View Full Version : To those with Blow Off Valves
Are you running an open loop system or closed? And if it is open, why did you choose that instead of closed?
HighPSI TSi Guy
11-11-2002, 02:11 AM
i don't have a BOV, i have a CBV (compressor bypass valve). jsut so you don't get flamed in the future aby any asses, i though i'd point out that a BOV vents to atmosphere, and a CBV is a closed system. other than that they are the same.
as for mine, i run a closed loop system because my car uses a karman vortex MAS, and fucking hates venting. if you run pure map or speed density you can vent to the atmosphere all you want.. i think.. you may not be able to with MAP, i can't remember. anything MAS based will have ot be a closed system to function properly.
hope that explanation helps.. going to sleep for tonight, i can explain further if needed later..
Ahh, thanks, i actually havent ever heard of a CBV. Thanks for the new info.
GreyGT-C
11-11-2002, 10:28 AM
2nd gen RX7's have MAS........they can be vented to the atmosphere w/o problems..... I have a 3rd gen w/ MAP......i definately vent out to the atmospere
drifter
11-11-2002, 11:03 AM
you can vent to atmosphere w/ MAF only if the BOV doesnt leak at idle....i know for a fact that the HKS super sequential BOV can be used on a MAF equipped car with no problems...there are a few others...you can also vent to atmosphere with a MAP equipped vehicle no problem
since i have BOTH a Maf, and Map sensor....venting to the atmosphere becomes a problem, depending on how my ecu wants to feel at that certain moment. my efi is tricky...so people among the wrx communty tend to either keep it reciruculated or go 50/50. to those wrx's who vent to the atmos. they either have idle problems....or run really really rich between shifts...which throws their fuel curves outa whack. then again...there are alot of wrx's out there that dont have a single problem with venting to the atmos. either they have their ecu specfically tuned for it, or they just got lucky and their efi has adapted accordingly.
my stock bov (compres bypass vavle) can handle up to 18 psi without leaking anyways...so i think ill keep mine for a while. :)
16g-95gsx
11-11-2002, 01:06 PM
The problem with venting a BOV on a non MAP sensored car, is the fact that you run rich between shifts. This is caused by the ECU not recognizing that air has escaped (the air is metered BEFORE the BOV) and therefore still adds the fuel for the air that has been released, causing a slightly rich condition between shifts. If you just want a nice ricey pshhh sound and dont care about performance, then if your BOV won't leak when its vented go for it. If not then I would highly suggest recirculating it, as that is the true performance oriented way of doing it on a non MAP sensored car. For you Map sensor guys, blow off your load all you want, just not in my direction :).
Mugent3/t4e
11-11-2002, 05:18 PM
My BOV vents to the atmoshpere because its makes a louder sound and people can hear it better when I rev on them....:D
16g-95gsx
11-11-2002, 07:36 PM
Originally posted by Mugent3/t4e
My BOV vents to the atmoshpere because its makes a louder sound and people can hear it better when I rev on them....:D
You also don't have a MAS, which is the real reason why you are venting Josh.
20psi 240sx
11-11-2002, 09:39 PM
i want to add a couple things....
i have a open bov and mass air flow sensor car. with out my s-afc, it tends to want to stall when i go to neutral. with my s-afc, its not really a problem. there is a feature that leans the car out when you let off the gas. my car runs fine this way and has for the past couple years.
another way to deal with this problem is to plumb your maf after the turbo and have it as a blow thru setup. afaik, most hot wire maf car will not have a problem doing this. if you have it 12" before the throttle body, and your bov is 24" before the throttles body, you have no unmetered air entering the engine. this is the first thing i would try. maybe a little difficult for some as fuc-n apc doesn't make a intake set up that does this for you. i hope that helped somebody out a little.
shaun
i swear it will hold 30psi for 3 seconds....
16g-95gsx
11-12-2002, 12:22 AM
Stock MAS's dont like pressurize air traveling through them. At least mine doesnt. About the Safc feature, I have heard that doesnt work well for my car at all. Can you explain the mechanics of how it works? Just curious, so that I can diagnose why it would or wouldnt work for my car.
