Dump valves and overfueling
02 January 2014, 11:53 AM
#61
02 January 2014, 12:54 PM
#62
Scooby Regular
Thread Starter
Consider non turbo cars, when you shut the throttle it stops pulling in air..... simples.
With a spooled turbo in that inlet tract, the momentum of the spooled impeller doesnt stop pumping air. If there was no pressure releif valve the air would either over pressurise the inlet or force its way back through the turbo, hence the chattering noise associated with a dv delete.
A recirculating dv simply cycles that pumped air around the turbo so no metered air is lost and intake pressures dont get excessive.
Modern high performance cars (150bhp + per litre) have to govern the amount of air and hence amount of fuel very accurately and in the mid 90's the best way to do this was to pass the inlet air through a known size tube containing a heated wire. Its resistance was then used by the ecu to measure the mass of air going in. Used along side the lambda signal you then have very accurate control of the air fuel mix.
By wasting air out of the system rather than just recirculating it around the turbo you are inevitably screwing with the complicated calculations going on in the ecu.
You talk about very fast gearchanges as if your left hand and left foot can move quicker than the air going into the engine at redline ........ trust me on thisun, you cant! Theres some fundamental thermodynamics you need to get your head round to understand this properly.
With a spooled turbo in that inlet tract, the momentum of the spooled impeller doesnt stop pumping air. If there was no pressure releif valve the air would either over pressurise the inlet or force its way back through the turbo, hence the chattering noise associated with a dv delete.
A recirculating dv simply cycles that pumped air around the turbo so no metered air is lost and intake pressures dont get excessive.
Modern high performance cars (150bhp + per litre) have to govern the amount of air and hence amount of fuel very accurately and in the mid 90's the best way to do this was to pass the inlet air through a known size tube containing a heated wire. Its resistance was then used by the ecu to measure the mass of air going in. Used along side the lambda signal you then have very accurate control of the air fuel mix.
By wasting air out of the system rather than just recirculating it around the turbo you are inevitably screwing with the complicated calculations going on in the ecu.
You talk about very fast gearchanges as if your left hand and left foot can move quicker than the air going into the engine at redline ........ trust me on thisun, you cant! Theres some fundamental thermodynamics you need to get your head round to understand this properly.
Isn't a re-circ technically a DV delete that quietens the car by relieving built up pressure into the intake bypassing the turbo and the associated chatter? Where does the pressurised air go if it's not used, I.e coming to a stop, easing off down hill and staying on overrun? Why does a DV delete cause overfueling and not a re-circ? Does a re-circ keep pressure in the intercooler but a DV delete sends it rushing out?
02 January 2014, 01:04 PM
#63
No, a recirc is a dump valve. An atmospheric is a dump valve. They do the same thing but direct the air to different places.
A dump valve delete means not having either and accepting the excessive inlet pressure and reduced turbo life.
When a recirc dv dumps to the inlet tract between maf and turbo it is no longer pressurised air and is then repressurised by the turbo.
A dump valve delete means not having either and accepting the excessive inlet pressure and reduced turbo life.
When a recirc dv dumps to the inlet tract between maf and turbo it is no longer pressurised air and is then repressurised by the turbo.
02 January 2014, 01:07 PM
#64
Scooby Regular
ooo some quality arguing going on here hahahaha.
To realy throw a spanner in the works, some cars don't drive any differently after a vta is fitted even when not setup specificly. Also cars setup for it run them fine so to say its better not to is rubbish.
Im yet to see any actual testing rather then guess work, this seems to be another myth and guess rather than hard fact.
To realy throw a spanner in the works, some cars don't drive any differently after a vta is fitted even when not setup specificly. Also cars setup for it run them fine so to say its better not to is rubbish.
Im yet to see any actual testing rather then guess work, this seems to be another myth and guess rather than hard fact.
02 January 2014, 01:08 PM
#65
Driving fast I can make the VTA sound off for less than a second but when I ease off without a gear change it vents for 2 seconds. Sometimes I ease off the throttle then reapply so I don't hit the back of my opponent, this makes the VTA sound for a very short time but I guess the drop in pressure causes rich running here?
