someone was trying to explain the finer points of BOV location me, and I was unsure of his opinion. he said that it was better to have the BOV before the MAF not after and to have it partially open at idle. Is that right?

 

why do you wan't to move it..? stock BOV?

 

i dont want to move it at all. im asking for a friend with a turbo silverado. i just want to know because im curious. whenever the conversation hits v8, i have to divide by 2 to understand.

 

none of the 73 people that viewed this thread know the answer. should i hit up the GM forums?

 

yes you want the bov to recirculate after the maf sensor...now you might need a maf adapter plus some other supporting electronics to make it work since it didnt come factory that way... the maf sensor monitors incoming air and uses that voltage as one way for the factory ecu to determine proper a/f ratio. if your recirculated it before the maf sensor the drivability will be horribly affected due to every pshhh of the bov will result in unstable velocity of air going over the maf, making your truck drive like a newb driver with a stick shift. so case in point tell your "buddy with the turbod silverado" make sure he buys a complete bolton setup for it, or hell be spendin a lot of time n money fu*kin with those issues.
good luck

 

Thanks for replying. We put the bov after the intercooler before the throttle body. It isn't a recirc valve though. That's why I'm at a loss because all my cars have used factory recirc setups.

 

well the only thing is if you dont recirc it u can run into stalling issues driveability issues....some maf sensors are sensitive some are not...

 

The point of recirculating the air (and having it come back in after the MAF) is to have an accurate measure of how much air is going into the engine. If you vent to atmosphere (or recirculate before the MAF for reasons I can't imagine), then less air goes into the engine than went through the MAF and you run rich.

And, just for Ss&Gs, may I suggest - nah, beg - that people stop calling it a blow-off valve (BOV)? A blow-off valve, as the name suggests, is opened by excessive pressure in the intake. BOVs are mostly used as back-up protection devices and/or ways for sanctioning bodies to limit boost. Our cars have a combination compressor bypass value and diverter valve, depending on when we are talking about. It's a compressor bypass valve at idle, as it allows air to enter the engine without going through the turbo. Get it? Compressor *bypass* valve. It's a diverter valve when it is pulled open when you lift to shift. In this case, it diverts some pressurized air away from the now-closed throttle body, so the turbo can keep spinning during the shift. In no case is it intended to be a blow-off valve. That was the whole problem with the old plastic valve (on older Evos and 2G DSMs): it acted as a blow-off valve by being a piece of crap.

 

It's on a silverado 5.3 liter. It is a blow off valve. I understand how the system flows air, and I understand how a maf works. I'm asking a turbo question on the evo forum because this is the only forum I'm remotely active on.

Now the question restated. On a car not setup up for a recirc valve or diverter valve for those who prefer that term. Is it better to have it before the maf and why?

 

Before the MAF is no different from just venting to atmosphere and has the distinct disadvantage of sending heated air back into the system. If you are set up for speed/density and don't have to recirculate, then just vent to atmosphere and be done with that particular batch of heated air.

 

This is validation to a potential argument I wasn't sure about. I know with speed density the location isnt as important, but I wasn't sure about monitored air being vented. The valve is located after the IC before the throttle body. This guy was saying that the valve should be move before the maf and a power gain would result. I haven't seen that setup before and I didn't want to eat crow.

It is not a diverter or recirc valve. It is a turbo xs rfl on a 5.3l truck. Im trying to understand the theory of bov location.
1) does it matter if the bov is located before or after the maf
2)does it matter if the bov is located before or after the IC
3)does it matter if the valve is open during idle if located before the maf

 

Well, some people do vent to atmosphere on their MAF cars. I've seen plenty of DSMs with those awful, squealing valves by TurboXS etc. They just go rich on shifts and forget about it. Maybe they like shooting flames and such, and don't mind rinsing their piston walls with fuel. Or maybe they were using DSMLink to program around it. I don't know. I simply stayed with the design of the air/fuel system as it was.

 

The design originally didn't have a turbo. In those cases a bov is as effective as a diverter. My issue was the fact I think this dude is crazy saying you should put the bov before the maf and I was hoping someone that knows about it would post.


Apparently none of the viewers here have boosted n/a cars before. All my experience is with cars that use recirc valves so I'm at a loss.

 

should it matter if the car was NA? doesn't the concept of recirculating air apply the same on any boosted vehicle whether it came boosted from factory or not?

 

Yes, the same concept applies, regardless of what the car was originally. Recirculating to a point before the air was measured is just silly since it's the same as venting to atmosphere with the one difference that you are now ingesting hot air.

Well, maybe there's another possibility, which ought to be mentioned for completeness. Some people have tried to set up their cars with the MAF in what's called the "blow-through" layout. They move the MAF from before to after the turbo. In this case, the air isn't metered until right before the throttle body, so recirculating in the usual way (i.e., from a point after the turbo and intercooler to a point before the turbo) doesn't cause you to measure the same air twice even though you are recirculating to a point that is before the MAF. This set up also allows you vent to atmosphere without going rich when the valve opens. The one problem is that most MAFs that were intended to be "sucked through" become wildly inaccurate when hot and pressurized air is sent through them, but I know that this has been done successfully a few times in the DSM world.

To be clear: the key to keeping things working is to measure the amount of air going into the engine accurately. That means you should avoid dumping air to any point outside of the system after it have been measured (i.e., don't vent to atmosphere) and you should avoid measuring the same air more than once (i.e., don't have the air go through the MAF and then recirculate back to before the MAF). As long as your set up measures the air once and only once, and doesn't lose any along the way, you'll be fine.