With the Greddy Type S BOV I have no problem venting to the atmosphere as far as stalling goes, but I only vent because I made my own 3" ABS intake pipe and havent had the time to recirculate it back in. Perhaps over thanksgiving break.
HighPSI TSi Guy
11-12-2002, 01:18 AM
Originally posted by 16g-95gsx
Stock MAS's dont like pressurize air traveling through them. At least mine doesnt. About the Safc feature, I have heard that doesnt work well for my car at all. Can you explain the mechanics of how it works? Just curious, so that I can diagnose why it would or wouldnt work for my car.
With the Greddy Type S BOV I have no problem venting to the atmosphere as far as stalling goes, but I only vent because I made my own 3" ABS intake pipe and havent had the time to recirculate it back in. Perhaps over thanksgiving break.
i will point out your riceness ever chance i get until you plumb that thing back in chris :p mine is loud as fuck without being vented it still never failed to scare everyone at the bus stop and produce a crowd of confusion and awe. anyways, you may not FEEL the difference when venting a BOV with MAS system, but your engine sure knows it... and spark plug companies will grow to love you.. an MAS system will ALWAYS run rich between shifts while vented.
chris, can you explain how MAP can vent? i don't know much about MAP and have been wondering...
Twelvz
11-12-2002, 08:02 AM
Originally posted by FutureProspect
my stock bov (compres bypass vavle) can handle up to 18 psi without leaking anyways...so i think ill keep mine for a while. :)
Ryan and I are holding 22 with stock just fine
1TZ JENN
11-12-2002, 10:42 AM
bovs are the coolest noise :p
highpsi tsi guy...im sure chris knows more about how air is metered through an engine...
but bascially a MAP sensor uses manfold pressure varience to meter air that is coming in the engine. if it has anything to do with pressure...im sure has to do with pv=nrt ( ideal gas laws).
sorry if this is knowledge u already know....^_^
20psi 240sx
11-12-2002, 12:18 PM
what the apex s-afc does is not too hard to explain so i'll try...
it has a bov feature that leans the car out at 2 different rpm points. i have mine set at 1000rpm and 2000 rpm. i tell it a percentage to lean it out whenever the tps signal is less then .05 percent. so when i'm off the gas, and the rpms are close to 2000, it starts to lean it out as to not stall the car or idle low from being too rich. as far as between shifts and still being rich...my bov only opens when i have 3psi or so. i have it set tight! if i have 3psi, its because i'm flooring it! ( ihave a lag problem) if i'm flooring it, my ecu uses the maf voltage for the sole purpose of choosing one of the many maps that jim wolf technologies put in my ecu to control fuel mixture and ignition timing. open bov or not, its not going to change the values of the map in my ecu. sure it might be missing some of the air, but not a big deal...heres why...my ecu also uses tps voltage to determine maps. when i let of the gas completely, my injectors flow at 0 % duty cycle. (i have an old school apexi multichecker that logs all my sensor values.) they are at 0% until it reaches about 2500 rpm. which is about when my safc starts to lean it out anyways.
i've heard that about maf not liking "blow thru" setups. but a friend has tried it on his 240sx and had good luck. dsm honey comb maf sensors i would think might have no problem either seeing as that honey comb stuff looks like it would smooth the flow, but only way to tell is to try.
shaun
HighPSI TSi Guy
11-12-2002, 01:44 PM
Originally posted by FutureProspect
highpsi tsi guy...im sure chris knows more about how air is metered through an engine...
but bascially a MAP sensor uses manfold pressure varience to meter air that is coming in the engine. if it has anything to do with pressure...im sure has to do with pv=nrt ( ideal gas laws).
sorry if this is knowledge u already know....^_^
thanks for the explanation, i knew it used pressure in some way but wasn't sure how it uses it to determine airflow, and why using MAP would allow for venting... actually nevermind it just hit me while i was typing this lol.. aight i get it now thanks.. :)
HighPSI TSi Guy
11-12-2002, 01:49 PM
Originally posted by 20psi 240sx
what the apex s-afc does is not too hard to explain so i'll try...
