adeel.a

I wanted to find out if a dump valve otherwise known as a blow off valve (BOV) make a difference to the power or performance of a scooby. Some say it does and others say it doesn't?

Please advise... I have a 95' Jap spec WRX

Thanks in advance

Billabong

Dump valves make NO difference to power, unless they are leaking.....they are a safety aid for the turbo.

jay-j

fitted one to MY95 uk spec, to me its just seems a bit smoother no apparent difference in performance, sounds brilliant

James_PowerMad

In this subject of DV's... I got a Forge atmospheric device recently. I had thought of the problems associated with the MAF sensor reading too much air, and squirting a bit too much fuel in when changing up etc. But figured that a little bit of wasted fuel would not be too much of a problem...

But, recently I have started considering the effect of occasional squirts of unburned / semiburned fuel on the (hot) Cat, and whether this would cause it much harm.

Plus the possibility of bore wash???

Does anyone have any ideas?

Adam M

Bore wash is not an issue.

The amount of fuel we aer talking is tiny. You need to be consistently running rich to get bore wash and the standard car does that anyway without problems. I asusme you will change the exhaust before changing a dumpvalve so you will have reduced that excess fuel buffer anyway (when on boost at least).

I dont understand this smoother pickup lark that some people seem to mention. The fact is, if the stamdard dump valve is not leaking, an uprated one simply will not be any different at all. period. If the hole is blocked, the hole is blocked. You can block with a stronger spring so that it takes a greater vaccum to release it, but this only affects things when you lift off.

If you just plant you foot down, there is no difference, simple as that!

James_PowerMad

What about the Cat though?

As for response, I don't really notice much difference with my Forge, but I can imagine that if the DV does a better job of 'letting go' just right, so that the turbo maintains the maximum spin through the gear change, then it could potentially make a bit of difference to response.

RICH WILD

Adam,

Now this is interesting. Please tell me if I am mistaken but I honestly thought that if the dumpvalve is quicker acting than the OEM one, by having a more powerful spring I presume, it will mean that you will lose less rpm in gearchanges, therefore effectively the car will be quicker on the road as it will get back on boost quicker. Is this wrong?

I was led to believe by stuff I've read and heard that the OEM item is very slow to react and you lose a lot of rpm relatively between changes.

One of the main reasons I thought this was that the HKS SQV advertises that it has two valves, one that is small and quick to react, thus retaining impeller rpm, and the second that is large to allow increased venting esp. on high boost engines. thus you would hope to be getting the best of both worlds as a big dv will be slow but a small one won't cope with high boost as well.

I'm sure all this is on TDi's website but I may have misunderstood.

What are your thoughts on this?

Thanks Rich

BIGRS

this might be of some help
when ford brought out the cossie the only reason they fitted a oe dump valve was that people didnt like the warbling noise(on closing throttle pressurized inlet hitting turbo impellor) produced without one so they fitted a recirclating d/v which gives hardly any noise.the cosworth does not need a d/v unless running a t4 or equivalent or 30psi+,and most people fit them just for the noise.im running a t34@26psi and dont run a d/v as it does no harm.from what i can make out, running without a dump valve increases response as when a d/v releases the boost the turbo has to build this up again when throttle is opened,so its swings an roundabouts really,with-you keep turbo speed up but lose boost,without-slows turbo but keeps boost pressure up,like i say there may be a good reason on the imprezza for it but if there isnt i would take oe d/v off and blank it off.
hope this helps

bigrs

JFB

I have a GGR dumpvalve fitted to MY00 and I really got it to see if it could induce flames from the decat exhaust. It does on backing off suddenly but accompanied by a backfire which is not too sociable really. No increase in power perhaps helps keep turbo spinning etc but we must be talking nano seconds here. One drawback is jerkiness when coming off throttle which does not make for perfectly smooth driving. Horses for courses.

Jerome

Cosie Convert

Is there likely to be a risk of damaging the MAF sensor on a Scoob without a DV

The thought of a blast of high pressure hot air hitting that fine wire sensor

Has anyone run, say 20 psi boost, without a DV whilst retaining the MAF meter ??

dowser

James_PowerMad - I'd be more worried about the unburnt fuel even getting as far as my turbo, forget the cat

If it ain't broke, don't fix it - as mentioned above, it's only there to protect your turbo; no more, no less.

A real 'between gear' performance increase comes from removing it and blanking it off - as long as you're quick with your changes the boost will stay in the system.....and hopefully the turbo wont stall But be prepared for reduced turbo life, and strange chattering sounds....

CC - assuming the turbo doesn't stall, the hot air is being forced away from MAF....and even if it does the OE setup has the MAF a fair way from the turbo. I'd have thought it wouldn't be a problem - but perhaps you should try it and confirm back?

Richard

EvoRSX

BigRS,
The cossies can run without DV's because they have 360 degreee thrust bearings in the turbos and so they can take the extra bashing caused by the air reversion pressure pulse. AFAIK, the scoobies (and Evo's) don't have the necessary to be able to handle the extra stress.

Andy

mole

adeel.a, see my thread entitled "Zoom zoom bumf bumf" that might give you some more thought provoking reading.

Good luck, Moles Dad.

submannz

Unless you are running more than 300Hp they don't give you much benifit. People just fit them to make there car give off that sound.

kenny.c

I did think about getting an aftermarket DV purely for the whoosh noise but recentely installing a HKS induction kit the OE DV noise is so much louder hence no need for changing the DV.

RICH WILD

Fitting a more responsive DV can improve your performance as your turbo impeller will lose even less speed than it does with the standard item. It won't give you any more power though.

When running high boost, it is an idea to uprate the dump valve as the standard item ain't that good and as Billabong says thay can leak losing you boost pressure. Craft's DV was leaking at the recent Well Lane rolling road day and it cost him around 20-25bhp.

Cheers
Rich

[Edited by RICH WILD - 2/7/2002 10:42:14 AM]