Dump Valve

[the squiggle]

<< with a d/v fitted apparently will help prolong the life of ur turbo as will a decat system. I cant understand how the dumpvale will make the car over fuel as posted by the squirrel555, excess fuel will not be able to run down the cylnder walls in to your sump past compresion rings and oil seals instead it will exit via the exhaust port and backfire in the exhaust system. And i also cant see how it will cause the car to run lean as posted by zeolite as a dump valve has nothing to do will the fuell system, plus there must be benefits of the slightly heated manifold pressure being dumped to atmopsphere, and a fresh intake being drawn, hope i have not offended anybody and im only trying to have a better understanding of this. >>

Righto

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 you release the throttle on a std recirc dump valve, the pressurised air will be dumped back into the inlet tract when the throttle is closed and the ecu will inject a corresponding amount of fuel to achieve a satisfactory off throttle AFR. 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 satisfatory 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 extra 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 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 was not mapped for

The extra fuel that is being drawn into the engine, minus the volume of air it was expecting will do 1 of 2 things.

1. It will explode when the rich mixture hits the piston crown, giving a flash of lift off DET. At full boost the temp of the exhaust gases can average 1000 and hit 1200 degrees centigrade after a spirited drive, the crowns of the piston can be as high as 800 - 900c. This temprature is more than enough to ignite the fuel mixture before the spark can do the job

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 the mixture has not fully burnt. Sometimes the rich fuel vapours not burnt from the time alloted in the combustion process will pop in the exhaust housing of the turbo.

The overly rich mixture will clean the oil off the walls of the piston bore when the overly rich Air/Fuel mixture is being drawn into cylinders. The excess 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 mixture being around 30c and the walls of the cylinder being around 400c. This fine petrol mixture will be transferred to the oil in the sump. 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. Graham Goode Racing sell an uprated oil pump which helps cool he under side of the piston

Personally i have no dump valve what so ever, not even a std recirculating one. This gives me the World Rally Car style wastegate chatter with the benefit of the metered air being drawn into the engine being properly compensated for fuel by the ECU.

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. Std recirc dump valve, i would aim to change the oil every 6000 miles. NO dump valve at all, i would go for every 4500 miles. Aftermarket Vent to Atmosphere dump valve, i would aim to change the oil every 3000 miles. I change my oil every 1000 miles due to the fact i get my oil for nowt.

Grant

[WRC No 1]

well see all the talking about the dump valves am gonnae take it off and remove my k&n and put in a panel filter back on.

wullie

[Gumball]

paddy-theres your technical explanation i do believe?

grant-Can subaru ie halleys change my oil for me? can anyone do it?

wullie-on yurself

anyone else-im still selling a fantastic HKS valve cheap.

note to self- take it easier,watch the mods,live longer

[wrxmania]

Good advice front The Squirrell there - Grant you must take ages typing up those notes re your two finger typing technique you were telling me about

Or do you dictate notes to the wizz Imy????????????

I think anyone trying to challenge long accepted wisdom must think why it is long accepted as technically correct - thanks for the explanation - I will STILL be sticking to my standard recirc - PPPTTTSSSSSSCCCCCCCCHHHHHHHHHHHHHHHH! (NOT)

Brian

[paddy247]

Cheers squirrel555 for your time and effort on that one, you appear to be very knowlable, but ill have to reserch your findings before i can come to a conclusion, but this is whot its all about sharing information.

Can i also ask wot if any mods you done to get your car to run without any d/v and would that not have the same efect as an atmospheric.

[the squiggle]

<< well see all the talking about the dump valves am gonnae take it off and remove my k&n and put in a panel filter back on.

wullie >>

Dont be daft young lad

We would miss all those loverly flames on our treks.

Just keep up the regularity of the oil changes and it will be cool.

Grant

[the squiggle]

<< Good advice front The Squirrell there - Grant you must take ages typing up those notes re your two finger typing technique you were telling me about

Or do you dictate notes to the wizz Imy????????????

I think anyone trying to challenge long accepted wisdom must think why it is long accepted as technically correct - thanks for the explanation - I will STILL be sticking to my standard recirc - PPPTTTSSSSSSCCCCCCCCHHHHHHHHHHHHHHHH! (NOT)

Brian >>

That reply took me 2 bloody hours to type due to my infamous 2 finger typing technique. Imy was on the bed giving me advice on the structure and presentation.

Grant

[the squiggle]

<< Cheers squirrel555 for your time and effort on that one, you appear to be very knowlable, but ill have to reserch your findings before i can come to a conclusion, but this is whot its all about sharing information.

Can i also ask wot if any mods you done to get your car to run without any d/v and would that not have the same efect as an atmospheric. >>

The mods i have on my car is where the std dump valve would enter the inlet tract, the nipple on the inlet manifold and the intercooler have all been blanked off. This means when the throttle is closed the pressurised air is sent back through the turbo and intercooler, creating the WRC style chiping sound when the turbo tries to run forwards and backwards very quickly. On a slow gentle gearchange the pressurised air will get back out through the induction but do a quick gearchange it is possible to catch the pressurised air still in the intercooler which in turn gives you a better stating point for the turbo to build up pressure again.

The pressurised air will have been metered and the corresponding amount of fuel injected because the majority of the air is still contained in the intercooler/turbo area instead of being expelled to the atmosphere.

Granted some of the volume of air will get back out through the induction but the majority of the air will be contained and the AFR will be more stable due to a more appropriate volume of air being present.

Granted that it cant be good for the turbo running back and forth very quickly but the TD05 turbos fitted to the early cars are strong enough to take the abuse IMHO

I must ask who you are gonna refer my answer to for clarification, the guy that works down the local garage or AndyF.

Absolutely everything i have ever learned about Subaru engines, i read off the back of a Frosties packet so blame Tony the Tiger if i am wrong on anything.

Grant

[the squiggle]

After reading the above posts, i would like to clarify that i have nothing against Vent to Atmosphere Dump Valves. I just want to point out the need for increasing the frequency of the oil changes if one is fitted.

Grant

[WRC No 1]

no prob grant i will think about it. i do an oil change every 3500 or 4000 miles so i think i am all right.

1 reason i dont want to put the recirculating valve back on is cause i have a book for the subaru by chris rees and that say for the my 97 my 98 it has problems with the valve not closing properly. with mine been the my 97 i dont know ???

wullie

[paddy247]

oioi

[~ ~ Cal ~~]

Holy sh1t Grant - I knew you were a knowledge beast but JAYSUS ! You should be in business like AndyF or sommit !

Thanks for your thoughts & harry potter style wizardy

Cal

[andrew_lally]

get a grip you big girls........dump valves are the buisness.......let it blow up......id rather that, than not hear it it wooooooooooosh all f$@kin day......woohoo

[imprezapete]

Eh no thanks m8, I like keeping my engine

Also im not a big girl.........

Well at least not in public

[paddy247]

Am i right?

Even if the car did over fuel the lambda sensor will anaylise the exhaust gas, and the fueling will be corrected instantly.

A rich mixture is extreamly unlikly to pre -ignite.

Running the car with no resirculation or atmophseric valve will couse the system to be over pressurised, ie the components have a tollarance level in relation to presure.

I dont think there will be enough manifold pressure to spin the turbo back and forth in an instant if run without any type of valve, as it will be spinning at thousands of rpm.

squirell555 nothing personal, but the truth is out there.