Dump valve = lack of power
 

I took my dump valve off and stuck a standard recirc one back on, after doing this my car drove like a bag of **** it would not boost to max 1.2 bar that I have set it struggled to reach 1!! and felt very hesitant.
My question is this, is that normal?, I thought they were just toys really to get on peoples nerves with that release of air and I have read on here they reduce power and you should not fit them!! this seems to be the opposite with my car, It really didn't like it, do they need mapping on and off to stop the loss of power as I understood you did not need a map to fit these.

Cheers
Brian

did u fit a new gasket?

Yes and it sounded as though it was working fine just big power loss, old one back on and no probs at all back up to 1.2bar straight away! and big whoosh sound which I don't want.

Sounds like you have either fitted the OE valve incorrectly or have a faulty/sticking/broken one.

Nah OE one went on fine not much to get wrong there, sounds like it's working but who knows though, I was offered a few by people off here for £20 so may well go back to some of the others now and buy another one, for that price it's worth a punt just to make sure it's working right.
I am right in thinking they don't require mapping though ???

It's a my05 spec c, mod's being cold air feed mapped on and non om dump valve with blitz boost control running 1.2bar 335bhp and 1.5bar 365bhp thats it oh and an sti genome back box.

Depends entirely on the context, doesn't it, and whether the car has already been mapped for the aftermarket one that's coming off. It would be easier to provide you with relevant advice if you had included a fair bit more info in your post(s).

If a previous owner has simply bolted on an aftermarket DV without having it mapped, then clearly you won't need to alter/remap anything if you go back to a standard valve (that works properly).

If the car has been mapped properly with the VTA valve in place, there may have been some changes to the high rev/low load fuel map zones to eliminate lift-off overfuel. Under these circumstances you might find it goes a bit lean with the standard dumpvalve back on.

Clearly none of us here can guess what's been done to your car, so if it has been custom tuned, the best person to speak to would be the mapper responsible.

Did you blank off the unused pipe that goes to the inlet when you fitted the VTA valve?
Did the small vacuum hose to the dump valve get refitted?

Yeah I took the blank off when fitting the OM one and replaced vacuum hose all fitted fine and reversed when going back to VTA :thumb:, I think I have found the answer I am looking for, it needs mapping back off by the sound of it, the car was not mapped in this country (done in N.I)so not so easy to find out who done it, I think I will just leave as is and have OM air box and OM valve mapped back on as soon as :thumb:
Thanks for the helpful replies guys:notworthy

boosting with the vta and not boosting as much with recirc tells me that the recirc is leaking.......nothing to do with the map.


is the car spooling later with the recirc in?

No it spools fine, only feels hesitant under high boost at higher revs, feels normal till you want to push on.

It shouldn't make a jot of difference at full throttle.

I can only say it as it was, full throttle it was struggling to make 1bar and felt really hesitant, swap back to VTA and back up to 1.2bar pulling strong to high revs!!

surely this tells you that the dump valve is at fault :confused:


pressure test your recirc or 'borrow' another one to try on it :thumb:

I will try it on my wrx, that was not mapped with a vta on so if i swap it back on to that, I guess that will show if it is the dump valve.

as long as your other scoob runs over 1bar as it is now then yeah that will tell you if the valve is at fault. (I'm guessing the valve starts to leak at/above 1bar)


but as said above its nothing to do with the map under full throttle.

I don't suppose the wrx boosts to 1bar does it(standard car).

What about what splitpin has said above about the map

"If the car has been mapped properly with the VTA valve in place, there may have been some changes to the high rev/low load fuel map zones to eliminate lift-off overfuel. Under these circumstances you might find it goes a bit lean with the standard dumpvalve back on."
would this not effect it at full throttle, I might just buy another OM valve and try it like I have said It's only £20.

if its a older wrx and standard then I doubt it will hit 1bar.....so thats no good to you.


what splitpin has mentioned has nothing to do with the issues your having, hes on about when you lift off the throttle.


just buy/borrow another and try that on there :thumb:

Will do, thanks for the advice :thumb: