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Thread: Early MFI air cleaner options

  1. #21
    Im not going to claim to be an engineering wiz (or should that be whiz) either, but is would have to assume that the enclosed air filter box with snorkel was done for the same reason that all of the American cars went with a closed air filter arrangement with snorkel around the same time. The PCV valve cannot be used effectivly in an open element system. This is my guess.......if anyone knows more, pease share.
    Renn-Spot - Cars & parts For Sale - http://renn-spot.blogspot.com/
    1970 911"S" - Black (originally silver)
    1974 911"S" - Silver
    1973 911"T" - Bahia Red - Now Sold
    10 sec 67 VW
    Early "S" Registry #439

  2. #22
    Porsche was using the Snorkel long before the advent of the PVC.
    Master of the Buffet

    Voice of Reasoned Conservatism

  3. #23
    good point. Maybe for noise control. I dunno......
    Renn-Spot - Cars & parts For Sale - http://renn-spot.blogspot.com/
    1970 911"S" - Black (originally silver)
    1974 911"S" - Silver
    1973 911"T" - Bahia Red - Now Sold
    10 sec 67 VW
    Early "S" Registry #439

  4. #24
    admin_old
    Guest
    Early 911s don't use a positive crankcase ventilation (PCV) valve. Crankcase fumes from the top of the case go to the oil tank. From there, another hose from the oil filler tube goes to the air filter housing. A little oil naturally accumulates in the housing. If there's a lot of blowby or continued high rpm use, a lot of oil ends up there. There's a small tube and hose that allows excess oil to drip on the rear of the engine on it's way out. Fumes are drawn into the intake tract when the engine runs.

    I suspect the shape and size of the filter housing and snorkel has to do with reducing intake air noise. The only venturi effect occurs in the venturi of the carb, that is unless you somehow have installed the aftermarket Tornado device. Any venturi effect caused by the air filter housing represents an air restriction, NG. The only thing inside that should normally cause a restriction is the filter element itself, especially if dirty.

    I believe the tube on the snorkel is for the hot air connection from the heat exchanger - better fuel atomization after a cold start.

    Sherwood

  5. #25
    Originally posted by admin


    I believe the tube on the snorkel is for the hot air connection from the heat exchanger - better fuel atomization after a cold start.

    Sherwood
    One thing that Tabs said, that there is no place for a hose to come from and connect to this tube attached to the 'snorkel' is evident on my car. I've wondered about this. By '72, that I know of, the 'snorkel' is a shorty oriented to the left.

    On VWs that I''ve owned, the tube IS connected to a hose that comes off the HEs. Much like the warm air for the MFI thermostat.

    Tabs, I don't disagree with the thought that the snorkel is a venturi, although the concept of venturi that I'm most famililar with is a narrowing of a passaage somewhere in the stream of the passage, not at the end. In any case, the venturi effect is to produce a lower pressure at that point. The rule in physics is, "Where velocity is greatest, pressure is least." There is no "ram" effect, as that would be opposed to the theory. As simple proof, I offer the design of a carburetor; there is no "push" on the air. It is drawn by the engine vacuum, past the venturi to pick up fuel, and on into the clyinders. With any positive air pressure in the carb passage, the fuel would be pushed back into the float bowl.

    At the very outside, Tabs, if you are thinking that the air starts in the snorkel at a small point and as the the passage enlarges, the air slows down and catches up with itself producing a positive pressure, you've just discovered the most profound bit of induction science ever. Everyone should put a small restrictive reverse air horn on thier machine immediately for a dramatic increase in performance. Better yet, six of them.

  6. #26
    That 30* pipe entering into the snorkel creats a vacume in the snorkel tube...thus drawing air in. Now because of the placement of the tube I would say they are trying to draw colder outside air in. All things being equal, why would Porsche go to all the trouble of using such a cumbersome device unless it was to maximize air intake. why wouldn't they go with the cheaper passive KN type of air intake?
    Master of the Buffet

    Voice of Reasoned Conservatism

  7. #27
    Senior Member
    Join Date
    Jan 2003
    Location
    UK
    Posts
    2,694
    People seem to be overlooking something here - one of the reasons that Porsche used the original 'enclosed' air cleaner/filter assembly was for noise suppression.

