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  1. #1
    Boilerman Bill BPnta's Avatar
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    Why a good intercooler makes a difference:

    Finally completed the data (7-17 PSI!). First off, let me make a few things clear:
    A) It is generally understood that density (number of molecules in a given volume) is the best way to measure how much air (and consequently, oxygen) is getting into the combustion chamber, not boost or temperature alone.
    B) The higher pressure a gas has, the more dense it is.
    C) When you pressurize a gas, it gets hotter.
    D) The hotter the air becomes, the less dense it is. This is because the molecules themselves are at a higher energy state and move faster, which makes them repel each other more.

    Basically, when you pressurize a gas, you increase it's density, but on the same hand it gets hotter which makes the gas less dense! So it is possible to get the same density with lower boost if you can get a low enough temperature! This relationship between density, pressure, and temperature can be quantified by the PV=nRT equation. NO MORE ASSUMPTIONS!!!

    Now onto the data!

    A few other things you must understand to use the data:

    1) The volume is constant across all measurements. We are, in fact, talking about the volume of the intake manifold for the SHO, and it doesn't change.
    2) Since the volume is constant, and density=mass/volume, then mass can be used to directly correlate density.
    3) The PV=nRT equation was used to solve for molar mass (basically just mass).
    4) Since statement #1 is true, the value of the volume doesn't matter, because the value of mass doesn't matter. We are only looking at the relationship between the mass, pressure, and temp. We are not actually trying to figure out the number of molecules (mass) entering the engine.
    5) I used 1440 cubic inches as the constant volume in the equation. Even if someone knew the actual volume of the intake manifold the relationship between the temp, pressure, and density would be the same. The first time I ran the numbers I used 1 cubic foot and the relationship was identical.



    Each line on the graph represents a different boost level, from 7-17 PSI.
    The Y direction represents the molar mass, which directly correlates density (see statement 2)
    The X direction is the temp, from 80-250 degrees Fahrenheit.

    The rest is up to you!

    Using the data you can see that a 12 PSI boost at 200 degrees gives you the same density as 10 PSI at 90 degrees!

    Use this data to make decisions about aftermarket I/C's and boost wheel configurations, because boost numbers and temps alone only tell half the story!

    There are scenarios where upgrading wheels alone will not give you a higher density, especially when upgrading a small increment such as a C1 wheel to a B1.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2

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    Theory only......... (until next week when the wheel finally gets here).

    So running a "18" psi ET wheel thru a very large (type 12) intercooler will show a significantly lesser pressure than an OEM intercooler at the same rpms and load mainly due to the drop in temp?

    Not due to restriction of the intercooler core but the dramatic drop in air temp. In other words squeezing more air in due to it been colder.

    The only true result I'll be able to measure the result is from very accurate GPS speed (20htz instead of 5htz) on a flat water lake with no wind and during the middle of the day so the intake air temps are stable. This is of course at a stable rpm which I can set with the motec rev limit.


    I have sucky expressive english skills so I hope this makes sense.

  3. #3
    It's not the destination, it's the journey!! Rip'nTear SHO's Avatar
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    Looks like a very comprehensive post....don't have time to absorb it now as I'm off to work,,,,but keep up the good work!

  4. #4
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    boost is not equal

    High boost and high temp is the same(power) as low boost and low temp
    Just depends on how efficent your intercooler is.
    Thats why some people run 82 mph with 15lbs of boost and others do 82 mph with only 12 lbs

  5. #5

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    Quote Originally Posted by onebadsho View Post
    High boost and high temp is the same(power) as low boost and low temp
    Just depends on how efficent your intercooler is.
    Thats why some people run 82 mph with 15lbs of boost and others do 82 mph with only 12 lbs
    Thanks.

  6. #6
    Thanks for that BPnta, I knew I need an intercooler, now I understand a bit more about why I need one.

  7. #7
    Boilerman Bill BPnta's Avatar
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    Quote Originally Posted by Gunna View Post

    So running a "18" psi ET wheel thru a very large (type 12) intercooler will show a significantly lesser pressure than an OEM intercooler at the same rpms and load mainly due to the drop in temp?
    Yep! Say your 18 PSI was 230 degrees before it hit the I/C, and 90 coming out, it would then drop to 15 PSI but have the same density.

  8. #8
    i will get all the rest i need when im dead corkycat's Avatar
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    Quote Originally Posted by BPnta View Post
    Finally completed the data (7-17 PSI!). First off, let me make a few things clear:
    A) It is generally understood that density (number of molecules in a given volume) is the best way to measure how much air (and consequently, oxygen) is getting into the combustion chamber, not boost or temperature alone.
    B) The higher pressure a gas has, the more dense it is.
    C) When you pressurize a gas, it gets hotter.
    D) The hotter the air becomes, the less dense it is. This is because the molecules themselves are at a higher energy state and move faster, which makes them repel each other more.

    Basically, when you pressurize a gas, you increase it's density, but on the same hand it gets hotter which makes the gas less dense! So it is possible to get the same density with lower boost if you can get a low enough temperature! This relationship between density, pressure, and temperature can be quantified by the PV=nRT equation. NO MORE ASSUMPTIONS!!!

    Now onto the data!

    A few other things you must understand to use the data:

    1) The volume is constant across all measurements. We are, in fact, talking about the volume of the intake manifold for the SHO, and it doesn't change.
    2) Since the volume is constant, and density=mass/volume, then mass can be used to directly correlate density.
    3) The PV=nRT equation was used to solve for molar mass (basically just mass).
    4) Since statement #1 is true, the value of the volume doesn't matter, because the value of mass doesn't matter. We are only looking at the relationship between the mass, pressure, and temp. We are not actually trying to figure out the number of molecules (mass) entering the engine.
    5) I used 1440 cubic inches as the constant volume in the equation. Even if someone knew the actual volume of the intake manifold the relationship between the temp, pressure, and density would be the same. The first time I ran the numbers I used 1 cubic foot and the relationship was identical.



    Each line on the graph represents a different boost level, from 7-17 PSI.
    The Y direction represents the molar mass, which directly correlates density (see statement 2)
    The X direction is the temp, from 80-250 degrees Fahrenheit.

    The rest is up to you!

    Using the data you can see that a 12 PSI boost at 200 degrees gives you the same density as 10 PSI at 90 degrees!

    Use this data to make decisions about aftermarket I/C's and boost wheel configurations, because boost numbers and temps alone only tell half the story!

    There are scenarios where upgrading wheels alone will not give you a higher density, especially when upgrading a small increment such as a C1 wheel to a B1.

    well done!! this is excactly what i was explaining to my pal just yesterday over here in the uk, i have all the mods and just a standard intercooler (with cfm kit) but this is still to small for my mods i got 81mph with the reflash and as soon as the engine got slightly heat soaked my speed dropped to 76mph, it is really cold over here (12 degrees on a beautifull sunny day) but the air going through the intercooler is restricting my performance due to the density. my next step is a larger diameter intercooler.

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