Dump valves and overfueling
04 January 2014, 09:35 PM
#121
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?
. But honestly, it doesn't read clearly. So I have to stick up for RS Mat in that respect.
My understanding is that the air passes through the air filter, the MAF work's out how much is passing and through the ECU tells the injectors how much fuel is required.
As the recirc throws air back into the manifold, that air isn't going past the MAF, so the MAF accounts for that initially. As a Vent to Air doesn't put that air back into the system, then there is a higher ratio of fuel to air with VTA than recirc.
Probably wrong, I normally am.
04 January 2014, 09:38 PM
#122
Possibly my favourite post for a while .
But honestly, it doesn't read clearly. So I have to stick up for RS Mat in that respect.
My understanding is that the air passes through the air filter, the MAF work's out how much is passing and through the ECU tells the injectors how much fuel is required.
As the recirc throws air back into the manifold, that air isn't going past the MAF, so the MAF accounts for that initially. As a Vent to Air doesn't put that air back into the system, then there is a higher ratio of fuel to air with VTA than recirc.
Probably wrong, I normally am.
. But honestly, it doesn't read clearly. So I have to stick up for RS Mat in that respect.
My understanding is that the air passes through the air filter, the MAF work's out how much is passing and through the ECU tells the injectors how much fuel is required.
As the recirc throws air back into the manifold, that air isn't going past the MAF, so the MAF accounts for that initially. As a Vent to Air doesn't put that air back into the system, then there is a higher ratio of fuel to air with VTA than recirc.
Probably wrong, I normally am.
04 January 2014, 09:58 PM
#123
Scooby Regular
Thread Starter
Possibly my favourite post for a while .
But honestly, it doesn't read clearly. So I have to stick up for RS Mat in that respect.
My understanding is that the air passes through the air filter, the MAF work's out how much is passing and through the ECU tells the injectors how much fuel is required.
As the recirc throws air back into the manifold, that air isn't going past the MAF, so the MAF accounts for that initially. As a Vent to Air doesn't put that air back into the system, then there is a higher ratio of fuel to air with VTA than recirc.
Probably wrong, I normally am.
. But honestly, it doesn't read clearly. So I have to stick up for RS Mat in that respect.
My understanding is that the air passes through the air filter, the MAF work's out how much is passing and through the ECU tells the injectors how much fuel is required.
As the recirc throws air back into the manifold, that air isn't going past the MAF, so the MAF accounts for that initially. As a Vent to Air doesn't put that air back into the system, then there is a higher ratio of fuel to air with VTA than recirc.
Probably wrong, I normally am.
When you back off the pedal and the car vents/re-circs or returns (via the Turbo dummies) the pressurised air is no longer needed but the fact vented air doesn't cancel out the Turbo's natural vacuum effect a slight amount of air passes the MAF and tricks the ECU into fueling for it. As many have said on here gear changes take a long time and the air/fueling will be metered again back on boost.
Hell knows what happens if you are lifting off and reapplying whilst driving as if revving up a car whilst moving. Maybe it just causes a briefer moment of richness. I've had a bit of a drive today with an AFR meter and it was generally back up towards 14ish when the pedal was pushed back down, the lowest AFR I recorded between shifts was 11.3 and the highest on overrun 24.2
04 January 2014, 11:39 PM
#127
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05 January 2014, 11:00 AM
#129
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You're wrong.
When you back off the pedal and the car vents/re-circs or returns (via the Turbo dummies) the pressurised air is no longer needed but the fact vented air doesn't cancel out the Turbo's natural vacuum effect a slight amount of air passes the MAF and tricks the ECU into fueling for it. As many have said on here gear changes take a long time and the air/fueling will be metered again back on boost.
Hell knows what happens if you are lifting off and reapplying whilst driving as if revving up a car whilst moving. Maybe it just causes a briefer moment of richness. I've had a bit of a drive today with an AFR meter and it was generally back up towards 14ish when the pedal was pushed back down, the lowest AFR I recorded between shifts was 11.3 and the highest on overrun 24.2
Sorry mate but you are talking ****. My explanations obv went clear enough. I did draw some pictures. I'll post them up latter if I get a chance
05 January 2014, 11:21 AM
#130
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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
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.
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
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.
now isnt that a much better explanation?
