Two S/C questions about the V
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2009-2014 Cadillac CTS-V General Discussion Discussion, Two S/C questions about the V in Cadillac CTS-V Series Forum - 2009-2014; #1 -- What is the boost guage actually telling me? Is it Xpsi relative to sea-level, or is it Xpsi ...
  1. #1
    Jayfrigginjones is offline Cadillac Owners Member
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    Two S/C questions about the V

    #1 -- What is the boost guage actually telling me? Is it Xpsi relative to sea-level, or is it Xpsi relative to ambient pressure. This matters to me since I'm over a mile in altitude, and wonder if the S/C is compensating, or if i'm suffering the same 20% power loss as the N/A cars.

    #2 -- What would happen if I drove the car with the belt off the S/C? Would something overheat? Seize? Would mpg increase? Would the engine fall out and explode beneath me?

    Thanks
    Jay

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    V Wagon is offline Cadillac Owners Fanatic
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    Re: Two S/C questions about the V

    There's really no reason to drive with the belt off the blower. Under cruise conditions it already opens a bypass and doesn't make boost. It takes very little power to turn it when it isn't compressing air. Nothing would overheat, or seize, MPG wouldn't increase any noticeable amount. The only thing you would notice is a lack of power when you floor it.

    ----------

    Oooops, forgot this isn't like the Lightning was where it had a separate belt for the blower. The blower belt is the accessory belt. So if you take it off the blower, it won't be tight to the other accessories and none of them will be driven. So yes, you will overheat the engine, seize, it will blow up and all that other doom and gloom you mentioned.

    I suppose you could get a shorter belt and then MAYBE you would be able to come up with an appropriate routing to drive all the accessories. But you would get no benafit from it so it'd be a big waste of time.

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    MacBuster is offline Cadillac Owners Fanatic
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    Re: Two S/C questions about the V

    I'm curious about the altitude question, also, since I'm much higher than sea level.

    N/A cars here lose something like 20% of their power. One benefit of Turbo cars here, is that they don't. What about the S/C?

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    Jayfrigginjones is offline Cadillac Owners Member
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    Re: Two S/C questions about the V

    Quote Originally Posted by MacBuster View Post
    I'm curious about the altitude question, also, since I'm much higher than sea level.

    N/A cars here lose something like 20% of their power. One benefit of Turbo cars here, is that they don't. What about the S/C?
    Maybe this is accurate, but maybe it's not. If the boost guage of *any* forced induction car is relative to ambient pressure, then it will loose power just like the N/A cars. If it is relative to sea-level pressure, then turbo and S/C cars should be able to compensate.

  6. #5
    larry arizona is offline Cadillac Owners Connoisseur
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    Re: Two S/C questions about the V

    boost is relative to ambient atmospheric pressure. Yes you will lose power similar to any other NA vehicle, however, you can increase boost to make more power too. Your power will always be relative to your given altitude and pressure.

  7. #6
    MacBuster is offline Cadillac Owners Fanatic
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    Re: Two S/C questions about the V

    Quote Originally Posted by Jayfrigginjones View Post
    Maybe this is accurate, but maybe it's not. If the boost guage of *any* forced induction car is relative to ambient pressure, then it will loose power just like the N/A cars. If it is relative to sea-level pressure, then turbo and S/C cars should be able to compensate.
    I think we are largely asking the same question. Basically, I want to know if the S/C gets us back up to "sea level"? I think your average turbo can just work harder to ensure the pressure going into the system is as close to spec as possible. With the S/C, I think they just spin at a rate relative to engine speed (?).

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    larry arizona is offline Cadillac Owners Connoisseur
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    Re: Two S/C questions about the V

    Quote Originally Posted by MacBuster View Post
    I think we are largely asking the same question. Basically, I want to know if the S/C gets us back up to "sea level"? I think your average turbo can just work harder to ensure the pressure going into the system is as close to spec as possible. With the S/C, I think they just spin at a rate relative to engine speed (?).
    to answer your question no. Your SC only moves based on engine RPM and pulley size/ratio. So your SC speed is fixed and only can compress less dense air at the given SC speed. So at sea level you will have more boost than at 5000 ft. You will always have more boost at sea level than at any greater elevation with a given SC speed/ratio.

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    Jayfrigginjones is offline Cadillac Owners Member
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    Re: Two S/C questions about the V

    Quote Originally Posted by larry arizona View Post
    boost is relative to ambient atmospheric pressure. Yes you will lose power similar to any other NA vehicle...
    Without knowing exactly how the engine management system measures pressure I'm uncertain, but L.Arizona's statement is my intuition. I hear claims similar to what MacBuster hears:"Turbo cars don't suffer altitude losses", but I've always been suspicious.