    Porsche no doubt considered that 'unsilenced' intakes wouldn't be acceptible to many perspective buyers back then (or now).
    Andy

    Early 911S Reg #753
    R Gruppe #105

  8. #28
    Member
    Join Date
    Jun 2003
    Location
    San Francisco Bay Area
    Posts
    41

    its music to the ears

    This has nothing to do with explaining the theory of ram air effect from that long snorkel of the metal air cleaner but I wanted to share my personal experience with you guys about running the engine w/o those stock metal air cleaner assembly.

    I drove my 69S on the street for over 3.5 years without the air cleaner including a couple of "very brisk" drive to the first two Cambria gathering. Yes all six unfiltered, unrestricted and "unsilenced stacks" kept open all that time. I was curious to see how it would drive w/o the air cleaner and decided to unbolt the complete stock metal air cleaner assembly off the engine. Without it, the sight of six tall metal intake stacks topped off by 6 polished metal velocity stacks (replacing the 6 stock plastic stock used on the 69 911 mfi engines) made quite a visual impact as it looked like a race engine (even w/o a twin plug set up). It was supposed to be a temporary set up as I was really curious to see how it would drive with open intakes. Maybe it was the sound that did it but the seat of the pants feel was there. It felt like it was that much more responsive and of course w/o any restriction on the air intake, the most obvious change was the sound it made from the intake. From that point on, I decided to leave it open for a little while longer... ; )

    Thoug I did mount a pair of 911R metal intake covers which doesn't filter air but at least kept some of the debris and foreign objects from dropping straight down the intakes. I later made up my own air filter with a set of fine nylon mesh with elastics to fit over the metal stacks which though not fully effective in filtering air, did offer some type of filtration. Though this set up wasn't really good for the engine in the long run, I drove the car only on nice clear days and cool nites. Not any more than those old hot rodders use to do when they ran those big GMC 671 blowers on the street or those Cal Look Bugs with their big bore hot rod motors running huge 48 ida Webers with open stacks (those DKP guys - Grago, Cornpanzer, Mike Gagen & company is probably amongst those : )

    I would have kept this set up but decided that for the sake of longevity of that high strung 2.0S engine, I opted to use a twin K&N filter mounted on a pair of the old Filtron twin metal air cleaner set up. It did muffle the sound a little bit but it still got pretty loud specially when that small displacement 2.0 liter got wound up and it would just pull as it gets near 5 grand on the tach. If you kept your foot on it and just let it wind up all the way near 7300 (thank God for rev limiter), it makes one of the most intoxicating sound I have ever heard from a normally aspirated motor. I know the sound very well as it was (and still is) music to the ears (my ears at least)

    One of those experience was such that I even remember sharing it in an e-mail to Chuck Miller after one of those late night "whopee run" where the S made so much noise it woke up some cows and goats from their deep sleep.

    Not trying to imply that I was driving reckless. I was just enjoying the sound that old 911S made with those "unsilenced stacks" and to borrow an old Porsche ad slogan, it was

    "driving it its purest form"

    just wanted to share this with you guys.

    godspeed,

    Cris

  9. #29
    Hey Cris, can you show me a picture of teh current set-up? Thanks

    P.S. what did you do about the cold-start squirters?
    Renn-Spot - Cars & parts For Sale - http://renn-spot.blogspot.com/
    1970 911"S" - Black (originally silver)
    1974 911"S" - Silver
    1973 911"T" - Bahia Red - Now Sold
    10 sec 67 VW
    Early "S" Registry #439

  10. #30
    http://www.itgairfilters.com

    http://www.itgairfilters.com/megaflow_jc90.asp

    And this company looks like the closest vendor short of going to the UK, Australia or Canada.

    http://www.ultimatecarparts.com/


    Tom
    Early S Registry #235
    rgruppe #111

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