Bad Idea To Fit Aftermarket Bov ?

[Rikki]

Just been scouring the net and have read that the Toyota standard BOV has a dual function. As well as venting boost pressure back into the induction system when coming off throttle it also works the opposite way and allows filtered air to enter the inlet bypassing the turbo at lower engine revs (before the turbo spools up).

Would this then cause problems when the stock unit is replaced with an aftermarket unit such as the HKS SSQV as an a/m part will not give the dual function and all air being drawn into the inlet will have to be pulled past the turbo.

I "thought" I felt a decrease in acceleration when I replaced my Toyota unit with the HKS but thought it might have either been my imagination or a small air leak with the HKS not being mated to the alloy pipe properly.

Another point would be I was running with my original Toyota unit vented to atmosphere for the last month (for the sound) and if its true the unit also sucks air in then unfiltered air was being pulled into my engine possibly causing damage.

Anyone got any thoughts on this one ?

Many thanks,

Rikki

PS: Its a rev 3 engine I have so that dispells any AFM issues right away.

[DeusMR2]

yeps youre spot on mate, although with a good air filter i doubt the difference would be very noticable. However when you were running with the recirc pipe unplugged the engine was indeed sucking in unfiltered air at idle and cruising.

Personally i cannot confirm this, but i believe it to be true cos i read it from a guy on the US board who knows what hes talkin about, ill fetch a link in a minute.

[msherry21]

John, your right. your HKS will be leaking some air as do alot of A/m bov's, I had a Blitz supersound originally but sold it due to this problem.

but hey, it sure does look bling!!! B)

I might try and get the standard one chromed.....

[DeusMR2]

Ok the link is http://jekylandhyde.madpowaz.com/bov.htm

but it doesnt seem to work at the moment...

meanwhile have a look at this thread from the US board (you'll need a login)

http://www.mr2oc.com/showthread.php?s=&thr...15&pagenumber=1

for those without logins:

page 2:

well, first off, JekylandHyde covered it better than I can:

http://jekylandhyde.madpowaz.com/bov.htm

the short version is: the stock BPV is a two way valve.

Under vacuum, it's open and allowing air to be sucked INTO the intake pipe, going around the turbo entirely. This reduces pumping losses and makes it easier for the engine to cruise without having to suck all the air through a turbine at lower throttle levels.

by venting it to atmosphere you are doing two things:

1.) You are allowing air to enter unfiltered and unmetered, into the engine. The ecu won't know what's going on and the engine will ingest dirt and debris, and it will run lean. This is bad.

2.) You are basically killing whatever throttle response you had. If by some chance your engine doesn't stall, you're going to have a real rough time driving around with the valve snapping open and closed as you change throttle settings. The engine will buck and the car will generally act like it hates you -- which it basically does

page 4:

QUOTE

Originally posted by ftc3

1. Do stock BOV's go bad? If so, what fails? 

Never heard of one.

QUOTE

Originally posted by ftc3

2. Would an aftermarket BOV (Turbo XS) venting into the intake be any different than a stock venting to the intake?

Yes, there are 2 big differences:

1. Aftermarket valves do not have the by-pass feature.

The by-pass feature allows air to go around the turbo and through the BPV (not BOV!) at all times that you are NOT boosted.

This is much better for gas milegage and responsiveness.

2. All but one aftermarket valve uses a spring type design.

Whenever you are adjusting a BOV with a spring, you are selecting an optimum range of function.

If the spring is too loose, it will open under very little pressur (not stay closed) ... not good.

If it is too tight, it may not come open at lwoer boost pressures.

All springs have an amount of psi that they wil give up at ... chances are you may never hit it, but it exists. Enoug pressure and the spring will open the valve.

The OEM design works on differences of air pressure so it functions optimally at all boost levels.

having quoted all of the above and agreeing with it, im still gonna get a BOV at some point lol :P

[Jimlad]

still get one.. good fun.

Saying that about throttle response tho...... I put my foot down in 2nd and it seems to take a second or so before it "kicks" in. Could just be me imagination.

[pizza boy]

Hmm but the 3rd generation 3SGTE was never released in the USA...they had the 2nd gen 3SGTE (detuned to 200bhp)which runs in the ST185 celica and rev1/2 mr2s. He is referring to the AFM setup...unless he has illegally imported a JDM spec 3rd gen SGTE engine.

It fits in with the mention of the lean burn situation which occures with rev1/2 cars when running atmo BOVs.

I checked the pipe and got sum1 to rev the engine at idle...I didnt feel any suction. Besides if this were true about stock BOVs im sure the boys at Dastek would ave mentioned it....they know the 3SGTE inside out. Ill ask him when I get my remap next Friday.

