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Originally Posted by RS_Matt
(Post 11309503)
...but when you suddenly come off boost that metered air isn't used either way. I can only see a leaky DV causing rich issues and that would be on moderate to elevated boost.
It recircs back into the inlet tract, post MAF, pre turbo. It is still being used. |
Originally Posted by mickywrx
(Post 11309506)
You're hard work!
It recircs back into the inlet tract, post MAF, pre turbo. It is still being used. So if it is down to the fact that the recycled air is still being used it must mean the engine still draws in a tiny bit of pressure on the beginning of overrun on just a re-circ system? Why does a delete set-up run rich on overrun then? |
Originally Posted by RS_Matt
(Post 11309503)
...but when you suddenly come off boost that metered air isn't used either way. I can only see a leaky DV causing rich issues and that would be on moderate to elevated boost.
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Originally Posted by mickywrx
(Post 11309506)
You're hard work!
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I give up rs_matt had proved he has no grasp about anything turbo or logic for that matter
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Originally Posted by marknjayne
(Post 11309525)
but it is used,its recirculated back to a point before the turbo and after the maf,then pulled back through the turbo again when needed,the volume of air is calculated and must be used,if its not used there will be too much fuel
Also how long does the pressurised unneeded air stay in the system if you are going down the gears? It can't possibly stay in the inlet tract for long?? Surely this would mean a re-circ system would run rich until the throttle was opened up again? On the contrary I believe the AFR tries to get back to 14.7 |
Originally Posted by swaynie
(Post 11309537)
I give up rs_matt had proved he has no grasp about anything turbo or logic for that matter
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Originally Posted by RS_Matt
(Post 11309521)
The answer is like 'the storm destroyed my fence' and not it was the wind/flying debris/lightening that destroyed it. :eek:
So if it is down to the fact that the recycled air is still being used it must mean the engine still draws in a tiny bit of pressure on the beginning of overrun on just a re-circ system? Why does a delete set-up run rich on overrun then? The throttle is closed on over-run..... |
Originally Posted by RS_Matt
(Post 11309542)
Certainly feels that way, I'm pretty sure the answer is pretty simple physics. :thumb:
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Originally Posted by mickywrx
(Post 11309544)
:facepalm:
The throttle is closed on over-run..... |
Originally Posted by marknjayne
(Post 11309549)
its just witchcraft mate,if you are happy with a VTA than :thumb:
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Taken from Enginemappers site
Originally Posted by Enginemapper
(Post 11309552)
Dump Valves and Blow off valves.
These are fitted purely to redirect the turbo pressure which builds up in the intake system, post turbo, pre-throttle plate when the throttle is closed quickly, i.e when you lift off. In all of the production based vehicles with MAF sensors reading ECU load it is highly likely that any dump valve will be of the recirculating type. Meaning the air pressure built post turbo, pre-throttle will be dumped back into the turbo inlet side, post MAF. This is a key point to note regarding what dump valve you choose and why. On a MAF system, all the air that enters the engine will travel through the MAF to be measured for the engine management to work out how much fuel is needed for the combustion process. When you lift off and the pressurised air back up against the back of the throttle plate, the dump valve, (on a standard recirculating system), will dump it back into the intake system, so the same total volume of air that the MAF has measured remains within the system and will still be consumed by the engine. Fitting an externally venting dump valve, or a vent to atmosphere, (VTA), valve will cause a number of problems when you lift off and general engine running, as that dumped air has been measured by the MAF, but is then not used by the engine, although it expects it. The other main issue regarding externally venting dump-valves and MAF sensors, is that the dumpvalve will always open under vacuum, i.e when not is boost, (positive pressure). This means that on idle and cruise, an external venting dump valve will always be letting in extra air post MAF, (essentially an air leak). This means that initially it will run leaner than it should until the ECU learns some corrections, (standard ECUs only). This problem is not applicable when running a mafless ECU, like a Simtek, Syvecs, Link etc. My advice; on a standard ECU stick with a recirculating dump valve for drive-ability and general integrity of the engine management control systems. As said before, if you are running mafless, then running an external dump valve won’t matter or not. |
Originally Posted by Aaron1978
(Post 11309575)
Taken from Enginemappers site
Going on that EM site I can't see why a car with a re-circ wouldn't run rich lifting off and then slowing down. You won't be using that pressurised air the MAF accounted for. |
this is literally all new to me but as i understand it surely its just a case of - For Example
1 litre of air enters maf maf then dictates how much fuel is need for that 1 litre but that 1 litre doesn't go through as its expelled into the air but the maf doesn't know that so still fuels for that original 1 litre im not here taking the mickey but is that pretty much a basic simpletons way of the process ? |
Originally Posted by ScoobyFanatic33
(Post 11309638)
this is literally all new to me but as i understand it surely its just a case of - For Example
1 litre of air enters maf maf then dictates how much fuel is need for that 1 litre but that 1 litre doesn't go through as its expelled into the air but the maf doesn't know that so still fuels for that original 1 litre im not here taking the mickey but is that pretty much a basic simpletons way of the process ? |
and there was me hoping that when it comes to modding i can spend a fortune for a gizmo bolt it on and job done lol i was so wrong !
