Lets start from the beginning. This
is a diagram on how the BOV mounts onto
the upper ic pipe.
Ideally, air enters the pipe from
IC and passes thru to the TB. The BOV
functions is to relieve pressure
in the intake pipe when the throttle plate
is closed momentarily (such as when
you shift gears) so that the highly
compressed air doesn't turn back
and hit the compressor's blade. The BOV is
activated by means of the vacuum
that it sees thru the top nipple, when
connected with a hose to the intake
manifold directly. When it receives
vacuum, it brings up the diagram
(green in pic.) that in turn bring the
valve (red in pic.) inside the BOV
up, letting compressed air to flow thru
and spit out the pipe thru the big
outlet port back to the intake tract.
Now you all know that the 2G stock
BOV leaks bad, some says that it only
hold boost up to 13-15psi max. What
does it means? Well, see the blue spring
in the pic.? Above the green diagram?
This spring is there to hold the valve
down when it is not supposed to
open. On the 2G, this spring is weak, that
plus the cheap assembly of the plastic
BOV doesn't provide tight seal
against the diagram and valve causing
boost made by the turbo to push the
underside of the valve, and leaked
out. So imagine you scratching your head
when you cant adjust boost to hold
above 13-15 psi because no matter how you
adjust the boost controller, the
extra air is just leaked out back to the
intake tract. All this while your
poor T-25 tried to push a constant 19psi
for an eternity. 19 - 15 = 4psi
leaked out the entire time!!
Fix? Install the 1G BOV. Made from
metal and with a stiffer spring inside,
the 1G BOV doesn't open as early
as the 2G BOV's. My stock one opens at
16inHg vacuum (1 inHg is the same
as 1psi, only negative, or at least that
is what I was told) and an extra
one that I bought opens at the same
pressure/ vacuum. But my boost gauge
says that with the stock uncrushed
1G BOV I am making 18psi you said.
Well, thats true and wrong. True
that your boost gauge shows you that you
are making 18psi, but because the
BOV, from opening early in the system,
leaks boost, so infact you see that
you are only making 18psi while actually
the turbo is spinning and producing
more than that, a lot more!! This is not
good for the top end and also for
efficiency because boost loose = wasted
energy = unstable top end response.
Q: How can you modify the stock 1G
BOV to hold more pressure at the top end
though?
A: Simple, crushed them. Crushing
the BOV is done by putting it between 2
pieces of soft wood and putting
the whole thing on a bench vice or a big C clamp.
Q: Do I just compress? When do I
stop?
A: There is this believe out there
that you can just put the BOV in a vise
and compressed it till the nipple
touch the base. Well, thats BS. Everything
in a car works with a measurement,
a precise measurement that makes the
single component works with the
system to achieve the end result that you
want.
Many believe that you can just
compressed the BOV till the nipple touch
the base of the BOV, well, I
believe this practice is up there with tightening
a bolt to just snug-fit...when
you want something to tighten properly, not too
loose and not too tight that
you'll stretch and broke the bolt, what do you do?
You use a torque wrench right?
You basically have to use a measuring tool !!
Like every components in a race
car, you would want to crush the BOV to an inch
of its life to achieve the max
performance from it. Meaning that you would
want it to hold boost till the
very last moment before it should open which is
when you shift the gear and the
intake manifold vacumm reached 24inHg. So
how do you crush as close as
possible to 24inHg without going overboard?
Vacumm pump, equipped with a
gauge, is the answer.
Besides, as many ppl. confirm,
when the BOV nipple touch the head base, the
BOV hasn't necessarily reached
the 20inHg figure yet..most confirm thru the
gauge reading that it still opens
at only 17-18inHg. So there you go, if you want
the BOV to perform to the max
(why in the world are you reading this article
otherwise?) then get yourself
a proper vacumm pump with a gauge.
Q: So....
A: You have to use a vacuum pump.
You've probably seen this tool used to
bleed brakes and etc. First you
connect the pump to the nipple of the stock
BOV, then you test at what vacuum
it opens. If it is a virgin BOV,
uncrushed, it will probably open
around 15-16inHG. Now what we want to
accomplished is to crush the BOV
thereby increasing the spring rate inside
the BOV so that it could hold more
compressed air before it starts to open.
You start by compressing it slightly,
then check...compress again, check, do
this repeatedly and do it in a very
small increment because once you crushed
it, there is no way you can un-compressed
it. It is also good to know that
when shifting gears, the intake
manifold vacuum of a good running, stock
cammed cars drops to 24inHg, so
you can crushed it to anywhere but don't
exceed the 24inHg mark otherwise
your BOV might never open. If you crushed
the BOV to 25inHg but the intake
manifold never reached this figure, then
you can be rest assured that the
BOV will never opens and you've just ruined
an $80 part.
Q: What if I have Greddy or other
adjustable aftermarket BOV?
A: Well, first off, you should know
better that even Bushur R. still uses
the stock 1G crushed unit on his
fast cars, so I cant even see the reasons
why you would put a $200 BOV on
your car in the first place... other than
(haha, this is the catch) the adjustability
factor. Where crushing the 1G
BOV is a one way route, the adjustable
BOV means that you can adjust and
tinker with it till you're bored
and would still be able to return back to
its initial state. Although I have
to admit that a lot of the ppl. that I
meet with this type of adjustable
BOV doesn't have any idea on how to
properly adjust the BOV though,
so I still think that they are just wasting
their money (ahem, they usually
are also the ones that frequent the rice
shops, thats another reason why
I hate rice shops, most of them lack the
real knowledge behind even a simple
concept like this...but that is another
whole topic).
The Greedy BOV (taken for example
out of the blue) can be opened and have
various spring put/ added to increase
the total spring rate pushing the
valve down. Brad De Grazia (a NW-DSM
member) has had a success
doing this with his adjustable Greedy
by putting another spring in the mix with
the original spring and adjusting
the end nut so the whole combo can hold 20lbs.
As I said, most owners fail to take
their time to understand the basics on how their
new wonderful $200 toy works. Another
"watch-out" for aftermarket BOV users is
boost leaks from the various nipples/
thread connections.
On a friend's Greddy purple top BOV
that I had tested, the BOV failed to hold even
5inHg, you can see the needle on
the pump gauge actually moving towards "0" as the
air leaked in/ out thru the leakage
areas. Brad was saying that the same thing had
happened to his BOV when he bought
it the first time, but he realized the leaks and fix it
by applying teflon tapes on the
thread before screwing on the connections.
No more leaks. The Greedy BOV also
sometimes leaks thru the many small bolts
surrounding the "head". Same applications
of teflon tapes and a bit of
silicon seems to fix the leaks.
The end results is a good multi adjustable
BOV albeit a rather pricey one.
If you are one of the small percentage
guys that really understands the basics of
how things works and glad to pay
the high price for the functionality of an item
(here, it is the adjustability factor),
then my hat is off to you... but if you just have
the Greddy BOV on your car because
it is colorful and etc...I advise you to take
a vacuum pump to it and see if it
even holds any vacuum at all. It might leaks, it
might open at the wrong setting
since it is never been adjusted properly, it might
not do anything at all, and
more than not you've probably spent $200
something on a colorful part to
decorate the engine bay, nothing more,
nothing less.