b.o.v. question

[93suby]

i have heard that you cant use a blow off valve on the subaru ea82, and the ej22 because they have a map sensor, instead of a m.a.f. sensor. is this true? does anyone have pictures? thanks

[sammydafish]

backwards... you can't release the air from your BOV to atmosphere because they have a MAF sensor (metered air system) not a MAP sensor (calculated air system). if you did, you'd release air that the MAF already read and confuce the computer as there would be less air in the system than it thinks there is.

[BAC5.2]

But if you release the air BEFORE the MAF, then you should be fine. Like Juniors blow-through MAF setup.

[waldo320]

Yah i have the blow through set up ckeck out my pics in the gallery, it works great. I also tried it the bov after the maf it does not work dont try it.

[BAC5.2]

A BOV After the MAF DOES work. I've done it and been doing it for a while. But putting it before the MAF is a pretty good idea.

[Imprezive]

The stock setup has the recirc valve venting to the intake of the turbo, and thats after the MAF. So why couldn't you vent a BOV to the same place?

[sammydafish]

The stock setup has the recirc valve venting to the intake of the turbo, and thats after the MAF. So why couldn't you vent a BOV to the same place?

you could, that would make it a recirculating valve though, not a blow off valve. you just can't release teh air to the atmophere after the MAF has read it.

[free5ty1e]

Yeah, you can. I have been doing that for almost a year now. It's just rich for that instant when the throttle plate closes, sometimes results in a happy backfire (no cats). But you can release the air after the MAF has read it, and the engine still runs fine.

Once I have it to do over though I am going back to a recirculating setup with my Type S, to keep the turbo spooled between shifts.

[scuzzy]

Yeah, you can. I have been doing that for almost a year now. It's just rich for that instant when the throttle plate closes, sometimes results in a happy backfire (no cats). But you can release the air after the MAF has read it, and the engine still runs fine.

Once I have it to do over though I am going back to a recirculating setup with my Type S, to keep the turbo spooled between shifts.

Yes it does work fine untill you get to pushing the limits.

What happens when you start pushing the limits is that the throttle plate slams shut, BOV dumps air to atmosphere, the ECU goes "OHSHITS" and pulls fuel quickly in the rich condition - the drawback is the turbo is still spooled.

if you move quickly (like you're driving hard) one punches the gas, throttle plate swings open, turbo builds boost pretty damn quickly then - but the ECU has already done the noble job of pulling fuel to keep from stalling the engine. suddenly there's alot more air than their is fuel to compensate for, and since there's a slight lag between what the O2 reads and what's actually happening in the cylinders, you run pretty damn lean for a few cycles.

pushing an engine to the max with a BOV that vents to atmosphere and an ECU that doesn't compensate for it means you can toast an engine in the lean condition.

Remember, engines predet all the time, even the factory STi predets some, but it only takes that one event to trash an entire engine.

[sammydafish]

Yeah, you can. I have been doing that for almost a year now. It's just rich for that instant when the throttle plate closes, sometimes results in a happy backfire (no cats). But you can release the air after the MAF has read it, and the engine still runs fine.

Once I have it to do over though I am going back to a recirculating setup with my Type S, to keep the turbo spooled between shifts.

Yes it does work fine untill you get to pushing the limits.

What happens when you start pushing the limits is that the throttle plate slams shut, BOV dumps air to atmosphere, the ECU goes "OHSHITS" and pulls fuel quickly in the rich condition - the drawback is the turbo is still spooled.

if you move quickly (like you're driving hard) one punches the gas, throttle plate swings open, turbo builds boost pretty damn quickly then - but the ECU has already done the noble job of pulling fuel to keep from stalling the engine. suddenly there's alot more air than their is fuel to compensate for, and since there's a slight lag between what the O2 reads and what's actually happening in the cylinders, you run pretty damn lean for a few cycles.

pushing an engine to the max with a BOV that vents to atmosphere and an ECU that doesn't compensate for it means you can toast an engine in the lean condition.

Remember, engines predet all the time, even the factory STi predets some, but it only takes that one event to trash an entire engine.

right on the money ...... what's the lesson we learned here boys and girls..... just because it might work, doesn't mean it won't screw things up, bottom line, don't do it.



if you do it becasue you like the phhhh sound, then just get one of those speaker things the ricers with civics they wish were turbocharged run... they sell em on fleabay all the time. If you think it's going to make your car faster, you need to get the pimp slap

[Legacy777]

Yeah, you can. I have been doing that for almost a year now. It's just rich for that instant when the throttle plate closes, sometimes results in a happy backfire (no cats). But you can release the air after the MAF has read it, and the engine still runs fine.

Once I have it to do over though I am going back to a recirculating setup with my Type S, to keep the turbo spooled between shifts.

Yes it does work fine untill you get to pushing the limits.

What happens when you start pushing the limits is that the throttle plate slams shut, BOV dumps air to atmosphere, the ECU goes "OHSHITS" and pulls fuel quickly in the rich condition - the drawback is the turbo is still spooled.

if you move quickly (like you're driving hard) one punches the gas, throttle plate swings open, turbo builds boost pretty damn quickly then - but the ECU has already done the noble job of pulling fuel to keep from stalling the engine. suddenly there's alot more air than their is fuel to compensate for, and since there's a slight lag between what the O2 reads and what's actually happening in the cylinders, you run pretty damn lean for a few cycles.

pushing an engine to the max with a BOV that vents to atmosphere and an ECU that doesn't compensate for it means you can toast an engine in the lean condition.

Remember, engines predet all the time, even the factory STi predets some, but it only takes that one event to trash an entire engine.

One comment to add. The ECU is not going to be basing it's fuel calculations off of the O2 sensor in that scenario. It's going to be in open loop and basing it off of air flow and throttle position.

I'm not condoning the atmospheric BOV setup, but the control philosophy you mentioned isn't correct.

[Imprezive]

I think I'm gonna go with a Forge recirculationg BOV.