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88RX BOV Questions


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19 replies to this topic

#1 Bussaca

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Posted 09 September 2005 - 01:52 AM

Ok now i know this probobly has been answered about a hundered times..but i can't seem to find the answer just by searching around. No my question is not about which BOV is the loudest or which one i should get or where i should get it..

First is i'm installing a Saab 900 Intercooler with a BOV i have laying around (it's an OLD OLD...HKS bov off an Supra turbo but it did my 2.2t justice so i'm sure it'll do fine) , but before i go about doing so i just want to make sure.. possiably find a picture or 2 so i have a plan..

Now here's my question.. Where is the BOV.. on the legacy or any other turbo car i've owned or have worked on the BOV was fairly easy to locate..just follow the plumbing..it useually came after the turbo but before the intercooler or throttlebody (if you didn't get an intercooler).. and most likely re-circed back into the intake or manifold.. But i can't find Anything that resembles a BOV...well not egzactly..

What i THINK subaru used for a BOV is the device that mounts over the thermostat cap..it's the only thing plumbed between the turbo and the throttle body and it recircs right back to the intake manifold.. Problem is it has all the charistics of a BOV but dosen't mechanicaly look like one.. first off every BOV has a vacume line attached to it, this only has a wire.. which leaves me scratching my head about when i install mine where the heck i splice a vacume line from my BOV into the system so that it'll function properly..

Now the Subaru Service Manual calls what i think is a BOV an AAC type B (Auxiliary Air Control) which function is as follows " The AAC valve provides air bypass when the engine is cold for fast idle. It consists of a bimetal heater and rotary shutter. When the temperature of the bimetal is low, the shutter opens and allows air to bypass from the air intake duct into the intake manifold. As the engine warms, the shutter closes and does not allow any air to circulate into the intake manifold. This condition continues untill the engine is stopped and the temperature of the engine block cools down"

THIS DOES NOT SOUND LIKE A BOV.. so i'm really scratching my head about if i should cut it off...if it's needed.. figureing if i need it, where in the line of plumbing i have to fit it in..wondering if it's an ECU monitored system.. to me it seems to be yet another restriction in a long line of restrictions on this car..

If some one could give me a hand maybee a couple pictures of a proper BOV install...get me pointed in the right direction.. I know it's there... i've removed the airbox and redone all the plumbing to the turbo and when you let off the gas under boost..you get an elephant blowing it's nose under the hood so i know it there..

One last thing.. (all you tree hugging hippies leave the room) I HATE RATS NESTS/Speggetti (or spelling) all these hundreds of vacume lines..Emmisions controlls..vacume canisters all over the car.. I LOVE old muscle cars, just the engine 2 cooling lines a gas line 8 park plug wires and a battery.. NOTHING ELSE.. a VERY CLEAN looking engine compartment.. and i've SEEN these cars in race/rally form the engine bays are SPARTIN..just the engine a big honking turbo (for it's day) and intercooler.. NOT MUCH ELSE... If someone could honestly tell me what !!HAS!! to be there to make the car run (reliably)..if it dosen't HAVE to be there let me know... i want it gone.. Russel steel braid the oil and cooling lines one or 2 vacume lines and the bare nesseitys thats all i want.. No my town does not have emmisions..is it a consern..No not really..will this car single handedly with out it's emmisions controlls bring the down fall of the plannet for 2 or 3 days of auto crossing i might do with it a month.....no..

So if some one could point me again in the right direction..much appreciated..

Thank You

David Carter

88 RX 1.8t
91 Legacy SS 2.0t 6speed Cusco LSD'sx3
00 RS 2.5

#2 Snowman

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Posted 09 September 2005 - 01:59 AM

The EA82T doesn't have a BOV/BPV in stock form. It just uses a dashpot to slow the closing of the throttle plates.

#3 Bussaca

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Posted 09 September 2005 - 02:18 AM

The EA82T doesn't have a BOV/BPV in stock form. It just uses a dashpot to slow the closing of the throttle plates.


Dashpot?? huh? i didn't understand the complete second sentince.. not saying you said it wrong.. i just don't follow..

So basicly leave the AAC alone ,work it in with my plumbing..but where do i splice the new bov vac line?..and all the other stuff i asked..

Seriously though thanks snowman for the timely reply.

David Carter

88 RX 1.8t
91 Legacy SS 2.0t 6speed Cusco LSD'sx3
00 RS 2.5

#4 Ross

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Posted 09 September 2005 - 02:51 AM

You should consider finding a BPV instead, such as on the saab. BOVs work fine with MAP based flow readings, but for MAF/VAF based systems the BOV will cause excess fuel to be supplied when the BOV operates.

#5 Snowman

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Posted 09 September 2005 - 03:06 AM

I don't know why it's called a "dashpot", but it is basically a little plunger that the throttle linkage pushes on when the throttle is closing. The resistance created by this keeps the throttle plate open a wee bit when you let off on the gas, preventing excess pressure buildup between the turbo and the throttle plate (basically what a BOV/BPV does).

