how universal is a blow off valve?
02-03-04, 06:51 PM
#1
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how universal is a blow off valve?
i was wondering how specific they are to a car. someone i know had a turbo jetta and totaled it and if it would work i was thinking about seeing if i could get it from him. so my question is how specific are they, is it just small differences or are there major differences when they are sold for different cars?
02-03-04, 06:57 PM
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universal, if you buy it "for your car", you might get a kit to mount it, but it's totally universal. BUT, if you are on the stock turbo's it's also totally useless, they stock BOV works great.
02-03-04, 08:10 PM
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Its not that universal from what I understand.
Inside the BOV there is a spring. That spring is calibrated to open at a certain boost level and release excess boost. If that spring is of an incorrect 'weight' it will vent boost too early or worse too late. If it opens too late, that is very very bad from what I understand.
Inside the BOV there is a spring. That spring is calibrated to open at a certain boost level and release excess boost. If that spring is of an incorrect 'weight' it will vent boost too early or worse too late. If it opens too late, that is very very bad from what I understand.
02-03-04, 08:10 PM
#4
No it's not Turbo'd
Depends on where you want to mount it, most aftermarket BOV's have a mounting kit that you usually have to buy with the BOV 
but sometimes you can aquire one... for my HKS SSQ it seemed impossible to find the stock mounting kit, but after a while I ended up getting a different ic setup anyhow, and the universal alluminum flange worked just fine....
It's just a pressure valve, and the car doesn't care what vents the pressure or even if it does, vent. It'll just reduce the life of your turbo and slow down the compressor if you don't have one... so it's important to have something to vent pressure, but if you're dealing with stock boost, the stock setup is fine I'd say up to 12-14 psi, if you're getting it for sound, then you have to deal with the cosmetic issues mentioned above...
Edit: Spings in aftermarket BOV's are adjustable, so you'd be fine, ifyou're taking a stock BOV from a VW, all I have to say is WHY ???
-DC
but sometimes you can aquire one... for my HKS SSQ it seemed impossible to find the stock mounting kit, but after a while I ended up getting a different ic setup anyhow, and the universal alluminum flange worked just fine....It's just a pressure valve, and the car doesn't care what vents the pressure or even if it does, vent. It'll just reduce the life of your turbo and slow down the compressor if you don't have one... so it's important to have something to vent pressure, but if you're dealing with stock boost, the stock setup is fine I'd say up to 12-14 psi, if you're getting it for sound, then you have to deal with the cosmetic issues mentioned above...
Edit: Spings in aftermarket BOV's are adjustable, so you'd be fine, ifyou're taking a stock BOV from a VW, all I have to say is WHY ???
-DC
02-03-04, 08:14 PM
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Originally posted by alberto_mg
Its not that universal from what I understand.
Inside the BOV there is a spring. That spring is calibrated to open at a certain boost level and release excess boost. If that spring is of an incorrect 'weight' it will vent boost too early or worse too late. If it opens too late, that is very very bad from what I understand.
Its not that universal from what I understand.
Inside the BOV there is a spring. That spring is calibrated to open at a certain boost level and release excess boost. If that spring is of an incorrect 'weight' it will vent boost too early or worse too late. If it opens too late, that is very very bad from what I understand.
Very similar to wastegates, except the wastegate diaphragm is actuated via positive pressure where as the BOV is negative.
They're pretty damn universal unless the BOV you're using has a very weak spring.
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02-03-04, 08:27 PM
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i'd still be cautious. people spend a lot of $$ for BOVs and I don't buy that they are useless or that the pressure limits don't matter as some have said.
search on that topic and see what comes up and make an educated choice.
search on that topic and see what comes up and make an educated choice.
02-03-04, 09:23 PM
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Originally posted by clayne
alberto, people spend a lot of money on pointless **** on all the time.
98% of the BOVs are all the same.
alberto, people spend a lot of money on pointless **** on all the time.
98% of the BOVs are all the same.
02-03-04, 09:23 PM
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stock jetta valves are shitty. but, jettas also run a lot of boost usually and that can have an affect on the longevity of it.
if you are trying to buy an uninstalled kit, then you are fine, but there will be parts you don't use in the box, and you'll have to make some other parts, possibly.
if you are trying to buy an uninstalled kit, then you are fine, but there will be parts you don't use in the box, and you'll have to make some other parts, possibly.
02-03-04, 09:27 PM
#12
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Originally posted by alberto_mg
Inside the BOV there is a spring. That spring is calibrated to open at a certain boost level and release excess boost. If that spring is of an incorrect 'weight' it will vent boost too early or worse too late. If it opens too late, that is very very bad from what I understand.
Inside the BOV there is a spring. That spring is calibrated to open at a certain boost level and release excess boost. If that spring is of an incorrect 'weight' it will vent boost too early or worse too late. If it opens too late, that is very very bad from what I understand.
A pop-off valve opens at a specific boost level set by an adjustment screw. Exceed the limit and it vents boost to atmosphere, limiting boost to the engine. Once the boost level falls, it closes again, which is why using one for boost control isn't ideal. The valve will "flutter" as it opens and closes as boost rises above and drops below the threshold, assuming that the valve is adjusted too low. That's why it's best used for a fail-safe device, set to open at 16-17 psi when you plan to run only 15 psi, for example.
A blow-off valve, on the other hand, opens under vacuum, not boost. When the throttle blades close after a WOT run, engine vacuum opens the valve venting boost, which keeps compressor surge to a minimum and improves boost response... or so everything I've read and heard says.
A blow-off valve is therefore absolutely universal, because all it takes is engine vacuum to activate it and it is independent of boost level. The only limiting factor is the amount of boost it can vent quickly, and that's why there are larger blow-off valves intended for use in high boost applications. These valves usually have a larger orifice to vent boost more quickly.
For the FD, however, the stock BOV is more than adequate with the stock twins, especially in non-sequential configuration where you can convert the CRV (charge relief valve) to BOV duty and have two.