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If you want that vta noise run a clrecirc with a pod filter and you get a little noise but nothing chav
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ive never been a fan of the noise really but as little as i know ive always been aware of the amount of pressure involved and how its better to reduce it to decrease wear on the turbo but never knew more than that in a nutshell, how naive i was :)
ive ordered a recirculating one now and will remove my current vta, lets just hope it comes with instructions ! just out of interest though would the vta dump valve really effect performance or not in the slightest ? is it just a case of the damage that can be done over time ? |
A vta on a mafless setup wouldn't really matter and some people will argue that a vta will prolong the life of your turbo. As long as the turbo is supplied with good clean oil it's happy and doesnt really matter what you do with em. A turbo will go usually around the 100k mark depanding how much boost they've run in the past and how regular oil services are.
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oh dear thats just opened up another question then if you dont mind ;)
is a turbo timer something that is best to go with ? ive heard it said that just stopping the engine after a good run causes the turbo to spin almost dry as no oil is pumping hence keeping the tick over going for 30 sec's or so ? or is this a whole new debate lol |
Originally Posted by ScoobyFanatic33
(Post 11309708)
oh dear thats just opened up another question then if you dont mind ;)
is a turbo timer something that is best to go with ? ive heard it said that just stopping the engine after a good run causes the turbo to spin almost dry as no oil is pumping hence keeping the tick over going for 30 sec's or so ? or is this a whole new debate lol The best way of combatting against this, is simply to drive off boost for the last mile or two of your journey, before switching off and parking up. This is because nice, chilling air is passing over the turbo housings, thus efficiently cooling them down. And of course, the oil is still circulating, which helps guard against localised hotspots from establishing themselves. The above course of action is better than just letting oil circulate on its own, by using a turbo timer for a minute or two. (Although, this is still better than shutting engine off immediately after a lengthy hoon, obviously). Despite all of the above though, modern day water-cooled turbos are pretty reliable, in terms of taking abuse. |
Originally Posted by RS_Matt
(Post 11309503)
...but when you suddenly come off boost that metered air isn't used either way. I can only see a leaky DV causing rich issues and that would be on moderate to elevated boost.
If you dump it to atmosphere, the car has already fuelled for it and the air is gone. TBH, bud, you are arguing against knowledge gained from YEARS of ownership, mapping etc. |
You must understand that even when you close the throttle, that a certain amount of air/fuel is still being put through the engine. Why you ask? How would the car idle without this? :wonder:
So, you shut the throttle, the ecu reverts to idle mixture. But, there is a higher % of fuel due to some of the air being vented to atmosphere when you came off the throttle. Hence why until the extra fuel is burnt, the mixture is rich. It isn't hard to work out. :thumb: Whether it is bad for your engine, probably not in the short term. But running rich on any car can cause issue long term, just as running lean. :thumb: |
Originally Posted by ScoobyFanatic33
(Post 11309708)
oh dear thats just opened up another question then if you dont mind ;)
is a turbo timer something that is best to go with ? ive heard it said that just stopping the engine after a good run causes the turbo to spin almost dry as no oil is pumping hence keeping the tick over going for 30 sec's or so ? or is this a whole new debate lol |
Originally Posted by Gear Head
(Post 11309910)
You must understand that even when you close the throttle, that a certain amount of air/fuel is still being put through the engine. Why you ask? How would the car idle without this? :wonder:
So, you shut the throttle, the ecu reverts to idle mixture. But, there is a higher % of fuel due to some of the air being vented to atmosphere when you came off the throttle. Hence why until the extra fuel is burnt, the mixture is rich. It isn't hard to work out. :thumb: Whether it is bad for your engine, probably not in the short term. But running rich on any car can cause issue long term, just as running lean. :thumb: So basically running a VTA causes a split second of richness on the overrun because the the engine is still trying to pull a tiny bit of non-existent pressurised air in on closed throttle/idle? I've run a AFR gauge and it's only straight after a gear change on the overrun that I notice a slight rich dip, not any other time. I have a stiff spring on my VTA that only opens at 4k, so I'm guessing the rich fueling only really comes into play when I ease off at high revs as changing gears lightening fast only sees a subtle pressure loss? Or would it still be bad at 4k and changing fast as the air is heading out of the intercooler and causes the air to vacuum away from the inlet? :wonder: |
Originally Posted by alcazar
(Post 11309863)
That air is put back in the system, AFTER the meter, but before the turbo, so it isn't metered again and does get used.
If you dump it to atmosphere, the car has already fuelled for it and the air is gone. TBH, bud, you are arguing against knowledge gained from YEARS of ownership, mapping etc. I can imagine after you vent/re-circ at high revs there is maybe a window of 800ms? |
Is this crap still going on :lol1:
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Originally Posted by banny sti
(Post 11309980)
Is this crap still going on :lol1:
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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. |
Originally Posted by banny sti
(Post 11309980)
Is this crap still going on :lol1:
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