The V8 Owners Forum -

Well I bought a dump valve as instructed by peeps,
and its horrible
light throttle it whistles like mad until you boost it then it goes quiet until you release the pedal then you get the whoosh
it is very annoying, have I bought the wrong thing for my charger????

have gone back to the recirc valve for now at least it is quieter now on light throttle,

What did you buy, and who instructed you ?

Really..there wasnt much wrong with what you had. And any you buy, if you want quiet, would need to have the option to re-circulate, or at least route the pipe out of ears way

What have you brought?
Is it adjustable? either via screwing the body in or fitting stronger spring?

I fitted the Bosch/VAG recirc valve on my supercharged rover (because I had one spare) and like yours it whistled while on light throttle, annoying. Basically the spring isn't strong enough to resist the vacuum and slight boost at idle/cruise. There's a common misconception that the spring should be rated to the max boost pressure your running. That is wrong. The spring should be rated to the vacuum you pull and to resist any slight boost you make at idle. Max boost is not important as at WOT what ever boost you make from the turbo/supercharger the vac ref pipe will apply the same pressure on the other side of the piston/diaphragm which will in effect cancel each other out - so the spring will keep the valve closed.

I got an eBay adjustable dump valve, fitted it and adjusted it so it doesn't leak while idling and not works fine. They are simple things, no need to spend hundreds.

Tom.

As far as i'm concerned a dump and recirc valve are the same thing - the only difference is that the recirc valve has an outlet that you plumb back into the inlet - and you do that because either you are running a flow meter or you dont want the noise/pssttt

So i dont understand your motivation for changing your recirc to a dump and then not liking the noise it makes.

Does seem odd. And the valve should be open at idle and cruise etc. Some will make more noise than others, but ultimately if you want quiet, it needs to be routed out of the way where it will be less audible.

read back on this topic and my charger post and see how many have said remove the recirc don't need that as you are not running an AF meter use a dump valve,

the pssst noise don't bother me, when changing gear etc what is annoying is the constant high pitch whistle while cruising,
hence why im back to the recirc that I have used from day one,

Not sure anyone said remove it. You asked what we used and we replied saying that as you have no MAF you don't have to run a recirc.

Sounds like you have not set the spring tension correctly as mentioned by SuperV8.

Did you buy a Forge Valve as they sell springs and shims to adjust the tension

And generally, valves for a SC application will have a softer spring than a turbo, because the SC needs to be open more, it needs to vent air under more conditions than is ever needed with a turbo setup.

Which is also why SC specific units tend to have fairly large diameter cans, so again the pressure acting on the diaphragm works better both to open it and keep it closed under boost.

im sticking with the recirc,
works fine and the car goes bloomin well so no point upsetting the apple cart as they say at present,

Might want to take on board what Stevie says. The recirc looks likes its off a SEAT, VW etc which are Turbo. If Stevie is happy then go with it but they do tend to get sticky and fail.

My Sons Cupra kept lighting a MIL with over boost which turned out to be the valve so we replaced with a Forge FMDV006 which solved the problem.

I'd be happy enough that the black Bosch valve is suitable. It'll likely be from a car with an airflow meter and re-circ, so have a fairly soft spring anyway. Plus Ive seen some places selling SC kits using that one.

I'd be more concerned about the suitability of aftermarket ones aimed at the turbo market, as most have strong springs so people can vent them to atmos, even if there is an airflow meter in the picture, so these tend to have a strong spring so they dont open at idle and part throttle.

You do NOT want that with a supercharged setup.

Even at say 2-3000rpm that blower is shifting a lot of air, so if you're just cruising and the engine is hardly using any, that air needs somewhere to go. If the valve is shut, it will try and go back out through the supercharger. Which is not good.

cheers Stevie,
I have noticed forge do a replacement black ally recirc to replace the plastic one like I have, the benefit is replaceable diaphragm etc so can be serviced and not thrown away when it fails,
that can wait though lol,

I presume what you had was working though ?

In general...if you hear a fluttering sound on changing gear, overrun, idle etc etc....then the air is backing up through the SC.

Now it may still back up and you dont hear it, but if you are hearing it then that is sufficiently bad you need to vent more air.

stevieturbo wrote:I presume what you had was working though ?

In general...if you hear a fluttering sound on changing gear, overrun, idle etc etc....then the air is backing up through the SC.

Now it may still back up and you dont hear it, but if you are hearing it then that is sufficiently bad you need to vent more air.

you do hear it under high rev gear changes mate, idle and light gear changes etc is fine, even mild boost its fine its when you wind her up round 8psi upwards its starts fluttering/chattering etc, the next thing I was going to ask is what size take off should I be using?
my current one is 25mm as that is what the recirc valve size is,

The valve will be the limiting factor anyway.

If you need more flow, you could just stick another Bosch on it

What was the new valve you bought ?