Isn't a re-circ technically a DV delete that quietens the car by relieving built up pressure into the intake bypassing the turbo and the associated chatter? Where does the pressurised air go if it's not used, I.e coming to a stop, easing off down hill and staying on overrun? Why does a DV delete cause overfueling and not a re-circ? Does a re-circ keep pressure in the intercooler but a DV delete sends it rushing out?
Isn't a re-circ technically a DV delete that quietens the car by relieving built up pressure into the intake bypassing the turbo and the associated chatter? Where does the pressurised air go if it's not used, I.e coming to a stop, easing off down hill and staying on overrun? Why does a DV delete cause overfueling and not a re-circ? Does a re-circ keep pressure in the intercooler but a DV delete sends it rushing out?
02 January 2014, 01:10 PM
#66
ooo some quality arguing going on here hahahaha.
To realy throw a spanner in the works, some cars don't drive any differently after a vta is fitted even when not setup specificly. Also cars setup for it run them fine so to say its better not to is rubbish.
Im yet to see any actual testing rather then guess work, this seems to be another myth and guess rather than hard fact.
To realy throw a spanner in the works, some cars don't drive any differently after a vta is fitted even when not setup specificly. Also cars setup for it run them fine so to say its better not to is rubbish.
Im yet to see any actual testing rather then guess work, this seems to be another myth and guess rather than hard fact.
02 January 2014, 01:18 PM
#67
Scooby Regular
Thread Starter
No, a recirc is a dump valve. An atmospheric is a dump valve. They do the same thing but direct the air to different places.
A dump valve delete means not having either and accepting the excessive inlet pressure and reduced turbo life.
When a recirc dv dumps to the inlet tract between maf and turbo it is no longer pressurised air and is then repressurised by the turbo.
A dump valve delete means not having either and accepting the excessive inlet pressure and reduced turbo life.
When a recirc dv dumps to the inlet tract between maf and turbo it is no longer pressurised air and is then repressurised by the turbo.
02 January 2014, 01:20 PM
#68
ooo some quality arguing going on here hahahaha.
To realy throw a spanner in the works, some cars don't drive any differently after a vta is fitted even when not setup specificly. Also cars setup for it run them fine so to say its better not to is rubbish.
Im yet to see any actual testing rather then guess work, this seems to be another myth and guess rather than hard fact.
To realy throw a spanner in the works, some cars don't drive any differently after a vta is fitted even when not setup specificly. Also cars setup for it run them fine so to say its better not to is rubbish.
Im yet to see any actual testing rather then guess work, this seems to be another myth and guess rather than hard fact.
02 January 2014, 01:21 PM
#69
Scooby Regular
Thread Starter
Sometimes I ease off for a split second as I don't want to be bumper to bumper with a car accelerating slower. I'm not an aggressive driver. The car vents but only a fraction of boost is lost.
I've never read up on if this scenario would cause a momentary rich dip.
I've never read up on if this scenario would cause a momentary rich dip.
02 January 2014, 01:23 PM
#70
Scooby Regular
Thread Starter
I'm not arguing, I genuinely don't know what fully happens in several scenarios, I'm thinking of moving to a DV Delete as I know my TD05 will take it all day long. It's an interesting talking point tbh, most people say DV delete destroys turbos, eventually, some say it doesn't just ball bearing ones etc, most say a VTA can't be mapped for some say they can. Most say VTA's cause ****ty running, some people say they don't cause any! Some say VTA's cause lean running some say wtf?
Last edited by RS_Matt; 02 January 2014 at 01:27 PM.
02 January 2014, 01:27 PM
#72
Scooby Regular
what did you expect?
02 January 2014, 01:29 PM
#73
Scooby Regular
based on what though? alot of people have an opinion which there perfectly entitled to.
what i mean has anyone got any actualy real back to back testing done? i bet not.
Whole point fo the thread is its not as clear cut as peopel say, if it was then the thread wouldn't be at 3 pages lol
02 January 2014, 01:29 PM
#74
Scooby Regular
Thread Starter
I know I know, the air is metered and has to be used as it stays in the intake permanently. The intake is like a balloon that doesn't have any holes.
02 January 2014, 01:35 PM
#75
Scooby Regular
Thread Starter
based on what though? alot of people have an opinion which there perfectly entitled to.
what i mean has anyone got any actualy real back to back testing done? i bet not.
Whole point fo the thread is its not as clear cut as peopel say, if it was then the thread wouldn't be at 3 pages lol
what i mean has anyone got any actualy real back to back testing done? i bet not.