#6 ausubaru92

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Posted 09 September 2005 - 03:06 AM

You could set up a plumb back BOV which is basically a BOV that instead of letting its air vent out into the atmosphere, it redirects it back before the turbo, and thus not confusing the MAF.

The dashpot is a little device that slows the closing of the throttle, ie. Instead of the throttle plate snapping shut the instant you take your foot off the accelerator, it makes it shut gradually which in turn prevents the backpressure of air in the throttlebody.

Hope this clears it up a little (and i also hope i have got it right :drunk: )

Gannon

#7 4WDFrenzy

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Posted 09 September 2005 - 04:07 AM

I agree with what everyone else has said. Sadly the EA82Ts don't come with BPVs or intercoolers from the factory.:-\ Anyway, about the BOV question, I wouldn't install it unless you plan on getting rid of the catalytic converter. It would be more beneficial to run an open air element(cone filter) and plumb the BPV back into the intake pipe, if you want to hear the BPV when it releases pressure(Believe it or not, it is actually quite audible). A better idea is to get a custom fenderwell intake made with a fitting to accomodate the BPVs return hose. So not only would you get the benefit of drawing colder air into the engine, but you would also have the pressurised air recirculating(when the BPV releases pressure) back to the inlet to the turbocharger, which, by the way, also helps to keep the turbo spooled.

#8 subyrally

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Posted 09 September 2005 - 06:38 PM

if you remove the aac, also know as an idle air control if im not mistaken. your car will have trouble idling when you are at a stop. if im not mistaken, not only does it control cold idle, it keeps your engine from choking when your foot is off the gas.

#9 4WDFrenzy

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Posted 10 September 2005 - 12:30 AM

Maybe I'm missing something, but what are you referring to as far as removing the IAC Valve?

#10 subyrally

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Posted 10 September 2005 - 12:44 AM

Maybe I'm missing something, but what are you referring to as far as removing the IAC Valve?


its the little thing ontop of the thermostat housing on normal intake manifolds. its the peice tha has a hose coming from the underside of the intake plenum and another behind the throttle body. its basically a throttle body bypass for when the throttle plate is closed so that the engine doesnt stall.

#11 Bussaca

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Posted 10 September 2005 - 02:20 AM

its the little thing ontop of the thermostat housing on normal intake manifolds. its the peice tha has a hose coming from the underside of the intake plenum and another behind the throttle body. its basically a throttle body bypass for when the throttle plate is closed so that the engine doesnt stall.


Well mine routes from the intake plenum to the AAC and then goes to the forward section of the intake manifold completely bypassing the throttle body all together..and in no way connects to the throttle body.. BUT that aside general consensus is to just leave it alone and plumb it in along with everything else.. my guess would be after the IC but before the throttle body as thats where it sits now..no reason to mess with what works.

So thankfully thats somewhat cleared up.. but i still have 3 questions un answered.. where do i run the vac line from the BOV/BPV on the engine so that it will function correctly? Boost gauge gets spliced in off of the little nipple on the compressor housing? and what can be ripped from the car..and still hold functionability?

Already i've illeminated alot of the vapor recirc (i.e the oil breathers) I've done this on several ea82's with no problems.. the AC is gone along with all it's hoses and under dash parts..at least 40-60 pounds there..but there is still alot of ratsnests to simplify..

Thanks again for all your feedback..

David Carter

#12 Myxalplyx

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Posted 10 September 2005 - 09:58 AM

One last thing.. (all you tree hugging hippies leave the room) I HATE RATS NESTS/Speggetti (or spelling) all these hundreds of vacume lines..Emmisions controlls..vacume canisters all over the car.. I LOVE old muscle cars, just the engine 2 cooling lines a gas line 8 park plug wires and a battery.. NOTHING ELSE.. a VERY CLEAN looking engine compartment.. and i've SEEN these cars in race/rally form the engine bays are SPARTIN..just the engine a big honking turbo (for it's day) and intercooler.. NOT MUCH ELSE... If someone could honestly tell me what !!HAS!! to be there to make the car run (reliably)..if it dosen't HAVE to be there let me know... i want it gone.. Russel steel braid the oil and cooling lines one or 2 vacume lines and the bare nesseitys thats all i want.. No my town does not have emmisions..is it a consern..No not really..will this car single handedly with out it's emmisions controlls bring the down fall of the plannet for 2 or 3 days of auto crossing i might do with it a month.....no..
David Carter

88 RX 1.8t
91 Legacy SS 2.0t 6speed Cusco LSD'sx3
00 RS 2.5


I absolutely agree with you on the rubber vacuum lines part. I can't stand them. My Subaru XT6s engine bays are much cleaner than my RXs.

As for the BOV, I just have mine vented to the atmosphere. It's welded onto an intercooler. The pic below was before I finished getting the intercooler in right and having all the vacuum hoses properly hooked up.
Posted Image

#13 BoostedBalls

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Posted 10 September 2005 - 07:30 PM

The BOV will not give you enrichment problems if you:
A. Plum the discharge to the turbo inlet downstream of MAF.
B. Lightly crush the canister while the engine is idling until the idle smoothens out. This keeps it closed until you really need it to be open. This will also allow it to operate at higher boost levels. I did this on my Eclipse BOV and it works awesome. Makes upshifting feel like you are spinning a 50lb flywheel.

