"cold air intake" piping size

Fuel and Air Systems

  1. diymirage

    diymirage HP@idle > hondaHP@redline

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    hey guys
    i am considering putting a "cold air intake" on my duster
    i would utilize a spectre air cleaner housing like this one
    98648 - Spectre , Low Profile 14 In. OD x 5-13/32 H - 135 Degree Chromed

    it would be much like the olds W30 ram air packages, with two aluminum intercooler style pipes going from the cowl to the air cleaner

    now, my biggest question is on the proper size of those two pipes

    the air cleaner has two four inch intakes, but it looks like i can only manage to hook up a 3 inch pipe to the cowl

    will two 3 inch pipes be enough to feed a 420 HP 408 ?

    and if i do have to choke it, where is the best place to go from 4 to 3 inches?
     
  2. LJ67barracuda340

    LJ67barracuda340 Well-Known Member

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    does this help?

    chart.jpg
     
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    • LJ67barracuda340

      LJ67barracuda340 Well-Known Member

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      4- 1 3/8" throttle bores are 5.936 sq/in
      2- 3" tubes is 14.13 sq/in
      the choke seems to be the 12.6" x 3" filter
      Specter has 3" tubed air cleaner boxes also, so no adapting.
      unless your at 6000 rpm all the time, dont see an issue. JMO.
      I'm working on a similar system.
       
    • diymirage

      diymirage HP@idle > hondaHP@redline

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      see, where I'm getting confused it the surface area
      a 14X2 round filter had a surface area almost 88 square inches

      (which according to your graph is enough for a 200 CUI engine at 5500)

      or am i looking at this wrong?
       
    • TrailBeast

      TrailBeast Slightly Twisted Member

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      88 square inches of flow reducing filter element.
       
    • 72Valiant4Door

      72Valiant4Door Trouble Maker

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      two weeks ago when I asked about a 14 x 2, i was only told it would work fine on a 318 with no noticeable difference between it an a 3"...

      ffs
       
    • 72bluNblu

      72bluNblu FABO Gold Member FABO Gold Member

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      Uh, a 12.6x3" filter has 118 square inches of surface area, so, quite a bit more than a 14x2.

      The Mopar Performance air cleaner is only 12 3/4" x 2.75", so, 110 square inches of surface area.
      [​IMG]

      And I run mine with a 13x2.3" filter for hood clearance. https://www.summitracing.com/parts/knn-e-2865

      Seems to work just fine with my 400+ hp 340. I didn't notice any difference at all going from the original MP filter down to the 13x2.3, and that's a change from 110 sq. inches to 94.
       
    • famous bob

      famous bob mopar misfit

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      I have tried, (in the past), running an approx. 600 horse -406 sbc, w/ and w/o a 14 x3" air filter. no diff in e.t.---k-n of course---
       
    • jbc426

      jbc426 Well-Known Member

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      I'm toying with the same issue as well. Have you considered using the 4" ovalized adapters that transition from 4" round to whatever-size oval adapters to attach them to the cowl? The ones with a built in flange that allows you to secure the feeds to a flat sheetmetal surface with screws.

      I bought a cast aluminum air cleaner hat to put on my 408" stroker, but I'm wondering if a single 4" inlet is enough.

      I don't have a lot of hood clearance, and have to keep the height below 3 1/2 something inches. I would prefer to use a twin 4" inlet filter, but one with a drop base and a 14" by at least 3 inch filter.

      I was using this conglomeration of the stock stuff with a K&N, but I was told it only flows about 600 cfm.

      eng2 (Large).png
       
    • diymirage

      diymirage HP@idle > hondaHP@redline

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      and that element will still be present in the intake system
      so what i want to be sure of is that i am actually improving the intake system, because at some point an abundance of hot air has the be better then a shortage of cold air?
       
    • diymirage

      diymirage HP@idle > hondaHP@redline

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      the oval ones seem like a great idea, but i have not been able to find one with mounting plates on them

      i called Spectre and they had a lot of info

      for starters, the cowl intake is LOUD
      does anyone have any experience with this?
      i know loud means different things to different people but this is a daily driver and i don't want it to be obnoxious

      CFM
      the guy i talked to said my 408 needs 701 CFM to make the power it makes
      their single 4 inch inlet boxes flow 900 CFMs and their dual 4 inch inlets flow 1200 CFMs
      (he said they do not make a 3 inch inlet box)
       
    • LJ67barracuda340

      LJ67barracuda340 Well-Known Member

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      Try looking at www.ramairbox.com they have some neat stuff up here in Canada.
      If your running a carb (float bowl vents) and you connect to the cowl, remember that's were your fresh air comes from for you heater system and air vents, there will probably be the smell of fuel in the car as well as being loud.
      Ill be using FI but I'm getting cold air from thru the rad support.
       
