Skylines Downunder NZ Car Club

General Automotive => Powered by Skyline => Topic started by: RB30DET-R30 on May 21, 2005, 08:48:07 PM

Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: RB30DET-R30 on May 21, 2005, 08:48:07 PM
I brought a factory A31 turbo cefiro a couple of months ago and havint done much to it except mince a exhaust wheel on the turbo. Today when puting a new one on I looked at the J pipe that goes to the inlet manifold and thought what the hell  where is the blowoff valve as it does not have one like a normal R32 RB20DET. Could anyone tell me what the story is with that?
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: Black Apple on May 22, 2005, 06:33:29 AM
it's not there...i found that out yesterday when i was changing my oil...just brought it home the other day...i live in canada btw

anyways you need to get a BOV
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: BROCKZILA on May 22, 2005, 08:35:03 AM
A31 turbos never came with a bov from factory. You can swap over the intake pipe to a r32 gtst one.
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: RB30DET-R30 on May 22, 2005, 10:45:35 AM
Ha thats buzy well I might have to do that
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: crankin on September 21, 2005, 05:27:22 PM
Would that have anything to do with the fact that most of them are automatic, so the throttle stays open the whole time , so no point to a bov
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: dr-psi on September 25, 2005, 01:52:21 PM
Quote from: crankin
Would that have anything to do with the fact that most of them are automatic, so the throttle stays open the whole time , so no point to a bov

 im not to sure about that, automatic r32 gts-ts still have a bov
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: mcknick on October 21, 2005, 04:16:32 PM
does a bov increase performance much?i can hear my ceffy spitting the excess boost out the pod filter i think i can hear it when i ease of the throttle
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: gtsr on October 21, 2005, 05:30:52 PM
From what I understand -

Without a BOV, when the butterfly shuts on the throttlebody,
as you back of the throttle, to change gear, the pressure
goes back towards the turbo (backpressure) and slows the
turbo down (RPM's). So when you apply throttle after changing
gear, the butterfly opens and the turbo is revving at a slower
rpm but has to get back up to speed and so there is a slower
response from the engine.

With a BOV, when the butterfly shuts on the throttlebody,
as you back of the throttle, to change gear, the pressure
goes back towards the turbo, but this time there is a valve
that opens and diverts the pressure, by a pipe that is
connected to the BOV and goes to the intake pipe, infront
of the turbo. Basically the pressure is going back through
the turbo, so the turbo is kept spinning at a higher rpm.
So when you apply throttle after changing gear, the
butterfly opens and the turbo is at the right revs
and there is instant response from the engine.

Basically the BOV increases the response time of
the engine/turbo after gearchanges.

Also I think without a BOV, it's not good for the bearings
(ballbearing), as it shortens their life, but it seems
sleeve bearings can take the shock.

I think the Cefiro motor has a sleeve bearing turbo
and is the reason why it doesn't need a BOV.

Also I read, with a dualballbearing core, what IHI turbo's
have and I noticed Garrett have adopted (R34 Ztune,
JTCC, old style turbocharged F1 cars, Apexi use IHI
turbo's), you can run the turbo without a BOV.

I guess auto's need them, because you have to back
of the throttle, when slowing down and the ignition timing
is retarded during gearchanges (similar to releasing the
throttle on a manual car), is another reason why an auto
needs a BOV.

Performance wise, it's like a dude in one car doing a slow
gearchange, compared to another dude in car, that is beside
him, doing a quick gearchange. Which car is going to be quicker
to 100km/h, on a drag strip??
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: mcknick on October 21, 2005, 05:41:00 PM
whoa awesome reply thanks heaps dude, i learnt alot 2day :-) haha cheers 4 that, so itd b in my benefit to source a j pipe off a gtst with a bov on it??
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: gtsr on October 21, 2005, 06:53:10 PM
You're welcome. :)

Yeah, a tad long. :D

Yep, it's worth it, for turbo longevity.

Also I think the ECU is tuned (fuel map), to accommodate for the
extra air being recirculated by the BOV.

I guess it might run a tad leaner than normal, on your car.

You'll need the recirculation pipe (hard pipe, made of I think aluminium,
painted black), plus the intake pipe infront of the turbo, which has
the hole for the recirc pipe + a small intake hoseclamp to clamp
the recircpipe to the intake pipe, infront of the turbo.

There's also the rubber joiner pipe from the side of the BOV to the
recirculation pipe and there are 2 small intake hose clamps on each
end of the that rubber joiner pipe.

Also there's what looks like brass piping on the side of the J pipe, 2
little joiner hoses on each end. One of the little hoses is for the BOV
to the hard brass piping and one for the plenum (next to the
throttlebody), to the hard brass piping. I guess the hose that
links to the top of the BOV, helps in keeping the BOV closed,
by providing pressure behind the valve and the pressure is
provided by the plenum.

Also I think 2 pipes of the brass piping, goes to the round looking
emissions canister and the other end, is linked to the motor and
fuel tank. From what I understand, the canister filters the fumes,
from the fuel tank and motor. I think the canister is located infront
of where the airbox is.

Be careful, remove the brass piping from the J pipe (screws onto the
side of the J pipe), leave it connected to the canister, as the fumes
can enter the engine bay and make you very giddy.
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: mcknick on October 24, 2005, 07:48:59 PM
o awesome thanks heaps man :-D as soon as i can get hold of of the j-pipe will attempt it
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: gtsr on October 24, 2005, 09:06:03 PM
You're welcome. :)
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: [RB2NVY on October 25, 2005, 04:29:34 PM
I also think that the RB20DETs in Cefiros/Laurels are slightly detuned, say 10Kw less than their skyline counterparts, althought i may be wrong, if so someone please enlighten me.

What gtstr is talking about when he is referring to compressed air flowing backwards through the intake, is called compressor surge, which is not healthy on any sort of bearings.

If venting your BOV to atmosphere you may notice that your car won't idle as smoothley as usual this is due to the fact that the valve is open while the engine isn't under boost, hence making it a manifold leak, so you may also run slightly leaner aswell. While if your BOV is plumbed back into you intake, you have already compressed air ready to head into the cylinders as opposed to having to wait for the turbo to spool up and compress th air. So really not only does a BOV keep boost up during gear changes etc but it also increased the life of your turbo internals aswell, which in anyones view can't be a bad thing can it:)

Thats how i understand it anyways, damn being off wortk and have nothing todo except browse the forums and write heaps haha :laugh:

Peace
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: mcknick on October 26, 2005, 05:54:02 PM
hmmm then y the hell would nissan bring out the A31's w/o em if the only do good ??
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: [RB2NVY on October 26, 2005, 11:04:07 PM
No idea aye man, could well be because they weren't designed for the same sort of market as the skyline, maybe it was a noise thing although i doub tthey would make that much differe3nce being plumb back anyway
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: mcknick on October 27, 2005, 11:34:47 AM
rite e o... well n e 1 gta spare j pipe wit a bov on it :D
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: lanzy61 on February 10, 2006, 10:56:02 PM
On the a31 turbs intake manifold they only have one vaccume outlet where skylines have two so you have to run a t section one to your B.O.V and one to your bosst gauge if you have one.
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: slideways_riot on March 23, 2006, 08:17:18 PM
yep all factory turbo laurels and ceffys are 10kw less power than the r32gtst
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: Gerbal on March 26, 2006, 04:06:42 PM
Interesting article...ive learnt something new.  Always wondered what that phsssssssss noise was when I quickly buttoned off the gas in the Cefy. Cant be to good for the turbo?  But than it makes you wonder why they didn't install a BOV in the first place if it was going to be that damaging to the turbo?
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: mcknick on March 28, 2006, 08:27:04 PM
well exactly it cant be THATTT bad i guess if nissan figured it wouldnt root the turbo and i mean lets be honest they arnt known for being robust turbos
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: RB30DET-R30 on April 24, 2006, 04:15:16 PM
So are the auto skylines due to a smaller sized turbo, compare the auto turbo's wheels compared to a manuals ones! and late 1992 and 93 GTS-T manuals have an even bigger turbo again not by much though and im not fully sure but I think thats when they changed to ball bearing aswel. Its only the ceramic wheel nissan garretts that are not robust.
Title: Factory turbo A31 cefiro doesint have a BOV! Why? Where is it?
Post by: Black Apple on May 29, 2006, 12:29:42 PM
come again?

a quick note on the difference in ecu's between gtst's and cef's/laurels.  gtst's use a 256k chip wheras the cef/laurel use a 128k chip

i cant belive this topic is still going.