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  1. #1

    ignorant question #49

    Recently I've been trying to figure out how to make breathing easier for my '05 RXT.

    The area of a 4" circle...about 12 1/2"sq. ------- 3.141 x 4 = 12.564

    The area of a 3" circle...about 7"sq. -------- 3.141 x 2.25 = 7.067

    Okay...a stock air intake is 7' or so long and has a few baffles but no filter or pre-filter with which to restrict air flow. It also draws in...warm air.

    A 3" Power filter is 4-5' long is less restrictive but still draws in warm air.

    A 4" hose directed up front breathes a lot easier but still draws in warm air.

    What isn't determinable...by me anyway...how much more difficult is it to draw air through a 3" hose vs a 4" hose

    Okay...next...would a 3" hose only 1' long be easier on the SC than a 4" line 7' long?

    Here's the ignorant question...would the 1' long 3" hose with a flow-rite pri-filter be easier to draw air through than a 7' long 4" hose?

    ...curious
    Last edited by VaRedneck; 05-14-2007 at 07:31 PM.


  2. #2
    Moderator two2curupt's Avatar
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    What you want essentially is the best quality (cool) air you can get... You will not pull that out of the hull..

  3. #3
    ...but if the SC has to work harder to get the cool air than the warm...is the loss in R's a push?

  4. #4
    JFizzleJR's Avatar
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    Going 1' away from the S/C is too hot unless you're going to do a rear intake. If you want the best performance without going with a rear intake then go for the 4" intake up front. You won't need more than 8' of the hose. I have a thread called "4 inch custom intake parts list" with just about everything there to make a $115-135 4" front intake. I don't think a pre-filter is necessary unless you're doing a rear intake and riding in surf with it.

  5. #5
    I am trying to figure a way to do a rear air intake...while saving the underseat storage.

  6. #6
    JFizzleJR's Avatar
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    I'm not familiar with the 3 seaters but i'm pretty sure you're going to have to cut some stuff up if you plan to make yourself one. I personally prefer the 4" intake up front because it's simple and I don't have to worry about water injestion, especially with a filter on it.

  7. #7
    The cutting's done.

    It's been mentioned elsewhere that you need x amount of pre-filter area in relation to the actual area of the intake in order to account...whatever...for the restriction of the pre-filter itself.

    My question really boils down to this...

    Will a cold air, 3" pre-filtered line 1' long offer better or worse performance than a 4" warm air 7' line.

    Here's an added question...

    Would the pre-filter be better mounted on the new 8.4sq inch "grill" or the throat of the 3" hose itself?
    Last edited by VaRedneck; 05-14-2007 at 09:00 PM.

  8. #8
    JFizzleJR's Avatar
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    I would say it's better to keep the pre-filter as far away from the hose as possible while still making the area waterproof. For example: if you're putting your hose through your rear storage I would put a big waterproof screen over the storage bin lip and keep the hose near the bottom of the bucket.

    If the pre-filter doesn't restrict performance than a rear intake is better than 7' up front. It really depends on the placement. 3" - 4" is about 100 rpms difference and rear intake - front intake is about 100 rpms difference so they kind of even out. I don't know if anybody has tested that combination yet.

  9. #9
    mxl16's Avatar
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    generally, the longer the hose the more friction. shorter is better. thats not all of it though, there is also diameter and fresh air supply to consider. a short 3" tube sucking hot engine air will result in probably not much gain at all (if any). just like those old R&D air intakes for the rxp/rxt . short 3" tube that sat right on top of a hot engine. this is why 4" rear air intakes yeild the best results...short distance to the sc, 4"= lots of volume, and only fresh cool outside air is being sucked in.

    as for the prefilter thing. you want as much prefilter surface area as possible. such as a 4" tube with a huge 9" long air filter with a prefilter, the prefilter in this case probably wouldnt make much difference because the surface area is so large compared to the 4" tube the air is being sucked into. i would mount the prefilter away from the end of the air intake tube but still in the path of the incoming air. the difference between mounting it that way and mounting it directly on the intake tube is about 150-200 rpms .

    so to answer some of your questions..im not sure . IMO, go big or go home. 4" rear is only way to go. u want the coolest air possible, traveling the shortest distance possible, with as much volume as possible.

  10. #10
    lugnut's Avatar
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    4" bilge fan. Install inside front intake tube.Cover opening of intake tube with outwears prefilter marterial

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