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pop off valve removal


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I kow just about everone will say not to do it but i did already.It was restricting the engine.I have a question before the pov would release at 15psi and it would do it loud now that it's gone out of the car it still does only go to 15psi but i noticed that the ic is alot more efficent when it says 15 on the pre ic gauge the post ic gauge reads about 14 and a half close to 15#.

Why is it not going any higher could it be a leak?My BOV is coming soon so i don't plan to run it too long with out protection.Between the fuel pressure being higher abd the pov being removed it made a big difference in all the gears i like it.It smokes a little when i take off but then clears right up when full boost hits.So what do you guys think?

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The difference in pressure is pressure drop across your intercooler. Nothing you can really do about that.

 

The POV is not the same thing as a BOV for your information. For all intensive purposes the POV is a safety valve incase your wastegate goes crazy or something. BOV just relieves boost pressure so the turbo impeller does not slow down as much between shifts.

 

Smoke? Hrm maybe your fuel pressure is too high? Its time for you to get an air fuel gauge or something to monitor whats going on in your engine. Besides, if your running way too rich your losing HP. icon_smile.gif

 

Evan icon_razz.gif

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I think the POV is overkill for even the stock engine. What other OEM setups use a POV in addition to the wastegate for boost regulation? None that I know of.

The BOV (compressor by-pass) has a different function and is on the other side of the throttle plate. The POV is a fail-safe, last resort mechanism; while the BOV relieves power robbing, impeller slowing pessure build up between a closed throttle plate and the turbo. BTW I've bought an expensive BOV before and found the one from an OEM Eclipse/Talon from the wrecking yard works as well.

I haven't removed mine yet but plan to. Did you use a pipe plug and, if so, was it a standard pipe thread of what size?

DAW

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I thought the bov acted as both the pov and the bov meaning it blows off any extra pressure incase the wastegate goes nuts.I know it does blow off the pressure when the throttle is closed by sensing vaccum.And i thought the adjustable part was for the over boost situation.Am i wrong?My ic is pretty efficent only 1 psi drop across it.It is running rich but i'll adjust it later but like i said i'd rather have it rich than lean.Air fuel gauge is next on the list know of where to get one at a diecent price?

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The BOV does not perform the same function as the POV. The POV is simply a safety device to keep the engine from being overboosted accidentally. Nothing more. The BOV works as you described, venting pressurized air between the turbo and the throttle plate when the plate is closed. Nothing more. Having one does not cover for the other.

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Likely how much boost pressure it can handle. The BOV will still see 15psi boost if you are running 15psi at the turbo outlet. You need to be able to adjust it, since your BOV at 15psi is the same one that someone else might buy for their 7psi application. Obviously the 15psi one would need to be stiffer not to leak, when compared with the same BOV in the 7psi environment.

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quote:

Originally posted by Drax240z:

Obviously the 15psi one would need to be stiffer not to leak, when compared with the same BOV in the 7psi environment.

 

This is true, but it may not need to be as much stiffer as you might think. The opening of the BOV is controlled by the pressure difference across the diaphragm that controls it.

 

Interestingly, if it is plumbed correctly, the two sides of the diaphragm will see the boost pressure at the point that the BOV is installed, and the pressure in the manifold on the other side of the throttle. The pressure difference between the boost pressure and atmospheric pressure should not come into play. Usually, they are set to open at only a few psi pressure difference, so that the BOV opens as soon as the throttle is closed, and the pressure surge is kept to a minimum.

 

The reason that the BOV needs to be adjustable is that this pressure difference varies, depending on where the BOV is installed. If it is installed immediately before the throttle, the pressure drop at WOT between the two reference points will be pretty small, and the BOV should not be affected by changes in boost pressure.

 

If, on the other hand, the BOV is installed before the intercooler, the pressure drop at WOT is now dependant on the amount of flow going through the intercooler. It is then very possible for the pressure drop across the intercooler to be big enough to crack the BOV open. Under these circmstances, it would be necessary to increase the spring pressure of the BOV, until the pressure drop across the intercooler was not big enough to open it.

 

[ July 29, 2001: Message edited by: TimZ ]

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  • 3 weeks later...

I think a refresher on turbo's for FI engines may be helpful for some. Check out "Super Street" Magazine 09/01, pg. 147.

In FI engines the wastegate, on the exhaust side, determines max boost pressure. The blow-off valve is on the intake side of the turbo, it's function is to reduce or eliminate compression surge, which occurs when you get off the throttle. Once the throttle plates close, the incoming air has nowhere to go but back to the turbo. At best, this slows the turbo so you get lag when you're back on the gas. At worst, it can damage the turbo. However, on my Carb'd turbo V-8, the carb is before the turbo so there's no blow-off valve. The Wastegate can be manually adjusted to +/_ 16 pounds.

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