Stavros

Do they often? On big boost cars?

Ive heard of it many times (TBH i think its why racers rarely use em).

The boost pressure overcoming spring pressure and lifting the valves from their seat slightly on full boost? Even if it dont do it enough to lose boost the turbo will overspeed to compensate, causing more heat, less efficiency, less power, and maybe killing turbo quicker.

I can imagine it even with a strong spring, as the assistance the pressure fed down the vac pipe to assist the spring isnt much.

I dont want to fit DVs on my car, but bearing in mind the huuuuge size of the turbo and the fact im most likely running 2-2.5bar full boost (turbo is a mega efficency job thats able to run silly pressure without heating the air badly), im worried il break summat without em

Got 2x Shiney Forge Diaghpram ones with the Cosworth strength spring in it. Anyone know if theyl be ok? I could put even harder springs in em from the forge piston ones made for jap cars with AFMs i guess

Thing is i bet 99% of people whos dumpvalves open slightly at full boost dont realise anyhow, as TBH youd only really see it on a rolling road and only then if you was watching for it.

Advice/Info appreciated, esp from peeps like Martin H, Stu, Sheady, etc, whos probably came across this prob 100s of times...

COSWORTHFORDS

I know of somone with a race car that runs a 580bhp cosworth engine and he has a piston dump valve with no problems.......!!!!

Stavros

But does it lift off the seat at all? I doubt he knows, youd almost deffo never notice while driving.

cossymad

We had this a few times on scoobies but not on high boost all the time, but usually at 100+ mph
Don't know why, but we fitted larger springs whcih solved the problem.
I reckon you'd blow a diaphram to pieces as even the best Neotech or kevlar ones split at 30+psi

Mike Rainbird

iTrader: (3)

I would personally stick with the Bailey piston ones to avoid the problems relating to split diaphrams (which can cause amongst other things an unwanted pregnancy).

As you rightly point out, you would only notice this happening on a rolling road. Otherwise the turbo will compensate as mentioned.

Stavros

Well Forge do really really good Piston ones that blatantly would flow more than the pissy bailey ones, and also they do ones with a bigger (about double) diameter inlet so they fit on S14 200SXs etc.

These are brand new, still in bubblewrap, i wonder if theyl do some kind of trade-in, they are nice folk down Forge

You think that diagphrams will split at 30-35psi boost? Thought theydve made em better than that

Stavros

So whats the deal with them lifting then? Just put in the strongest goddamn spring ever, or they be ok? Overspeeding it will take it out of its efficency, wouldnt it?

Mike Rainbird

iTrader: (3)

Yes, but if you had an ACT gauge and an EGT, you would soon get a feel for what is normal and what isn't .

GARETH T

cant see it happening myself,,,
the differantial pressure on the spring side is always the greatest

force =pressurexarea

the spring side has an larger area and spring pressure
the other side has a smaller area and no sping

Mike Rainbird

iTrader: (3)

Gareth,
In my experience, sometimes they stick open / half open.

Rhys

What do you call big boost for this to happen?

How do Spec-r D/V rate too?

Stavros

That sounds like a sales pitch to me

Dont worry, there a fair few bits n pieces il be buying off you actually...



Gareth- Good point

GARETH T

Mike Rainbird, my motto is

"look after your dump valve,,, and it'll look after you"

cossymad

We get loads...well did.....of split diaphrams back.
We found the scooby ones (bailey) opening up on motorway and you could actually hear them leaking!!!

RWD_cossie_wil

iTrader: (9)

on some dumpvalves, you can make them stay half open and whistle if you get the throttle just right, which indicates to me that the spring is weak, I got a forge one on my cos at the moment, and it dosn't dump untill 10psi, so I assume it has a far stronger spring.

Stavros

I can get diagphrams for owt and i used to always check mine every week or so anyhow when i ran em, so thats not bothering me much.

Its that lifting thing that worried me.

In all honesty id much prefer to run no DVs, and im soo unconvinced they do anything worthwhile, but would YOU want to risk a top technology fancy as fuck huge turbo running 2bar+?

I was gonna risk it, but im getting scared

St3V3_C

I think that has more to do with the fact that you have a lower pressure from throttle plate to engine than you do from turbo to throttle plate

I can get mine to do it for short periods (usually on a slight uphill) and have actually checked it on the RR, it was not leaking at full chat. Only 20-something psi though.

Big Andy W

The pressure will be the same on both sides i'm sure as pressure is uniform ie the same everwhere!

Surely you can't have 32 psi in one place then 22 some where else in the same system, unless you have a regulater!

The spring is there to increase the force on the diaphram to push it closed and over come the identical pressure on both sides of the diaphram!

I've been running the same GGR dump valve(with kevlar composite diaphram) and it ain't never split in 4 years!

GARETH T

pressure might be the same,, but the area if different so the force is

NathR

Could this happen on a standard Bosch re-circ through a cone filter?? I occasionally get a strange whistling noise when on boost?!

Mike Rainbird

iTrader: (3)

Nath,
That's probably your piddly little turbo blades going supersonic .

NathR

More than likely

*cough*TWAT