Which Dump Valve
28 October 2010, 01:15 PM
#1
ScoobyWorx
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Which Dump Valve
Firstly i know the standard one is the best etc and also the baileys one i currently use is about as much use as a grain of sand in the desert but i am going for 350bhp with my bugeye and want a suitable dump valve that will be right for power im running etc
28 October 2010, 02:50 PM
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The standard one should deal with that fine.
28 October 2010, 03:05 PM
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I dont have one as mine came with the throw away bailey one lol. its ok at the minute but they start to cause issues on cars with more than 270bhp ive heard, i do like the sound of em if im honest so i just want a decent one. possibly a part atmospheric part recurc.
28 October 2010, 03:20 PM
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The combination atmos/recirc valves are more than a bit pointless, as they become atmospheric during the the moments you most need them to recirculate. If you're thinking about one of those because you "like the sound", but were figuring a 50/50 one will give you some sort of "best of both worlds" scenario, you may as well just fit an atmospheric one.
OEM DV's easy and cost-effective to get hold of - so if you don't have one right now, there's no reason not to give one a try.
OEM DV's easy and cost-effective to get hold of - so if you don't have one right now, there's no reason not to give one a try.
28 October 2010, 03:55 PM
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The combination atmos/recirc valves are more than a bit pointless, as they become atmospheric during the the moments you most need them to recirculate. If you're thinking about one of those because you "like the sound", but were figuring a 50/50 one will give you some sort of "best of both worlds" scenario, you may as well just fit an atmospheric one.
OEM DV's easy and cost-effective to get hold of - so if you don't have one right now, there's no reason not to give one a try.
OEM DV's easy and cost-effective to get hold of - so if you don't have one right now, there's no reason not to give one a try.
OEM is the way im now thinking
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28 October 2010, 04:55 PM
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Now heres where I prob need correcting but as they are twing piston dont they just clamp more under load??
I know you can get ectra internal bits from FORGE though so there is probably what you need under one company.
I know you can get ectra internal bits from FORGE though so there is probably what you need under one company.
28 October 2010, 05:16 PM
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The one which cdm1 has for sale is silly money - if it were me I would buy that one now, think about it later, and then either fit or sell on when you've made your mind up
Last edited by P1#1015; 28 October 2010 at 05:17 PM.
28 October 2010, 09:12 PM
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Your suggestion that a twin piston DV "prevents higher boost levels forcing the valve open" doesn't really stand up to too much scrutiny, given that there's no good reason why a functional conventional/single piston valve should leak under boost.
Don't forget that there's a pipe connecting the the inlet manifold to the un-pressured side of the DV. When you are on wide open throttle - no matter how much pressure you run, the DV will be blown shut via pressure from the inlet manifold as well as the spring. In other words, if you are running 2 bar of boost, there will be 2 bar in the intercooler trying to force the DV open, but 2 bar on the other side of the diaphragm plus the spring, forcing it shut.
If there is a pressure differential at all, it will be whatever drop you get across the throttle body, and won't be particularly significant.
The main point of different springs and shim kits is (or should be) to ensre that the valve opens at the correct points (and stays shut at normal idle vacuum) rather than to withstand greater levels of boost. Although the best way of avoiding having to muck about with different springs and stuff is simply to use the OEM DV, which works out of the box.
Where there is a technically grounded reason to use a non-standard dumpvalve, it's less the need to "withstand" greater levels of boost, and more an imperative to dump out greater volumes of air than the OE item can comfortably cope with.
29 October 2010, 11:12 AM
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Thanks Splitpin - That got my head around it. My thoughts were along the equal pressure route just didnt quite reason the backwards open close method in the twin piston.
29 October 2010, 11:17 AM
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Not really. The main purpose of a twin piston dumpvalve is to create a "Oooh, it's got two, it must be twice as good" selling point to assist the manufacturer's perfectly legitimate desire to sell stuff to people who don't really know any better.
Your suggestion that a twin piston DV "prevents higher boost levels forcing the valve open" doesn't really stand up to too much scrutiny, given that there's no good reason why a functional conventional/single piston valve should leak under boost.
Don't forget that there's a pipe connecting the the inlet manifold to the un-pressured side of the DV. When you are on wide open throttle - no matter how much pressure you run, the DV will be blown shut via pressure from the inlet manifold as well as the spring. In other words, if you are running 2 bar of boost, there will be 2 bar in the intercooler trying to force the DV open, but 2 bar on the other side of the diaphragm plus the spring, forcing it shut.
If there is a pressure differential at all, it will be whatever drop you get across the throttle body, and won't be particularly significant.
The main point of different springs and shim kits is (or should be) to ensre that the valve opens at the correct points (and stays shut at normal idle vacuum) rather than to withstand greater levels of boost. Although the best way of avoiding having to muck about with different springs and stuff is simply to use the OEM DV, which works out of the box.
Where there is a technically grounded reason to use a non-standard dumpvalve, it's less the need to "withstand" greater levels of boost, and more an imperative to dump out greater volumes of air than the OE item can comfortably cope with.
Your suggestion that a twin piston DV "prevents higher boost levels forcing the valve open" doesn't really stand up to too much scrutiny, given that there's no good reason why a functional conventional/single piston valve should leak under boost.
Don't forget that there's a pipe connecting the the inlet manifold to the un-pressured side of the DV. When you are on wide open throttle - no matter how much pressure you run, the DV will be blown shut via pressure from the inlet manifold as well as the spring. In other words, if you are running 2 bar of boost, there will be 2 bar in the intercooler trying to force the DV open, but 2 bar on the other side of the diaphragm plus the spring, forcing it shut.
If there is a pressure differential at all, it will be whatever drop you get across the throttle body, and won't be particularly significant.
The main point of different springs and shim kits is (or should be) to ensre that the valve opens at the correct points (and stays shut at normal idle vacuum) rather than to withstand greater levels of boost. Although the best way of avoiding having to muck about with different springs and stuff is simply to use the OEM DV, which works out of the box.
Where there is a technically grounded reason to use a non-standard dumpvalve, it's less the need to "withstand" greater levels of boost, and more an imperative to dump out greater volumes of air than the OE item can comfortably cope with.
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