Blow Off Valve ?'s - Toyota Nation Forum : Toyota Car and Truck Forums

thefullmonte · 01-06-2004, 09:36 PM

What initiates the opening of the valve on the BOV? there is some hose that runs to it that I would assume sets it off but where does that hose go to? What type of BOV could have its waste plumbed back into the intake system?

P.S. Any turbo specialists wanna help me figure out my turbo system?

Flashmn · 01-07-2004, 12:22 AM

intake vacuum is what sets it off...

88 LE · 01-07-2004, 04:04 AM

Quote:

Originally posted by thefullmonte
there is some hose that runs to it that I would assume sets it off but where does that hose go to

To a vacuum source. Usually somewhere on the intake manifold.

Quote:

What type of BOV could have its waste plumbed back into the intake system?

Any of them. Some of them require a adapter to plumb back into the intake though.

I would just let it blow off into the air.

SolaraTRD · 01-07-2004, 09:39 PM

Pppppssshhhhhh! Pppsssshhhhh.

I wonder if it's possible to do some ghetto mechanical thing to make out stock engines make that noise.

HHHmmmm...

88 LE · 01-08-2004, 04:20 AM

Quote:

Originally posted by SolaraTRD
Pppppssshhhhhh! Pppsssshhhhh.

I wonder if it's possible to do some ghetto mechanical thing to make out stock engines make that noise. HHHmmmm...

There is a electronic blowoff valve.

***MRQtwinturbo*** · 01-08-2004, 10:17 AM

ya...he can buy a fake FMIC to go with that too.....

the hks ssq bov allows u to reicirculate back into ur intake....

thefullmonte · 01-08-2004, 09:06 PM

could i just substitute a bypass valve for the BOV or CBV? what would be a good one? and if someone had a thorough explanation of how a bypass valve works that would be very cool.

Flashmn · 01-09-2004, 02:19 AM

Bypass and dumpvalve are the same as a bov. I'd seek a turbosmart or a forge motorsport dump/bov... they're good quality and will last quite long.

88 LE · 01-09-2004, 05:04 AM

Quote:

Originally posted by thefullmonte
could i just substitute a bypass valve for the BOV or CBV?

Most ppl go the other way around, but yeah you can use a recirc/bypass valve.

Just won't have that awesome blowoff sound.

Quote:

and if someone had a thorough explanation of how a bypass valve works that would be very cool.

A bypass / recirc valve has 3 connections on it. In, out, and vacuum source.

One end connects between the discharge pipe from turbo and throttle body or between intercooler (if you have a intercooler) and throttle body.

The other end connects to the compressor inlet pipe of the turbo.

The vacuum source. Well that gets connected to a vacuum source.

Under vacuum the valve is open. As you go from vacuum to boost the valve closes. When you let off the gas the valve opens and dumps the air back into the intake (the pipe connected the compresser inlet of the turbo).

Pic of bypass / recirc valve from my friends MKIII Turbo Supra:

pulsedriver · 01-09-2004, 05:35 AM

the bov is opened by vacuum that builds up in the intake manifold when the throttle body is closed.

Here is how you determin if you need to BOV or a BPV (by-pass valve or diverter valve). If your car did not come stock with a turbo then you can safely run a BOV. If your car came with a turbo stock then it also came with a BPV stock. A BOV will cause havoc on the MAF sensor because it will think that you have an enormous boost leak since there is no air recirculing back through it like with a BPS. A BPV will recirculate the excess air back into the airbox through the MAF. If you want to run BOV and not get a check engine light on a stock turboed car, either get a BOv/BPV hybrid (I have the GFB one, works great) or just get an open element intake (cone filter) insted of your airbox, tho it wont be quite as loud.

crazy_camry · 01-10-2004, 12:55 AM

with my camry 3s-fe, putting my turbo stuff on (hopefully in a month), with a normal BOV will cause the same problems with it's AFM. i too though have the GFB hybrid, so it should be fine

***bgrieger*** · 01-10-2004, 01:45 AM

Quote:

Originally posted by pulsedriver
If your car did not come stock with a turbo then you can safely run a BOV. If your car came with a turbo stock then it also came with a BPV stock. A BOV will cause havoc on the MAF sensor because it will think that you have an enormous boost leak since there is no air recirculing back through it like with a BPS.

Ummmm....close, but not really.

BOV's wreck havock on any car with a mass airflow system, be they flapper door, hot wire or Karmann Vortec. MAP sensor setups are the only one that can run BOV's without problems, and that is because they meter by air pressure, not flow. THey also usually cause only minor effects, but may lead to a stall if you were to run under boost and then just step on the clutch to coast.

BOV's are also not open except when the pressure in the intake pipes is significantly greater than the manifold. The vacuum only assists the pressure in the pipes in overcoming the resistance of the spring inside the valve. Hence many have adjustment screws to set the tension, and almost every one you hear will flutter at low pressure (keeps opening and closing up until the turbo slows enough). Bypass valves tend to be open more, and hence they are lousy to release to atmosphere, and their design allows unmetered air back in. BOV's seal before this occurs.

When a BOV releases, it dumps metered air out to atmosphere, creating a short lived rich condition. In some cars, this will trigger the check engine, in others, you get a backfire or stumble. Bypass valves recirculate charge air to a point before the turbo, but after the airflow metering device.

Not all turbo cars had either of them, and none made since the 70's have BOV's (emissions regulation...no intake charge can be atmosphere dumped).

To answer the why question, the idea is to release the charge air before the shock wave gets back to the turbo. Slamming the throttle plate closed causes this pressure wave to move back through the system. Unchecked, it slams into a compressor wheel and can cause blade damage, or shaft failure in extreme cases. Venting this wave keeps the impact down, and minimizes deceleration of the turbo compressor, leading to less lag on application of the throttle again (ie when shifting).

Sorry for the length...kinda late and rambly...

Bob

Aussie Ed · 01-11-2004, 07:32 AM

would i need to get a bov when i turbo my auto v6 camry to be on the safe side????

thefullmonte · 01-11-2004, 10:30 AM

yes you would. so if i am using a blow-thru system I don't need to recirc the air do I?

Flashmn · 01-11-2004, 10:56 AM

Well depends on the turbo, it wont shatter the blades or brake off the shaft. It would play havoc with the bearings... Ballbearing turbos will take more of this abuse than a non ballbearing, but it would increase lag when you need power again.

Quote:

yes you would. so if i am using a blow-thru system I don't need to recirc the air do I?

Carb turbo setups sometimes dont use blowoff valves. If theres gasoline in the air, I'd think twice about venting it into the engine bay thats for sure. Then again venting it before the turbo and intercooler is also an interesting equation... get gasoline soaked inside the IC isnt exactly the happiest of thoughts. Old suck through setups didnt have ic's so it wasnt really a problem, besides the turbo was so close to the carb, there really wasnt any problems with having a bov.