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blow off valve?


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Just curious about how much diff it makes?I was reading the book maximum boost(sweet book)and saw that in it and was wondering if it is necessary to have one.How it works like what makes it blow off when the throttle is closed diff in vacuum?It seems mine goes better after i run it once thru the gears and then after that first has really good pull but if i don't first sucks it still goes up to 9# but not as much pull if i slo down and try again it pulls like a mother.....Could this be causing my prob?One more question should the gauge line be put in the turbo housing? I have mine in the intake to see what the engine is getting.Let me know wise ones nobody around where i live knows about this stuff icon_smile.gif

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The compressor wheel spins at a very high RPM, some as high as 90,000. The pressure it develops (boost) is being forced through the open TB into the engine. When you let off the gas, the TB closes and causes a restriction that reverses the pressure against the compressor. With large turbos and high HP engines, this can have a damaging effect because there is more boost pressure coming back against compressor blades with a larger surface area. In all cases there can be a long term damaging effect. The most obvious effect is that the compressor wheel slows down and needs time to ramp back up to the speed when you get back on the gas.

 

The BOV fits between the TB and the turbo, senses manifold pressure and opens to relieve that reverse pressure. That pressure escaping helps keep the compressor wheel spinning at high speed and the combination of both is what makes that whoooosh sound when vented to the atmosphere. I do not know what the manifold pressure is that the BOV uses for activation, but since you are immediately in vacuum when you let off the gas, I would put the line on the intake.

 

HTH and anyone can chime in and add or correct.

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My BOV is plumbed right to the intake - works fine and is adjustable. Porsche actually uses a pretty cheap BOV on some of their cars that costs only about $20. I'm not sure I've still got th epart number but it was the SAME valve that Vortech and others have been selling for close to $100 for years icon_rolleyes.gif Greddy and others make VERY nice billet units too.

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Okay - here'a secret place to find parts like that used icon_smile.gif

http://www.thepartstrader.com/mainpage.cfm

 

Look through the Supra, RX7, Z, and other turbo car forums. Since for your purposes you just need a BOV that will have to be fabricated into the setup anyway it won't matter much where it comes from. The Porsche valve I mentioned is cheap but it's plastic and not really very showy (ahem). Th eGreddy and other types are VERY nice, pricey, and have to be bolted onto a welded flange. Check out Greddy's WEB site to learn more and then go hunting in the forums I linked up above. Heck, I'll bet there are other OEM valves you could use too. Talons, RX7, and others came with them from the factory and those guys tend to dump stuff like that cheap so maybe..? Read up on what works and then start hunting and barganing - this is how I got one for my RX7 used... icon_biggrin.gif

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Heck, just go into a DSM forum and ask - they yank those things off and upgrade all the time!

 

BTW on the link I left above someone is selling some Volvo intercoolers that might be helpful to some of you turbo guys...

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