Whole point fo the thread is its not as clear cut as peopel say, if it was then the thread wouldn't be at 3 pages lol
I've always wanted to know what technically happened to the air on a re-circ system though, nobody has answered that yet. Pressure drop, directions, does it enter the intercooler and under high boost does it leave causing a hint of chatter if the throttle isn't reapplied? Does it stay pressurised? Does air still entering the intake keep it under pressured?
Last edited by RS_Matt; 02 January 2014 at 01:37 PM.
02 January 2014, 01:49 PM
#76
Scooby Regular
vta air is dumped into the engine bay
recirc its dumped back into the intake system, after the maf.
i'd assume its own pressure sends it back until it balances with the pressure its going to. the chatter you refer to is actualy air trying to go backwards through the system the wrong way.
recirc its dumped back into the intake system, after the maf.
i'd assume its own pressure sends it back until it balances with the pressure its going to. the chatter you refer to is actualy air trying to go backwards through the system the wrong way.
02 January 2014, 01:58 PM
#77
Scooby Regular
Thread Starter
I just wondered what causes over-fueling when you first lift off and is there different levels of how bad the overfuel depending on scenario/pressure loss.
I can imagine the pressure balancing out is when the ECU is ready to read via the MAF again? How long does it take to balance out? 500ms? 3 seconds?
02 January 2014, 07:39 PM
#79
Scooby Regular
Thread Starter
I'm thinking of no DV but I wondered if it over-fuels more than running a VTA, or does nobody know?
03 January 2014, 11:46 AM
#82
Scooby Regular
iTrader: (1)
Join Date: May 2013
Location: bedfordshire, UK
Posts: 429
Likes: 0
Received 0 Likes
on
0 Posts
i understand exactly what matt is saying!
you guys are missing the bit he is struggling on
matt
the air enters through the maf and is messured ect ect,
with a recerc system when you take your foot off the throttle the plate closes and the air gose round the recerc root. the air going past the maf drops down to almost nothing because there is no air being consumed. just like an NA car
in this system the car has no idea how much air is going past the throttle plate and into the engine. its just assuming that because its a closed system "air past maf" = " air into engine"
when you put a VTA on there the air exits the system. and the turbo keeps pulling air through the maf. theres no actualy air going into the engine but the ECU still thinks its a closed system therefor the air going past the maf "must" be going into the engine. its got no idea that you have closed the throttle plate so it keeps dumping fuel into the engine!
so theres loads off fuel going in but no air! running a bit rich for a few seconds is fine but loads off fuel and no air is basically flooding the engine
now isnt that a much better explanation?
you guys are missing the bit he is struggling on
matt
the air enters through the maf and is messured ect ect,
with a recerc system when you take your foot off the throttle the plate closes and the air gose round the recerc root. the air going past the maf drops down to almost nothing because there is no air being consumed. just like an NA car
in this system the car has no idea how much air is going past the throttle plate and into the engine. its just assuming that because its a closed system "air past maf" = " air into engine"
when you put a VTA on there the air exits the system. and the turbo keeps pulling air through the maf. theres no actualy air going into the engine but the ECU still thinks its a closed system therefor the air going past the maf "must" be going into the engine. its got no idea that you have closed the throttle plate so it keeps dumping fuel into the engine!
so theres loads off fuel going in but no air! running a bit rich for a few seconds is fine but loads off fuel and no air is basically flooding the engine
now isnt that a much better explanation?
03 January 2014, 12:20 PM
#83
Scooby Regular
Thread Starter
i understand exactly what matt is saying!
you guys are missing the bit he is struggling on
matt
the air enters through the maf and is messured ect ect,
with a recerc system when you take your foot off the throttle the plate closes and the air gose round the recerc root. the air going past the maf drops down to almost nothing because there is no air being consumed. just like an NA car
in this system the car has no idea how much air is going past the throttle plate and into the engine. its just assuming that because its a closed system "air past maf" = " air into engine"
when you put a VTA on there the air exits the system. and the turbo keeps pulling air through the maf. theres no actualy air going into the engine but the ECU still thinks its a closed system therefor the air going past the maf "must" be going into the engine. its got no idea that you have closed the throttle plate so it keeps dumping fuel into the engine!
