BrettC

Hi everybody.

Can someone out there please explain to me the benefits of a atmospheric dump valve 'v the recirculating type. From looking at commercial web sites selling these items I get the impression that Atmospheric is best? Is this the case or are they just trying to sell the most expensive item.
I appreciate that the atmospheric you get the whoosh noise but in real terms, which is best? As my scoob already has the recirc. type is that the type I should stick to?

Does subaru put on the recirculating type simply for cost reasons or is there more to it than that?

Thanks for any advice.
Any recommendations as to manufacturer?

Cheers

Brett

PS Don't get me wrong I kind of like the whoosh noise but if the recirculating type has more benefits for the turbo (ie lag reduction etc) then thats what I would rather go for?

Gedi

Stick with the recirc.

The VTA confuses the ECU and can make your car run rich due to the fact that the ecu is expecting the air to be dumped back into the intake.

Also they sound a bit silly

mikeDaBike

Is there a definitive answer on this matter? Some folks say they work, and reduce turbo spool-up time, etc, and some say they're detrimental and just a gimmick.

Has anyone ever done proper tests on this subject?

The car I've just bought has one and if the only benefit is noise, the detrimental effects (jerky on throttle off, running rich, etc) don't seem worth it and I'll remove it and replace it with a standard one.

[Edited by mikeDaBike - 8/28/2003 12:18:10 PM]

Attu

Yep i did a proper test..it went like this,

Took old dump vale off
Replaced with new forge VTA dump valve
Didnt like it
Took VTA off
Refitted old dump valve
End of test

To be honest apart from the noise I dint notice nuch of a change, maybe the car felt as though it kicked a bit harder when the turbo came in but that could have been caused by more lag.
One thing that was noticed was when I realy pushed the car black smoke came out of the exhaust...over fueling ??... which didnt happen with the standard dump valve.
My car feels alot smoother and pulls nicer with the standard dump valve.

Andy

BrettC

Thanks everybody.

Based on all your advice I think I'll stick with what I've got!

Cheers

brett

mikeDaBike

Might refit the original - wait a minute, I've not got the original one! Damn! Looks like I'll have to buy an aftermarket recirc.....

Gedi

It should overfuel as the manegement thinks it has more air than it actually has. It is not aware that it has been dumped to atomsphere. Thus it will fuel to suit.

Although this can't be good for fuel consumption, I don't know if it can reduce engine life.

All I know is, I was told from many different specalists to always use a recirc dv on scoobies.

Maybe someone like John B or Greasemonkey can hit us with some technicalities

NelsonUK

Same here with respect to atmos d/v - Fitted a Forge VTA and the car was very jerky etc. and I couldn't get on with the pssst. Re-fitted original re-circ and the car felt much smoother and none of the jerkiness. I have however uprated my recirc to a Forge one

SiHethers

Running without a dump valve is best for minimal lag, but bad for turbo bearings.

VTA dump valves make a noise, cause overfuelling and may cause borewash.

The standard dump valve has a very weak spring and does leak at higher boost pressures - reducing turbo efficiency.

Simon

BrettC

Thanks.

Any recommendations for an upgraded recirculating DV?
At the mo the car is running standard boost pressures but (soon I hope) boost will be increased via the MoTec system.

Cheers
Brett

SiHethers

Brett

The Forge recirc works for me. I use the stiffest (red) spring with three shims. This means it stays shut at low boost/rpm, retaining boost pressure within the intercooler and aiding response, but opens at high boost/rpm, hopefully preserving turbo life.

The reality is I'm probably shortening the turbo's life, but the MHI TD series turbos are supposed to be able to take more of this than the IHI VFs. The turbo chatter is good at scaring the elderly too (I've got an induction kit so you can hear this and the dumpvalve).

Simon

mikeDaBike

Spoke to TSL yesterday - they do recirc valves that are variably adjustable by hand, so you can easily change the spring strength when you need to - think I'm going to go for one of them....

BrettC

Cheers Simon.

BrettC

mikeDaBike

At the risk of sounding stoopid.

Why would you need a variable spring rate DV? Is this simply in case you alter the amount of boost? Also, is it a specialists job to set the spring rate accordingly?

Thanks.

Brett

mikeDaBike

Yes, I'm presuming it's so that you can adjust the valve without needing a new spring if you ever change boost, get engine work done, etc... Sounds like a good idea.

BrettC

Thanks m8.

Would reliability not be an issue? or no different to a fit and forget unit?
cheers

mikeDaBike

I don't really know - this is my first turbo car!

But I would imagine that they're decent items, or TSL wouldn't be flogging them. Certainly going to be better than the original Subaru item anyway...

greasemonkey

Jesus, since when did I qualify to be mentioned in the same breath as the likes of JB? I'm just a casual tinkerer by comparison!

Seriously though, all the good words have already been said, there's very little that needs to be added.

In reality there's nothing at all wrong with the functionality of the standard dump valve, and no reason to change a functional one unless you're running enough boost to make it leak.

It was interesting to read Brett's comment about all the resellers pushing the most expensive valves though. In reality dump valves are very simple pieces of equipment, and they're also extremely cheap to manufacture. I'd imagine that a £300 Blitz valve probably costs about £4 to make. Still, if there are people prepared to pay that price, power to Mr Blitz's elbow...

[Edited by greasemonkey - 8/29/2003 9:32:56 PM]