Placement, locate it as close to the throttlebody as possible. I did testing on this with mine. The air in the intake system should never have to change directions. If you have it too far from the throttle body, the pressurized air will have to stop when the throttle closes, turn around, dump, then turn back around again when the throttle opens back up. This will be a notacable hesitation. I put mine on the outlet side of the intercooler and it really made a difference compared to having it on the inlet side.

#14 Bussaca

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Posted 15 September 2005 - 08:52 AM

Placement, locate it as close to the throttlebody as possible. I did testing on this with mine. The air in the intake system should never have to change directions. If you have it too far from the throttle body, the pressurized air will have to stop when the throttle closes, turn around, dump, then turn back around again when the throttle opens back up. This will be a notacable hesitation. I put mine on the outlet side of the intercooler and it really made a difference compared to having it on the inlet side.


Now this is your recomended placement of the BOV/BPV..? This i'm not haveing an issue with, it's the Vacume line that comes off of the BOV/BPV where does this route to as the RX dosen't have a stock location...where would i splice it into?

I'm gonna start posting pictures and asking it's level of importance....and the ability to re-route/remove..

David Carter
88 RX 1.8t
91 Legacy SS 2.0t 6speed Cusco LSD'sx3
00 RS 2.5

#15 4WDFrenzy

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Posted 15 September 2005 - 09:22 AM

I tee'd mine into one of the vacuum lines that comes off of the throttlebody. It works like a charm. I'm sorry that I have no pics right now.

#16 oddcomp

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Posted 15 September 2005 - 09:40 AM

any vacum line thats conected directly to the intake manifold will be fine

just go and add a "T" connector and run it to the bov
on a stock based maf system like you have if you vent it to the air
it is venting air that has been already calculated as to how much fuel it needs to burn correctly by the ecu so when it vents to the air you will usally get a nice little back fire sound from the excess fuel/not enough air combo

if it vents back into the intake after the maf sensor but before the turbo anywhere then it will solve that problem

and boosted is correct bov placement does matter
closer to the throttle body is the best

as far as a loud bov goes. well in my rx i have a hks ssqv bov vented to the air and you can hear it about a block away when i shift and am in a hurry to get somewhere.. or so i have been told

i can run mine to air since i have a standalon injection/ignition system that no longer relies on a maf based system.. yay for me :)

if you choose the hks route <and i recomend it if you can afford it>
you can get a adapter or make one for it that will provide a way to vent it back into the intake system after the maf and before the turbo

even after it vents back into the intake i pretty much gaurante it will be loud enough for people to look confused and say wtf ?

#17 NorthWet

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Posted 15 September 2005 - 11:47 AM

any vacum line thats conected directly to the intake manifold will be fine...

Oddcomp speaks from experience... but I will throw in some related-field (but not turbo boost management) theory.

The further away from the BOV/BRC you hook the actuator line the more chance that you can get into an oscillation. Better, in theory, to have the sense/actuator line closer to the controlled device. Now, the device may be so slow in operation compared to intake length and air flow/pressurization that it will not get into the BOV's "resonant frequency", but if you are already plumbing in the BOV why not just add a manifold pressure "port" right next to it?

#18 BoostedBalls

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Posted 15 September 2005 - 01:16 PM

Yup, plumb the vac line anywhere downstream of the throttle plate. Just remember, the bigger the hose and the shorter the line, the quicker the BOV will actuate.

#19 nkx

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Posted 16 September 2005 - 02:45 AM

Boost gauge gets spliced in off of the little nipple on the compressor housing?

the problem with tapping in that spot is the reading only indicates how much boost the compressor is making and nothing more. if you tap one of the lines that connects after the TB, the gauge will indicate how much pressure the intake manifold is seeing. theres a vac line that goes from the manifold to a little boost sensor which activates a light on the dash which says 'turbo'. thats the line i tapped.

i suppose you could say the reading at the compressor would be gross boost and the reading after the tb would be net boost.

#20 oddcomp

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Posted 16 September 2005 - 04:27 AM

the problem with tapping in that spot is the reading only indicates how much boost the compressor is making and nothing more. if you tap one of the lines that connects after the TB, the gauge will indicate how much pressure the intake manifold is seeing. theres a vac line that goes from the manifold to a little boost sensor which activates a light on the dash which says 'turbo'. thats the line i tapped.

i suppose you could say the reading at the compressor would be gross boost and the reading after the tb would be net boost.


especially if your intercooled the internal restriction of a intercooler will show a higher boost psi if the signal is taken from the compressor housing before the intercooler and a lower psi reading <but it will be the true psi reading the motr actually see's> if the signal is taken from after the intercooler/below the throttle body somewhere on the manifold

not to mention if your using a boost/vacum type gauge then you want to see the vacum inside the manifold anyways so just t it into a line off the manifold

if for some wierd reason your using like a old compressed air psi gauge and are only interested in the amount of boost your producing
then by all means place the fitting anywhere between the throttle body and intercooler/turbo if you don have a intercooler




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