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Old 01-25-2001, 06:53 PM   #1
djerickd
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Question Blow-off valve on a WRX

Can this be done without screwing up the car?? I'm wondering because someone said that the boost in controlled by the ECU with gets readings from the intake manifold and it's a closed system. Now if you were to put a blow-off value this closed system would now become open and pressure readings will flucuate wildly in the intake tract. Possibly screwing up the ECU readings.
Am I right about this??
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Old 01-25-2001, 07:21 PM   #2
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Worst thing that will happen when you vent the bov to the atmosphere is the car will run rich and you'll stall during shifting(this is when the bov vents the air). This can be corrected with a vpc, but thats costly.
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Old 01-25-2001, 09:59 PM   #3
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Rather than vent the BOV discharge to air, run a tube from the BOV discharge to the intake tube in front of the turbo, behind the MAF. This will just circulate the pressurized air in the intake after the throttle blade closes. The air circulating back in front of the turbo's inlet will reduce the airflow through the MAF, and decrease the MAF signal to the computer. This will keep the engine from running rich when the throttle closes while there is still manifold pressure and a large draw on the intake side of the turbo.
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Old 01-25-2001, 10:09 PM   #4
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I will vent it to the atmo, but then again, hehe, I have TEC II.
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Old 01-26-2001, 12:26 AM   #5
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Aargh! Why why why?! Why would you take a Low Emission Vehicle and turn it into a gross polluter? Is there really that much to be gained over rerouting it? Or is it just for the sound? Isn't the air up there bad enough already?
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Old 01-26-2001, 12:54 AM   #6
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I think the bov just vents fresh air, nothing toxic, seems the recirculating idea is pretty slick, and it accomplishes the same thing?
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Old 01-26-2001, 02:50 AM   #7
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HUH, why? Performance gain....NO.
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Old 01-26-2001, 05:32 AM   #8
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Uh, performance gain YES! Blow off valve releases pressure in the intake tract to keep the compressor blades spinning, while changing gears. It also prevents compressor surge.
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Old 01-26-2001, 05:58 AM   #9
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Ummm the WRX has a Blow Off Valve, no?

Here's a pic from detroit that I circled the part in question.

Now, are you thinking of a manual boost controller that will by-pass the wastegate so it doesn't see the 13.5 psi until later? If so, then the answer is yes. Very easy to do. You can get either an electronic one or a manual one.

<IMG SRC="http://www.kcprod.com/images/cbv.jpg" border=0>

--KC

[This message has been edited by KC (edited January 26, 2001).]
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Old 01-26-2001, 05:58 AM   #10
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The BOV return pipe on WRX is extremely long. About 2' to be exact. It goes from ones side on the IC under the intake manifold runners into the turbine inlet pipe at a 90' angle. In which case, released pressure from the BOV will do very little to keep the turbine spinning.

Now, on some cars it really works. On 2G Eclipses for example. The BOV return pipe is very short and enters the inlet pipe at a nice angle pointing directly onto the turbine blades.

So, the performance gain of venting the BOV back into the intake system is minimal. A rich condition might occure for a moment or so, but an Apex Super AFC can fix that.
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Old 01-26-2001, 06:07 AM   #11
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Alex...

I'm thankful we had DSM's before the WRX. Now we have 11 years of DSM experience to apply here.

--KC
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Old 01-26-2001, 06:18 AM   #12
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Hehe, true, my friend, very true.
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Old 01-26-2001, 07:25 AM   #13
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Figured there might be other DSMers around here. I had a 92 Laser AWD for a couple years, and did all the basic stuff to it. So you can chalk up another couple years of DSM experience! Not that I'm an expert, but I played around with it a little.

