Surging problem now sorted

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s4mark

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Hi everyone. Replaced my DV today for peace of mind and now my surging issue has disappeared. Didn't think that a faulty DV would have caused it but touchwood its ok now but may have just been coincidence and it will probably happen again soon. Also did the N249 valve bypass mod whilst I was there. DV is definately working faster and gear changes smoother than before. Very happy with the outcome.

One more question I have is regarding the DV fitment. Can these be mounted / fitted the other way round and if so what are the benefits of this? cheers
 
Did you check to see if any of the hoses you removed were split?

Yes you can run it the other way, none really, makes a slightly louder noise.
 
Dani_B19 said:
Did you check to see if any of the hoses you removed were split?

Yes you can run it the other way, none really, makes a slightly louder noise.
Click to expand...

Couldnt find any split hoses etc and all seemed tight. Thought i'd change the DV anyway as its not expensive.
Does rotating the DV shorten its life at all. May try it but if its only the sound issue may not bother.
 
was wary of doing it earlier
so just swap the two large hoses on the dv? sorry to sound thick but don't usually get involved in tinkering of this kind but starting to get a bit hooked
 
Like steve said, undo exsisting pipeing etc, turn DV around and reattach pipe's etc, done.
 
i run mine the wroung way around also makes no difference to it being able to do the job its made to do, if itsfitted the correct way around the valve will work on vaccum so there is no chance of the valve opening under boost as it will be pulling more vaccum (i guess thats how they get away with making cheap plastic ones) with it the other way around your valve is having to stop the boost pressure pushing the valve open and leaking boost off, forge do different pressure springs so you can still maintain the correct boost by using the correct spec spring..
 
So what problem did you have with the car then ?
 
Dazboss said:
Mines kinda doing this but not the jerky'ness so much.
Click to expand...
personally I think the jerkiness was caused by the n249 myself and getting rid seems to have done the trick. Doubt the DV had anything to do with it, I only replaced it for peace of mind. If it does start playing up I would suspect the MAF as I had similar problems on my a4 and it was a knackered MAF.
Unplugged the MAF on the S3 and took it for a drive and the surging was still there on boost so didn't really think that was at fault
 
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s4mark said:
personally I think the jerkiness was caused by the n249 myself and getting rid seems to have done the trick. Doubt the DV had anything to do with it, I only replaced it for peace of mind. If it does start playing up I would suspect the MAF as I had similar problems on my a4 and it was a knackered MAF.
Unplugged the MAF on the S3 and took it for a drive and the surging was still there on boost so didn't really think that was at fault
Click to expand...
dont you just hate making more than 1 change for a result....witch one cured it .....lol
 
s3_kev said:
i run mine the wroung way around also makes no difference to it being able to do the job its made to do, if itsfitted the correct way around the valve will work on vaccum so there is no chance of the valve opening under boost as it will be pulling more vaccum (i guess thats how they get away with making cheap plastic ones) with it the other way around your valve is having to stop the boost pressure pushing the valve open and leaking boost off, forge do different pressure springs so you can still maintain the correct boost by using the correct spec spring..
Click to expand...


Under boost conditions, there is no vacuum. The boost pressure in the inlet manifold finds it's way down the signal pipe, and equalizes the pressure coming from the other side of the diaphragm (charge pipe side), preventing the valve from opening. When you back off the throttle, you introduce vacuum which pulls the diaphragm open, releasing the charge air. Principal is the same whichever way around the valve is fitted.
 
id rather have the charge pipe trying to force air into the side of the dv rather than up against the diaphragm as its more likely to push the disphragm up
 
Matt82 said:
id rather have the charge pipe trying to force air into the side of the dv rather than up against the diaphragm as its more likely to push the disphragm up
Click to expand...

Yep, that's obviously the preffered way to fit the valve.