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      • spl440

        spl440 Everybody's Fool FABO Gold Member

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        Made my cowl induction air cleaner from a used base and top that had a single snorkel that I got from a friend, Gary at Winkel auto in Milford NH. actually got the whole car as a project from him. Air cleaner takes a 13 x 3 3/8 air filter so I think it is from a big block motor. with the mouth cut down it fits under the hood. the tubes where made by hand by cutting and rolling some cheap thin metal shelving. tubes are ovalled, 4 1/2 by 3 inches. there was a little bit more volume of the thermoquad when it kicks in, not much more, but I like it!
        air cleaner.jpg
         
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        • nm9stheham

          nm9stheham Well-Known Member

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          2x3" tubes will be fine. I run 2.6L Mitsu rally engine at 14-15" boost through a single 2.5" tube from the air cleaner into the turbo inlet at 275 HP. Never an issue with getting enough air.

          Your engine will like the cooler air. Just watch the mixture. I am looking into the same thing for my son's 340.
           
        • diymirage

          diymirage HP@idle > hondaHP@redline

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          any chance you feel like making another one?
           
        • spl440

          spl440 Everybody's Fool FABO Gold Member

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          Would like to help, very car specific though. whish you where closer. The small block filter assy would be easier to make and you would only lose about 3/8 of filter height.
           
        • diymirage

          diymirage HP@idle > hondaHP@redline

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          anyone else have any thoughts on this?
          right now my main concern is if a dual three inch intake is enough for a naturally aspirated engine
           
        • LJ67barracuda340

          LJ67barracuda340 Well-Known Member

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          OMG,,, unless your runnin' at Bonneville, run it!!! it'll get the job dun.
           
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          • nm9stheham

            nm9stheham Well-Known Member

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            Don't compare free airflow area of the 2x3" pipes to the recommended flow area of an air filter; it's apples and oranges. And the free flow area of 2x3" is around 3 times the area of the carb throats. If it bothers you, adapt up to 4" as soon as you can. It might lower the pressure drop by a tenth of an inch or so.....
             
          • diymirage

            diymirage HP@idle > hondaHP@redline

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            I came across this chart on ramairbox.com comparing some flow numbers

            Flow Testing

            I'm guessing the 2X3 would be close to the ford unit at 535.8 which is too low for what my engine needs
            so I decided to go with the 2x4 spectre unit which flows 1200 CFM
             
          • nm9stheham

            nm9stheham Well-Known Member

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            The numbers there are flows with an air filter....so can't be used to decide if the hoses by themselves are big enough. Apples and oranges..... but you have a direction and a plan.
             
          • diymirage

            diymirage HP@idle > hondaHP@redline

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            i ended up going with the 180 degree dual snorkel set up
            (need a 408 call out though)

            [​IMG]


            so, for the time being i am using the kit supplied flex tubes BUT i want to figure out a way to replace them with steel or aluminum tubes
            my question is, where should i draw air from?

            the cowl might be add too much of a fuel smell into the car, and make it too loud

            the straightest way seems to be right into the fenders?
            does that sound like a bad idea with road debris and possibly getting caught in the rain ?

            running them to the front might add to the ram air effect but the tube might interfere with some other things mounted to the front

            what are you guys' thoughts on this?
             
          • diymirage

            diymirage HP@idle > hondaHP@redline

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            well, since i seem to be on my own here, i ordered some 4 inch aluminum pipe and two 90 degree silicone couplers
            I'm going to go straight out into the fenders (already moved the washer reservoir) and install the 90s in there, facing up and to the front of the car
            that should keep the road debris out and work as a ram air set up...sorta
            then run a straight tube into the air cleaner

            easy peasie lemon squeezie
             
          • diymirage

            diymirage HP@idle > hondaHP@redline

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            got the holes drilled, and all the parts ordered
            once I get the aluminum tube in, I will run it just like this

            1470076108_zpsbg70rp67.jpg
             
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            • diymirage

              diymirage HP@idle > hondaHP@redline

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              and....done

              (well almost, I still need to buy some vacuum hose to run around the cut edge, so that it doesn't damage the pipe as the engine rocks, but for now, there is some electrical tape on there)

              1470259101_zpsrrxsk9bt.jpg

              it took a LOT more cutting to get the bottom of the holes to nicely follow the tubes, but 2 dozen cut of wheels on the dremel took car of that

              what you cant tell from the pictures are the two 90 degree silicone couplers hidden inside the fender
              these are pointed forward and slightly up to keep the road debris, kicked up by the wheels from being sucked into the engine
              they may or may not also work as a little bit of a ram air intake
               
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