05 January 2014, 12:02 PM
#132
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what joshnosh said basically sums it up with the exception of the fact that the ECU DOES know when the throttle is open or closed. on a fly by wire engine it knows the throttle position and on a cable setup it also knows the throttle position thanks to the TPS sensor. i cant speak definitively for subaru ECU's but i am a specialist in mapping OEM ECU's in older BMW's and in those applications i use an emulator in place of the standard eprom which allows me to tune in real time as well as hit trace any map the ECU is using so i can see what cells the ECU is reading or when it starts or stops reading a particular map.
i would assume (actually id bet money) that all petrol ECU's will return to either an idle or decel map on gearchange when the throttle closes. also to further complicate the operation of subaru ECU's i know some, maybe all also have MAP sensors to monitor manifold pressure so on the MAF front air is measured passing the MAF, with a VTA the measured air is vented out of the system and this causes a momentary rich spike, in terms of the MAP sensor whether the air is recirculated or vented does not matter as in both scenarios the MAP sensor would register a drop in manifold pressure when the throttle closes. in terms of TPS sensor there is no reference to boost, simply throttle open/partially open a certain % or throttle closed. all 3 of these sensors are used by the ECU to determine what it should do in various circumstances so its not quite as simple as MAF measures X amount of air and injects fuel for X amount of air as there is more going on (lets also not forget the O2 sensor is constantly inputting to the ECU as well) than just that but it does seem to bias itself towards the MAF measurements rather than MAP measurements on the standard layout which primarily uses the MAF for air metering and the MAP serves other purposes, perhaps relating to boost pressure at various RPM's or in different gears, etc, etc as there are alot of boost or boost target related maps in the subaru ECU and the only sensor which would provide input for these maps would be the MAP sensor which explains why its there when there is also a MAF inputting to the ECU as well.
on the standard subaru ECU if you patch the software (using opensource tuning software like romraider or sharptune) to change operation from the normal MAF based setup to MAP based (aka speed density) or a 50/50 between the two then this alleviates the momentary rich spike issue with a VTA valve, though you could still also use a recirc with no issues.
now onto my own personal (and very limited) experience with my 06 WRX. i have run the OEM recirc as well as run the OEM recirc but with the recirc hose removed and capped off (thus making it a VTA) as well as running (my current setup) a cheap, no frills ebay VTA valve. with OEM recirc connected up as normal theres no rich spikes, no hesitation, no problems. with OEM recirc venting to atmosphere the engine wants to stall alot when it vents at lower revs to the point you would need to give it throttle sometimes to prevent it from stalling, i assume this is due to the spring in the OEM recirc probably being a bit weak, it also will pop or backfire alot of the time when changing gear after it vents due to the momentary rich spike. on the cheapo ebay VTA valve there are none of the stalling issues as with the OEM recirc venting to atmosphere as it seems to have a stiffer spring, it will pop or backfire on gearchange due to the momentary rich spike but aside from that it works just fine on the standard ECU though very, very occasionally (maybe like 1% of the time) the engine will stall after it vents at lower revs, seems to be if it vents at just the right point in lower revs but i cant make it happen so seems like there might be other factors at play when that happens such as a combination of the momentary rich spike and some other function within the ECU (happens extremely rarely though).
and just incase your not clear on what happens with the air in a recirc system.. basically instead of venting out of the system the throttle closes, the recirc valve opens and the air essentially prevents more air being drawn past the MAF by the spinning turbo while the air thats already pressurised after the turbo basically loops around the system and passes back through the still spinning turbo until the throttle is opened again, the valve closes and the air enters the engine again. i would suspect that not all of the pressurised air loops around and back through the turbo given that it is pressurised but since the turbo is still spinning and the air is recirculated and dumpedo ut before the turbo then the fact that the turbo is still spinning will pull most of the air back through it while a smaller amount probably either flows backwards through the MAF (which wouldnt register the same as air flowing through it in the correct direction) a little or simply halts any incoming air to the MAF. i would hazard a guess that even with a recirc valve there would still be a slight rich spike as it wouldnt 100% cancel out what air has already been measured by the MAF but it certainly cancels out the vast majority of it whereas with a VTA the MAF basically thinks the engines still pulling air for that split second before the ECU determines fron the TPS sensor and/or MAP sensor that the throttle has closed and it not needs to switch to decel or idle maps.
