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CFM: Air Filters/Engine Requirements

Discussion in 'Engine/Drivetrain/Suspension' started by LPD111, Aug 11, 2004.


  1. LPD111

    LPD111
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    Ok, I need some technical info on CFM and surface filtering area of air filters and engine CFM requirements.



    My 5.9L V8 360 cid motor is rated:

    -245 HP @ 4,000 RPMS

    -345 TQ @ 3,200 RPMS



    The stock paper air filter size is 13.5" long x 6.5" wide x 1" tall.



    Three main questions to start with:

    1) What is the total surface filtering area be of this sized filter?



    2)What is the CFM air flow rate be for this sized air filter?



    3? What is the CFM requirements for my 5.9L V8 360cid motor?



    I have heard that the 360 motor only 'needs' 350 CFM-425 CFM, so 'function'. I just would like to clarify this CFM number. Is there are calculator I could use to determine the CFM for my motor?



    Lastly, what is the the stock 5.9L V8 throttle body rated at? I have also heard anywhere from 635 CFM upto 690 CFM.



    Thanks for any and all info on this.
     

  2. SalvagExpert

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    (1) - cant be computed that way, to many variables.

    (2) - cant be computed that way, to many variables.

    (3) - no idea
     

  3. BB_Tony

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    Can't help on 1 or 2, but on the 3rd question you can use this generic forumla to figure the required cfm for your motor.



    cubic inches times max rpm of motor, divided by 3456 (360 * 5500rpm / 3456 = 572cfm)



    Hope that helps
     
  4. LPD111

    LPD111
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    BB Tony,

    Thanks for the info. Helps alot.
     
  5. LPD111

    LPD111
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    Also, to get a general estimate of the total surface filtering area of my stock sizzed filter, can't I just take the size of the filter:



    -13.5" x 6.5" x 1" and = 87.75 square inches



    Right? I think that it is.



    Now, all I need to do is it figure out what CFM this size filter is capable of flowing.



    I want to say it is somewhere in the 520-540 CFM area. A 10"x2.75" round filter has 86.35 square inches of filtering area and it flows 520.69 CFM.



    A slightly larger 10"x3" filter round filter has 94.2" square inches and flows 555.97 CFM.



    So, can I a$$ume that it will be somewhere between 520 CFM and 555 CFM?? The average comes out to be 537.5 CFM.
     
  6. 00DodgeGuy

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    I think you have to factor in all the pleats(surface area). I think it is much more difficult to figure out than you think. :dunno:
     
  7. steved

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    Umm, you figuring volume cause inch*inch*inch is cubic inches...a volume of the area the filter exists in, not the volume it can flow.



    You would need to know the number of pleats of the filter (to figure out the total area of filter media) and average flow per given area that particular filter media will flow, and size of the filter to figure it out...I mean think about it, a K&N will outflow a stock filter of the same size. This ain't nearly as easy as you think it is.



    steved
     
  8. SalvagExpert

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    you gave volume not surface area, its sorta like the surface area of a golf ball, all the dimples made the surface area larger. well the filter has ridges on it which the only way to tell the surface area would be to take the damn thing apart, unfold it all and lay it out flat...



    and the CFM flow rating for a filter is different for each brand filter....



    and what the hell are you trying to figure this out for...



    its like asking how many licks it takes to get to the center of a tootsie roll pop.... no one cares because the center taste like crap.
     
  9. LPD111

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    Just trying to figure out what the engine requirements are CFM-wise and then trying to figure out what the stock filter flows, and if the stock filter is 'choking' the engine. I already know my TB is flowing enough CFM for the engine to breathe efficiently. This will then help me determine if I want to spend the $40-$50 on a drop in high flow panel filter (K&N, Accel, Holley, etc) or if I will have to go to an aftermarket setup; either being a cone style or a 14" round style setup. The 10" and even 12" round filters do not flow enough CFM unless you want to run a 5" tall filter setup. Also, Intense Performance makes some really nice setups, whether in the open element round style or the cone style setups. Plus they are very helpful with answering questions, and there prices are good too. Their 7" PowerStack cone filter flows 1272 CFM!!!