so theres loads off fuel going in but no air! running a bit rich for a few seconds is fine but loads off fuel and no air is basically flooding the engine
now isnt that a much better explanation?
you guys are missing the bit he is struggling on
matt
the air enters through the maf and is messured ect ect,
with a recerc system when you take your foot off the throttle the plate closes and the air gose round the recerc root. the air going past the maf drops down to almost nothing because there is no air being consumed. just like an NA car
in this system the car has no idea how much air is going past the throttle plate and into the engine. its just assuming that because its a closed system "air past maf" = " air into engine"
when you put a VTA on there the air exits the system. and the turbo keeps pulling air through the maf. theres no actualy air going into the engine but the ECU still thinks its a closed system therefor the air going past the maf "must" be going into the engine. its got no idea that you have closed the throttle plate so it keeps dumping fuel into the engine!
so theres loads off fuel going in but no air! running a bit rich for a few seconds is fine but loads off fuel and no air is basically flooding the engine
now isnt that a much better explanation?
Cheers for the answer, it wasn't the reason I thought or anyone gave. TBH on those principles I can't fathom out why a delete would make the car run rich though.
So what makes the Turbo stop spinning and pulling in extraneous air when it re-circs? I would have thought the compressed air trying to re-circ would keep the turbo spinning or does the pressurised air stop fresh air entering, like a pressure block per se?
Last edited by RS_Matt; 03 January 2014 at 12:23 PM.
03 January 2014, 12:49 PM
#84
Scooby Regular
iTrader: (1)
Join Date: May 2013
Location: bedfordshire, UK
Posts: 429
Likes: 0
Received 0 Likes
on
0 Posts
I know, they are seriously dumb sheep, and I must have asked about 60 related questions that all conveniently ignored..
Cheers for the answer, it wasn't the reason I thought or anyone gave. TBH on those principles I can't fathom out why a delete would make the car run rich though.
So what makes the Turbo stop spinning and pulling in extraneous air when it re-circs? I would have thought the compressed air trying to re-circ would keep the turbo spinning or does the pressurised air stop fresh air entering, like a pressure block per se?
Cheers for the answer, it wasn't the reason I thought or anyone gave. TBH on those principles I can't fathom out why a delete would make the car run rich though.
So what makes the Turbo stop spinning and pulling in extraneous air when it re-circs? I would have thought the compressed air trying to re-circ would keep the turbo spinning or does the pressurised air stop fresh air entering, like a pressure block per se?
on the deleat, i would speakulate that the maf has no idea which way the air is going therefore. air keeps going past the maf for a short period as the turbo continuous spining and pulling in air. then the air forces its way back past the turbo and out the maf pusing more air over the maf. therefor (if the maf on scoobys works like all the others iv seen) it cools down the heated plate makeing the ECU think air is still going in (even though its going out)
as for the recirc. in normal operation the air after the turbo is pressurized and before is slightly vacuumed. when you come off throttle the valve opens and the pressurized air goses back to the befor turbo side and equlises the vacume. alot off the air will go round in a big loop as the turbo is still pumping air into the pressurized side and it flows back to the vacume side through the valve. the total pressure though will still be largely positive as there is only a small intake vacuum and a large pressure stored behind the turbo. this means that the vacuum side will be equilised and then become positive. this means it will go back out the maf the same way the deleat dose.
it wont be as violent as the delete though nor will as much air flow
theres a chance that its mapped out off the car so that nothing happens. if it did happen there would still be much less fuel injected. as i said before running rich for a couple seconds isnt really going to do any harm where massive over fueling can do.
03 January 2014, 01:06 PM
#85
Scooby Regular
iTrader: (1)
Join Date: May 2013
Location: bedfordshire, UK
Posts: 429
Likes: 0
Received 0 Likes
on
0 Posts
on a side note. if you want more noise do what im doing
take the snorkus out. then possibly change the recerc valve to see if you can get a nosier one
change the air intake ect.
the recerc valve is a part off the desine off the air/fueling system.
you cant really just remove it/change it for a vta. you have to design a new air/fueling system that dosent need a valve.
ie when people say go mafless there fitting a diffrent ecu that uses a diffrent air/fueling system
another side effect off the overfuleing is it causes the labda to read rich and can cause the ecu to go lean in an attempt to compensate
take the snorkus out. then possibly change the recerc valve to see if you can get a nosier one
change the air intake ect.