/thread
i would assume (actually id bet money) that all petrol ECU's will return to either an idle or decel map on gearchange when the throttle closes. also to further complicate the operation of subaru ECU's i know some, maybe all also have MAP sensors to monitor manifold pressure so on the MAF front air is measured passing the MAF, with a VTA the measured air is vented out of the system and this causes a momentary rich spike, in terms of the MAP sensor whether the air is recirculated or vented does not matter as in both scenarios the MAP sensor would register a drop in manifold pressure when the throttle closes. in terms of TPS sensor there is no reference to boost, simply throttle open/partially open a certain % or throttle closed. all 3 of these sensors are used by the ECU to determine what it should do in various circumstances so its not quite as simple as MAF measures X amount of air and injects fuel for X amount of air as there is more going on (lets also not forget the O2 sensor is constantly inputting to the ECU as well) than just that but it does seem to bias itself towards the MAF measurements rather than MAP measurements on the standard layout which primarily uses the MAF for air metering and the MAP serves other purposes, perhaps relating to boost pressure at various RPM's or in different gears, etc, etc as there are alot of boost or boost target related maps in the subaru ECU and the only sensor which would provide input for these maps would be the MAP sensor which explains why its there when there is also a MAF inputting to the ECU as well.
on the standard subaru ECU if you patch the software (using opensource tuning software like romraider or sharptune) to change operation from the normal MAF based setup to MAP based (aka speed density) or a 50/50 between the two then this alleviates the momentary rich spike issue with a VTA valve, though you could still also use a recirc with no issues.
now onto my own personal (and very limited) experience with my 06 WRX. i have run the OEM recirc as well as run the OEM recirc but with the recirc hose removed and capped off (thus making it a VTA) as well as running (my current setup) a cheap, no frills ebay VTA valve. with OEM recirc connected up as normal theres no rich spikes, no hesitation, no problems. with OEM recirc venting to atmosphere the engine wants to stall alot when it vents at lower revs to the point you would need to give it throttle sometimes to prevent it from stalling, i assume this is due to the spring in the OEM recirc probably being a bit weak, it also will pop or backfire alot of the time when changing gear after it vents due to the momentary rich spike. on the cheapo ebay VTA valve there are none of the stalling issues as with the OEM recirc venting to atmosphere as it seems to have a stiffer spring, it will pop or backfire on gearchange due to the momentary rich spike but aside from that it works just fine on the standard ECU though very, very occasionally (maybe like 1% of the time) the engine will stall after it vents at lower revs, seems to be if it vents at just the right point in lower revs but i cant make it happen so seems like there might be other factors at play when that happens such as a combination of the momentary rich spike and some other function within the ECU (happens extremely rarely though).
and just incase your not clear on what happens with the air in a recirc system.. basically instead of venting out of the system the throttle closes, the recirc valve opens and the air essentially prevents more air being drawn past the MAF by the spinning turbo while the air thats already pressurised after the turbo basically loops around the system and passes back through the still spinning turbo until the throttle is opened again, the valve closes and the air enters the engine again. i would suspect that not all of the pressurised air loops around and back through the turbo given that it is pressurised but since the turbo is still spinning and the air is recirculated and dumpedo ut before the turbo then the fact that the turbo is still spinning will pull most of the air back through it while a smaller amount probably either flows backwards through the MAF (which wouldnt register the same as air flowing through it in the correct direction) a little or simply halts any incoming air to the MAF. i would hazard a guess that even with a recirc valve there would still be a slight rich spike as it wouldnt 100% cancel out what air has already been measured by the MAF but it certainly cancels out the vast majority of it whereas with a VTA the MAF basically thinks the engines still pulling air for that split second before the ECU determines fron the TPS sensor and/or MAP sensor that the throttle has closed and it not needs to switch to decel or idle maps.
/thread
Last edited by DmcL; 05 January 2014 at 12:06 PM.
05 January 2014, 12:03 PM
#133
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05 January 2014, 12:05 PM
#134
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So basically I'm right in both respects; how the over-fuel happens and that nobody on here fully knows the workings of the 5 or 6 DV options/alternatives.
