"Chatter" sound dumpvalve
07 June 2005, 12:56 PM
#32
What I don't understand is people always make refrence to rally cars (I presume WRC) saying that the peep,peep,peeep noises are air backing up against the compressor wheel (basically the compressor wheel cavitating) as there is no dump valve. What they don't say is that the ALS on WRC cars flows so much air through the engine off thottle that it has to be more effective than any dump valve at preventing this....?
07 June 2005, 01:31 PM
#33
Originally Posted by Pavlo
There can be problems with it though, it will make driveability suffer in some situations
Paul
Paul
In what way would driveability be effected?
Just wondering if it may be worthwhile taking my OE dv off and blocking it up on my daily driver (FE-TD05, STi8 TMIC).
Bob
07 June 2005, 03:12 PM
#35
Originally Posted by crice
What I don't understand is people always make refrence to rally cars (I presume WRC) saying that the peep,peep,peeep noises are air backing up against the compressor wheel (basically the compressor wheel cavitating) as there is no dump valve. What they don't say is that the ALS on WRC cars flows so much air through the engine off thottle that it has to be more effective than any dump valve at preventing this....?
Paul
07 June 2005, 03:26 PM
#36
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I have a HKS SSQV - don't think it is safe to risk it with a VF28 though (although would love to run without a DV for the sound - if I knew it wouldn't bugger the turbo up - I only use the car for 4k miles a year!)
Has anyone got a sound clip that we can listen too!
Has anyone got a sound clip that we can listen too!
07 June 2005, 04:14 PM
#38
\m/ ^_^ \m/
that would do it Bob 
not noticed any side effects from running without one just yet 
unless of course that was the reason for my oil feed pipe coming loose 
not noticed any side effects from running without one just yet unless of course that was the reason for my oil feed pipe coming loose
07 June 2005, 04:19 PM
#41
You don't need ALS to make the chirping noise, the ALS will add that "running like a bag of nails" quality to the sound, with a few pops and bangs just for luck.
What I am saying is that (and i understand there are few of us who run the kind of boost levels senn in WRC cars) if there is no chirping with an effective dump valve because the air has somewhere to go, equally there should be no chirping on the rally cars because although they have no dump valve the air still has somewhere to go - through the huge bypass valve into the engine!
This is the bit which doesn't make sense to me....
Last edited by crice; 07 June 2005 at 04:23 PM.
07 June 2005, 04:21 PM
#42
\m/ ^_^ \m/
you know, im actually not sure now 
can't remember if the vac opens or closes the DV now 
best ask someone who knows what they're doing
can't remember if the vac opens or closes the DV now best ask someone who knows what they're doing
Theres me thinking it was 'work in progress'
07 June 2005, 04:31 PM
#49
I think dump valves and BOVs are often confused. My understanding is that the manifold vacuum will (depending on the sping tension) either just pull the DV open and allow any air to flow of, or at the least assist the built up pressure escaping once the throttle is shut. A BOV on the other had I don't believe use a vacuum has, and vent simply if the preset pressure is exceeded. A DV will not open under boost because the pressures are equal either side of the diphram or piston, but a BOV could leak air under boost if the spring is set too soft. I think a BOV is as good as not running a DV at all. IMO runnig with or without a DV makes little difference, I personally find the standard Bosch recirc' DV found on most turbo cars does a good enough job of keeping the turbo happy, but to be honest I can't belive you'd kill a turbo without one if only running standard boost levels.
07 June 2005, 09:16 PM
#60
No working experience of this on a Scooby, but in a former life with Cosworths my guru tuner said that dump valves (for real men that meant the re-circ ones) gave a crisper and sharper response on Cossies. I then installed an uprated Grp N re-circ valve on my Escort Cossie (after taking the standard one off for a long while) and it did make it sweater. Then when I went the 500bhp route on my RS500 I was told I must run a dump valve, unless I wanted to muller my turbo (running 2.3bar).
When I bought my Spec-C which had a Bailey DV to atmos on it, I immediately changed it back to the OE one.
I suspect this is one of those subjects that has opinions from all angles.
Regards,
Shaun.
When I bought my Spec-C which had a Bailey DV to atmos on it, I immediately changed it back to the OE one.
I suspect this is one of those subjects that has opinions from all angles.
Regards,
Shaun.