How much HP does one psi of boost equal
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This is a discussion on How much HP does one psi of boost equal within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Does anyone know this? I can't remeber were I saw this but what I remember is something like for each ...

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    Registered User scoob's Avatar
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    How much HP does one psi of boost equal

    Does anyone know this? I can't remeber were I saw this but what I remember is something like for each pis of boost equals 16 hp. Let me know what's up.

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    A general rule of thumb is 1psi=10hp at the flywheel.

    Later,

    Dale

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    Registered User scoob's Avatar
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    Good lookin out man.

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    tan
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    Thinking Man's Engine tan's Avatar
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    From talking to one of Craig Paisley's crew members:

    For every 14 psi of boost, you double the horsepower (from a naturally aspirated engine).

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    so how much horses do you think the rex would have without the turbo? just curious

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    Registered User Root's Avatar
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    The engine in the WRX is made for a turbo. It runs lower compression than say a honda engine. In the WRX it is about 8:1 and a Honda is about 11:1. If you took the turbo out and actually got it running well it would get beat down by a Yugo. This is one heavy little car made to be turboed.
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    I know this is probably stupid to revive this incredibly old thread, but I found this query kind of interesting.

    First off, I agree with Tan 14psi = doubled hp over natural aspiration

    Baluch on the other hand...thats an overgeneralization and psi/hp is relative to the original performance of an engine.

    Here's the theory.

    Assuming tuning is done correctly, you get a stoichiometric mix of O2 and fuel igniting in the combustion chamber. We can establish that we have a set ratio of oxygen and fuel and it should never change. So if we dump in twice as much gas then we MUST have twice as much oxygen for proper combustion.

    On planet Earth, there is a constant air pressure, 14.7 psi at sea level (this is the base air pressure in the combustion for all non turbo vehicles). So without turbo on a car, people can honestly say they are running their cars slightly over 14psi (relative to the vacuum of space anyways).

    We indirectly measure amount of gas particles with pressure, so if we turbo our cars to lets say 14.7 psi (on top of the 14.7 psi the Earth already gives us [totalling 29.4psi]) then we effectively have twice as much oxygen before ignition. Therefore the amt of fuel being pumped in is doubled, then at ignition we should theoretically get doubled the explosive power. So yeah, as Tan said if you do a 14 psi boost then you've nearly doubled the amount of oxygen in your turboed engine for double the power.

    Of course you lose potential power the higher you go because you encounter more resistance in the change of inertia of the internal components.

    So if your NA car makes about 100 hp
    -Boosting it to 14.7 psi will theoretically give you 200hp
    -Boosting it to 7.35 psi will theoretically give you 150hp and so on
    [ (HP of NA car) x (1 + (boost psi/14.7)) = HP at boost psi ]


    As for Baluch, his numbers are close enough but not for all engines. If you want an easy psi to hp conversion just divide your NA hp by 14.7 and that's it.

    -If your Suby is 147 hp NATURALLY ASPIRATED stock then, sure, 1psi boost = 10 hp (147/14.7)
    -But for a car that is 240 hp NA stock, a turbo would yield an equivalency of 1psi = 16.3hp

    To put it more accurately for Baluch, every 1 psi will get you approx 6.8% extra hp over a naturally aspirated setup (again, theoretical).

    Cheers

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    Holy poop an 8 year old thread bump!

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    So is that true a pound of boost equals 10 hp?

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    LOL, actual responses. Yeah, I did a quick search on the topic and this one was one of the first ones that came up. And since I am a proud new Suby owner, I decided to check this thread out.

    Quote Originally Posted by ScoobyDew View Post
    So is that true a pound of boost equals 10 hp?
    I suppose, but remember its only guess. I would ask other members that has played around with turbo. Although there's only a handful that are brave enough to turbo their NA cars, we can calculate backwards what a WRX or STi might have in terms of a NA HP.

    It'd be nice to get some real numbers. All that is really needed is just Dynoed HP and corresponding air pressure. Then the rest is basically algebra. In fact if people are willing enough to dump enough numbers in this thread. We can actually calculate the rate of inefficiency turbo gets as the PSI values go higher.

    I hope none of you guys are one of those that think having a turbo makes your car run more efficiently.

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    Administrator Trainrex's Avatar
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    Quote Originally Posted by Henry H View Post
    LOL, actual responses. Yeah, I did a quick search on the topic and this one was one of the first ones that came up. And since I am a proud new Suby owner, I decided to check this thread out.



    I suppose, but remember its only guess. I would ask other members that has played around with turbo. Although there's only a handful that are brave enough to turbo their NA cars, we can calculate backwards what a WRX or STi might have in terms of a NA HP.

    It'd be nice to get some real numbers. All that is really needed is just Dynoed HP and corresponding air pressure. Then the rest is basically algebra. In fact if people are willing enough to dump enough numbers in this thread. We can actually calculate the rate of inefficiency turbo gets as the PSI values go higher.

    I hope none of you guys are one of those that think having a turbo makes your car run more efficiently.
    You will only be able to possibly calculate for specific turbos with specific operating parameters, but it will still be close to impossible. A larger turbo will push more CFM. Air/fuel ratio ,timing, and temperature changes will also change the outcome. There are too many variable to even fathom a solid number.

    And yes, a turbocharger does increase the efficiency of an engine by using the engine's waste product to increase power.

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