Jay kay

I was wondering, those who run dump valves, at what RPM do they start venting?


No need to tell me that not having one is better etc.

ZANY

When you go "BEAST MODE" is it a forge or a baileys hks blitz or an eBay special? Also depends on other mods on car and if it's modded or mapped mine is an aps recirculating item and goes off every time I change gear usually bout 2600rpm unless I'm in beast mode

Tidgy

its not rpm related, its boost pressure related so depends on when boost comes in on your car.

ossett2k2

iTrader: (9)

Plus there are different spring rates.

Jay kay

I ask as I just fitted a turbosmart vee port pro. I believe my car is mapped and the dv is adjustable. Even on hard setting is starts venting at 2500rpm. On soft it starts at around 2100rpm. I wasn't sure if that was too low or not?
I actually quite like the noise it makes but may still consider selling it to buy an HKS

rickybobby

it shouldnt be venting/dumping anything til you let off the throttle, if it is then you have a massive boost leak, especially at that RPM.

You understand how a dump valve works right?

Jay kay

Yeah thats what I mean, when changing gear, at what revs does it start venting. Obviously it's going to do it when changing at high revs but how low can you change and it starts venting. The lowest rpm gear change i managed was approx 2100 and I hear a tiny hiss. Just wondered how hard I should be setting the spring

trevsjwood

iTrader: (2)

the turbosmart dv works on the equalisation of pressure eitherside of the throttlebody i.e. on boost the boost pressure is the same intercooler/manifold and the dv can't move. Immediately, as you release the accelerator, throttlebody closes, pressure drops on manifold side and the dv dumps pressure from turbo/intercooler side either to atmosphere or back into the intake as with plumb back/OEM DV. The spring adjustment (tighten/slacken) on the top adjusts how quickly or slowly the valve responds to the changes in boost pressure when the TB opens/shuts. Might be worth re-checking installation notes. The valve can't/ should not move when you have your foot down otherwise it must be faulty.
Trev

Samwise

You're really not understanding this are you?

As it was mentioned above a dump valve does not open depending on RPM, its all dependant on boost pressure. If you drive hard and build up a load of boost in low RPM's and then let off the throttle the valve will open at low RPM's, likewise if you drove like an old lady all the way up to red line without once going on boost the valve won't open, even at high RPM's.

The only way a valve could open "Too soon" is if you heard it opening while you're still on boost or if the valve is floating open when idling.

Ash Webster

just in case you dont understand "let off the throttle = same as putting clutch in :"

as other have said, if your DV is venting while you are pressing the gas, you have a problem

alcazar

iTrader: (2)

And of course, you DO understand that ALL Impreza Turbos come with a dump valve?

neil-h

Come again? I don't think any of that's actually correct (with the exception possibly of the last line).

That's only true if you let off the throttle at the same time.

byrnsie44

what?

Jay kay

Wow, I've really started something here.


Yes, I do indeed know how a dump valve works. No it doesn't vent while accelerating. And yes I do know that as standard the Impreza comes with a recirc valve (not technically a dump valve). When I asked when do others start venting, I was of course referring to letting off of throttle or gear changing - Zany immediately understood this hence his reply.


If I drive like a granny, even at just over 2000 rpm the car will still boost and therefore the valve will vent on lift off. My question was basically is there an optimum rpm for when the valve should start kicking in when lifting off and I ask as I can change this by adjusting the valve. Drive like a granny on softest setting and the valve vents at around 2100 rpm when lifting off. Still driving like a granny but wound to hardest setting, venting begins at around 2500rpm.


I must assume there is no right or wrong, I just wondered what other people experience in case venting at a higher rpm is preferred to a lower rpm?


Hopefully that will make things clearer?

alcazar

iTrader: (2)

From Wikipedia:
They are ALL dump valves, but not all are BOV.

trevsjwood

iTrader: (2)

your question is more to do with turbo size and how quickly the turbo spools up. Small turbo spools lower down the rev range and more quickly than something twice the size., so the spring wont have much effect, I would set the spring adjustment in the middle and have done with it.
The oem dv is a dump valve, it just recirculates the pressure. Aftermarket dv are the same principle, some recirculate, more vent to atmosphere. The Turbosmart has a softer spring than the standard oem dv and relies more on the pressure difference which make it more reliable than standard who's stronger spring can give way at higher boost pressures.
Trev

ZANY

Put it onthe hardest setting then half a turn back first thing Andrew Carr did on my gfb item before he mapped it back in the day along with other checks and was perfect there after
before that if too soft car doesn't seem to have that punch and to hard it won't vent properly I was forever messing with it
after that on my second map I had a genuine hks item and wow it certainly felt much better

Samwise

What makes you say that? a Dump valve will open when the pressure on the pre-Throttle body side of the system is greater than that of the pressure after the throttle body (+ The preload offered by the spring inside). This occurs usually when letting go of the throttle whilst on-boost but if you simply drive so calmly or without accelerating (like cruising at 3k RPM on a Motorway) you're not going to be creating boost for it to dump.

What?
See above.

The point im trying to make is that there are circumstances that would mean that a dump valve doesn't need to open even when you happen to be at high RPM but just lightly floating on the throttle.

Maybe I was being too nit-picky for this thread.

neil-h

That's not what you said in your original post though. The only way I can see your original post works is on a car with some pretty serious anti lag or a nackered turbo.

Samwise

Oh, fair enough sorry about that
Obviously just worded my point badly