05 January 2014, 12:14 PM
#135
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people know what happens in a nutshell but not to the extent of how the ECU reacts once all sensor inputs are taken into account. also there is a very small split second delay between map switches or even the ECU's reading and then acting on sensor inputs as computers technically do not function instantly after an input has been recieved, it takes an extremely short time for voltage/current/whatever to go from the sensor to the ECU and then for the ECU to register that input and work out and then adjust or switch what maps it is or should be reading from.
also another myth is that a VTA will increase lag over a recirc while the turbo must spool to re-pressurise the intake after a gearchange. allthough this is true to an extent having run the OEM recirc both plumbed into the intake and venting to atmo + the cheapo VTA i can say that on my OEM WRX TD04 i cant really notice much of a difference in spool in the next gear either way. yes it would need to re-pressurise the system with a VTA but as the turbo would still be spinning and doesnt instantly stop when the throttle closes it seems that its very quick to re-pressurise the system once the throttle opens again.
so basically it boils down to whether you want the between gear or lift off "pssshhh" and fairly occasional pop/backfire accompanied by the momentary rich spike or if you would rather no loud noises between gears and no pop/backfire. ofcourse once you get into built engines with big turbo's and either speed density OEM ECU patching or aftermarket speed density ECU's the game changes a bit and in some instances a VTA may be preferred.
in terms of blanking off the DV entirely and having no vent at all the pressurised air has nowhere else to go but back through the turbo and the cha cha cha sound is basically cavitation of the air around the turbo as the turbo blades continue to spin and try to pull air while air is being forced backwards through the turbo the sound is the air shearing at the blades, much the same as boat propellor cavitation if you wanted to youtube it for a visual idea of what happens. i would assume that this would also cause the turbo to slow down alot quicker than with either a VTA or recirc valve fitted. it sounds f-in cool if you ask me but id say it would be a worse setup than either a VTA or a recirc.
the majority on here will also tell you pistons are weak and will basically just let go because of engine modification and increasing power. from what i have read and the digging i have done (especially since i have the "softer" 2.5) it seems as though ringland failure is not just the result of X amount of power or XYZ modifications but seems to be related to combustion chamber temperatures. the manufacturing process of the standard pistons makes them hard and to an extent fairly brittle and as far as i can tell it seems to be a case of one of the piston rings expanding too much due to combustion chamber temps getting beyond a certain level. what someone who has examined some failed pistons reckons is that thermal expansion of one of the rings in particular causes ringland failure because the ring gap is very tight as are the cylinder bores and once the ring expands to a point it will contact the other side of itself and have nowhere to expand further so deforms shape and puts pressure on the ringland and as the pistins are hard/brittle this causes the ringland to fail. so assuming that is all correct (seems so as open source tuners have run fairly high HP numbers on OEM internals up to or beyond the point most on here would say pistins will fail at) the main safety precautions to take would be to ensure the engine is not allowed to overheat/get too hot, ensure your tune/tuning is not too agressive causing detonation/knock (which spikes combustion chamber temps) and ensure your engine mods/bolt ons are suitably tuned for and dont allow the engine to run in such a way that combustion temps will rise significantly due to less than ideal air/fuel mixtures. also they reckon sustained high speed driving can increase engine/combustion chamber temps as at speeds over a certain speed (dont remember off hand) the air passing over the front of the car essentially will jump over the bonnet scoop rendering it ineffective at cooling the incoming hot/pressurised air from the turbo.
also another myth is that a VTA will increase lag over a recirc while the turbo must spool to re-pressurise the intake after a gearchange. allthough this is true to an extent having run the OEM recirc both plumbed into the intake and venting to atmo + the cheapo VTA i can say that on my OEM WRX TD04 i cant really notice much of a difference in spool in the next gear either way. yes it would need to re-pressurise the system with a VTA but as the turbo would still be spinning and doesnt instantly stop when the throttle closes it seems that its very quick to re-pressurise the system once the throttle opens again.
so basically it boils down to whether you want the between gear or lift off "pssshhh" and fairly occasional pop/backfire accompanied by the momentary rich spike or if you would rather no loud noises between gears and no pop/backfire. ofcourse once you get into built engines with big turbo's and either speed density OEM ECU patching or aftermarket speed density ECU's the game changes a bit and in some instances a VTA may be preferred.
in terms of blanking off the DV entirely and having no vent at all the pressurised air has nowhere else to go but back through the turbo and the cha cha cha sound is basically cavitation of the air around the turbo as the turbo blades continue to spin and try to pull air while air is being forced backwards through the turbo the sound is the air shearing at the blades, much the same as boat propellor cavitation if you wanted to youtube it for a visual idea of what happens. i would assume that this would also cause the turbo to slow down alot quicker than with either a VTA or recirc valve fitted. it sounds f-in cool if you ask me but id say it would be a worse setup than either a VTA or a recirc.
