what would be better for my blow off valve?

[EasTSide DRiFto]

Does anyone know what would be better for my blow off valve. I have a s13 red top and want to know if I vent the blow off valve back it to the maf or vent it to the atmosphere.Any knowlge of this subject would be helpful..Thanks


P.s can anyone make custom avitars.

[Nemesis]

ummm depends on what you want. Supposebly putting the air that your "losing" back into the MAF wil increase power efficeincy. I have very little experience with this so i'm not too sure. My friend had it that way, but went open BOV because 1)it sounds mucho's better 2) the power increase wasn't as sufficient as it was said to be. I'd personally go with a open BOV.

p.s. i can make custom avatars...

[Boro86driver]

the only time it will matter what your blow off valve is doing is during shifts and when you let off the throttle. then the car will run rich if the blow off vavle is AFTER the MAF. but i don't know about you, but i really don't care if the car runs rich when i'm shifting. so i'd go with open venting, just so you don't have to pipe the recircualtion tube across the car.

[180fan]

you will run rich at the moment you let off. the ecu's already accounted for the air in the system and has set that much fuel to dump. that unburnt gas will continue to burn as it passes through your system and unless you've got metal gaskets all the way through, you'll burn them and also increase the amount of soot you get in your exhaust system. It can also lower your mileage through the excessive dumping of fuel your ecu will do as it's venting atmospheric. Recirculate if you can unless you're some poseur ricer dude who's in it just for the sound to try to impress their peers. Or possibly tip off some pigs and get another sr'ed car impounded and further tipping off the pigs to be on the look out for SR's. In which case your local 240 community will want to lynch you. Good luck.

[Ichi-Go]

If you have a K&N or some open free flowing air filter you can still here it blow off. It is just muffled. When you have it dump open the MAF accounts for the air that isnt there.


Hondas can have an open BOV with no problems becuase they dont have MAF's.

[Boro86driver]

if you want it to vent into the atmosphere you can pipe the BOV before the MAF. but that depends on your underhood arangement.

[Ichi-Go]

There is one problem if you pipe the BOV before the MAF. It would not blow off. and would probably be inside the air filter.



MAF's are before the turbo so they measure the amount of air going into the engine. It doesnt matter how much pressure you run the MAF with measure the volume of air the turbo inhales.

[EasTSide DRiFto]

COol thanks guys.Im going to Vent it in to the maf.thats diffenintly the best way.Thanks

[Boro86driver]

uh, yeah i understand the MAF, and guess what, you can put the MAF where ever in your piping you want. but saying put the MAF after the blow off valve, i ment between the throttle body and the blow off valve. for example on my engine you would pipe the maf just before the throttle body and after the BOV. then all you need on the intake side of your turbo is an air filter.
see what i'm saying?

[Ichi-Go]

I see what you are saying but i think by definition a MAF can not be in the pressurized side of the piping. MAF's read airlflow not pressure so if you put it in the pressurized part you would read the airflow but not the pressure thus having to much air. Way to much. You could program the computer to read psi from another source, factor this in and have the car run fine. But after spending that much on stand alone you would be better off not doing it.

[Boro86driver]

you know all a MAF is is a little flapper door right? and a sensor that reads how much the flapper is open. that door doesn't care if its being pulled open or pushed open, volume of air is volume of air either way. pressure doesn't matter in the least. you are intaking the same volume of air into the engine if the AFM is before or after the turbo, so it sees the same amount. why would it matter if it was pressurized? think about blowing on a piece of paper, it moves forward right, now suck in the same VOLUME of air, and it will move the same amount. the turbo doesn't create something from nothing, thats impossible.
so, volume of air has nothing to do with pressure of air. if there is more pressure, the door will just open wider. and it reads more air.

[Ichi-Go]

Yes you are correct it doesnt matter if the air is pressurized or not it does the same thing. But your motor cares if the air is pressurized. Pressurized air has more O2 which means it can use more gas to create a bigger explosion. If the MAF does read this pressurized air not enough gas would be added. If it didnt matter if the air was pressurized or not then what would the point of forced induction be.


The reason the MAF needs to be on the sucking side of the turbo is becuase a turbo works on compression. So lets say the turbo has a compression ratio of 2:1 then for every 2 units of air in 1 unit comes out. In the same space. so it could move twice the air in the same space. Well it has to suck all air that gets pressurized. Kinda like a helium tank you could take the air out a thousand balloons to fill the tank. The tank has the same volume as 7 balloons. So if you measure it after it was in the tank you would get 7 balloons worth of air. But if you measured it as it went it. every balloon of helium would get measured as it was sucked by.

So since the MAF is before the turbo it measures all the air before it gets pressurized.

[180fan]

Originally posted by Boro86driver
you know all a MAF is is a little flapper door right?

You sure about that? From my own work on the MAFS it's two hot wires. You can even consult the Apexi S-AFC (or II) install manual. They're very thin wires with a voltage that passes through them, with that voltage it heats up and when the air passes over it, it reduces the temperature of the coil that makes the MAFS. It measures that voltage difference since when metal heats/cools it changes the resistance across that wire, changing the voltage.

I've seen the MAFS installed right before the throttle or before a turbo. Quite frankly I'm not too sure if it makes a difference. Just that the air that's entering the cold pipe has gone through the turbo, picked up heat from the turbo, etc and may not be as accurate a representation for the volume of oxygen molecules in the system.

but back to the original question about a more ideal location for the BOV, it should go to the coldpipe for better throttle response and recirculate behind the MAFS but before the turbo. Reasoning is that the cold pipe has all the condensed air from the intercooler and makes it more ideal than the hot air that's from the hot pipe to send back into the turbo since the hot air from the hot pipe would expand further making the work for the IC that much worse. That makes for a difference in concentration in oxygen molecules. But it would have to be after the MAFS because the system has already accounted for all that air and is expecting that air to go through the system at one point and putting the recirculation hose before the MAFS would make it count that bunch of air twice causing the motor to run richer than it should.

[Thai Juku]

This may be a little off topic...But I found this interesting...Every 1000 feet you go up, the engine loses 3% of it's power...