Horsepower Vs. Blower boost.
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Horsepower Vs. Blower boost.

  1. #1
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    Default Horsepower Vs. Blower boost.

    Is there a correlation of how blower boost affects horsepower?

    As an example, if an engine makes 1000 horsepower while producing 9 lb. of boost,
    what should that same engine produce if the boost is increased to 11 lb. of boost with no other changes?

    Is there a predictable correlation of increased power?

    Assume the engine is not at a critical point of its potential. That is the 11 lb. of boost doesn't
    put it into a detonation situation or the blower is not being overdriven to excess.

    Basically, every thing stays within reasonable limits.
    Would the potential increase be essentially the same for roots as a turbo?

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    To the last part of your question I would say no. It takes hp to turn the roots blower, the turbo is using the exhaust to spin it, (free power) so I would say at the same boost levels the turbo would make mor power jmo.

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    Couple test that I looked at, saw approx 140 hp per 5 lbs of boost
    this was a 1000 hp roots blown pump gas 572, close to the boost level you spoke of

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    I think 1# of boost is good for about 20,30 hp depending on the combo, so best case 1060hp

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    Quote Originally Posted by jimsplace View Post
    As an example, if an engine makes 1000 horsepower while producing 9 lb. of boost,
    what should that same engine produce if the boost is increased to 11 lb. of boost with no other changes?

    Is there a predictable correlation of increased power?
    You can calculate it, with a fair degree of accuracy. However, you would need to know, or have a good idea what the compressor (blower) efficiency, intercooler efficiency (if equipped), and Brake Specific Fuel Consumption is. Or, if you had it dyno'd and know both, the N/A and boosted horsepower, the rest can be calculated. Not too many dyno that thoroughly though.


    Quote Originally Posted by jimsplace View Post
    Would the potential increase be essentially the same for roots as a turbo?
    The calculations are similar, with the addition of calculating parasitic losses.

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    Quote Originally Posted by Budweiser View Post

    The calculations are similar, with the addition of calculating parasitic losses.
    They are not even close. They aren't even playing the same game, by the same rules.

    A boost increase with a roots will increase power/torque across the entire powerband, top to bottom, 1500 to 8000+ with approximately the same % of increase over the lesser boost.

    A turbo running the same turbo with the waste gate cranked up will not change power until the point where the waste would have opened, and at that point it will increase the power. The turbo will supply the same air flow up to that point. The roots is supplying more air the instant you start the engine.

    The turbo will tend to have a higher increase on the top, the roots will increase it everywhere, and a pretty much equal % increase.



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    Quote Originally Posted by gn7 View Post
    They are not even close. They aren't even playing the same game, by the same rules.

    A boost increase with a roots will increase power/torque across the entire powerband, top to bottom, 1500 to 8000+ with approximately the same % of increase over the lesser boost.

    A turbo running the same turbo with the waste gate cranked up will not change power until the point where the waste would have opened, and at that point it will increase the power. The turbo will supply the same air flow up to that point. The roots is supplying more air the instant you start the engine.

    The turbo will tend to have a higher increase on the top, the roots will increase it everywhere, and a pretty much equal % increase.
    You're right. Within the context you are speaking to, I agree.

    However... Within the context of the quote and conversation, calculating peak horsepower, the calculations are similar with the addition of calculating parasitic losses.

    ( < is this the right smiley to keep this conversation non-argumentative? )
    Last edited by Budweiser; 05-23-2013 at 12:48 PM.

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    I understand the turbo has to spool up, but would'nt the turbo make more torque at some point because its not being driven by the crank?

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    Quote Originally Posted by twoblade View Post
    I understand the turbo has to spool up, but would'nt the turbo make more torque at some point because its not being driven by the crank?
    Short answer is yes.
    Quote Originally Posted by jimsplace View Post
    Would the potential increase be essentially the same for roots as a turbo?
    Short answer is no.
    Last edited by Budweiser; 05-23-2013 at 12:42 PM.

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    Quote Originally Posted by Budweiser View Post
    Short answer is yes.

    Short answer is no.
    The question was about potential increase, not peak increase. The potential increase @ equal boost is more for the roots since the average goes up considerably, where it doesn't with the turbo.
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    Quote Originally Posted by steelcomp View Post
    The question was about potential increase, not peak increase. The potential increase @ equal boost is more for the roots since the average goes up considerably, where it doesn't with the turbo.
    I read the following as a question about peak HP increase. Not sure where you're seeing a question about average increase, but you may be right... sometimes I misinterpret questions and intentions.

    Quote Originally Posted by jimsplace View Post
    As an example, if an engine makes 1000 horsepower while producing 9 lb. of boost,
    what should that same engine produce if the boost is increased to 11 lb. of boost with no other changes?
    And perhaps I misinterpreted the whole thread. I thought he was asking about calculating power increase on a blower deal. I don't see why turbo's even matter in the conversation, other than similarities in calculations.
    Last edited by Budweiser; 05-23-2013 at 01:29 PM.

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    Quote Originally Posted by Budweiser View Post
    I read the following as a question about peak HP increase. Not sure where you're seeing a question about average increase, but you may be right... sometimes I misinterpret questions and intentions.



    And perhaps I misinterpreted the whole thread. I thought he was asking about calculating power increase on a blower deal. I don't see why turbo's even matter in the conversation, other than similarities in calculations.
    I take it you are one of those guys that only drives his boat with the pedal floored from the time he starts the boat until he shuts it off. Maybe you should do more racing.

    Peak HP is over rated.



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    Quote Originally Posted by gn7 View Post
    I take it you are one of those guys that only drives his boat with the pedal floored from the time he starts the boat until he shuts it off. Maybe you should do more racing.
    No and yes
    Quote Originally Posted by gn7 View Post
    Peak HP is over rated.
    No argument from me on this at all, I completely agree. But, the best I can tell, it's not what jimsplace asked. Maybe we're using different secret decoder rings to answer what we think the "real" question is?

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    Quote Originally Posted by Budweiser View Post
    I read the following as a question about peak HP increase. Not sure where you're seeing a question about average increase, but you may be right... sometimes I misinterpret questions and intentions.


    I didn't see the word peak anywhere. Are you saying that potential only applies to peak power? I know you know better than that.
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