    14" Round Filters:

    -14"x2.5" K&N flows around 662 CFM

    -14"x2.75" K&N flows around 728 CFM

    -14"x3" K&N flows around 795 CFM



    Cone Style Filters:

    -6"x9" cone: 1017 CFM

    -5"x"7" cone: 659 CFM



    KN 8" Cone #RE-0810 flows 833 CFM.

    KN 4.5"x7" Cone #RE-3130 flows 528 CFM.



    There are a TON of K&N cones out there, I mean a TON!!! I just want to match up my TBs CFM flow rate with a filter setup that is around 900-1000 CFM. I do not want the engine to starve for air, like I am sure it is right now with my completely stock setup and a paper Fram filter. If I am going to spend the money, I want to do some research and find out what will work the best for the money I want to spend. Plus, this CFM measurements and flow rate requirements are interesting to learn about.



    Everyone thinks that the stock setup draws cool air from the front of the truck, since it has the large rectangular box ontop of the TB and then has the plastic tube running to and into the passenger's side fender. Has anyone actually traced where this tube draws this alleged 'cold air' from?? I believe it still comes from the engine bay/compartment!
     
  10. SalvagExpert

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    well you certainly have... alot of.... free time? :D:
     
  11. LPD111

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    \



    I work 7 days a week, and I am on my 15th in a row right now and finish up Sept 9TH, so no, I do not have a lot of free time.



    I am just doing some research here and there and trying to figure out what I need and don't need, and what will be the best way to upgrade in my air intake system for my engine's needs and how I use my truck. No sense in just going out any buying a $300 K&N FIPKII if I don't have to.



    Right now, I am kind of skeptical about buying a higher flow drop in replacement panel style filter. Without having specs on what CFM they flow, it would just be another 'blind purchase'.



    I am leaning toward a 14"x2" round open element with an X-treme (Intense Performance model, not K&N) style top cleaner lid, or a 14"x3" (795 CFM) round open element kit. I would want the X-stream cleaner lid only on the 2" tall filter because the 2" tall round filter would be flowing around 600 CFM, and the air cleaner lid would help flow a tad more air. The 3" would already be flowing enough air, but I have also heard that the 3" tall filter is a very tight fit.



    The cone style filters are also an possibility, but i dont want anything else in the engine bay because I will soon be running a dual battery setup. Oh well, gotta to go work, again......
     
  12. steved

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    You could email K&N and ask them what their filter flows. They should even be able to give you a comparison to a paper element.



    steved
     
  13. LPD111

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    Just to let everyone know, after waiting 2 weeks, I finally received a response from K&N concerning their drop in replacement air filter for my truck.



    K&N stated that their direct replacement panel filter for my truck flows 537 CFM. This rating is for K&N PN#33-2084.



    So now, here are some facts:



    360cid 5.9L Motor:

    -572 CFM



    360cid 5.9L STOCK TB:

    -650 CFM



    -K&N Direct Fit Filter:

    -537 CFM



    While the stock TB is flowing enough for the motor, the stock sized panel filter is not. If the K&N filter is only flowing 537 CFM, I can only imagine what a generic paper filter is flowing.



    My current TB is flowing around 825-850 CFM. So my stock setup (completely stock including paper panel filter) is obviously restricting CFM flow, this hurting MPG and overall performance.



    What I am going to do:

    -I am going to completely take off the entire stock air fitler a$$embly (minus that 'air inlet tube' which connects into the rectangular filter housing).

    -I bought a used K&N GenI open element kit along with a K&N Extreme Air Cleaner Lid.

    -I will fully clean and properly 're-charge' the K&N round filter and the K&N Extreme Lid.



    K&N stated the GenI kit with their Extreme Lid will flow right around 1000 CFM. Plenty of air flow now.



    I am going to leave the 'air inlet tube' which runs from the passenger side fender to the TB. I will fab up a bracket to hold this tube in place (where it 'hovers' over the motor) so that is runs right to the passenger side the the GenI open element filter. While I have serious doubts that this inlet tube actually draws in cool air, I will leave it in place for right now. I most likely will take this tube off also.



    I will repost my power findings and any MPG changes.
     
  14. JeepCrawler98

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    to calculate CFMs for a 4 stroke you - enter bore and stroke in inches.



    [([Pi x Bore^2]stroke)(number of cylinders)(peak RPM/2)]/12
     

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