im looking to buy one but do i have to watch out for single piston or twin piston like you do if your buying an atmospheric one?

or will any recirculation dump valve be ok to use on a coop?

It doesnt matter on recirc valves, its only atmospheric ones that need to be twin piston.

I would recommend the Forge DV006, best one IMHO.

thanks matt

so a oe one ie a vw/audi standard one would work too?

As long as the spring is the correct strength. One that is designed for 0.7 bar of boost would be no good for example.

I have one of these on my coupe. It's a single piston, quite massive, and I love it.

i thought 20vt should be twin piston?

Why?

something to do with the single piston giving bad iddle and the twin one sorts it out

It does, you MUST have a twin-piston type or you'll get stalling and bad idle. Recirc or Atmos. I'd go for a Forge DV006, of the 5(!) dump valves I've had on coops, it's definately the best. Well made and you still get the "psstch" sound, but not as loud as a DV26.

I have a hks sqv love it love it love it, not sure if it's hurting the car but sounds cool!

Sounds like a mouse sneezing! Not my cuppa.

Well, I don't have a twin piston and my car idles just fine and has never stalled.

maybe yours is a twin piston but you dont know it?

Mouse???? It's different not normal stuff reminds me of my old mr2

is a DV006 twin piston? I've had a lot of them apart and there's only one piston in there that I can see

How does that work then?

Just checked DV006 is single piston

How does it make a difference if the air is going straight back into the intake after the MAF?

in a pm between myself and nigel this statement might help


You really should get a re-circulating dump valve like the DV006

the reason is that the MAF sensor on the 20VT fuels the engine according to the airflow that is has "seen" going past it - with a dump-to-atmosphere DV, a substantial amount of air is lost out of the inlet when you change gear, but the ECU doesn't know this, so it fuels for the amount of air it THINKS is in the system - this leads to momentary over-fuelling - its probably not a huge issue, but its not correct for the car

A recirc DV drops the air back into the inlet system, just before the turbo, but AFTER the MAF, which means the air isn't "lost" and the ECU fuels correctly

Yep, I'm wrong, the Recirc design is a single piston, it is only the Atmospheric that needs to be twin-piston. You learn something new every day!

Well, I went to see the legend that is Barbz yesterday to check the car over and make sure she's ready to run quite a bit more power in the near future. I asked him about my dump valve being atmospheric and fooling the air flow meter into over fueling. Here is the bit I don't quite understand - he said there are two systems on the coops, an open loop and closed loop system. On the closed loop system, you couldn't run the atmospheric dump valve as the car will stall and give all sorts of problems. And on the open loop system, like mine apparently is, it's fine.

I won't argue with the man, as he clearly knows his stuff. Has anyone ever heard of this?

possibly the difference between the 16v and 20v variants?

As far as I could tell, it's both on 20VT's.

He must be referring to a 16vt, because the 16vt uses a MAP sensor to measure air rather than the MAF sensor that the 20vt uses. With a MAP sensor, only the volume of air about to be burned is measured, so whether the dump valve releases air back into the system or into the atmosphere makes no difference as the car hasn't measured the air yet. The 20vt, on the other hand, uses a closed loop system and air is measured after the air filter so any air loss into the atmosphere from the dump valve is not accounted for the by the ECU.

Gareth

I have used 2 different brands of atmospheric dump-valve on my 20vt and not had a problem with idling. Could there be a difference between early 20vts and late 20vts (like there is with the gearbox etc.)

Exactly mate. Mine runs sweet as a nut and I've not had any idling/stalling problems.

That said, I'm not sure whether it's over fuelling or not.

As I've been told, idling/stalling problems are related to single-spring BOV - the BOV has only 1 spring, it opposes the boost, but on idle/vacuum in the mainfold can leak air into the system (the other way around), messing with the a/f ratio. As the ECU gets the signal from lamba, it tries to adjust but messes things even further (because it's unaware of the additional air entering past the MAF)

Aren't open- and closed-loop related to ECU algorithms, different for idle/light load and full load?

IIRC, doesn't the ECU on full-load run in open-loop, adjusting the fueling according to MAF data and internal fueling tables, omitting the lambda readings!?