the majority on here will also tell you pistons are weak and will basically just let go because of engine modification and increasing power. from what i have read and the digging i have done (especially since i have the "softer" 2.5) it seems as though ringland failure is not just the result of X amount of power or XYZ modifications but seems to be related to combustion chamber temperatures. the manufacturing process of the standard pistons makes them hard and to an extent fairly brittle and as far as i can tell it seems to be a case of one of the piston rings expanding too much due to combustion chamber temps getting beyond a certain level. what someone who has examined some failed pistons reckons is that thermal expansion of one of the rings in particular causes ringland failure because the ring gap is very tight as are the cylinder bores and once the ring expands to a point it will contact the other side of itself and have nowhere to expand further so deforms shape and puts pressure on the ringland and as the pistins are hard/brittle this causes the ringland to fail. so assuming that is all correct (seems so as open source tuners have run fairly high HP numbers on OEM internals up to or beyond the point most on here would say pistins will fail at) the main safety precautions to take would be to ensure the engine is not allowed to overheat/get too hot, ensure your tune/tuning is not too agressive causing detonation/knock (which spikes combustion chamber temps) and ensure your engine mods/bolt ons are suitably tuned for and dont allow the engine to run in such a way that combustion temps will rise significantly due to less than ideal air/fuel mixtures. also they reckon sustained high speed driving can increase engine/combustion chamber temps as at speeds over a certain speed (dont remember off hand) the air passing over the front of the car essentially will jump over the bonnet scoop rendering it ineffective at cooling the incoming hot/pressurised air from the turbo.
Last edited by DmcL; 05 January 2014 at 12:35 PM.
05 January 2014, 12:46 PM
#136
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Thread Starter
My new favourite member.
I would have thought in casually spirited driving, where changes are pedestrian but boost is high, a VTA is better as the other two options would see a bit of pressurised air going the wrong way down the inlet tract?
Tbh DmcL I'm trying to straighten a few myths out as I'm sick of all the bitching and bullying every time I search for an accurate answer.
TDO4 270-310bhp
Newage WRX engine or "restrictive heads" 320-400bhp
Newage box 350-560bhp
Newage WRX 380 injectors 290-320
Walbro Pump 250-320
Newage WRX top mount 280-360
VTA runs fine-runs horrible/massively over-fuels.
STI top mount 400-450
Panel filter usually 400 surprisingly.
Some say boost going through the turbo the wrong way won't slow it down.
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.
I would have thought in casually spirited driving, where changes are pedestrian but boost is high, a VTA is better as the other two options would see a bit of pressurised air going the wrong way down the inlet tract?
Tbh DmcL I'm trying to straighten a few myths out as I'm sick of all the bitching and bullying every time I search for an accurate answer.
TDO4 270-310bhp
Newage WRX engine or "restrictive heads" 320-400bhp
Newage box 350-560bhp
Newage WRX 380 injectors 290-320
Walbro Pump 250-320
Newage WRX top mount 280-360
VTA runs fine-runs horrible/massively over-fuels.
STI top mount 400-450
Panel filter usually 400 surprisingly.
Some say boost going through the turbo the wrong way won't slow it down.
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.
Last edited by RS_Matt; 05 January 2014 at 12:48 PM.
05 January 2014, 08:17 PM
#137
Unmapped 12.4s @ 105
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My new favourite member.
TDO4 270-310bhp Very rare on a standard one, 260-280 is more common IIRC.
Newage WRX engine or "restrictive heads" 320-400bhp
Newage box 350-560bhp
Newage WRX 380 injectors 290-320 My 380's do 330
Walbro Pump 250-320 My Walbro does 330
Newage WRX top mount 280-360
VTA runs fine-runs horrible/massively over-fuels.
STI top mount 400-450
Panel filter usually 400 surprisingly.
Some say boost going through the turbo the wrong way won't slow it down.
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.
TDO4 270-310bhp Very rare on a standard one, 260-280 is more common IIRC.
Newage WRX engine or "restrictive heads" 320-400bhp
Newage box 350-560bhp
Newage WRX 380 injectors 290-320 My 380's do 330
Walbro Pump 250-320 My Walbro does 330
Newage WRX top mount 280-360
VTA runs fine-runs horrible/massively over-fuels.
STI top mount 400-450
Panel filter usually 400 surprisingly.
Some say boost going through the turbo the wrong way won't slow it down.
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.
When you going to answer my question? Also, how's your engine.
05 January 2014, 08:21 PM
#138
Unmapped 12.4s @ 105
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Location: Newcastle. 330bhp-289lb/ft @ 1bar boost - 12.4s @ 105mph
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(especially since i have the "softer" 2.5) it seems as though ringland failure is not just the result of X amount of power or XYZ modifications but seems to be related to combustion chamber temperatures. the manufacturing process of the standard pistons makes them hard and to an extent fairly brittle and as far as i can tell it seems to be a case of one of the piston rings expanding too much due to combustion chamber temps getting beyond a certain level.
05 January 2014, 08:39 PM
#139
Scooby Regular
Thread Starter
Over rich/suspect OE map, crap material, after market parts, aggressive driving in the bedding in stages.
05 January 2014, 08:48 PM
#140
My new favourite member.
I would have thought in casually spirited driving, where changes are pedestrian but boost is high, a VTA is better as the other two options would see a bit of pressurised air going the wrong way down the inlet tract?
Tbh DmcL I'm trying to straighten a few myths out as I'm sick of all the bitching and bullying every time I search for an accurate answer.
TDO4 270-310bhp
Newage WRX engine or "restrictive heads" 320-400bhp
Newage box 350-560bhp
Newage WRX 380 injectors 290-320
Walbro Pump 250-320
Newage WRX top mount 280-360
VTA runs fine-runs horrible/massively over-fuels.
STI top mount 400-450
Panel filter usually 400 surprisingly.
Some say boost going through the turbo the wrong way won't slow it down.
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.
I would have thought in casually spirited driving, where changes are pedestrian but boost is high, a VTA is better as the other two options would see a bit of pressurised air going the wrong way down the inlet tract?
Tbh DmcL I'm trying to straighten a few myths out as I'm sick of all the bitching and bullying every time I search for an accurate answer.
TDO4 270-310bhp
Newage WRX engine or "restrictive heads" 320-400bhp
Newage box 350-560bhp
Newage WRX 380 injectors 290-320
Walbro Pump 250-320
Newage WRX top mount 280-360
VTA runs fine-runs horrible/massively over-fuels.
STI top mount 400-450
Panel filter usually 400 surprisingly.
Some say boost going through the turbo the wrong way won't slow it down.
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.
If several people say the same thing, then you're probably as close to fact as you will get without experts such as Enginetuner, API, WMS or JGM getting involved.
05 January 2014, 09:03 PM
#141
TDO4 270-310bhp Very rare on a standard one, 260-280 is more common IIRC.
Newage WRX engine or "restrictive heads" 320-400bhp Depends on how you drive it and if you are monitoring oil temp/pressure, Heads will do 400
Newage box 350-560bhpDepends on how you drive it, Torque, Unsympathetic gear changes and launches destroy boxes not BHP
Newage WRX 380 injectors 290-320 My 380's do 330
Walbro Pump 250-320 My Walbro does 330
Newage WRX top mount 280-360 just get an sti one
VTA runs fine-runs horrible/massively over-fuels, Crap put it in the bin unless youre gonna run 400+bhp
STI top mount 400-450, Yep correct, Obviously you benefit from a FMIC in the torque department and obviously IT`s will be higher with a TM
Panel filter usually 400 surprisingly, on the limit i`d say
Some say boost going through the turbo the wrong way won't slow it down....and some dont
I'm about to ask what causes caliper pistons to start sticking as it happens on all my cars. It's gonna be epic.. Wear & Tear,cracked seals,overheating and poor mantinece.
05 January 2014, 09:42 PM
#142
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05 January 2014, 09:42 PM
#143
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but seriously
i saw you edited the first post on the thread
your explanation there is correct
then kiwis explanation is also correct and you tell him his wrong and spout ****e
don't get me wrong i completely understand. half the people on this forum are completely intolerable and they very very very rarely read the question your actually asking. im not takeing sides though. i just want the infomation to be right!
05 January 2014, 09:47 PM
#144
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Thread Starter
Me, you and DmcL are on the money.
