is up gradeing the dump valve to the whooosh type one worth doing and is it just for the noise? which i think sounds awsome
are they abit boy racer?

 

If you are running a Subaru ECU, a "whoosh" (aka vent to atmosphere) dumpvalve will make your engine run worse, so if you care more about your car running properly than you do about posing, stick with a recirculating one.

 

i didn't know that cheers mate

 

gm - why do you say a vta dump valve makes an engine run worse than recirc ? (I guess I could trawl through previous threads but I'm lazy)

When you have the throttle open the dump valve, recirculating or VTA, is closed so has no effect on how the engine runs.

With a VTA dump valve, when you back off the throttle the dump valve vents to atmosphere there is a momentary over fuelling because the air intake through throttle has been measured and therefore corresponding fueling calculated, but then the air is dumped before it gets to the combustion cylinder. But as you are closing the throttle anyway the engine is not really under load, so it's not really a problem is it ?

Or is the problem that the ECU leans off the mixture because the lambda readings show unburnt fuel and therefore when you open the throttle again you get momentarily lean mixture ?

 

Beat me to it.
Daz.

[Edited by Daz WRX - 1/20/2004 10:24:23 AM]

 

Do you get pops and bangs from your exhaust on high revs throttle lift off? If so, that's unburnt fuel. And it doesn't get to your exhaust via magic...!

Excessively rich fuel can wash oil from the cylinder bores leading to piston, bore, and ring wear, and excessive oil consumption. Is it really worth if for pppsssssshhhhtttt...?

 

We're talking about excess fuelling for some fraction of a second, the engine isn't continually running rich. Is any excess wear due to cylinder bore washing even measurable ?

P.S. Also that's a wear/reliability question, doesn't suggest the engine would run any worse.

[Edited by Brit_in_Japan - 1/20/2004 1:29:55 PM]

 

It doesn't matter whether it's measurable or not (and I think it probably would be over the lifetime of the car), or indeed how momentary the overfuel, the underlying point is that the use of a VTA dumpvalve in this application quite definitely does cause a situation that is outside the ideal operating parameters of the engine.

While there are plenty of people who like their cars to sound like a pensioner with emphysema, and are willing to put up with/ignore any risk to the engine, the question Peachy asked was whether these things are actually an upgrade for the engine, or whether they're just a boy racer thing. The answer to that question is clear, and it's the latter.

 

ok... I was thinking of buying a Atmo Dump Valve for my WRX03, but now I saw this thread...


Nicky

 

But surely when the throttle is released the throttle pos sw' tells the ECU its closing the ECU turns off the injectors then as the pressure changes to depression the D/V actuates, so no overfueling, bore wash and if you use the correct D/V, no poor running also on the plus side is no stall affect on the compressor wheel as the pressure backs up against the vains. to top that you get your noise........IS IT CHRISTMAS again.

Len

 

fair enough gm, re-reading the original the post I agree that a VTA dump valve is not a performance upgrade.

However I'm still interested in knowing whether there is a quantifiable risk of using a VTA dump valve. The reason is the MY99 WRX Wagon I bought here in Japan already had a HKS SSQV fitted. With your extensive experience with these engines, does running with a VTA dump valve shorten the life or degrade the performance of the engine over time ? Do you have some empiracle data about engines with VTA dump valves needing rebuilds earlier than non VTA ? I'd value your feedback.

 

TBH Brit I've not been playing with Subaru engines for as long as you seem to be thinking, so there'd be plenty of people better qualified to offer this sort of information. However, I know a few people who will be in posession of this sort of info and I'll be seeing them over the weekend, so I'll report back on anything interesting they say.

No! The fuel supply doesn't get cut off on a shutting throttle. If it did there'd be melted pistons all over the place. The ECU reduces the IDC but fuel still goes through. As the MAF values are still used to calculate the required amount of fuel, venting waste air off to atmosphere throws the readings out of whack, which is where the overfuelling comes from.

[Edited by greasemonkey - 1/21/2004 7:56:18 AM]

 

Thank you gm.

 

Greasemonkey,

I bet you enjoy telling small children that Santa Claus doesn't exist too!

You killjoy!

(only joking)


Rich

 

Humbug!

 

60,000 miles and I have had absolutley no engine problems with my VTA. I have one because I like it

If you want one get one. There is no performance gain at all although some say the spool up time for the turbo is reduced. Personally I think that is a placebo thing.

WhenI got my scoob, I was told "Never do this Never do that" and guess what I spent 6 months heeding thier advice and expecting my car to blow up at a moments notice unless i spent a fortune on the "BEST" bits.

3 years down the line and my Car and I have survived the "Don't fit a DAWES unless you are a fool" debate, the "Only use Good Year tyres unless you want to kill yourself" debate, The "You are irresponsible if you don't use DS2500 pads" Debate, the ITG WILL Kill your MAF" Debate and obviously the "If you haven't got a Knock Link or Lambda Link your car will explode within the next week! If it doesn't you are lucky" Debate.

