BOV necessary? Wastegate size guides?

[barryogen]

I'm off work sick, got bored, decided to read... my post is effected by drugs, so my thought patterns are somewhat erracit.

Now...

Firstly, BOV...

Are they really necessary?
Do stock turbo cars usually come with them?(I know caldina and MR2 does, but others?)

I understand they release pressure from the intake to keep the turbo from slowing/stalling/surging when the throttle plate is closed, but with todays ballbearing and otherwise fast spooling turbos, is it really that noticible on the daily commute? or just when fanging it on a track?

Is it less of an issue if pressures/boost are low?

I guess having a BOV would put less pressure on the shaft inside the turbo too?


Secondly, wastegates.
I gather that choosing one of a suitible size is done by figuring out how much it will need to flow, to make sure that the turbo doesn't receive more exhaust than it needs to maintain whatever boost level you are trying to run.

So using that theory, bigger is better, as, assuming design is consistant barring size, a bigger one should have the ability to flow more.

Am I over simplifying?

[escortman]

most turbo cars comes with bov or recirc valve form factory
i drove my car for one day with out a bov, only driving to work and back no thrashing it and i got pissed off with the constant turkey call

with external wastegates it depends on engine size turbo etc etc the bigger the longer it can take to open

[evil_si]

having no bov or a malfunctioning bov can kill the turbo,

when the throttle body snaps shut, the boost builds up behind it and surge back track thru the turbo,
this can stall outthe compressor wheel and while the exhaust side is still trying to turn it undoes the nut, once this happens theres no going back


ive had this happen with mitsi turbos in the past,

[barryogen]

Thanks guys, thats the BOV side of it answered... needed to prolong turbo life, to stay away from surging.

Too big of a turbo seems to put you in constant surge(left of island) too... right?
like this(ignore numbers, I was just tinkering with it)
http://www.squirrelpf.com/turbocalc/graph.php?version=4&pr0=1&pr1=1.07&pr2=1.77&pr3=2.47&pr4=2.47&pr5=2.47&pr6=2.47&pr7=2.47&airflow0=2.2&airflow1=7.3&airflow2=13.6&airflow3=21.1&airflow4=25.1&airflow5=27.5&airflow6=37.2&airflow7=45.3&product_id=109

escourtman:
Say it were a high compression(~11:1), 2L, running low boost(6-8lb).. much like say, and altezza like mine.

[escortman]

38mm would be fine then i think, i only went 42 or 40mm (cant remember now) because it cost 70 buks held 15psi fine

[MR2BOY23]

I heard they are making these illegal. Is this true?

[escortman]

I heard they are making these illegal. Is this true?

if ur talking about bovs? theyr talking about making them either have to plumb like factory recirc or be filtered

something along those lines

[barryogen]

not a fan of vent to atmo BOV... drove me nuts in ~10mins on a mates car, don't understand why it is "cool", maybe I'm getting old

[escortman]

yeh thats getting old haha na i used to like my hks copy 1 when i 1st got it not every 2nd car had it but now as common as a chosen few sticker

[IH8TEC]

my factory gtr ones i have on my car vent to atmo, but are actually pretty quiet, probably the quietest ones i've ever heard to be honest.

[holden_fan2005]

The old maxima I had was factory with no bov. All it had was a alloy tube going from the turbo directly into the t/b. It didn't seem to have any problems.

[Dell'Orto]

Lots of 80's turbo cars had no BOV/recirc valve. Look at the reputation 80's turbo cars had for reliability

[barryogen]

So, BOV
Not strictly necessary, but in the interestes of reliability, a bloody good idea.

And Wastegate... unless I go HP/boost crazy, 38mm should be fine.

Thanks.

[xnickx]

Atmo venting BOVs will be illegal as of June this year but if its plumbing back in its ok.

Similar deal with external gates, atmo = no.

Lag was really bad in my car as with the turbo kits, there isnt a factory BOV in the system, changing gears at full revs ment the car would bog while it took just that split second to respool the compressor wheel again and to get air flow going in the right direction.

The HKS SSQV sorted that out well and now flat throttle shifts are a blessing

[rollaholic]

wtf is wrong with atmo vented bovs

plenty of wanky ones designed to make the noise louder but thats a personal choice, whats the basis for making it illegal? its just hot air

[barryogen]

something about once passed the air filter, air should either be passed through the engine and muffled, or filtered before it exits.

I'm pretty sure it is around emmisions, havent looked at it that closely, happy it is happening.

[Heylin]

wtf is wrong with atmo vented bovs

Well for a start if your car has a flap style Air Flow Meter (AFM) then that air has been measured , venting to atmos make the car run rich for a second.

Its well known on MR2 if replacing the factory BOV to atomos venting then the car runs runs a bit crappier.

[rollaholic]

fine fine, so the car fails under emission laws. but thats due to muppet owners, an outright ban on atmo venting is just another small corner gradually being sliced off our modification freedom.

[Dell'Orto]

They're not being banned, they just cant be excessively loud.

[Lloyd]

Similar deal with external gates, atmo = no.

Like it has been for years and years?

BOVs aren't a huge issue really, not as annoying as exhaust noise. Depends who you ask I guess