sparky_sj04 Posted November 14, 2007 Posted November 14, 2007 Fitted a Bailey DV12 dump valve to the 03 uk sti, obviously it dumps to atmosphere, but the standard valve re-circs back to the intake..... Now I would have thought that the re-circ (standard valve) would be more efficent as its blasting air back into the intake and should give that little added push when you're changing gear... (If you're booting it obviously..) Can anyone enlighten me?
thefastone Posted November 14, 2007 Posted November 14, 2007 Nah, its pretty much as you said, Your just giving your self a bit more lag... More noise - nice... More lag - Yeah if you like that sort of thing.....
~ ~ Cal ~~ Posted November 14, 2007 Posted November 14, 2007 See below - best to avoid but if you do fit one get a Forge, HKS, Blitz or TurboXS one <P>Righto <BR><BR>The Impreza runs off the MAF sensor when in open loop fuelling, when you are giving it some stick. The Mass Air Flow will meter the amount af air being drawn into the engine and inject the corrosponding amount of fuel amount to achieve a rich enough Air to Fuel Ratio when on boost/load conditions. <BR><BR>When you release the throttle, to change gear or slow, on a std recirc dump valve, the pressurised air will be dumped back into the inlet tract between the MAF and turbo inlet. When the throttle is closed on gear change on slow down the ecu will inject a corresponding amount of fuel to achieve a satisfactory AFR to compensate for the extra volume being drawn in. When you fit a Vent to Atmos dump valve, the pressurised air will be released to the atmosphere when the throttle is closed but the ECU will still dump extra fuel in trying to achieve a satisfactory AFR. The ECU thinks there is an extra volume of air being drawn in the engine and will inject the right amount of fuel to compensate, this metered volume of air has now been dumped into the atmosphere instead of the inlet tract. A std ECU has no way of knowing that the Air volume that has passed the MAF , which has been metered for and compensted for accordingly has been released outside the inlet tract instead of being drawn into the engine. This will in turn make the AFR be very RICH due to the air part of the AFR being expelled through a valve the ECU has no knowledge of <BR><BR>The extra fuel that is being drawn into the engine, minus the volume of air the ECU was expecting will do 1 of 2 things. <BR><BR>1. It will explode when the rich mixture hits the piston crown, giving a flash of lift off DET. At full boost and at the point of ignition the temp of the exhaust gases can average 800 and hit 900 - 1000 degrees centigrade after a spirited drive, the crowns of the piston at the point of ignition can be as high as 700 - 800c. This tempreture is more than enough to ignite the fuel mixture before the spark can do the job and be a cause of lift off det and lift off dat can be damaging as DET under load <BR><BR>2. It will not expolde but as the mixture has ignited by the spark from the plugs and the flame front travels across the piston, by the time the exhaust valve has opened on the exhaust stoke the overrly rich mixture has not fully burnt by the inappropriate igntion level . Sometimes the rich fuel vapours not burnt from the time alloted in the combustion process will pop in the exhaust housing of the turbo when the gases exit the combustion chamber. Sometimes these pops will be sufficient to produce a a flame strong enough to travel the length of the exhaust syatem resulting a nice wee flame for everyone to go aaaaaawwwwww at but every time you do not get a flame the unburt fuel will be lingering somewhere in the exhaust tract, headers, hot side of turbo or even the chamber walls<BR><BR>The atomised fuel droplets that cling to the wall in the combustion chamber will clean the oil off the walls of the piston bore every time the overly rich Air/Fuel mixture is being drawn into cylinders. The unburnt fuel mixture will get past the compression and oil control rings due to petrol mixture being a lot finer than oil and the excess mixture that has not been ignited will stick to the cylinder walls due to the condensation effect of the AFR that is being pumped into the engine every time the inlet valves open, mixture being around 10-30c and the walls of the cylinder being around 200 - 400c, the retaining temp from the previous combustion cycle which at 6000 rpm (avg gearchange rpm) would have happened millisecs beforehand . This fine petrol mixture will be transferred to the oil in the sump, getting past the oil control rings as atomised fuel is a lot