Why place the dump valve close to the throttle?
Turbo Mini Forums

I've been trying to get my head round this for a while but it seems beyond the ability of my little sparky brain.

From everything I've heard you want to place the dump valve as close to the throttle as possible (most people including myself have them on modified plenum chambers & even Rover put the pressure release valve on the plenum) however the roll of a dump valve is to stop the turbo from stalling due to back pressure created when you snap the throttle shut (changing gear, breaking, etc) Now the way I see it is that surely you'd be better off trying to release the excess air pressure as close to the compressor wheel as possible as it's the turbo which you are trying to protect.

I'm quite happy to accept I've got something wrong as what seems like the sensible option to me is the opposite of what every & his dog are doing, but could someone please explain the reason why you put the dump valve as close to the throttle as possible (and as far away from the turbo as possible for that matter)

i thought it was due to the way the dump valve works, i.e on the pressure differential between the inlet and the plenum.

if you put the dump valve near the turbo, it might always have a higher pressure than the inlet (especially if you run an IC), so might continually vent when on boost.

Again, no experience of this, just regurgitating what i have heard somewhere along the line...

Also, and im most probably wrong about this one, but releasing pressure is releasing pressure, no matter where you do it from the same system (im sure the location of the dv will ever so slightly effect the efficiency of the 'local' pressure drop, but it probably would make neglible difference in our case...???

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

TBH, I dont think it makes any odds....

Some would say after the IC, as you are plessing less heat loads on the DV.
Others say close to teh turbo, which is placing much higher heat loads on the DV.

Some say close to the throttle....


The heat issue is possibly relevant to DV life, as some DV's are pretty crap.

But I really dont think it would make pick of difference where it is located within the system, in terms of ability to release air when required.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

When the butterfly closes it makes a dead end,If you put the d/v further away from the dead end, then the pressure will have to return back down to the d/v


Thats my verdict

Metro turbo weekend driver,Mini turbo in the making again!

I think it has a lot to do with the inertia of the air.

When the throttle closes, you have both pressure and inertia to deal with. With the velocity involved the inertia is probably as potentially damaging as the pressure.

The only way to vent the inertia is with the dump valve as close to the butterfly as possible.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

As far as I understand it a combination of the last two posts is the actual answer, that along with trying to keep the signal line as short as possible (I know we are only walking a few microseconds difference with the speed of sound in air but .....)

Every day is a school day ...........

How fast and how expensive ...... the same question...

Edited by stevieturbo on 3rd Feb, 2007.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Steve, that is a good analogy with the hose pipe. I was trying to think of one that wouldn't sound insulting and also put things simply.

Every day is a school day ...........

How fast and how expensive ...... the same question...

I know that air and water are both fluids but isn't there still a bit of difference? Like would air not be way more compressable than water? Meaning air might not actually be flowing but pressure could be higher at the back of a closed butterfly that further back towards the turbo for that split second after the throttle is shut before it would equalise out?

It is compressible of course, but it will make no odds.

If we are getting that fussy, mount one at the Throttle, and one directly at the compressor outlet.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Hi,
I think it's to do with reducing "lag"
If you put the DV right by the comp when you open the throttle again, as in changing gear the turbo has to pressurise the entire intake system again.
Whereas with the DV close to the butterfly the system is still partially pressurised.
Cheers,
Gavin :)

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Seriously, you will not noitce any difference in lag, whether its mounted at the TB, or the Compressor.

In fact, try not using one at all, and see if you notice a difference.
The biggest difference a DV made on my car, was it made part throttle a lot smoother.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Good post this, i thought everyone knew lol, i can see where bat is coming from.

Hi,
I notice a difference on my cossie without the DV. Turbo makes a horrible growling noise when changing gear!
I've noticed on OE DV installations they can be on the hot or cold side, but I can't say as I've seen any right by the compressor or right by the butterfly..... Someone will come along now and "educate" me!
Like with most things in tuning there's a lot of BS spouted, so much in fact it's hard to tell what's right!
Cheers,
Gavin :)

Edited by Bat on 3rd Feb, 2007.

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It may make a different noise....but does performance change ?? I suspect not.
In most cases, a DV will make no noticeable difference to performance. Not all, but an awful lot, especially low boost setups.

As for BS, you are so right. the only right answer, is to fit the DV, wherever is easiest.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Cheers guys, there some interesting food for thought there.

The DV will not help performance!

If you want to make it quicker loose the DV and go the boost spike as you change gear

Alex

AlexF

Of course, if you neer lift your foot off the accelerator, you will never need a dump valve lol.....

Flat shifting anyone ? IF you run MS, then surely you can hook up a flat shift ign cut.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Hi,
Stevie you're right, it would be a waste of money if you were fitting one for a performance gain.
But then I guess a blown to bits turbo is going to make a drastic reduction in performance
Cheers,
Gavin :)

VEMs Authorised Installer / Re-seller. K head kits now available!

WB/EGT gauges. Click here for customers write-up

Visit www.doyouneedabrain.co.uk

My Mini build diary

isnt the cosworth dv take off on the intercooler itself?

I thought a DV on something as small as a mini increases lag? I.e. if it vents completely the turbo has to rebuild the boost?

On 4th of Feb, 2007 at 07:35pm Bat said:
Hi,
Stevie you're right, it would be a waste of money if you were fitting one for a performance gain.
But then I guess a blown to bits turbo is going to make a drastic reduction in performance
Cheers,
Gavin :)

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

from what ive been told and have found out is that a dump does only one thing and that is sound good.

mine went better when it was stuck closed through the gears.

all i do is when going down the strip is to wind it in a few clicks.

always looking for them bigger bunches of bannanas

the theory behind the dump valve is to stop the turbo stalling between geachanges thus helping it to spool up faster but a dump valve doesn,t become efective until a turbo is running at around one bar approx14 psi so as for running 4-7 psi a dumo valve isn't really necessary but an still sound great