Has anyone tried not running a valve at all, maybe in a track-day only or race application? you wouldn't lose as much metered air throught the turbo's compressor inlet as you would via an externally venting dump valve - I know they would run badly like this. In my experience with other blown motors, turbo response has a marked improvement without any type of BV/dump valve in place. Yeah you may get some compressor surge/stall between changes but I've never experienced any detrimental effects to the turbo from this. I'm not suggesting it's a good idea to remove the BV - I'm fully aware of the few reasons why it's fitted in the first place, just curious if it's been experimented with.
 
Matt82 said:
id rather have the charge pipe trying to force air into the side of the dv rather than up against the diaphragm as its more likely to push the disphragm up
Click to expand...

I actually misread what you put there Matt, I disagree. The design of the valve and how the diaphragm, cup and spring sit in the body really needs the air coming straight into the face of the diaphragm. I think the seal could be compromised the other way around.
 
5teve L said:
Undo valve, turn round & refit.. Simples
Click to expand...

So just so I'm clear the bottom main section of the T (imagine that's the dump valve, brill I know) that sits in the tip still stays positioned there... Just the other 2 pipes either side of it are reversed?
 
Lee H said:
Yep, that's obviously the preffered way to fit the valve.

Has anyone tried not running a valve at all, maybe in a track-day only or race application? you wouldn't lose as much metered air throught the turbo's compressor inlet as you would via an externally venting dump valve - I know they would run badly like this. In my experience with other blown motors, turbo response has a marked improvement without any type of BV/dump valve in place. Yeah you may get some compressor surge/stall between changes but I've never experienced any detrimental effects to the turbo from this. I'm not suggesting it's a good idea to remove the BV - I'm fully aware of the few reasons why it's fitted in the first place, just curious if it's been experimented with.
Click to expand...
it would run under actuator pressure only would it not?
 
Lee H said:
I actually misread what you put there Matt, I disagree. The design of the valve and how the diaphragm, cup and spring sit in the body really needs the air coming straight into the face of the diaphragm. I think the seal could be compromised the other way around.
Click to expand...
but if the charge pipe is pushing up against the valve it has a chance of lifting the valve and leaking. if it goes in sideway, itll have to push the valve through the side of the body (exagerated)

i think wed need pics of the inside of the dv to see how the seal sits as you mentioned
 
a car im working on tonight has fun with no dv whatsoever for about 2-3 years. charge pipe is bunged and so is the return on the tip

massive compressor surge every time she lifts off, sounds great, but no ill effects in that time

ive had the tip off just to check for play in the impellor. none

Lee H said:
Yep, that's obviously the preffered way to fit the valve.

Has anyone tried not running a valve at all, maybe in a track-day only or race application? you wouldn't lose as much metered air throught the turbo's compressor inlet as you would via an externally venting dump valve - I know they would run badly like this. In my experience with other blown motors, turbo response has a marked improvement without any type of BV/dump valve in place. Yeah you may get some compressor surge/stall between changes but I've never experienced any detrimental effects to the turbo from this. I'm not suggesting it's a good idea to remove the BV - I'm fully aware of the few reasons why it's fitted in the first place, just curious if it's been experimented with.
Click to expand...
 
s3dave said:
it would run under actuator pressure only would it not?
Click to expand...

Sorry, I should have said assuming there was no electronic boost control going on, N249 bypass. So yeah, actuator pressure only, maybe with a mechanical boost control device.
 
Matt82 said:
but if the charge pipe is pushing up against the valve it has a chance of lifting the valve and leaking. if it goes in sideway, itll have to push the valve through the side of the body (exagerated)

Not when there's equal pressure applied the other side of the diaphragm via the signal pipe that's attached to the inlet manifold. That, combined with the spring that's helping to keep the valve closed also.
Click to expand...
 
Matt82 said:
a car im working on tonight has fun with no dv whatsoever for about 2-3 years. charge pipe is bunged and so is the return on the tip

massive compressor surge every time she lifts off, sounds great, but no ill effects in that time

ive had the tip off just to check for play in the impellor. none
Click to expand...


