?
Now, if you lift off the throttle suddenly, the excess pressure in the manifold is dealt with by the Dump Valve.
In a recirculating valve, the air is dumped back into the inlet, no longer under pressure and, mixed with the fuel that was measured for it, burns as normal.
However, if you use a VTA dumpvalve, the air is dumped to atmosphere, "lost" to the engine, so to speak. The FUEL however, which was measure for that air, is still in the system, and enters the cylinders with insufficient air, making the rich mixture.
Result: (all possible, none definite, but do you want to take the chance?):
borewash,
damage to cats if fitted,
dilution of oil,
lack of upper cylinder lubricant,
possible valve/manifold damage,
and, of course, due to the sudden excess of fuel, rough running.
If you doubt this last, get hold of an old type engine with a choke, let it warm up, then pull out the choke: rough enough for you?
Now, as I said, NONE of the above WILL DEFINITELY happen, but I've lost count of the number of people who have reported rough running after fitting a VTA valve, which has disappeared after going back to the recirc type.
They FAR outweigh those who say everything is OK.
And even though it MAY appear to run OK, do you WANT to take the chance?
Approximate cost of a rebuild if it does let go: £2000.
And for what? A daft noise? No power OR ANY OTHER gains?
Scooby Regular
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I would presume that most cases of rough running are due to poor fitment. My car was running rich when I first took it for mapping but turned out that the previous owner had used a champagne cork to block the return pipe! which was drawing air needless to say. After a proper blanking cap was fitted the car ran sweet with no dodgy fuel trims (confirmed during a mapping session). I understand your argument but with the throttle closed surely no air is entering the engine? (well a negligible amount anyway). Recirculated air goes un-metered anyway as it passes back into the inlet on the engine side of the MAF sensor. I understand that you don't like the noise but quite a lot of people obviously do so each to their own so to say.
your not getting it,
look at the pic, note where the dv is fitted, the air meter is near the air filter, so it measures air going in, say 14 parts, then the ecu says i must inject 1 part fuel, to run well. the dv releases a little bit of air to make noise, then you only have 10 parts air going into the engine, but still the 1 part fuel, this is how it over fuels, the air is not redundant.
look at the pic, note where the dv is fitted, the air meter is near the air filter, so it measures air going in, say 14 parts, then the ecu says i must inject 1 part fuel, to run well. the dv releases a little bit of air to make noise, then you only have 10 parts air going into the engine, but still the 1 part fuel, this is how it over fuels, the air is not redundant.
I would presume that most cases of rough running are due to poor fitment. My car was running rich when I first took it for mapping but turned out that the previous owner had used a champagne cork to block the return pipe! which was drawing air needless to say. After a proper blanking cap was fitted the car ran sweet with no dodgy fuel trims (confirmed during a mapping session). I understand your argument but with the throttle closed surely no air is entering the engine? (well a negligible amount anyway). Recirculated air goes un-metered anyway as it passes back into the inlet on the engine side of the MAF sensor. I understand that you don't like the noise but quite a lot of people obviously do so each to their own so to say.
You obviousdly totally failed to understand it.
Dumpvalves have NOWT to do with idling.
The rough running I describe is on high revs gearchange and is a fact in many, many cases.
It's caused by OVER fuelling, nothing else. Not air leaks, not faulty dumpvalves NOTHING else.
Go back and read my post again, please.
Dump valves are ok for driving round McDonalds car parks making daft noises to attract the
Young fat teenager miners who dream of a lad with a scooby ,rearward facing baseball cap ,dodgy gold from Argos and ultimate aim is their own council house 3babies and a ticket for jermany Kyle
Read up all the threads this has been debated for over ten years with the same message
Dump valves don't work
Ruin engines
Cause severe running problems
Are sad and all the purists will laugh at you driving past going PpsStt
What's next lights on your washers and Neon lights
Young fat teenager miners who dream of a lad with a scooby ,rearward facing baseball cap ,dodgy gold from Argos and ultimate aim is their own council house 3babies and a ticket for jermany Kyle
Read up all the threads this has been debated for over ten years with the same message
Dump valves don't work
Ruin engines
Cause severe running problems
Are sad and all the purists will laugh at you driving past going PpsStt
What's next lights on your washers and Neon lights
