ianch

hi
seen a hybrid recirc & atmos dumpvalve made by mrt on the jap innovations site! have any of u heard of these or have one? are they a good idea as they offer the best of both worlds?
thanks ianch

greasemonkey

They don't offer "the best of both worlds", as you will still get overfuelling when lifting at higher boost levels.

What they do manage to do is keep the car quieter than a true VTA while pootling around at town speeds.

Unless you are running a MAP based ECU, the best option for your engine remains either the standard Subaru DV, or an aftermarket recirc only product.

p1doc

how much damage could an atmospheric dv do to the engine as well known tuners sell them eg tsl scoobysport so they cant be that bad can they?
do you require a remap to run one and is there any real benefit apart from the noise?
martin

greasemonkey

It's unclear what the longer-term effects of the overfuelling caused by a VTA DV are. There's certainly potential for consequences like bore wash and oil contamination, but it's impossible to put a figure on the reduction in MTBF or however else you'd want to quantify it.

Think you'll find that people like TSL and SS sell them for no reason other than they're fulfulling market demand. The "they wouldn't sell them if they're bad for your car" argument simply isn't applied.

You don't require a remap to run one, most of the people who run them seem to view the overfuel-inspired popping and banging as an advantage, and no, there's no benefit in performance terms whatsoever, assuming that all other things are equal.

p1doc

ok thanks
if i got a remap at the same time would that stop the overfuelling or create even more problems?
martin

harvey

iTrader: (48)

The vent to atmosphere BOV, causes overfueling momentarily and in a serious performance engine is a BAD thing. It is nothing to do with the map, just inherent in the fact that the ECU knows how much air is in the system so it fuels for that. If some is vented to atmos the ECU does not know that and has already fueled accordingly. VTAs are OK for scaring grannies at the bus stop or getting people to look at you driving in town like a loon on a Saturday....if you are into that sort of thing.

red wrex

Scaring grannies is cool and a defo sunday pass time of mine ...lol

scoobiestu

havent had any trouble with mine and car seems a fraction of a second quicker to 60 which is nice

greasemonkey

Yet. Whether you have had "problems" or not, the overfuel is undesirable and contrary to the optimal performance of the engine.

Unless you've adjusted it in such a way that it doesn't open, any perceived differences would be a placebo effect rather than a real increase in performance

scoobiestu

oh well works for me, matey at tsl assured me that because of its quicker shutoff, lack of seepage etc that there would be slight difference Mine is a turbosmart adustable jobbie

Neil W

How do you recognise a fraction of a second?

greasemonkey

Lol, nothing like a good sales pitch!

red wrex

So is it fact or fiction that when the DV is atmospheric it lets off more pressure from the turbo allowing it to spool up quicker reducing lag and increasing performance (not bhp or torque)
?????

greasemonkey

Complete bollocks, who told you that?
It's the size of the valve itself that primarily determines how quickly the air is bled away from the pressurised side of the induction tract, not whether or not it vents to atmosphere.

Even if we took the "atmospheric dumpvalves let air off quicker" suggestion as fact, a quicker bleedoff of air from the pressurised side of the induction tract would, if anything, mean it taking longer to refill when the throttle was reopened, and thus the result would be more lag, not less!

red wrex

i agree its more about size that where the air goes

but if it does empty more air, then does it not take pressure off the impellor allowing it to spin more freely (in the same way a de cat does) and therfore spool up quicker???

greasemonkey

Yes, exactly. That's what it does, and that's the last thing you want. The inlet side of a turbocharger is a compressor, not a fan, and it's not meant to "spin freely". You want it forcing inlet charge into the engine, not blowing it freely out of a hole in the side of the intercooler.

No. Because you've let all the air out of the compressed side of the induction tract, it's got to re-establish a head of pressure, which takes time. The time taken to do that is lag.

The way to minimise lag is to remove the dumpvalve completely, so the charge air is kept under pressure inside the induction tract. That way, as soon as the throttle is reopened, there'll be a head of compressed air already waiting to go straight into the cylinders.

Sure, the turbo won't "spin freely" in this scenario, but as the held boost will go straight through the engine when the throttle is reopened, there'll be plenty of gas running through the turbine to kick it quickly back up to speed.

Don't confuse what happens on the exhaust side with what happens on the inlet side. The reason a decat makes the turbo spool quicker is because the reduction in back pressure increases gas velocity through the turbine blades, imparting more energy into the turbine.

red wrex

Looks like i have been lied to all my life then ...lol


Mum....Dad....A word....

explore

atmo and recir dv whatever one you have doesnt make a diff to the car as with a recir dv the air would not reatch the air box in time for the ecu to notice anyway.
End of arguement.
also look at bailey, there dv are great all hand made piston type, been used in cossies for years, think about it (there the daddys that came up with the piston dv)

greasemonkey

No, you're right, the type of dumpvalve used makes no difference at all, and both Harvey and I are talking sh*t.

