CFM airflow coming out of the turbo
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CFM airflow coming out of the turbo

  1. #1
    Highaboosta Unchained's Avatar
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    Default CFM airflow coming out of the turbo

    I read an interesting thing on a turbo forum that got me thinking.
    This would likely apply to any compressor.

    A member posted that the CFM airflow coming out of the turbo is always less that what goes in, and that at one bar (14.5 # boost pressure) there is half the CFM coming out than what went in because it has been compressed.
    Makes sense to me,
    I've been thinking about this backwards all this time.

    To me that throws a new slant on any trying to optimise with large diameter tubing, throttle bodies, porting, big cams, etc.
    I've been downsizing on my cam specs for the last three consecutive years and am down to a .630 lift and 255 duration at .050
    I haven't noticed any performance decrease or loss of WOT rpm at all and that explains it.
    Last edited by Unchained; 02-22-2009 at 10:27 AM.

    Twin Turbo 1800 HP V-Drive lake boat

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    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

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    Cantard 71hallett's Avatar
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    You would be amazed at how much a 3" pipe can feed.........big cams.....no point.
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    mo balls than $cents$ IMPATIENT 1's Avatar
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    i agree, i don't do cams over 660 lift at all, i just don't see the merit in the extra valvetrain abuse. i'll give alil hp up for reliable service everytime.

    Dare to be different, if it turns out great you can claim you planned it that way.

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    Senior Member GT Jets's Avatar
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    Same theory would apply to an intercooler.

    The air get more dense as it is cooled..It equals more "pounds of air per foot".

    GT
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    mo balls than $cents$ IMPATIENT 1's Avatar
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    that's something i don't understand about some set-ups i see that are marine built. why go so small on the ic even if its water to air. i ordered big water to air ics with a super low pressure drop. did i add alil turbo lag due to the increase of volume on the cold side? maybe, but i didn't give a shit , i was looking for low iat's up top and over 1/2mile passes get that shit cold so it'll like pump gas too!

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    Highaboosta Unchained's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    that's something i don't understand about some set-ups i see that are marine built. why go so small on the ic even if its water to air. !
    For me its a matter of space.
    It takes a lot of 3" tube to go to and from a large remote mounted intercooler besides the size of the core itself.

    With the core size I'm using (11" x 9" x 3 3/4") the IAT is 125 - 130 at 8 sec WOT and by then I'm going faster than I should be anyway. I'm sure the E85 provides some additional cooling past the injectors also.

    1/2 mile at WOT !!!

    Twin Turbo 1800 HP V-Drive lake boat

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    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

  9. #7
    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by Unchained View Post
    For me its a matter of space.
    It takes a lot of 3" tube to go to and from a large remote mounted intercooler besides the size of the core itself.

    With the core size I'm using (11" x 9" x 3 3/4") the IAT is 125 - 130 at 8 sec WOT and by then I'm going faster than I should be anyway. I'm sure the E85 provides some additional cooling past the injectors also.

    1/2 mile at WOT !!!
    we've got some nice spots on the lake that demand it i told ya we will know what the motor and boat can top out at before june rolls around

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    senior member turbo wog's Avatar
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    and over 1/2mile passes hell yeh!

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by turbo wog View Post
    and over 1/2mile passes hell yeh!
    let r rip tater chip we talked about this last nite and he said "well hell yeah, if the turbos don't stop pulling in 1/4mile, gotta see when they do" got alot of parts in yesterday and the ics came in this mornin, sending them straight over to teh radiator shop to be checked on both sides with 100psi of water pressure

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    senior member turbo wog's Avatar
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    i have been doing some top speed runs & testing the diverter settings, loader etc. & after i top out then i make changes & watch the gps. then i let her cool down & do it again with different settings

  13. #11
    Senior Member superdave013's Avatar
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    if the ducts are the same on the inlet and outlet the CFM on the outlet will be much higher due to the increased temp. You need to convert the outlet to ACFM if you want to compare it to the ~70 degree inlet.

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    Highaboosta Unchained's Avatar
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    So if we're talking about 1 bar of boost pressure you're saying that the heat generated during compression will have caused the air to expand beyond the volume it was before it was compressed ?

    Twin Turbo 1800 HP V-Drive lake boat

    http://s621.photobucket.com/albums/t...t=MAH05771.mp4

    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

  15. #13
    Senior Member superdave013's Avatar
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    Quote Originally Posted by Unchained View Post
    So if we're talking about 1 bar of boost pressure you're saying that the heat generated during compression will have caused the air to expand beyond the volume it was before it was compressed ?

    yup, it's not how you heat it. It's how much you heat it. Hot air expands and that will cause the velocity inside the duct to increase. We used to shoot for 45' per second and the hotter the air the bigger the duct.

    SCFM is referenced @ 70 degrees
    ACFM is what it is after your turbo heats it.

    Gotta love google. A quick search turned up some nice fan tech. http://www.pyebarker.com/TechTips/techtip2.htm

  16. #14
    Highaboosta Unchained's Avatar
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    Well then if the intercooler brings the IAT down to ambient, the volume and cfm would then be less than what went into the compressor by the amount is was compressed down to.
    So the hot air/volume factor is only going to apply between the compressor and the intercooler.
    That would mean that having the throttle body(s) past the intercooler would be more desirable.
    Mine are before the intercooler. No wonder it was always such a slug.

    Remember several years ago when you had to straighten me out on
    intercoolers ? LOL
    Lots of water under the bridge since then.
    Thanks for that info on the heated air volume.

    Twin Turbo 1800 HP V-Drive lake boat

    http://s621.photobucket.com/albums/t...t=MAH05771.mp4

    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

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