graememk
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| posted on 18/2/07 at 12:20 AM |
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turbos and dump valves
ok..... i have a dump valve that u bought for my turbo indy (didnt cost much), its not a noisey one but still will make a wooshing noise if i fitted
it, is there a benifit of using one or are they just boy racer snake oil crap ?
[Edited on 18/2/07 by graememk]
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jambojeef
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| posted on 18/2/07 at 12:50 AM |
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There should be a genuine benefit but of course its a choice boy-racer add on!
The idea is that without a dump valve when the throttle is shut quickly (eg between gear changes) the turbine blades begin to slow but remain spinning
for a time thus building boost with nowhere for it to go.
Sometimes this produces pressure spikes of up to 50psi and can bend throttle spindles amongst other things. The other alleged benefit is that with the
boost vented the turbine is less likely to stall and can keep its inertia in readiness for the next generation of boost (eg when the next gear is
selected) - a kind of anti-lag idea.
A dump valve is usually fitted from the factory in production cars but it recirculates the "dumped" air back in front of the turbine
blades and isnt heard very easily.
It could be argued that in a BEC when you hardly lift off the throtte between gear changes, the pressure spikes are less of an issue but I included
mine as a kind of safety valve.
Its worth mentioning that Rally cars have entirely different anti-lag system where an injector in the exhaust manifold opens and spools the turbo up
artifically. It sounds unbelievably brutal and on a friends Sierra Cosworth, I thought I was about to see bits of molten metal under the car when he
switched it off!
Geoff
[Edited on 18/2/07 by jambojeef]
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greggors84
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| posted on 18/2/07 at 02:37 AM |
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A mate who works for a ECU company has been playing about with a customers group N evo at the moment. He was explaing the anti lag system to me, it
was on a night out and I had drunk a few, so the details are a bit sketchy, but im sure he said that the throttle was constantly open and the car
speed was controlled using the anti lag, meaning the turbo was always up to speed. Sounded crazy as you were always trying to hold the car back. Will
find out the proper details when he gets back from his trip (at Kyalami with a customer and his ex Ferrari F1 car! Lucky bastard!)
Chris
The Magnificent 7!
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UncleFista
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| posted on 18/2/07 at 03:33 AM |
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quote:
Originally posted by graememk
ok..... i have a dump valve that u bought for my turbo indy (didnt cost much), its not a noisey one but still will make a wooshing noise if i fitted
it, is there a benifit of using one or are they just boy racer snake oil crap ?
[Edited on 18/2/07 by graememk]
The noisy "dump to atmosphere" ones are supposedly better, 'cos the hot gas isn't recirculated into the intake,
"They" say that you don't get a blast of unmetered hot air in the intake like you do with the silent recirculating type.
I reckon it's all just a made-up excuse to fit something shiny and noisy. As if we need an excuse 
Tony Bond / UncleFista
Love is like a snowmobile, speeding across the frozen tundra.
Which suddenly flips, pinning you underneath.
At night the ice-weasels come...
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graememk
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| posted on 18/2/07 at 08:42 AM |
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not sure if i would get a kicking if i turned up to a meet making wooshing noises
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marcjagman
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| posted on 18/2/07 at 08:49 AM |
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A dump valve basically does what is says on the box, it's a valve the dumps excess pressure in to the atmosphere. Make sure that you get the
pressure set right or your engine could go bang.
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bilbo
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| posted on 18/2/07 at 09:17 AM |
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I'm going to be sticking with the factory fit one on mine. Had no issues with lag when the engine when it was in a tin top. The air is
recirculated, but it still has to pass throught the intercooler before reaching the intake, so it shouldn't be hot.
quote:
not sure if i would get a kicking if i turned up to a meet making wooshing noises
I have to say that eveytime a car goes past going 'KAPOOOOSSH', I think 'Prat!'. Not sure why you'd want to make your
car sound like a bus with air brakes? 
[Edited on 18/2/07 by bilbo]
[Edited on 18/2/07 by bilbo]
---------------------------------------
Build Diary: http://bills-locost.blogspot.com/
Web Site: http://locost.atspace.com
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the_fbi
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| posted on 18/2/07 at 10:00 AM |
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quote:
Originally posted by marcjagman
Make sure that you get the pressure set right or your engine could go bang.
Care to explain that?
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SeaBass
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| posted on 18/2/07 at 02:01 PM |
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quote:
Originally posted by zilspeed
the car now has a free flow air filter
Did you ever put those neons on?
In terms of the dump valves just don't get one of the cheapies with a trumpet like flare to make the noise even louder.
I would be inclined to look under the bonnet of some of the WRC machinery. They will have done the testing required to see what works best.
[Edited on 18/2/07 by SeaBass]
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meany
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| posted on 18/2/07 at 02:48 PM |
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as a scooby owner for 4 years...here goes.
1. if you are happy with a normal re-circ fitted and not interested in the woosh noise...then leave that on.
2. if you want the Whoosh noise, choose a piston type and not a diaphram type.
3. as for sounding like a pratt...each to their own....but think about this, what do you think you look like in a small 7 type. especially with a
screaming engine.
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MikeRJ
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| posted on 18/2/07 at 03:02 PM |
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quote:
Originally posted by meany
3. as for sounding like a pratt...each to their own....but think about this, what do you think you look like in a small 7 type. especially with a
screaming engine.
I'm pretty sure that the image of (if not the day to day practicalities of driving) a screaming 7 appeals to far more people than a Scooby that
sneezes when you change gear
[Edited on 18/2/07 by MikeRJ]
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meany
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| posted on 18/2/07 at 03:59 PM |
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Its not what you have, its what you do with it,
problem is, there is too many idiots out there that have now given the scooby a bad name...mine has a re-circ one on so is quiet....as i said...each
to their own.
anyhow...going off topic here.
1. I reckon all turbo engines should have a dumpvalve on, for smoother responses and reduced turbo lag.
2. no power gains to be had from a VTA dump valve...maybe slight better response through gear changes.
this is all from my own experiences, yes i had a VTA on my previous scoob, a Forge one, not too loud, just right, in my opinion.
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martyn_16v
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| posted on 18/2/07 at 06:21 PM |
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What management are you using to run the engine, or more to the point how does it sense engine load? MAF/AFM systems do not like atmospheric dump
valves, MAP sensors however are fine with them. Atmos valves are not good with a MAF because they are generally dumping metered air out of the system,
the ecu doesn't see this so fuels as if the air is still there (so it overfuels). The lambda sensor then sees a rich exhaust and tells the ecu
to cut a bit of fuel, just as you are whomping the throttle back on. Most of the time you'll be alright, but if your engine is tuned close to
it's limits it could be enough to push you into detonation
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