Ow

I hope you dont mind me "targeting" you like this, but reading your various posts, you seem knowledgeable on the subject of dump valves...

Anyway, I'm sure I read on here a while ago that vent to atmos DV's can cause problems/damage e.g. borewash. I can't find the thread, hence the question: is this the case? I noticed you have an HKS SS BOV, which is the one I am considering, but obviously dont want to damage my pride and joy!

BTW, it seems my standard DV is on the way out; it's making the "blowing over bottle-top" noise on acceleration. The car is a 98MY Terzo.

Thanks in advance, and if anyone else can shed light, it would be much appreciated.

Regards, Owen

Moles Dad

Ow, I dont mind at all.

I am no expert though, all that I know about dump valves has come from my "tuning" on my car. (UK '99).

Now that we are in the realms of 300bhp and running circa 1.3bar there was a need to "uprate" the dv.

Was suffering big time shuddering on liftoff of the gas (at high rpm) and found that the HKS cured it BIG TIME.

From what I have read the MY98 if it is the phase one engine, *can* suffer from idle problems and poor running, the later engine phase two seems more tolerant.

As for bore wash, well I have only ever read that it would be such a small level of "overfuel" that it would not cause said problem.

Anyway, when it ignites in the exhaust it proves that it must be a) atomised and b) going through the cylinder head not the rings.

And...IT SOUNDS GGGRRREEEAAATTTTTT

Cheers, MD.

PS Try to borrow one to see how your car behaves, £250 is a lot to gamble.

Ow

Thanks for the info....not sure if I'll be able to borrow one though

Incidently, why do VTA DV's sometimes cause irregular idle etc.?
Is it because the ECU basically thinks more air is entering the engine than actually does? Not very technical, I know, hence the question

Cheers, Ow

tweenierob

think it is because the valve doesnt shut properly on idle eg. too much air?????????????????
Rob

dowser

The OE DV puts the air back into the system after the MAF - VTA doesn't. Hence, ecu thinks there's more air than there really is, so overfueling on lift-off. Supposed to be good for flames with a decat if that's your bag...

MD - strange you report your DV cured the stutter on lift-off, every car I've tried with an aftermarket DV (recirc or VTA, Scoobs & Evo's) has actually suffered from this? Almost as if it's dumping boost too quickly (b4 you've got your foot right off the pedal). Could this be a spring strength issue? Or is my right foot too slow?

Richard (not a great lover of DV 'upgrades' )

EvoRSX

Ow,
VTA's sometimes cause idle problems because when there is no throttle opening, there is a high vacuum in the plenum chamber and therefore there is a differential pressure across the diaphragm in the dump valve. This can sometimes cause the valve to partially open and leak air into the intake system. Because this air has not been seen by the airflow sensor the ECU does not add the fuel for it and so at idle you run lean and lumpy and sometimes stall.

On the other side of it, after fitting a VTA then when you lift off the throttle, the air that was going to the engine (that has already passed the airflow meter) vents to atmosphere and so the ECU provides fuel for this 'dumped' air and so you run rich and have the potential for generating nice flames out of your exhaust.

Hope this helps

Andy

Ow

Thanks for replys; it seems no real damage will be done, then

But the flames do raise another question...My car isn't de-catted at the moment (insurance issues ). If I fit a VTA, will the cats be damaged by unburnt fuel passing through them at high boost?

Regards, Owen