05 January 2014, 09:56 PM
#148
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what joshnosh said basically sums it up with the exception of the fact that the ECU DOES know when the throttle is open or closed. on a fly by wire engine it knows the throttle position and on a cable setup it also knows the throttle position thanks to the TPS sensor. i cant speak definitively for subaru ECU's but i am a specialist in mapping OEM ECU's in older BMW's and in those applications i use an emulator in place of the standard eprom which allows me to tune in real time as well as hit trace any map the ECU is using so i can see what cells the ECU is reading or when it starts or stops reading a particular map.
i would assume (actually id bet money) that all petrol ECU's will return to either an idle or decel map on gearchange when the throttle closes. also to further complicate the operation of subaru ECU's i know some, maybe all also have MAP sensors to monitor manifold pressure so on the MAF front air is measured passing the MAF, with a VTA the measured air is vented out of the system and this causes a momentary rich spike, in terms of the MAP sensor whether the air is recirculated or vented does not matter as in both scenarios the MAP sensor would register a drop in manifold pressure when the throttle closes. in terms of TPS sensor there is no reference to boost, simply throttle open/partially open a certain % or throttle closed. all 3 of these sensors are used by the ECU to determine what it should do in various circumstances so its not quite as simple as MAF measures X amount of air and injects fuel for X amount of air as there is more going on (lets also not forget the O2 sensor is constantly inputting to the ECU as well) than just that but it does seem to bias itself towards the MAF measurements rather than MAP measurements on the standard layout which primarily uses the MAF for air metering and the MAP serves other purposes, perhaps relating to boost pressure at various RPM's or in different gears, etc, etc as there are alot of boost or boost target related maps in the subaru ECU and the only sensor which would provide input for these maps would be the MAP sensor which explains why its there when there is also a MAF inputting to the ECU as well.
on the standard subaru ECU if you patch the software (using opensource tuning software like romraider or sharptune) to change operation from the normal MAF based setup to MAP based (aka speed density) or a 50/50 between the two then this alleviates the momentary rich spike issue with a VTA valve, though you could still also use a recirc with no issues.
now onto my own personal (and very limited) experience with my 06 WRX. i have run the OEM recirc as well as run the OEM recirc but with the recirc hose removed and capped off (thus making it a VTA) as well as running (my current setup) a cheap, no frills ebay VTA valve. with OEM recirc connected up as normal theres no rich spikes, no hesitation, no problems. with OEM recirc venting to atmosphere the engine wants to stall alot when it vents at lower revs to the point you would need to give it throttle sometimes to prevent it from stalling, i assume this is due to the spring in the OEM recirc probably being a bit weak, it also will pop or backfire alot of the time when changing gear after it vents due to the momentary rich spike. on the cheapo ebay VTA valve there are none of the stalling issues as with the OEM recirc venting to atmosphere as it seems to have a stiffer spring, it will pop or backfire on gearchange due to the momentary rich spike but aside from that it works just fine on the standard ECU though very, very occasionally (maybe like 1% of the time) the engine will stall after it vents at lower revs, seems to be if it vents at just the right point in lower revs but i cant make it happen so seems like there might be other factors at play when that happens such as a combination of the momentary rich spike and some other function within the ECU (happens extremely rarely though).
and just incase your not clear on what happens with the air in a recirc system.. basically instead of venting out of the system the throttle closes, the recirc valve opens and the air essentially prevents more air being drawn past the MAF by the spinning turbo while the air thats already pressurised after the turbo basically loops around the system and passes back through the still spinning turbo until the throttle is opened again, the valve closes and the air enters the engine again. i would suspect that not all of the pressurised air loops around and back through the turbo given that it is pressurised but since the turbo is still spinning and the air is recirculated and dumpedo ut before the turbo then the fact that the turbo is still spinning will pull most of the air back through it while a smaller amount probably either flows backwards through the MAF (which wouldnt register the same as air flowing through it in the correct direction) a little or simply halts any incoming air to the MAF. i would hazard a guess that even with a recirc valve there would still be a slight rich spike as it wouldnt 100% cancel out what air has already been measured by the MAF but it certainly cancels out the vast majority of it whereas with a VTA the MAF basically thinks the engines still pulling air for that split second before the ECU determines fron the TPS sensor and/or MAP sensor that the throttle has closed and it not needs to switch to decel or idle maps.