it has a bov feature that leans the car out at 2 different rpm points. i have mine set at 1000rpm and 2000 rpm. i tell it a percentage to lean it out whenever the tps signal is less then .05 percent. so when i'm off the gas, and the rpms are close to 2000, it starts to lean it out as to not stall the car or idle low from being too rich. as far as between shifts and still being rich...my bov only opens when i have 3psi or so. i have it set tight! if i have 3psi, its because i'm flooring it! ( ihave a lag problem) if i'm flooring it, my ecu uses the maf voltage for the sole purpose of choosing one of the many maps that jim wolf technologies put in my ecu to control fuel mixture and ignition timing. open bov or not, its not going to change the values of the map in my ecu. sure it might be missing some of the air, but not a big deal...heres why...my ecu also uses tps voltage to determine maps. when i let of the gas completely, my injectors flow at 0 % duty cycle. (i have an old school apexi multichecker that logs all my sensor values.) they are at 0% until it reaches about 2500 rpm. which is about when my safc starts to lean it out anyways.
i've heard that about maf not liking "blow thru" setups. but a friend has tried it on his 240sx and had good luck. dsm honey comb maf sensors i would think might have no problem either seeing as that honey comb stuff looks like it would smooth the flow, but only way to tell is to try.
shaun
i think there are some people trying the blow through method on DSMs.. but then again... what is the purpose? recirculating is not a restriction..
on another note, your metering system has to be the most complicated thing i have ever heard of.. and if i understood it right, it sounds very inefficient..
16g-95gsx
11-12-2002, 02:25 PM
Originally posted by FutureProspect
highpsi tsi guy...im sure chris knows more about how air is metered through an engine...
but bascially a MAP sensor uses manfold pressure varience to meter air that is coming in the engine. if it has anything to do with pressure...im sure has to do with pv=nrt ( ideal gas laws).
sorry if this is knowledge u already know....^_^
Yep, just find anyone with a Vafc on their honda and you can watch the manifold vacuum change. Because it measures airflow closure to the head, in the intake manifold area, the BOV is before the metering device, therefore the vented air hasnt been counted just yet, and no rich condition will be met.
20psi 240sx
11-12-2002, 04:54 PM
Originally posted by HighPSI TSi Guy
i think there are some people trying the blow through method on DSMs.. but then again... what is the purpose? recirculating is not a restriction..
on another note, your metering system has to be the most complicated thing i have ever heard of.. and if i understood it right, it sounds very inefficient..
what part do you think is inefficient? the multichecker or the way nissan's use their maf? <---mitsu does it the same way. if they didn't rely on maps, they wouldn't need a ecu. i can meter my pulsewidth ultra-accurately, and in real-time.
the reason for going to non-recirculating valve is for the noise, and most valves that you can recirculate are hard to find, or leak.
HighPSI TSi Guy
11-13-2002, 02:37 PM
Originally posted by 20psi 240sx
what part do you think is inefficient? the multichecker or the way nissan's use their maf? <---mitsu does it the same way. if they didn't rely on maps, they wouldn't need a ecu. i can meter my pulsewidth ultra-accurately, and in real-time.
the reason for going to non-recirculating valve is for the noise, and most valves that you can recirculate are hard to find, or leak.
i guess i misinterpretted your wording.. ours uses karmen vortex Hz readigns to adjust the ammount of fuel used.. it's not really a set "map" or anything.. at least as far as i know.. chris probably knows better than i do but that's the way i thought ours worked..
DSMPOWER
12-03-2002, 08:11 PM
tsi guy
I am driving the same car you are, and i vent to the atmosphere, with no problems.
HighPSI TSi Guy
12-03-2002, 10:42 PM
dude is that your car on the site? it looks nice.. yeah you can vent, you will stil lrun slightly rich between shifts though.. you have a valve that's made to be able to do it.. the stock valve can't unless it's crushed.
marshall
12-04-2002, 02:19 PM
my talon didn't really have _problems_ back when i tried venting mine, but the car did run rich according to the logger. the fuel trims jumped all over the place with it vented, it was a nightmare to keep up with it on the S-AFC...
no matter which BOV you use, you can't get around the fact that'll it'll run rich after it blows off. you're releasing metered air out of the system, the ECU expects it to be there because the MAF has counted it already...
my CBV is plumbed back into the intake, the sound isn't worth it to me.
marshall
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