Obviously, in order to stay in the IN crowd and talk about your car down the pub, you had to spend 3-4 times as much
"Oh yeah mate, I've got 4 Defi gauges, Knock Link, Lambda link, Just changed my Toyo's for SO3's, whipped out my mintex while I was at it and dropped in some DS2500's, took my ITG out and threw a green filter in this morning though, can't be too careful eh, oh and I had irridium tipped spark plugs put in this afternoon"
"That must have cost a fortune mate?"
"Oh yeah but needs must!"
"What needs?"
"Well you gotta have the best to get the most out of the car!"
"But you've only done 10,000 miles in the last 2 years and no track days"

I could go on but you get my point

Your Scoob is a machine, treat it with mechanical sympathy and it will be fine. IF however you are going to take it on track or start drag racing it or upgrading the power, then things like Recirc v VTA become FAR more relevant. Generally though, when folk enter into that realm they tend to know enough themselves to be able to asses the risk.
If you are unsure about a subject, use the search facility AND the telephone/e-mail to speak to specialists and Dealers and find out for yourself using as many sources as possible. Scoobynet IS a good resource but it certainly AIN'T the only source. I must have saved myself thousands of pounds over the last 2.5 years by making a few calls before buying/doing something to my scoob

Sorry for the length of the post, but it does upset me when someone who was going to do something to thier car to increase the enjoyment factor suddenly feels that it's Too dangerous due to a few holier than thou posts and thus doesn't

Mikey < Offering a view from the other side of the advice fence >

 

That's a fair enough opinion (albeit a tad over the top ), but the way I see it is there is no "right" or "wrong" and everyone is entitled to their opinion. If someone asks a question, then someone will reply to it. And that reply is applicable to the person that replied. It may not represent the opinions of everyone else, and so it's up to someone with a differing opinion to post their reply as well. The topic starter then has more than one opinion to consider, and make his/her OWN decision. It would be a very boring bbs if there weren't differing opinions.

However, as people seeking advice will no doubt act upon advice given (NickyWRX for instance), and if that advice *could* potentially cause a problem, I personally prefer to err on the side of caution...

 

 

I removed my std dump valve and blanked off the hoses when i done this everyone said that the turbo would explode and would you credit it 1 year later and its still going and it sounds like the WRC cars

Cheers Grunt

 

Here Here Mikey!

 

it depends where...if u fir the wsgte b4 or fter the a/f meter m8. if not ur ecu will read data all wrong n ur car will start 2 go bonkers

ie. it does not control boost level.
extrnally venting "confuses" the a/f meter, resulting in
1)ecu has no clue that air has been vented =>fuel mixture change -very rich-
2)misfires
3)flat spots
4)high mpg

thats wat i know anyway

[Edited by jackieFMbrunei - 1/24/2004 3:05:36 AM]

 

gm - so did you find out anything this weekend regards long term effects of using VTA dump valves ?

 

No, sorry Brit. My travel plans got changed and I had to stay in UK unfortunately. Will have to make some phone calls...

 

Have a Blitz BOV on my car. Have had it it on there since August 2000. No problems. Runs smooth and the exhaust will sometimes pop slightly on accelerator liftoff when going to change gear, after light throttle only. It never pops at above 1/4 throttle. My fuelling logs on Delta Dash show all is well. John Banks who mapped my car with a Tek 3 didn't find anything out of the ordinary either.

Cheers,

George.

[Edited by WREXY - 1/29/2004 11:46:21 PM]

 

No probs gm, any info you can find out would be appreciated. Knowledge is power and all that...

WREXY - cheers for the info, any chance of a bit more detail ? What model scooby do you have ? What miles did it have when you fitted the Blitz BOV ? How many miles have you done since ? What sort of driving do you do shopping runs/motorway runs/enthusiastic twisities/track ?

Cheers
BIJ

 

I have had a Forge VTA on my STi7 for 18 months with no problems and the same goes for my girlfiend's MY99 Turbo. I have heard these theories about bore wash etc. and was initially concerned. I even sought advice from Mervyn at PE, who did an Ecutek remap on my car, and he said there was nothing to worry about. I do know that Bob Rawle is not keen on VTA dump valves though.

My Scoob has a SECS which monitors the air fuel ratio. When I lift off the throttle and VTA dumps, the SECS shows the air fuel ratio (Lambda) momentarily going rich before then going lean due to the closed throttle. However I observe exactly the same when I lift off at small throttle openings when the dump valve is not operating. Therefore it would appear that there is negligible "extra" richening when the VTA operates.

Alan

 

i have a TAS piston re-circ one fitted with maximum preasure, it wont dump at all unless the boost is over 18/19 psi

most of the time it just gives nice chattery noises, which i love :mrgreen:

chatter = cool
VTA = bit gay like

 

BIJ,

The car is a MY00. Had 200km on the clock when I fitted it. In other words the car was brand new. I have 28000km on the clock now. Up untill 19000km the car was stock with the BOV. It now has a VF23 turbo, 5 Zigen exhaust, APS cold air induction kit with K&N filter, the Blitz BOV still, JB Ecutek Tek 3 remap and an uprated Walbro fuel pump, along with Knocklink and Delta Dash monitoring diagnostic software. As for type of driving, mixed street driving, which includes twisties, straight line drags, normal driving, etc. No track runs though.

Cheers,

George.

 

i have a my03 had a baileys at dv on it from almost new had no probs with it what so ever, no popping etc. any case a car is a car it wont last forever! drive it like its ment to be driven!