BOV theory

[tang0]

now, i'm a membrt of the SES, and as part of our training we had to learn all about hydraulics, its been a while since i learnt about pascals theory from physics in school, so i read up about it, and can now apply the pascal theory to a BOV.

A BOV will open up when there is vacume pulling on it, there is a spring in side that allows this operation only at a pre determined vacum pressure ... in a similar way, it is closed when above atmospheric pressure is applied to it ...

the simple matter is, when you run MORE boost, there is no way for the bov to leak, as an equal amount of pressure is closing the value as to the amount of pressure being applied to try and open it from the bov inlet side ...

is my thinking correct here so far ?

so if this is true, there is NO performance gain over having an aftermarket bov, there is no LOSS to keeping the standard bov as in pascals theory, it is unable to leak .. aparently simple physics determins it true ....

have i got it all wrong ?

comments anyone ?

cheers

[NZM.031]

thats how it works with more expensive BOV's like the HKS super sequential. the boost pressure forces the valve shut. however with your cheaper ones like turbosmart and GFB they just have a piston and a spring inside a trick housing. the spring can handle so much boost and not compress but when the throttle is closed that pressure increases and compresses the spring and pushes the piston past the ports and releases the air.

these cheap bovs can leak under idle and full boost if they cant handle the pressure. standard bovs can leak under boost aswell.

it is worthwhile upgrading them, and also spending dollars on them, usually stock ones are better then most cheap a/m ones.

hope that helps

cheers

Linton

[MonstaS4]

NZM.031, i'm not sure which turbosmart BOV you're talking about, but i'm sure they work in the way Tang0 has described. (My plumback does anyway). The port on the cap is connected to the intake manifold, so when on boost the combined pressure of the spring and boost pushing against the BOV piston is greater than boost only on the inlet side of the BOV, hence the valve stays shut.

[Cubes]

tang0,

correct.. This is why the stock RB bov is known for holding such high boost pressures.

The stock bov does age and tend to get a little weak, causing leaking on idle and leaking when on boost. I've seen one that leaks just a little too much. Well compared to my stock bov.

[NZM.031]

MonstaS4, thats the way my old turbosmart type 1 worked, and same has my mates type 3s with the trumpets. they are just a spring pushing a piston against the boost pressure.

cheers

Linton

[Roy]

My std BOV was leaking so i replaced it (yes i tested it with a magnahelic gauge from work)

When i replaced it i had a look at the std jobbie, and i reckon the only reason it was leaking was it wasnt seating properly because of the all the carbon/oil etc build up. A clean and i reckin it would have been alright, but by then i already had my HKS jobbie on and liked the sound:whackit: