BOV which is best?

[Draven]

This is what stu was after:

http://www.performanceforums.com/for...php?t=67199575

[rob1]

I loved this quote:
"Ironically, the noise that a compressor makes during reversion is far more obnoxious than even the largest superspacegoatmegasonicarseflow can produce."

Good link Draven

EDIT: also- "supermegasoundpowerflow"
"superpowermegawhoosh2000's"
"Supermeggergay2000KWsonic"

[oldcorollas]

This is what stu was after:

http://www.performanceforums.com/for...php?t=67199575

cheers thanks, the site periodically goes down for some reason (at my end)... but that link worked... weird...

[Draven]

it was down yesterday for me, working today. who knows?
apparnetly a HDD on the server died

[JustCallMeOrlando]

I loved this quote:
"Ironically, the noise that a compressor makes during reversion is far more obnoxious than even the largest superspacegoatmegasonicarseflow can produce."

This is so true, get off the loud pedal on boost and everybody knows about it, and not a BOV to be seen.

[rob1]

Agreed. I am building a turbo motor for the fist time atm, and if I CAN justify getting a bov I will get the cheap bosch one mentioned in that thread, and plumb it back.
I would like to see a sort of "two sided debate" about bovs. Get two relevently qualified people to put their argument forwared about the necessity or not of having one. Then you can make your mind up for yourself. Having every man and his dog give their opinion is pointless in my view.
Do two people want to put there hand up?

[rob1]

Let's decide on two people, one for each side, then let each have their say, then everyone can make there own decision. I would love to see something like this. That's what the tech forum is about.

[kemicalx]

Hmmm, I've read some conflicting reports on the bosch blow off valves..

Apparently the model to get is the Bosch # 0 280 142 108 this one has a tighter spring, shorter valve travel and a brass dome on the valve face that might help flow.

bypass valve comparison here

However I think the info on the site below is stating that all the older weaker valves have been superceded with the newer heavy duty version

Conflicting info here

Presuming they can handle over 15psi without leaking I'll definatly be getting one

[45aken]

ok i'll give the main positive point on running a BOV, but im unsure if you want these points to be vs. no BOV, or an aftermarket vs 'stock' BOV. im not after a mind war, just saying what i know. opinions will not be flamed either

running a bov vs not

1) increases throttle response between gearshifts very noticeably.

this is due to the 'X'psi in your Intercooler piping not having anywhere to go but back out through the turbine and out your filter (due to the throttle body blocking off the inlet). this is where you get the flutter noise from (the break up of air as it passes out the turbine blades). the turbine wheel will either stop spinning, spin backwards, or (lower <10psi boost) alternate between spinnin and spinning backwards. therefore when you get back on the throttle the turbine has to spool back up to reach full boost again.

now if in this situation you run a bov, the air passes out the valve, which keeps the turbine spinning at 'full' speed. when you get back on the throttle, the boost will therefore ramp up alot quicker as the turbine wheels doesn't have to spool up.

this leads on to point 2,

2) it is hard to say that running a bov will increase the life of the turbo, but it is a fact that not running one will decrease the life of the turbo.

personally i cannot see any performance gain between an atmospherice (vent to atmosphere) BOV and a pumb back (air goes back into the inlet system). the main idea of the bov is to keep the turbine spinning, and the only problem with running an atmo bov, is sometimes it will create a miss/backfire when it opens (due to an extremely rich mixture). also some cars do not like running big atmo bov's, it will cause them to idle erratically.

hope this helps.

[monkeymajik]

I have a Sard valve on my setup, 4agte and AFM. It will puff a little on a HARD gear change with lots of RPM, but otherwise is fine. Not stupid loud either, I'm very happy with it.

[45aken]

one of the better designs i have seen is the apexi one. it uses the pressure created by the turbo to hold down the piston, and a small spring to give it that extra bit of force (and to hold it down when there is no boost).

this is good, because unlike using just a spring, the force holding the piston down rises as the boost rises.

[Norbie]

Sigh. All you've done is regurgitate all the BOV myths that everyone else has been hearing for years, with no facts toback them up.

the turbine wheel will either stop spinning, spin backwards, or (lower <10psi boost) alternate between spinnin and spinning backwards. therefore when you get back on the throttle the turbine has to spool back up to reach full boost again.

Rubbish. A turbo can be spinning at upwards of 100,000 rpm at full song. Do you really think it's possible for something spinning that fast to come to a complete stop, reverse its direction, stop again, then accelerate back to 100,000 rpm - all in the space of about one second? The forces involved would probably rip a hole in the fabric of space and time, and you'd find yourself surrounded by dinosaurs or something.

2) it is hard to say that running a bov will increase the life of the turbo, but it is a fact that not running one will decrease the life of the turbo.

How is it a fact? You haven't presented any solid evidence, or even any anecdotal evidence! How do you explain all the 15-20 year old 1G-GTE's getting around without a BOV?

This thread needs Mythbusters on the case, there are far too many myths being propagated.

[45aken]

alrighty then mate instead of flaming me, why dont you come up with something to add?

if the air doesn't some out of the turbine, then where does it come from? how does it get broken up?

and yes i do think it is entirely possible, as the turbine is very lightweight with very very little rolling resistance, and is very efficient in turning the incoming air into rotational movement. even if it doesn't fully stop, it still slows down a great deal.

mate i dont have the resources or the time to go and get 2 cars, one with a bov and one without and test them for 20 years. if you truly believe that it doesn't cause any difference, then why did car companies spend lots of $$ researching and engineering these products?

[kemicalx]

I'm with 45aken on this one, although i don't how damaging the back pressure caused by closed throttle is, i would think the fact that most turbo cars released today (and for some time now) come with a standard bypass valve setup, would be testimate to there worthiness.

[Norbie]

alrighty then mate instead of flaming me, why dont you come up with something to add?

That was hardly a flame. Don't be a skirt.

if the air doesn't some out of the turbine, then where does it come from? how does it get broken up?

Who said the air didn't come out of the turbine? (Actually it's an impellor, the turbine is on the exhaust side).

even if it doesn't fully stop, it still slows down a great deal.

Does it? Where's your evidence? This is what I'm getting at here - you're presenting assumptions and preconceptions as fact, which only confuses the issue further.

Turbos use a centrifugal compressor, which can stall quite easily (ie the air stops flowing) even while the blades are spinning at very high speed. A good example of this is a garden-variety vacuum cleaner, which uses an impellor not too dissimilar to a turbo compressor - obviously it spins a lot slower but it works on the same principle. You can stall the airflow quite easily by blocking the vacuum nozzle completely. Airflow stops altogether, but you can clearly hear the motor spinning faster. This is because the impellor has stalled and is no longer doing any work.

mate i dont have the resources or the time to go and get 2 cars, one with a bov and one without and test them for 20 years.

There's no need, as we already have 20yo examples to look at (as noted above). 1G-GTE turbos tend to be quite reliable when running stock boost, and not a BOV in sight! Ditto for other older BOV-less turbo engines (eg 3T-GTE and M-TEU).

if you truly believe that it doesn't cause any difference, then why did car companies spend lots of $$ researching and engineering these products?

The reason BOV's are fitted to modern turbo engines has already been covered, but to re-iterate: noise suppression, and possibly emissions.