/thread
i would assume (actually id bet money) that all petrol ECU's will return to either an idle or decel map on gearchange when the throttle closes. also to further complicate the operation of subaru ECU's i know some, maybe all also have MAP sensors to monitor manifold pressure so on the MAF front air is measured passing the MAF, with a VTA the measured air is vented out of the system and this causes a momentary rich spike, in terms of the MAP sensor whether the air is recirculated or vented does not matter as in both scenarios the MAP sensor would register a drop in manifold pressure when the throttle closes. in terms of TPS sensor there is no reference to boost, simply throttle open/partially open a certain % or throttle closed. all 3 of these sensors are used by the ECU to determine what it should do in various circumstances so its not quite as simple as MAF measures X amount of air and injects fuel for X amount of air as there is more going on (lets also not forget the O2 sensor is constantly inputting to the ECU as well) than just that but it does seem to bias itself towards the MAF measurements rather than MAP measurements on the standard layout which primarily uses the MAF for air metering and the MAP serves other purposes, perhaps relating to boost pressure at various RPM's or in different gears, etc, etc as there are alot of boost or boost target related maps in the subaru ECU and the only sensor which would provide input for these maps would be the MAP sensor which explains why its there when there is also a MAF inputting to the ECU as well.
on the standard subaru ECU if you patch the software (using opensource tuning software like romraider or sharptune) to change operation from the normal MAF based setup to MAP based (aka speed density) or a 50/50 between the two then this alleviates the momentary rich spike issue with a VTA valve, though you could still also use a recirc with no issues.
now onto my own personal (and very limited) experience with my 06 WRX. i have run the OEM recirc as well as run the OEM recirc but with the recirc hose removed and capped off (thus making it a VTA) as well as running (my current setup) a cheap, no frills ebay VTA valve. with OEM recirc connected up as normal theres no rich spikes, no hesitation, no problems. with OEM recirc venting to atmosphere the engine wants to stall alot when it vents at lower revs to the point you would need to give it throttle sometimes to prevent it from stalling, i assume this is due to the spring in the OEM recirc probably being a bit weak, it also will pop or backfire alot of the time when changing gear after it vents due to the momentary rich spike. on the cheapo ebay VTA valve there are none of the stalling issues as with the OEM recirc venting to atmosphere as it seems to have a stiffer spring, it will pop or backfire on gearchange due to the momentary rich spike but aside from that it works just fine on the standard ECU though very, very occasionally (maybe like 1% of the time) the engine will stall after it vents at lower revs, seems to be if it vents at just the right point in lower revs but i cant make it happen so seems like there might be other factors at play when that happens such as a combination of the momentary rich spike and some other function within the ECU (happens extremely rarely though).
and just incase your not clear on what happens with the air in a recirc system.. basically instead of venting out of the system the throttle closes, the recirc valve opens and the air essentially prevents more air being drawn past the MAF by the spinning turbo while the air thats already pressurised after the turbo basically loops around the system and passes back through the still spinning turbo until the throttle is opened again, the valve closes and the air enters the engine again. i would suspect that not all of the pressurised air loops around and back through the turbo given that it is pressurised but since the turbo is still spinning and the air is recirculated and dumpedo ut before the turbo then the fact that the turbo is still spinning will pull most of the air back through it while a smaller amount probably either flows backwards through the MAF (which wouldnt register the same as air flowing through it in the correct direction) a little or simply halts any incoming air to the MAF. i would hazard a guess that even with a recirc valve there would still be a slight rich spike as it wouldnt 100% cancel out what air has already been measured by the MAF but it certainly cancels out the vast majority of it whereas with a VTA the MAF basically thinks the engines still pulling air for that split second before the ECU determines fron the TPS sensor and/or MAP sensor that the throttle has closed and it not needs to switch to decel or idle maps.
/thread
i did know that the ecu can read the TPS but if im right the ECU dosent account much for the throttle position untill its fully off and then your on coast/idle? ether way i thought it would be best to ignoor that as it would have confused my explanations
05 January 2014, 10:04 PM
#149
Scooby Regular
Thread Starter
some more good info there
i did know that the ecu can read the TPS but if im right the ECU dosent account much for the throttle position untill its fully off and then your on coast/idle? ether way i thought it would be best to ignoor that as it would have confused my explanations
i did know that the ecu can read the TPS but if im right the ECU dosent account much for the throttle position untill its fully off and then your on coast/idle? ether way i thought it would be best to ignoor that as it would have confused my explanations
Unless that is if BT/Google start censoring Car ****.
05 January 2014, 10:12 PM
#150
for what its worth i ran a vta briefly when i fitted a fmic while i was waiting for the recirc pipe to be delivered.
it ran fine,only difference i found was it popped occasionally on gear changes.
make of that what you will as to the cause.