the recerc valve is a part off the desine off the air/fueling system.
you cant really just remove it/change it for a vta. you have to design a new air/fueling system that dosent need a valve.
ie when people say go mafless there fitting a diffrent ecu that uses a diffrent air/fueling system
another side effect off the overfuleing is it causes the labda to read rich and can cause the ecu to go lean in an attempt to compensate
03 January 2014, 01:28 PM
#86
Scooby Regular
Thread Starter
that's a bit difficult to explain with typing
on the deleat, i would speakulate that the maf has no idea which way the air is going therefore. air keeps going past the maf for a short period as the turbo continuous spining and pulling in air. then the air forces its way back past the turbo and out the maf pusing more air over the maf. therefor (if the maf on scoobys works like all the others iv seen) it cools down the heated plate makeing the ECU think air is still going in (even though its going out)
as for the recirc. in normal operation the air after the turbo is pressurized and before is slightly vacuumed. when you come off throttle the valve opens and the pressurized air goses back to the befor turbo side and equlises the vacume. alot off the air will go round in a big loop as the turbo is still pumping air into the pressurized side and it flows back to the vacume side through the valve. the total pressure though will still be largely positive as there is only a small intake vacuum and a large pressure stored behind the turbo. this means that the vacuum side will be equilised and then become positive. this means it will go back out the maf the same way the deleat dose.
it wont be as violent as the delete though nor will as much air flow
theres a chance that its mapped out off the car so that nothing happens. if it did happen there would still be much less fuel injected. as i said before running rich for a couple seconds isnt really going to do any harm where massive over fueling can do.
on the deleat, i would speakulate that the maf has no idea which way the air is going therefore. air keeps going past the maf for a short period as the turbo continuous spining and pulling in air. then the air forces its way back past the turbo and out the maf pusing more air over the maf. therefor (if the maf on scoobys works like all the others iv seen) it cools down the heated plate makeing the ECU think air is still going in (even though its going out)
as for the recirc. in normal operation the air after the turbo is pressurized and before is slightly vacuumed. when you come off throttle the valve opens and the pressurized air goses back to the befor turbo side and equlises the vacume. alot off the air will go round in a big loop as the turbo is still pumping air into the pressurized side and it flows back to the vacume side through the valve. the total pressure though will still be largely positive as there is only a small intake vacuum and a large pressure stored behind the turbo. this means that the vacuum side will be equilised and then become positive. this means it will go back out the maf the same way the deleat dose.
it wont be as violent as the delete though nor will as much air flow
theres a chance that its mapped out off the car so that nothing happens. if it did happen there would still be much less fuel injected. as i said before running rich for a couple seconds isnt really going to do any harm where massive over fueling can do.
. So taking it all into account a re-circ with a very strong spring is the way forward?
Am I right in thinking fast changes on a delete wouldn't cause rich gear changes as the 'chattering' air won't reach the MAF before the throttle is swiftly reapplied? Can a Turbo really turn pressurised air around so fast?
03 January 2014, 01:38 PM
#87
Scooby Regular
Thread Starter
on a side note. if you want more noise do what im doing
take the snorkus out. then possibly change the recerc valve to see if you can get a nosier one
change the air intake ect.
the recerc valve is a part off the desine off the air/fueling system.
you cant really just remove it/change it for a vta. you have to design a new air/fueling system that dosent need a valve.
ie when people say go mafless there fitting a diffrent ecu that uses a diffrent air/fueling system
another side effect off the overfuleing is it causes the labda to read rich and can cause the ecu to go lean in an attempt to compensate
take the snorkus out. then possibly change the recerc valve to see if you can get a nosier one
change the air intake ect.
the recerc valve is a part off the desine off the air/fueling system.
you cant really just remove it/change it for a vta. you have to design a new air/fueling system that dosent need a valve.
ie when people say go mafless there fitting a diffrent ecu that uses a diffrent air/fueling system
another side effect off the overfuleing is it causes the labda to read rich and can cause the ecu to go lean in an attempt to compensate
Incidentally does a re-circ vent at any psi?