[Mister2]

hmmm.. so i thought bovs could only handle so much.. thats why people replace them.. u know what i mean? like.. if you are running a lot of boost and are producing a large amount of hp.. isnt an aftermarket bov recomended as to not suffer from compressor surge or something like that? hmm.. this is all too confusing..

[Hedgehog Dodger]

Rikki

Your posting this little post everywhere aint ya

[Bibbs]

Have a read of the sticky thread ..

And the HKS bov's (the Super BOV and the SQV) were actually designed like the Denso one .. to hold boost better than the basic Bailey type ..

[ZeroBlade]

Ill ask him when I get my remap next Friday.

how come ur gettin it remapped, r there problems with the unichip?

-Z

[DeusMR2]

hmmm.. so i thought bovs could only handle so much.. thats why people replace them.. u know what i mean? like.. if you are running a lot of boost and are producing a large amount of hp.. isnt an aftermarket bov recomended as to not suffer from compressor surge or something like that? hmm.. this is all too confusing..

in our cars the stock BPV can handle more boost than most aftermarket BOVS because it uses intake pressure to close the valve, so if you increase the boost, the closing pressure increases with it which means no leaks.

most aftermarket BOV's use a simple spring to close the valve which can leak at high enough boost, (e.g. the Blitz BOV)

The best aftermarket BOV is the hks ssqv since it operates in the same way as the stock one (except it doesnt recirculate unless you want it to)

however the best BOV/BPV altogether is the stock one, unless youre creating insane amounts of boost like 30psi or somethin!

[Jimlad]

Ill ask him when I get my remap next Friday.

how come ur gettin it remapped, r there problems with the unichip?

-Z

his downpipe was cracked when he got the chip. He got a new downpipe, so getting it re-mapped.

[pizza boy]

Apparently the best atmo bov to run is the Sard r2d2 good for 600bhp...and ye also got 100db paatish! And they make one specifically for the 3SGTE not some universal cack. Id still stick with my stock un tho. :)

[KiwiMR2]

Bah...a bov is a bov is a bov.....there either crap or good I reakon. Can't really go wrong with the main brands...GFB, TurboXS, Greddy, HKS, Turbosmart etc etc, a handful of them make MR2 specific adaptors which makes it easier to fit but not crucial as it's a peice if ***** to get one made. Some make typical pssshhh sounds, some make whistle sounds as well, some are sound adjustable, some can be feed back into the intake like the oem and one of the above brandes does one that can do both.

To much choice ;)

Cheers

KiwiMR2

[KiwiMR2]

On Gen II & Gen I engines the air passes through the AFM before getting to the turbo, so if you vent some of it back to atmo then it's already been metered, and, since there is now less air than the ECU thinks there is, it runs rich. Any BOV vented to atmo will do this. Where the stock BOV differs from aftermarket is that it also functions as a bypass valve, bypassing the turbo off boost, if the stock BOV is vented the incoming air that flows (when it's functioning as a bypass valve) is not metered and the engine will run lean. However, as this is only off boost, and reduces as the manifold pressure increases (AFAIK it will not IMO be sufficient to melt pistons)

It runs rough because there is only a limited range of AFR's where combustion is possible, go too lean and no combustion event takes place (same if you go too rich). When it doesn't ignite because it's too lean you don't have a high cylinder temp problem, but you can cause backfires and damage to the cat as the unburnt mixture accumulates in the exhaust, when there is sufficient fuel it is ignited by the residual heat in the exhaust system. Simple answer is don't vent the Stock BOV, if you want the pssst noise by and aftermarket one.

There is something else wrong if engines are melting pistons as any leaks under boost will cause the engine to run rich not lean. Gen II's have a habit of melting pistons in sustained high speed runs due to an inadequate fuel system which runs the injectors past their max duty cycle, do this for any length of time and the injector will malfunction, causing the engine to run lean just when you don't want it to, result hole in the piston(s).

Cheers

KiwiMR2

[Jimlad]

for rev1 and rev2's , get a vent to atmo BOV, then get a Unichip fitted. They can correct fueling issues.

[LORD_ED]

Bah...a bov is a bov is a bov.....there either crap or good I reakon. Can't really go wrong with the main brands...GFB, TurboXS, Greddy, HKS, Turbosmart etc etc,

GFB in my opinion are some of the best bovs about i had one on the 200 and the build quality is second to none sound is gtreat and your not paying for the name as much as hks for example. but anyway

[ZeroBlade]

his downpipe was cracked when he got the chip. He got a new downpipe, so getting it re-mapped.

ah yeh. forgot about that jim,

cheers fella

-Z