BOV with MAF on Subaru
 

I have a volvo BOV on my legacy with a mass air flow meter style injection system. How can I vent this to the atmosphere so I can scare little old ladies??? It just gets hooked to the manifold right? This causes it to die at idle because the valve is open and the maf doesn't measure the extra air. WRX's have the same sys. but I see aftermarket bov's on them that dump out. WTF?? do I have to hook the hose to something else?

Re:BOV with MAF on Subaru
 

ive always heard that they go rich and stall sometimes like stoping at a stoplight b/c the maf sensor knows that air should be in thier or something and then its no longer thier and the car goes rich,but like u said people still use a bov that vents into the atmosphere on these style cars

Re:BOV with MAF on Subaru
 

problem is you're trying to use a recirc/bypass valve as a bov. get something like a dsm bov. a lot of the OE valves are designed to open almost fully at idle to allow the engine to pull air directly after the AFM instead of across the compressor for better throttle response.

on my MR2, i have a greddy type s BOV which is dumped to atmosphere despite the afm. the greddy stays closed at idle though. what i did was use a secondary bov on the intake side of the turbo, between the compressor and the afm. connected to the same vac line, it opens when the greddy valve opens and allows some of that blown off air back into the system (without it being re-accounted for by the afm).

to keep the secondary (i used a 2g dsm valve as they only cost about $10) valve closed, i made a small bleed valve using a plastic tee and a set screw. cut a slot in the side of the bottom leg of the tee and thread the set screw into the hole to control the size of the orifice. make it as small as you can before the engine starts to stumble.

look here (http://forum.mnsportcompacts.net/viewtopic.php?t=10290) if you want the whole write up with pics.

some people have said that there's no way the turbo can pull in through the secondary bov the amount of air expelled when the greddy valve opens. there are two answers to this question:
1. it may not be the same, but it's close enough.
2. a freewheeling compressor at 100k rpm and a pr of 1.0 flows about 30% more air than a compressor at 100krpm and a pr of 2.0. when it blows off, suddenly there's no resistence to compressor flow as it's not building pressure, so it will flow more air. like i said, it's close enough.

i've been using this on my MR2 for about 2 months now with no ill effects. in fact, it drives better than it did before..

Re:BOV with MAF on Subaru
 

your pictures don't work.

Re:BOV with MAF on Subaru
 

I tried being a stunna and vented my Talon, it ran like poop between shifts... basically you're releasing air thats already been metered & calculated. You could modify your car to a blow-through style hotwire maf with a translater and properly vent.. thats how I do it now. I use a 3.5" MAF from a 1999 Trans Am.

Re:BOV with MAF on Subaru
 

let me try again, wiht pics that work..

here's what i did:
i knew the the air coming out of the valve had already been accounted for by the AFM, so i figured i needed a way to introduce air back into the system, post AFM to restore some balance to the system. (yes, this air is unmetered, but i am filtering it.)

SOOOOOOOO... i happened to have an old 2g DSM BOV lying around. i attached the BOV to the recirc line post AFM, but i used the outlet instead of the inlet (so the vaccuum on the inlet side of the turbo can help open it), and plumbed it inline with the vaccuum line on the greddy BOV. on initial startup, the engine stumbled and hunted etc because the DSM valve was opening at idle. i built a bleeder valve (i would suggest a vaccuum relief valve) to limit vac. to the valve at idle, but allow enough vac to open it between shifts.

what's happening when i shift is this: the BOV opens, vents pressure to atmosphere making that pshhhhhhh sound we all love. at the same time, the DSM valve opens, allowing the turbo to pull in extra air to compensate for the air in the system that was lost by venting (obviously, it's not perfect, but the turbo should be able to pull in plenty of air). the system is completely closed off under WOT and boost. both valves are held shut by turbo pressure, so the only air going in under boost is going through the AFM.

like i said, initial testing is very promising. it doesn't stumble, it doesn't stall, it doesn't hesitate. in fact, the car used to drive like absolute sheeet when the engine was cold (a common issue, or so i hear). this problem was completely solved as well. again, no stalling, hesitation, bucking, etc. the car drives like any other car, immediately after start-up. (i'm going to investigate this further seeing as how this points to other problems though).

all's i know is the car drives better than it did with the valve recirculating into the intake, and sounds far cooler. i didn't do this to get that bov sound, i just wondered if it would work. it did.


here's the dsm valve:
http://www.imagestation.com/picture/...b/fa225358.jpg

here's the bleed valve:

http://www.imagestation.com/picture/...2/fa22535d.jpg

basically, i just used a plastic tee, cut a slot in it, and inserted a set screw into the top opening to control the size of the orifice. basically, without this, the dsm valve flutters open during idle, making it hunt and stumble. this reduces slightly the vac going to the valve. when the plate slams shut though, the manifold is trying to pull more air through the orifice and it can't keep up, so vac increases enough to the valve to open it. that's my take on it anyway..


a pic of the setup:
http://www.imagestation.com/picture/...a/fa225353.jpg

as you can see (sort of) the dsm valve is on the intake side of the turbo, on the low pressure pipe that connects the afm to the compressor inlet. when i shift, this valve opens too and allows the turbo to draw in some unmetered air to make up for the air it lost when the greddy valve on the charge pipe blew off...

it drives awesome. no stumbling or backfires.