    Quote Originally Posted by MacBuster View Post
    With the S/C, I think they just spin at a rate relative to engine speed (?).
    Spin is relative to engine speed yes, but the S/C can create excess boost which is regulated by the ECM, so it can merely "throw away" less boost at a given rpm (above the rpm at which excess is possible for the load). At least I think this is how it works. I may have some part of that wrong though...

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    MacBuster is offline Cadillac Owners Fanatic
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    Re: Two S/C questions about the V

    Quote Originally Posted by Jayfrigginjones View Post
    Without knowing exactly how the engine management system measures pressure I'm uncertain, but L.Arizona's statement is my intuition. I hear claims similar to what MacBuster hears:"Turbo cars don't suffer altitude losses", but I've always been suspicious.



    Spin is relative to engine speed yes, but the S/C can create excess boost which is regulated by the ECM, so it can merely "throw away" less boost at a given rpm (above the rpm at which excess is possible for the load). At least I think this is how it works. I may have some part of that wrong though...
    Some google-fu revealed this same discussion on the audi boards. Audis have S/Cs that produce more boost than is utilized. This boost is then dumped by a waste-gate to achieve the "target pressure" as specified by the engineers. As a result, at higher altitudes, this valve simply closes more, releasing less (relative) pressure, ensuring that the manifold pressure stays quite close to sea level. The Audi guys are saying they only lose about 0.5% power per 1000 feet of elevation, compared to 3% for a N/A car.

    I have no idea if the V has a similar system.

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    Re: Two S/C questions about the V

    The SC belt ONLY drives that, nothing else. I had to drive mine a few weeks w/o it, and no issues at all. I never floored it though either, so I'm not sure if it run rich or lean at WOT. I also heard the 3%/1000' for NA cars a lot, and max 1% for SC cars.

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    Jayfrigginjones is offline Cadillac Owners Member
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    Re: Two S/C questions about the V

    Quote Originally Posted by MacBuster View Post
    Some google-fu revealed this same discussion on the audi boards. Audis have S/Cs that produce more boost than is utilized. This boost is then dumped by a waste-gate to achieve the "target pressure" as specified by the engineers. As a result, at higher altitudes, this valve simply closes more, releasing less (relative) pressure, ensuring that the manifold pressure stays quite close to sea level. The Audi guys are saying they only lose about 0.5% power per 1000 feet of elevation, compared to 3% for a N/A car.

    I have no idea if the V has a similar system.
    Nice googlestyle. I think this makes sense. The V should experience altitude power loss through the low rpm only.

    Quote Originally Posted by baabootoo View Post
    The SC belt ONLY drives that, nothing else. I had to drive mine a few weeks w/o it, and no issues at all. I never floored it though either, so I'm not sure if it run rich or lean at WOT. I also heard the 3%/1000' for NA cars a lot, and max 1% for SC cars.
    Good to know. Thanks

  13. #12
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    Re: Two S/C questions about the V

    Quote Originally Posted by MacBuster View Post
    Some google-fu revealed this same discussion on the audi boards. Audis have S/Cs that produce more boost than is utilized. This boost is then dumped by a waste-gate to achieve the "target pressure" as specified by the engineers. As a result, at higher altitudes, this valve simply closes more, releasing less (relative) pressure, ensuring that the manifold pressure stays quite close to sea level. The Audi guys are saying they only lose about 0.5% power per 1000 feet of elevation, compared to 3% for a N/A car.

    I have no idea if the V has a similar system.
    It should. TVS makes both the units for the LSA and the 3.0T.
    MacBuster and MacBuster like this.

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    larry arizona is offline Cadillac Owners Connoisseur
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    Re: Two S/C questions about the V

    The easiest way to come to understand this is no matter if your car is NA or FI, for the same set-up/mods you will always make more HP/TQ at a lower altitude. Density Altitude is a huge factor in performance.

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    6104696 is offline Cadillac Owners Connoisseur
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    Re: Two S/C questions about the V

    in other words, the best 0-60 and performance times for any given CTS-V (or any other car with an internal combustion engine) will be attained in New Orleans or in Holland (or in a sub-sea level tunnel?), in cool weather (and proper tires for the temps).......

  16. #15
    larry arizona is offline Cadillac Owners Connoisseur
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    Re: Two S/C questions about the V

    that is why DA (density altitude) is important when understanding 1/4 mile times.

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