Dave944t

so i am looking to add a little flavor to my car that seems to have a problem with any mods i try to do to it (ape stage 2 chips sent my fuel system running for the hills). so i was looking into adding a blow off valve. few questions, does this replace the cycling valve (not sure if that is what it is called, i can see where it goes and what it replaces but im not sure about the name). also does this add any kind of performace factor? any info/ experiance would be nice, dave

*WiZaRD- 951

I was thinking about that 993 blowoff valve, because I'm going to be buying a replacement anyway, I figured why not 'upgrade' if it's worth it.

lou951

The 951 comes w/ a blow off valve from factory. It is located between the coolant tank and the airbox on the air intake tube. Basically what it does is maintain boost between gears and prevents the turbo from trying to spin backwards when the accelerator is released and the pressure drops. You won't really gain any performance by just switching to an aftermarket one unless your's has a torn membrane, which is not rare. An aftermarket blow off valve is only good if you have upgraded your turbo, intercooler tubes and switched to MAF. Basically it calls for a different mounting flange so you will have to modify the intercooler tube or buy an aftermarket one w/ a flange already on it. Check <a href="http://www.speedforceracing.com" target="_blank">Speed Force Racing</a>. Hope this helps.

Ski

Here is a pic of the blowoff valve, with the small vaccum line attached. You can do a simple vaccm check on yours with mighty vac to see if it is blown. You can get a 930 one for about $7 more than a standard 951 valve. I had to change mine when I upgraded pipes and intercooler.

Luke

[quote]Originally posted by Craig944[951]:
<strong>I was thinking about that 993 blowoff valve, because I'm going to be buying a replacement anyway, I figured why not 'upgrade' if it's worth it.</strong><hr></blockquote>


I dont think the 993 item is much of an upgrade. but it's brass so It probably wont tear like mine did. I have seen them range from $30-$60!?! I dont know why? From what I understand all bv are pretty much equual unless you're running huge top fuel dragster boost numbers (30+lbs)

correct me if i wrong. ( i also think the Monster BV's are gawdy)

fc-racer

Check out the Forge valve from <a href="http://www.stratmosphere.com/forge_valves.htm" target="_blank">http://www.stratmosphere.com/forge_valves.htm</a>

I'm using the 007P in black. Fits like stock, looks like stock, runs way better than stock. The factory valve seats only 95% of the time, the other 5%, it doesn't seat properly. I've tested and played around with 10-15 valves, both the stock 944 unit and the stock 993 unit, both of them really aren't up to task.

That's for a perfect valve, get one with a torn membrane and you're really losing performance.

Farzaan

jurg

Im using an Hks Super Sequential blow off valve.
Cant really say theres a performance factor,but hey,what can I say.Although one thing about the Hks ss bov that is good and bad,is its sound..sweet,yet annoying.

Jurg

2zeroes

Hi Farzaan,

I've got a 89 944t also. How do you know if you have a faulty valve, without actually having to remove it?

Would you recommend replacing it even if the stock one is working?

Thanks man!

Paul

Luke

[quote]Originally posted by fc-racer:
<strong>Check out the Forge valve from <a href="http://www.stratmosphere.com/forge_valves.htm" target="_blank">http://www.stratmosphere.com/forge_valves.htm</a>

That's for a perfect valve, get one with a torn membrane and you're really losing performance.

Farzaan</strong><hr></blockquote>

Mine is seriously torn. The tear is very visible. And when I inverted the unit there was no audible noise. What exactly would you say this is robbing me of? Would it mostly affect boost threshold or peak boost? I have always made peak boost @ around 2900rpm. I think it has always been bad. <img src="confused.gif" border="0">

Konstantin

try to suck on the top at teh small hose. If it is not sealed and it van not hold vacuum you need a new one

Konstantin

Konstantin

&lt;I'm using the 007P in black. Fits like stock, looks like stock, runs way better than stock&gt;

Farzaan. what you mean it runs better than the stock one?
More power, build faster boost or what?

If teh 951 is your favour why do you buy a 911 Turbo????

Konstantin

Luke

[quote]Originally posted by Konstantin:
<strong>try to suck on the top at teh small hose. If it is not sealed and it van not hold vacuum you need a new one

Konstantin</strong><hr></blockquote>

O yeah! Goes right through. Gonna order a Forge valve tomorrow. I can't wait to feel the difference. I've never had a good one.

*eurospeed951*

[quote]Originally posted by jurg:
<strong>Im using an Hks Super Sequential blow off valve.
Cant really say theres a performance factor,but hey,what can I say.Although one thing about the Hks ss bov that is good and bad,is its sound..sweet,yet annoying.

Jurg</strong><hr></blockquote>

What does it sound like? Can it be used on stock pipes?

fc-racer

To tell if your CBV is faulty, there are some hard tests you can do:

1. Blow through the valve. If air gets through the valve, it's defective.
2. Blow into the vacuum fitting and/or hook up a vacuum pump. If you can blow through, the valve is faulty, if you can't pull vacuum, it's also faulty.
3. Check to see what vacuum level the valve opens. If by 14" of vacuum the valve has not opened, it's stuck shut.

In terms of soft tests, when you change gears, feel how the boost comes on, if the car falls on its face for a moment after a quick shift, the CBV is not working correctly. With a good CBV like the Forge unit, you can actually hold boost during quick shifts so that when you engage the clutch in the next gear, you will have 5-7psi of residual boost left in the intake.

On cars with more open intakes, you can hear something that sounds like "cha-cha-chaaa" when you lift off the throttle, that is the noise of the compressed air trying to get out between the turbocharger and the throttle plate. It can also cause compressor surge and the destruction of the compressor wheel.

In testing I've done on my 911, the factory valve allowed boost pressure to spike to 15psi on lift off. With the 993 valve, it does not spike and only rises to about 11psi on lift off in certain situations. With the Forge valve, I get no pressure spike at all, the boost just falls during lift off, that's how it should be.

On my racecar, we knocked 0.75 seconds off the 1/4 mile time by venting the excellent CBV to atmosphere rather than back into the intake. If reducing the backpressure on a good valve made such a dramatic difference, imagine what you're losing with a faulty valve!

Konstantin, you ask why I went for a 911T if the 944TS is my favourite car. The reason is that I had the 944TS for 5.5 years and wanted a change. I was somewhat bored with the car after owning and racing it for so long. I didn't realize how much I loved that car until I got the 911 Slowly, with more and more modifications (which were not necessary on the 944TS), the 911T is becoming a much more competant and fun car to drive. I think I'm a lightweight flywheel away from a really great car . . .

Hope this helps,
Farzaan

jason952

Hi,
I read the thread and I was wondering just what the cycling valve does exactly. It connects the low pressure intake side of the turbo to the high pressure manifold side, right? Does that little vaccuum line hold the valve closed (boost up) as long as the intake mainfold pressure inside the manifold is equal to the pressure where the CV inserts into the intake pipe just before the butterfly? How does venting to the atmosphere help? does this put atm pressure on the value to hold it closed at 15psi (sea level)?

Jason