BOVs on MAF sensored cars

[Mophead]

First off i would like to apologize if i posted wrong i didn't see any rules posted. That said I was watching a videos on youtube of WRX STIs and i read a comment that went like this. "you cant put Blow off valves on Mass Air Flow sensored cars because they will run rich and stall when you shift". Now I am taking the automotive course at WTC and we have'nt got into forced induction yet but this does'nt make sense to me. Now I know these comments are coming from people who may or may not actually know something but I was wondering if anyone here can enlighten me on how legit this statement is. Now from what I understand the car has a throttle position sensor (TPS) which will tell the ECU that the Throttle is darn near closed which is what the BOV is for, to relieve the throttle on hard acceleration so to speak, and cut back on fuel. If anyone can clear this up that would awesome....especially if I am correct

[bhazard]

First off to make it clear, the point of the BOV is to relieve the pressure created between the turbo and throttle when the throttle is closed under boost (ie shifting). If the pressure is not relieved, it travels back to the turbo and pretty much stops it. When the pressure is relieved, the turbo stays spooled up for the next gear, and boost comes on quicker. It also increases the longevity of the turbo.

I had a BOV on my tbird for a while. The bird uses a vane meter a lot like festivas. It essentially does the same thing as a maf. Sometimes it did run a bit rich between shifts, but if you get a good bov with an adjustment you shouldnt have too much problems. Its just something that sorta happens but is easy to deal with. Never had any stalling problems or anything of the sort.

[FestYboy]

well there are 2 ways of aproaching this (Jim back me up on this or correct me please).

1: (prefered) place the MAF Before the turbo and recycle the BOV output back in to the turbo inlet tubing AFTER the MAF. this ensures that all the measured air is accounted for and used.

2: place the MAF right before the TB and the BOV close to the turbine outlet tube. this is supposed to account for only the air that enters the intake plenum.

i do recomend using a MAP with both set-ups (more so with option #2)

i do know for sure that the statement above is NOT true because a co-worker has just finished building a DSM with a MAF only set-up with a BOV before the MAF. it does not stall or bog on up shifts.

[piratewilly]

actually if i may toot in here, all turbo cars come with some sort of system known as a compressor bypass valve (CBV). It is a vacuum-actuated valve designed to release pressure in the intake system of a turbocharged or centrifugally supercharged car when the throttle is lifted or closed. This air pressure is re-circulated back into the non-pressurized end of the intake (before the turbo) but after the mass airflow sensor. NOW a blow of valve is a peice, or part, that you can put on, does basically the same thing, but releases the air to the atmosphere. This creates a very distinctive sound desired by many who own turbocharged sports cars. so really it doesn't matter wither or not you have a bov on a turbo car or not, and in some causes can be a little benifitual to not have one if it recirculates because it is designed to help keep the turbo spooled up. To answer ur question, if it is a recirculating type of car, it recirculates AFTER the MAF, so really it wouldn't matter if u have a bov or not as far as if the car is going to run rich

[Kraig]

Not true. My Ford 2.3 turbo cars do not have a "CBV". There is no stalling or surging on throttle lift as the intercooler piping and cooler volume are very minimal. BOVs are more beneficial on cars with a large piping/intercooler volume as there is a larger volume of compressed air to deal with. I think the longevity issue is BS (at least on my Fords) as I rebuilt the turbo on my Turbo Coupe at 157K and all the internal components mic's within acceptable specs and the car has no BOV CBV etc. Oh yeah, the turbo is still going at 281K..... and if you power shift the turbo never stops spooling anyway

[Hot_Wheels]

im leaveing this topic alone my advice is with a vaf or maf car i would recomend a by-pass valve and if your running a stand alone and runnign a map sensor you can run a bov. bypass will help with better throttle resonps on lower boost

[bhazard]

Youre right kraig, no 2.3 turbo ever came stock with a bov/bpv. And yea, plenty of stock turbos go on for hundreds of thousands of miles. It DOES make sense though that not having a relief in the system to keep the turbo from being stopped would decrease the life of the turbo though. Apparently the stock turbos are just tough though.

When I had a bov on my car, I did notice boost came on much smoother and quicker after shifts. Almost accelerated like an auto.

[Mophead]

Thanks for clearing that up.

[Kraig]

I've never had one (BOV) so I guess I don't know what I'm missing...I did make two at work to try out though...