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2009-2014 Cadillac CTS-V Performance Mods Discussion, P-valve Question in Cadillac CTS-V Series Forum - 2009-2014; Originally Posted by wait4me Correct, Even though you get about .5 lbs of boost extra by tweeking the bypass valve ...
  1. #31
    stealthjr is offline Cadillac Owners Fanatic
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    Re: P-valve Question

    Quote Originally Posted by wait4me View Post
    Correct, Even though you get about .5 lbs of boost extra by tweeking the bypass valve on the stock one to make it fully closed. Even a slight gap will cause a pressure loss, so make sure it is fully closed.
    Makes sense, thanks.

    Also, I added to my last post when you were typing this response...could you clarify for us and answer my edited question please?

    Robert

  2. #32
    backup is offline Cadillac Owners Fanatic
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    Re: P-valve Question

    Thanks for the legend! post edited after reading Jesse's response!

  3. #33
    CadV is offline Cadillac Owners Connoisseur
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    Re: P-valve Question

    I am confused

  4. #34
    1-2-N-V is offline Cadillac Owners Fanatic
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    Re: P-valve Question

    You Know, There was a pdf download from Hennesse site a while back describing a module that will control the boost on a SC. I thought this was on a Vette, I do not recall. As i am thinking what vette besides the ZR1 has a SC? Anyway I know i saw it but i can't seem to find it now. I should have saved it. Well if it works like a Waste gate it may have a higher preset than stock and will bleed of the excess psi when necessary. Just plugging that off seems dangerous to me unless you have a way of purging that extra boost. On my GN i had a manual waste gate adjustment though a dial controller valve which when the boost got up to about 18 PSI at WOT i could dial it down on second and third gear and open the waste gate before i would get any over boost or lean condition. Worked great.

    Anyway maybe someone can find it. Maybe do a search on the web about it. According to Jesse i thought this mod would only get you a .5 lb of boost probably not much to worry about an over boost condition. Now if this is blowing past 15 lbs i would say that there may be a need for a controller and this indeed is a way of a few extra ponies. Just my 2 pennies worth

  5. #35
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    wait4me is offline Cadillac Owners Connoisseur
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    Re: P-valve Question

    The boost bypass still works just fine with this mod. you are only changing / removing the overboost protection.

  6. #36
    1-2-N-V is offline Cadillac Owners Fanatic
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    Re: P-valve Question

    Jess,I am not following that. Plugging the P port i think they said will yield more boost but there is no fear of an over boost as this bypass is still working? I have to really have things broken down to me in the progression of how something works in order to really understand this completely. I could understand the simple waste gate theory for my GN but this may be a bit more sophisticated. When you guys get through with your testing this weekend can you let us know what the result was? thanks guys.

  7. #37
    jwa999 is offline Cadillac Owners Fanatic
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    Re: P-valve Question

    ^^^^^^^^^^^^^^^^^
    I think the bypass is the process of not generating boost.

    Your supercharger is always spinning. However it's not always generating boost.

    You can be running at 6000rpms, it can generate 9lbs of boost, but unless the engine is under load, the supercharger is instructed *not* to boost or only to boost a certain amount.

    I think that was what backup was playing with. Mess with the bypass control (the X connection), so the supercharger would generate the maximum boost for what ever rpms it's running.

    The overflow valve is there to leak any excess boost. Sounds like the overflow valve is normally leaking .5lbs of boost.

    Question is, what can cause an overboost situation that the engine needs protection from?

    Hans.

  8. #38
    Nutz's Avatar
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    Re: P-valve Question

    My assumption:

    Safe to assume we make 9 lbs. stock.

    There are everyday things that can lead to 1-2 lbs. of slight increases in boost such as barometric pressure, increased octane, and significant air temperature drop which can lead to an unexpected lean condition. I assume the P Valve seems to protect/prevent such conditions.

    Soooo, it sounds like you need to perform this procedure only when significantly increasing boost with such as a pulley kit. (over 10 lbs.)

    It also sounds to me as if those that are experiencing seat of the pants increase are one of the three above ambient effects resulting in slight boost increase.