Don't think this has anything to do with the BOV, but is the little bleeder valve fooling the wastegate trick going to work on the WRX? Does anyone know yet? Seems like it works on some turbos but not on others. Sure would be nice not to have to buy a chip/new ECU to bring the boost up.
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Old 01-26-2001, 07:31 AM   #14
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Had a sub-14sec 96 GSX so chalk up three more years. By the way, I had a HKS sequential blow off valve venting to the atmosphere and NEVER had any problems. My car always ran a little rich, but that was a plus with the boost cranked up and three inch piping all the way back.
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Old 01-26-2001, 07:33 AM   #15
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WRXSVT - It should work, although I haven't seen under the hood yet. There has to be a soleniod controlling the wastegate and all we need to do is confuse it by changing the diameter of the inlet tubing.
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Old 01-26-2001, 07:40 AM   #16
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Damn, being that it doesnt make a big differnce..I think I'll just get that fake bov
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Old 01-26-2001, 09:02 AM   #17
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I think I was a little all over the place with my point. I was at work. Heres some clarification;

(I want a BOV vented to the atmosphere, but I'm thinking it may cause some lean conditions.) This is wrong, my mind was all on boost controlers, sense I am looking for one right now. See below...

If we force the car to make peak boost until readline, the ECU may cut fuel, or may not provide enough and cause a lean run condition which might lead to ka-boom maybe.
In any case, I think a replacement ECU is a must and since I plan on upgrading the turbo anyway its a good idea. Make more sense now?Again, I was at work, mind all over the place. As you can see I wasent even on the right topic.

I can assure you I don't need the benefit of the turbo faq. But it may help some folks.
And better me also.

Now here is some on topic info, A BOV will help the turbo stay in boost, why? The venting stops pressure from backing up into the turbo and slowing the turbo (This backpedeling can damage the turbo also). This helps the turbo retain as much shaft speed as possible. Yes it does still lose RPMs, but the reduction is in effect reduced and time spent off boost is minimized. OK?

Ken

[This message has been edited by DeliciouSpeed (edited January 26, 2001).]
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Old 01-26-2001, 10:34 AM   #18
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Deli, why would venting the BOV into the atmo cause the car to make peak boost until redline? Fuel cut because of the BOV being re-routed? No, no, no and no, no, no.

I think I will have to make a turbo FAQ ASAP. People seem to make make mistakes trying to answer an elementary questions.

The only think BOV-to-the-atmo can cuase a rich condition for a moment during the shifts. What happens is you have air in the intake piping that was counted by the MAS. It gets pressurized and goes into the intercooler. Then you shift, the BOV releases some of the pressure/air into the atmo but the ECU thinks that that air went back into the intake system after the MAS and supplies fuel for it. So basically it supplies fuel for non existing air. Get it? Thats all there is to it. It doesn't really matter if you vent it into the atmo, into the cockpit or into a party balloon. What matter is that it is not sent back into the system and ECU doesn't know about it.
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Old 01-27-2001, 12:02 AM   #19
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so what's BOV good for other than the sound it makes? seems like it's doing more harm to the engine than good...
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Old 01-27-2001, 12:06 AM   #20
djerickd
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Well I know some cars need it to prevent compresser surge. (BAD) Though I heard a compresser surge sounds cool too, but is bad for the turbo.
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Old 01-27-2001, 12:08 AM   #21
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On a somewhat related topic...
Ive read that in the WRX, pressure past the turbine is gradually bled off as rpms increase past, oh lets say 3k. Im wondering why this is the case? Is it an issue of:
-too much air to cool effectively,
-overheating the turbo,
-too high pressure for the cylinders (if that is even a concern),
-or something else?
Im a wee bit of a turbo newbie, i understand generally how they work. Seems like easiest way to make more power would be to deal w/ the above.
Am i making ne sense here?
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Old 01-27-2001, 12:11 AM   #22
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Ok, cool sound..... that is more like it. Like I said before, HUH performance...no.
The stock unit will work fine on a stock motor.
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Old 01-27-2001, 12:15 AM   #23
djerickd
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Id say more of a longevity gain to the turbo with a little gain from less turbo lag between shifts. Oh, Yes it sounds cool too!
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