WTF are you talking about? Of course it makes a difference to the car. With a recirculating dumpvalve, all the metered air is kept within the induction tract, so the readings the ECU gets from the MAF sensor will be an accurate indication of the amount of air in the system.

If part of that air is vented off to atmosphere, the ECU will overfuel as it is injecting on the basis of air that is no longer in the induction tract.

Your point being?

BedHog

Is this, in reality, a problem? I can see how too little fuel can have adverse affects, but momentarily having a rich mixture shouldn't do any permanent damage should it?

To be honest, I'm no boy-racer, but I quite fancy a VTA BOV - but I won't do it unless I'm sure it has no serious adverse affects

BedHog

Sorry about the last post - just read this and it explains it well. Seems like however much I want one, it just doesn't make sense

greasemonkey

Think you've answered your own question BH. If you're not a boy racer, you don't need a VTA DV!

harvey

iTrader: (48)

GM: I admire your persistence. These days after I state the facts as I know them to be, usually learned or confirmed from hard and sometimes expensive experience, I tend to leave it to the "experts" who know far more than those of us who have actually done it.

greasemonkey

It was a close-run thing Harvey, but I was bored and decided to visit Explore's homepage, and noted that, in addition to the Bailey dumpvalve, chief among the mods were six (count 'em!) neons.

Thus, I felt justified in sticking to my guns. Everyone knows that people with more than four neons aren't to be trusted!

harvey

iTrader: (48)

Yes GM. Not many people know that if you have more than four neons you can use them to increase engine braking and save on the pads. !!!

Would you confess to having neons on your car ?

greasemonkey

Of course! Greater electrical load on the alternator results in more drag on the engine through the auxiliary belt!


Only time I've had them anywhere near my car was when I brought some home from the pet shop!

I don't think it's a case of confession in Explore's case though, he seems to be positively boasting about them. Six, FFS! Call me narrow-minded, but I never trust a man with more than two. Come to think of it, I'd never trust a man who calls his car a name he can't even spell. "Nemisis" indeed...

Tone Loc

iTrader: (1)

I keep reading that Recirc DVs don't overfuel because the air is still in the inlet track. But the ecu fuels for the air going past the MAF and expects all this to go into the engine, however when you suddenly lift off the air does not go to where the ecu expects it... i.e the engine. Instead this air (or some of it should i say) goes all the way back to pre turbo. This is why when i lift off with my OEM recirc dump valve the lambdalink goes rich for a split second and this is also shows up in the logs i have from the ecu.

This has been the same with OEM dump valve, forge recirc and baileys atmos.

Is what i've said all wrong, if so why do i witness this 'overfueling' with the standard DV?

Tony.

THOMO

OVERFUELING IE RUNNING RICH IS BAD IM JUST AS CONFUSED . IVE GOT A HKS SS.
ALL I NOTICED WAS MORE PICK UP AFTER CHANGING GEAR.AND YOUNG LADS GIVING IT LARGE WHEN I DRIVE PAST.WHAT I WILL SAY IS THAT I AM BORED OF IT NOW AND I WILL BE GOING BACK TO THE ORIGINAL.I AM DUE FOR A REMAP IN FOUR WEEKS AND I FEEL ITS BEST MAPPED WITH OUT ONE.

Dan J

Interesting thread this. My MY00 has a Forge VTA on it that was already there when I bought it. I'm not concerned with it's sound can happily live without it to be honest. Have always been worried that it's doing more harm than good by being on there though and from reading this thread it seems that may be the case. Think I may well go back to an OEM one at my next service now.

Would others recommend this...???

Dan.

Trebor69

Well heres my few cents worth :O)

I have a My93 WRX with FMIC, HKS SSQV Dump valve, HKS Intake amongst many other mods.

I got the car in October 2003 and boy was the Dump valve dumping to Atmos bloody loud... In fact too loud and I got so bored with it, Owning a Subaru impreza is more than enough Qudos so why show it off I thought..

So I fitted a recirc adaptor to my dump valve and recirc'd it into housing between Air flow sensor and turbo inlet....

Because I have a HKS Intake kit, I still get the dump noises but much much quieter and it doesn't blow off for that long because as soon as I have changed gear and throttle on again, the intake of turbo sucks the air in so stops the ,shoosh shoosh shoosh noise. Just one quick Shoosh.... NICE!!!

But the main thing that impressed me was this:

Before Recirc, when coming of throttle lightly and re-applying lightly the car engine would shudder very slightly... With recirc this does not happen at all, Proper Fuelling now ?

Also before recirc after changing gear my boost gauge read 0.1 - 0.2 bar and then made its way back up (refilling the FMIC)..... Now its recirc'd, after changing gear and the turbo sucking all that air back in the boost gauge reads about .5 bar straight after changing gear and spools so much quicker!

Best thing I have ever done to my car I reckon IMHO!!