BOV explained!

[Littlestan]

Hello all,

As some of you know, I just recently bought a almost new and almost

completely stock 1990 TT Supra. The engine (a 1G-GTEU) has been

untouched, so I am eager to start adding parts and have some fun!

However, one of the most confusing things I have come across is the

question of adding a Blow Off Valve (BOV) or modding the Bypass Valve (BPV

or just BV). Several sources/sites/opinions state that adding a BOV can and

most likely will cause a stumble in between shifts since a BOV vents air

directly to the atmosphere resulting in an overly rich air/fuel mixture. I've

literally searched for 30+ hours online for an answer to this problem.

Well, here it is;

The BOV has to be mounted before the MAF. This is because the BOV
vents to the atmosphere. If it was mounted after the MAF, the BOV would
release air that has already been metered. If it vents metered air, then it will
throw off the fuel and will make the A/F mixture rich, since the air that should
be there isn’t there. This is called a blow through sytem.

Phew!! Easy to understand now, hey?

This one's for all the n00bs... ,

-=Littlestan=-

P.S. If you have a AFM (Air Flow Meter) rather than a MAF, then you will probably have to do a AFM ---> MAF conversion in order to mount it after the intercooler. Oi, striving for perfection is a horrible curse...

[joel w]

ya but when you bolt on a k&n filter directly onto the MAF meter there is no way to plumb the bov air into the filter since the airbox is removed? mine works fine this way, no stumbles...

[Littlestan]

Originally Posted by joel williams

ya but when you bolt on a k&n filter directly onto the MAF meter there is no way to plumb the bov air into the filter since the airbox is removed? mine works fine this way, no stumbles...

Here's a picture of what I mean;



(The 1 and 2 are switched, sorry about that.)

As you can see, air comes through the air filter, is compressed by the

turbo, flows past the BOV, into the intercooler, through the MAF, and finally

into the throttle body. On my Supra, I believe this will involve taking my MAF

off, and installing a aftermarket one (that can measure more air without

"pegging") AFTER the intercooler.

Just because it doesn't stumble, doesn't mean it's not running

excessively rich in between shifts. Which, I know, isn't particularily bad for

the engine, but can foul/plug things up. Plugs, ports, etc.

It's all preference, but I would like to keep things running the way they're

meant to be running.

Cheers,

-=Littlestan=-

[joel w]

Hmmm see... that is different than my set up... air goes through filter, then afm then the turbo and out to intercooler and back up to BOV and then into the throttle body. so on your diagram , #5 goes between #1 and #2 but i guess i could move the afm anywhere huh? but still the hks ssqv bov that i run has no way to attatch a large tube back to the intake? so no point for me i guess anyways. i like the noise of the bov and if it runs rich. then thats better then lean.

Is a AFM(air flow meter) the same as a MAF(mass air flow) sensor?? Then there is the MAP sensor like the newer supras use and dont use a AFM or MAF??

[GreenChevelleSS]

We did a supercharger on a 89 Camaro MAF and first off we had the MAf before the supercharger and the thing never ran right and always idled funny. Well we decided to try the other way, mounting the MAF after the supercharger and we have never had a problem with it and the thing idles great and all. Also one thing we noticed was the closer the Maf is to the intake the better since there can be tiny air leaks at joints that can also throw it off. This is a non intercooled centrifical supercharger.

[joel w]

ya my afm is at the beginning before turbo but it idles soo smooth and runs awsome. all my ic piping is hand made by me and pressure tested to 50 psi and no leaks and i use hi temp silicon hose and all t-bolt clamps so no leaks here at all.

[joel w]

ok,to clerify. for my part..i did some reasearch and...

an AFM(air FUEL meter) has the flapper door inside with the gears, and i have the MAF(mass air flow )meter with the wire resistor that will ONLY work before the turbo? ok, so, if this is true?, then the stock BOV vented after the MAF sensor into the accorian hose before the turbo from the factory?..correct?

[suprra_girl]

yep... it vents back to the intake

most ppl just tighten up the ssq so that it doesn't cause excessive richness on shifts....

our afm is a karman vortex afm

[Littlestan]

I'va also found that some people buy an aftermarket BOV, then hook it up

with a "recirculation" kit. This usually only involves one hose and some clamps,

effectively making the BOV operate like a BV while still retaining some of

"whoooosh" we all love. Using a metal pipe rather than a hose makes this

effect louder as the rubber absorbs some of the sound.

Anyways, I'll post some sound bytes of my Greddy Type S hooked up

with/without recirculation kit when I get it. Might be awhile...

Cheers!,

-=Littlestan=-

[SupraMan1784]

i have a recirculation kit...it doesnt really do much...just reroutes unused boost back into teh intake...relieves back pressure too...its a good thing to have