I've had plenty of experience of turbocharged cars with no dv, never seen any evidence of that causing the turbo damage you hear talk of - snapped shafts, broken off vanes from the compressor wheel etc. Myth.
 
lots of interweb myths. love busting them

hers is remapped by amd too. runs 15-16psi. ive seen her run 15.2s at pod too. she does death it.

its a 98 AGU so its no spring chicken, but its coming up for a clutch change soon (dmf dying)
 
Matt82 said:
lots of interweb myths. love busting them

hers is remapped by amd too. runs 15-16psi. ive seen her run 15.2s at pod too. she does death it.

its a 98 AGU so its no spring chicken, but its coming up for a clutch change soon (dmf dying)
Click to expand...

What blower is on that AGU dude?
 
Lee H said:
Under boost conditions, there is no vacuum. The boost pressure in the inlet manifold finds it's way down the signal pipe, and equalizes the pressure coming from the other side of the diaphragm (charge pipe side), preventing the valve from opening. When you back off the throttle, you introduce vacuum which pulls the diaphragm open, releasing the charge air. Principal is the same whichever way around the valve is fitted.
Click to expand...

ok i have heard of it being explained in the way i described which makes sense to me as with the valve the correct way one end that goes into the tip will be where the pull would be from the 'vacumm'??? surley if the turbo is pulling in air from the filter then there will be no pressre against the dump vlave piston as there is no positive pressure in the intake?? then when you let off the vacumm in the charge pipe would open the piston and draw the air into it??
with it the other way surley you would have positive pressure in the charge pipe pushing the piston of the dv open?? then when you let off the vacumm would be pulled this time through the tip side to open the valve??

thats how i have understood it sorry if im mistaken just made sense to me
 
Kev, the 'vent' part of the valve - which is fitted to the tip, regardless of which way around the valve is fitted is irrelevent in it's operation. As far as opening and closing is concerned. You could vent it to atmosphere and it wouldn't make a difference.

The only vacuum the valve is making use of comes from the inlet manifold, via the small vacuum hose attached to the top of the valve. On closed throttle overrun, or very partially open throttle the engine is trying to pull air in but it is 'throttled'. This builds vacuum in the inlet manifold and the DV is open at this time. The second you open the throttle and allow the engine to breathe, the vacuum disappears. The valve closes. Boost pressure starts to rise as the turbo spools. This boost pressure fills the vacuum pipe attached to the valve and forces the valve to stay closed, despite the boost pressure in the charge pipe acting on the diaphragm trying to open it. It stays closed until you close the throttle, introducing vacuum again which opens the valve and vents the charge air into the tip.

s3_kev said:
ok i have heard of it being explained in the way i described which makes sense to me as with the valve the correct way one end that goes into the tip will be where the pull would be from the 'vacumm'??? surley if the turbo is pulling in air from the filter then there will be no pressre against the dump vlave piston as there is no positive pressure in the intake?? then when you let off the vacumm in the charge pipe would open the piston and draw the air into it??
with it the other way surley you would have positive pressure in the charge pipe pushing the piston of the dv open?? then when you let off the vacumm would be pulled this time through the tip side to open the valve??

thats how i have understood it sorry if im mistaken just made sense to me
Click to expand...
 
I used to run the dv reversed when i had a green cotton panel filter. It makes a loud chirp whistle sound which i liked! But then i got a BMC kit so i put it back to the normal way and i get a nice loud whoosh. The other day i reversed the dv to see what it'd sound like with the BMC kit and it sounded duff! It was like a metal against metal sound like a 'ching' kinda noise.
 
Ok so can someone explain how to reverse it? Do all the pipes have to be undone including the top small breather hose?
 
fran-s3 said:
Ok so can someone explain how to reverse it? Do all the pipes have to be undone including the top small breather hose?
Click to expand...

Simple. You have 3 ports on the valve. #1 Vacuum connection (small one at the top), #2 going to the tip and #3 connected to the charge pipe.

You leave #1 alone. Then just swap #1 and #2 around. job done.

bosch_side.jpg
 
Cool thanks Lee, do the pipes stretch out ok?
 
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