Blow Off Valve? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 16 Old 12-29-2015, 11:15 AM Thread Starter
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Blow Off Valve?

70mm on 3 - 15-18psi - 75mm TB - 75MM MAF

Who uses them? And if you do use them (or recommend using them) where is the best placement?

I have read all sorts of theories, mostly from honda guys, with no clear answer. Just alot of "he said she said" and people yelling at each other...

Thanks!


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post #2 of 16 Old 01-12-2016, 07:13 AM Thread Starter
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Nothin?


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post #3 of 16 Old 01-12-2016, 09:30 AM
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I use one and I prefer to have it to ease the stress on the turbine and turbo seals when slamming the throttle shut after going WOT. It's mounted on the MAF tube just as it exists the IC.

ks


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post #4 of 16 Old 01-12-2016, 03:26 PM Thread Starter
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How close is you MAF to the exit of your inter cooler?

'83 Capri: 351w Roller, TKO 500/600, Intercooled 70mm On3, GT40X, F303, Shootout EFI, 60# Deka, BA5000, McLeod 75307
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post #5 of 16 Old 01-12-2016, 04:09 PM
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Quote:
Originally Posted by PancakeShake View Post
How close is you MAF to the exit of your inter cooler?
About 4ft.

ks


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post #6 of 16 Old 01-12-2016, 08:10 PM Thread Starter
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Quote:
Originally Posted by KEVIN$ View Post
About 4ft.

ks
So just so I have this correct...

IC ---> 2 inches ---> BOV ---> 4ft of Piping ---> MAF ---> 6in of piping ---> TB

That basically what it looks like?

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post #7 of 16 Old 01-12-2016, 08:17 PM
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Quote:
Originally Posted by PancakeShake View Post
So just so I have this correct...

IC ---> 2 inches ---> BOV ---> 4ft of Piping ---> MAF ---> 6in of piping ---> TB

That basically what it looks like?
Yep.


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post #8 of 16 Old 01-12-2016, 08:30 PM
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I have my BOV before the intercooler. I kinda figured why cool air you're not going to use. Plus less of a chance interfering with maf signal on opposite side of intercooler.

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post #9 of 16 Old 01-12-2016, 09:28 PM
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Quote:
Originally Posted by MJs89GT View Post
I have my BOV before the intercooler. I kinda figured why cool air you're not going to use. Plus less of a chance interfering with maf signal on opposite side of intercooler.
The BOV never opens until the throttle is closed after a high boost run then it bleeds off the spike in pressure between the turbos and the throttle body.


ks


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post #10 of 16 Old 01-14-2016, 07:17 PM
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I have my BOV mid way between the turbo and TB. I use a tiny BOV for the pipe size, but it is working. You can hear it here:

https://www.youtube.com/watch?v=UZPLBa73ER0

It's bleeding 24-25 psi of pressure

You can see it at the end of the video. It works fine where it is.



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post #11 of 16 Old 01-14-2016, 09:07 PM
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Here is where mine is mounted......


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post #12 of 16 Old 01-15-2016, 11:44 AM
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Optimal place is pre intercooler. Closer to the compressor outlet the better. If you run a maf, it obviously needs to be pre maf so your not dumping metered air.

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post #13 of 16 Old 01-15-2016, 10:05 PM
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Quote:
Originally Posted by lightblade View Post
Optimal place is pre intercooler. Closer to the compressor outlet the better. If you run a maf, it obviously needs to be pre maf so your not dumping metered air.
Why would that be?


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post #14 of 16 Old 01-17-2016, 12:16 AM
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BOV mounted close to the compressor will relieve pressure faster than a BOV positioned far away from the compressor. As far as dumping metered air, the ECU is still matching its fuel tables based on MAF readings. The ECU dosent know that a portion of the air has been dumped, it will be pig rich.
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post #15 of 16 Old 01-17-2016, 12:39 AM
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My concern is not the turbo compressor running into pressure, it doesn't know the difference between feeding the engine or the BOV. My concern is the boost pushing past the throttle plate when the boosted fast air just slams against it. My BOV works perfect, even though it is small, tied in about midway between the turbo and throttle body.

I agree about the MAF, I'm not so sure about the BOV having to be on the inlet of the IC. It sure doesn't need to be there with short pipes like I have.


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post #16 of 16 Old 01-22-2016, 01:58 PM
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The blow off valve's sole purpose is to protect the compressor wheel and prevent compressor surge when coming off the throttle fast/hard, not to prevent it from hitting the throttle blade, that is a given regardless. The manifold is instantly in vacuum and what minute amount of pressure goes past the throttle blade is pulled into the motor like normal.

The problem is path of least resistance if now back out the compressor wheel in the wrong direction, this surge creates a lot of vibration and shock to the wheels and guts of the turbo. It can crack/break the edges of the vanes and damage the shaft, bearings and seals over time. Hence why the optimal spot is closer to the turbo compressor outlet. Now all the volume of pressurized air is between the throttle blade and now wide open bov and pressure is relieved there vice trying to go back through the compressor wheel. Also in your system pressure is highest at the compressor outlet and lowest and the throttle body/manifold. A standard piping setup and charge cooler can see 2-3psi difference from pressure reading at the compressor scroll and the manifold.

Will the bov work and help regardless of placement, yes of course, but the optimal place is right at the compressor outlet. This is why you often seen alot road race turbo setups that have a lot of wot to off throttle transitions weld the bov flange right onto the outlet of the compressor cover scroll itself.

The less charge piping you have the better as well since there is less volume, which would make optimal placement less critical. Bov size required is governed more by volume/flow needed not so much boost pressure itself. If you have smaller volume to fill there is less to release and the valve can be smaller. That's why you see big motors 351,427's etc running dual bov's They will make 1k hp on 10-12psi which is relatively low boost but because there is alot more volume of motor/piping to fill there is more cfm of air to divert away from the compressor.

Between the compressor outlet and prior to charge cooler or on the charge cooler itslef are the most common places selected on street setups. Freezy74's placement in the pic above is excellent.

Another note is a lot of drag setups wont run a bov as its a source of possible leakage of boost during the run. They will often just ease off the throttle slower to bleed the pressure through the motor after they cross the stripe.

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