03 January 2014, 01:47 PM
#88
Scooby Regular
iTrader: (1)
Join Date: May 2013
Location: bedfordshire, UK
Posts: 429
Likes: 0
Received 0 Likes
on
0 Posts
Cheers for the reply, it seems a lot more technical than I thought. Each explanation creates more questions! Like an air (or water) loop actually creates suction, but some pressurised air going the other way must equal it .
So taking it all into account a re-circ with a very strong spring is the way forward?
Am I right in thinking fast changes on a delete wouldn't cause rich gear changes as the 'chattering' air won't reach the MAF before the throttle is swiftly reapplied? Can a Turbo really turn pressurised air around so fast?
. So taking it all into account a re-circ with a very strong spring is the way forward?
Am I right in thinking fast changes on a delete wouldn't cause rich gear changes as the 'chattering' air won't reach the MAF before the throttle is swiftly reapplied? Can a Turbo really turn pressurised air around so fast?
the loop itself dose not creat any suction its the turbo thats creating the suction. the recerc air will cancel that vacume out though and then turn it positive.
the spring in the valve simply keeps it closed. the higher the spring the higher the pressure taken to open it. a recerc with a strong spring would only vent its max pressure (or non at all depending on the spring)
this could be beneficial as it would keep pressure in the intake befor the TB between gear changes but then again it could cause your turbo to spin backwards like a deleat
yes turbos are an amzing bit off kit
they spin very very fast, some off them 100,000 rpm.
the pressures the produce are relatively low. they produce say a bar compared to air tool compressors which make about 8 normally
however a very large compressor dosent even come close to supplying the volume of air a turbo can.
the ideal system your are looking for is one that keeps the turbo spinning in the right directin and a small amout off pressure in the pre TB intake
this is quite hard to acheave though. the standard valve dose ok at it though!
03 January 2014, 01:51 PM
#89
Scooby Regular
iTrader: (1)
Join Date: May 2013
Location: bedfordshire, UK
Posts: 429
Likes: 0
Received 0 Likes
on
0 Posts
I currently run a GFB adjustable VTA, I have it on the stiffest setting so I only vent at 4k, (at 5k it chatters and VTA's simulataneously!) so presumably I'm not over-fueling during steady to moderate driving. I have no running issues besides the odd pop on lift-off and the occasional lambda bank 1 engine light but this come on when when I'm driving in too high a gear or haven't driven hard for ages.
Incidentally does a re-circ vent at any psi?
Incidentally does a re-circ vent at any psi?
depending on what way you look at it. if its chattering its not really doing its job. the air is going though the turbo instead off the valve!
personally i would turn it down a bit
03 January 2014, 01:59 PM
#90
Scooby Regular
Thread Starter
the loop itself dose not creat any suction its the turbo thats creating the suction. the recerc air will cancel that vacume out though and then turn it positive.
the spring in the valve simply keeps it closed. the higher the spring the higher the pressure taken to open it. a recerc with a strong spring would only vent its max pressure (or non at all depending on the spring)
this could be beneficial as it would keep pressure in the intake befor the TB between gear changes but then again it could cause your turbo to spin backwards like a deleat
yes turbos are an amzing bit off kit
they spin very very fast, some off them 100,000 rpm.
the pressures the produce are relatively low. they produce say a bar compared to air tool compressors which make about 8 normally
however a very large compressor dosent even come close to supplying the volume of air a turbo can.
the ideal system your are looking for is one that keeps the turbo spinning in the right directin and a small amout off pressure in the pre TB intake
this is quite hard to acheave though. the standard valve dose ok at it though!
the spring in the valve simply keeps it closed. the higher the spring the higher the pressure taken to open it. a recerc with a strong spring would only vent its max pressure (or non at all depending on the spring)
this could be beneficial as it would keep pressure in the intake befor the TB between gear changes but then again it could cause your turbo to spin backwards like a deleat
yes turbos are an amzing bit off kit
they spin very very fast, some off them 100,000 rpm.
the pressures the produce are relatively low. they produce say a bar compared to air tool compressors which make about 8 normally
however a very large compressor dosent even come close to supplying the volume of air a turbo can.
the ideal system your are looking for is one that keeps the turbo spinning in the right directin and a small amout off pressure in the pre TB intake
this is quite hard to acheave though. the standard valve dose ok at it though!
RE: VTA. Could a mapper momentarily bypass the MAF readings on full lift off?