finer than thick engine oil. The classics lubricated the piston bores and under the piston crown with the end of the crank scooping oil up and throwing the oil up the bores, apart from STI RA's which had under crown oil cooling jets to cool the underside of the piston. The oil that has been thrown up by the crank to lubricate the bore is prevented from entering the combustion chamber by the rings on the piston but atomised fuel can easily get past these rings assisted by the pressurised gases in the combustion chamber above helping it on its way and once past the rings the tiny droplets of fuel will soon find its way to the sump abley assisted by the laws of gravity. Over time these droplets of fuel will be sufficient to start to thin the oil down to a dangerous level and increase the chance of picking up a big end bearing<BR><BR>My advice for the peeps running a Vent to Atmoshere is to, apart from dump them in the bin, is to increase the regularity of oil changes. </P><P>Hope this helps<BR></P> <P>All my own work</P>
whitenuckleride Posted November 14, 2007 Posted November 14, 2007 (edited) blimey thats my lunch break gone reading just one thread top info though cal nice one - certainly made my mind up on wether to go to atmosphere Edited November 14, 2007 by whitenuckleride
RA Dunk Posted November 14, 2007 Posted November 14, 2007 blimey thats my lunch break gone reading just one thread squiggle certainly knows his stuff
sparky_sj04 Posted November 14, 2007 Author Posted November 14, 2007 Nah, its pretty much as you said, Your just giving your self a bit more lag...More noise - nice... More lag - Yeah if you like that sort of thing..... More lag from the atmospheric dump valve???
sparky_sj04 Posted November 14, 2007 Author Posted November 14, 2007 See below - best to avoid but if you do fit one get a Forge, HKS, Blitz or TurboXS one But you're off boost etc for a second or so when you're changing anyway, and you're saying the fuel is always injected because the ECU thinks it's needed and it can't measure from the MAF because the air comes in after it... so basically with the re-circ type the same thing will happen but the mixture won't be as rich and won't breakdown the oil film on the liners or deposit in the exhaust system....??? Yah? What about turbo lag? More with the re-circ or with the atmospheric valve?
thefastone Posted November 14, 2007 Posted November 14, 2007 More Lag with the Vent to Atmosphere. but its not just a second for the gear change, because you need to let the boost build up again anyways after you come off the power... and with a vent to atmosphere dump valve, it will take a little longer to build back the boost pressure... you think that you can react in a second, the ECU can react a LOT quicker, and at the end of the day, if you are going to be running lean, with the potential of DET, then thats a problem... I dunno, Ive just had a drink, so I might be speaking pants.... If Ive lied or am wrong about any of what ive Said then I'm sure I'll be corrected... Read what Grant (squirrel/squiggle) said again, you might need to read it a few times to understand it like... but worth reading and UNDERSTANDING...
sparky_sj04 Posted November 15, 2007 Author Posted November 15, 2007 More Lag with the Vent to Atmosphere.but its not just a second for the gear change, because you need to let the boost build up again anyways after you come off the power... and with a vent to atmosphere dump valve, it will take a little longer to build back the boost pressure... you think that you can react in a second, the ECU can react a LOT quicker, and at the end of the day, if you are going to be running lean, with the potential of DET, then thats a problem... I dunno, Ive just had a drink, so I might be speaking pants.... If Ive lied or am wrong about any of what ive Said then I'm sure I'll be corrected... Read what Grant (squirrel/squiggle) said again, you might need to read it a few times to understand it like... but worth reading and UNDERSTANDING... Cheers for that, i've read what Grant said and understood it. Just to clarify I only said "a second or so", i wasn't actually saying it was one second, just indicating there was a time period... I'm an engineer anyway (ships not cars right enough) so I can understand what he's saying.... Think i'll stick the standard valve back on, always thought i got more of a push in the back with that on - had put it down to being new to the car and thought it was in my head but maybe i'll try it again..... Cheers for your help dudes..
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