    IF my guess work above is correct than I have questions (Jesse):

    1. Does the stock PCM adjust fuel for such changes?

    2. Does your (W4M) PCM adjust?

    3. The obvious one. Will this hurt the car by offering a dangerous lean condition?


    Don't flame me guys. Just my thoughts. Plus, I think these are valid questions.

  9. #39
    backup is offline Cadillac Owners Fanatic
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    Re: P-valve Question

    Quote Originally Posted by wait4me View Post
    The boost bypass still works just fine with this mod. you are only changing / removing the overboost protection.
    Guys I think Jesse has the key here. In my experimentation, I could not get the boost much over 9psi. The best thing I could get was perceived faster boost build, which felt stronger, and maybe a little extra on the boost gauge (.5lb?). This was by capping the P port or removing the X-line (both do the same thing - removes the pressure feed to the P port). I got a hunch this little mod might be worth a few HP, or at least a few HP earlier. The car certainly felt more responsive.

    I don't think the supercharger can make more than about 9 to 10psi in stock form anyway. You need pully swap to increase rpm to get beyond that. Jesse, is that right?

  10. #40
    CadV is offline Cadillac Owners Connoisseur
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    Re: P-valve Question

    So if you cap X you could cap everything right?

  11. #41
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    Re: P-valve Question

    The way i understand it, is if you cap O and leave the line open that connects to it, your set. Cecil...............

  12. #42
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    Re: P-valve Question

    Quote Originally Posted by CadV View Post
    So if you cap X you could cap everything right?
    Yes, capping X is the same as capping P, it removes the boost pressure from the P port. I have simply pulled the O line off the port on the OX valve which does the same thing. From what I have seen, the car builds boost fast and maybe .5-1.0 extra boost. The car certainly feels more responsive, and the boost gauge is clearly a little higher this way. I think it is more than placebo.

  13. #43
    The Tony Show's Avatar
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    Re: P-valve Question

    If there was no risk to doing this and the car performs better this way, GM would have done it from the factory. I sincerely doubt that they'd intentionally handicap their flagship performance car in this manner unless it somehow provided better performance, longevity or protection.
    Rest in Peace, J.D. (aka Dirt_Cheap_Fleetwood)

  14. #44
    musclesbmf is offline Cadillac Owners Connoisseur
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    Re: P-valve Question

    Quote Originally Posted by The Tony Show View Post
    If there was no risk to doing this and the car performs better this way, GM would have done it from the factory. I sincerely doubt that they'd intentionally handicap their flagship performance car in this manner unless it somehow provided better performance, longevity or protection.
    Two words: Warranty Claims.

    So when we decide to up the boost, they still had protection to bleed off the boost. That's like saying GM/Cadillac will tune the ECM for max performance. No they won't. Or that their intake will perform better than aftermarket, etc. Can be applied to anything. I guess aftermarket headers and exhaust don't perform better either....

  15. #45
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    Re: P-valve Question

    You must have missed the part where I said "provided better longevity or protection". I have no doubt that putting a bigger crank pulley, upping the boost and defeating the boost limitations and bleed off make the car more powerful. Anyone who thinks they aren't taking a huge risk though, is kidding themselves.

    I never said that they tune it for max performance- every carmaker sets the car up in the "sweet spot" between max performance and realistic durability. I've been modding cars for years, and the reality is simple: Every time you add power, you remove some of the margin for error in how bad things break if something goes wrong. Top Fuel engines sure make awesome power, but then they get torn down and rebuilt after one quarter mile pass.

    Things like overboost protection are there to keep you from shattering a piston if something causes a boost spike. Does defeating it make more power? Sure it does- just like headers and tunes. But just like headers and tunes, it becomes a lot easier for something to get damaged if something happens.

    I'm not trying to rain on anyone's parade, but based on a lot of the comments I'm reading here I think a lot of the posters on this forum are new to modding (not all, but some). They need to be aware of what exactly they're doing when they tinker with overboost protection.
    Rest in Peace, J.D. (aka Dirt_Cheap_Fleetwood)

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