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Individual Runner intake manifolds - need to know runner length

Discussion in 'The Garage' started by Twiz, May 14, 2003.

  1. Twiz

    Twiz 1/2 ton status

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    Buddy of mine is building a Hemi for his '32.
    He wants to run a I/R manifold, 8 individual intake runners leading to 8 single barrel carbs. I've done some research on this set-up, and "get" the theory, could still use some help with it tho'. *Any and all info, would be helpfull*

    We are looking for the formula - to find the correct dia and length of runners for the RPM/cam, ect...

    Any input would be helpfull!!!!!!!!

    ( TPI guys might wanna check this out too, as this is the "tuned" part of TPI )
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    ( TPI guys might wanna check this out too, as this is the "tuned" part of TPI )

    [/ QUOTE ]

    Stock TPI runners are about 17-19" IIRC. Which is also why the engines make a good deal of low end power, and are limited at about 5000RPM with stock runners.

    I've got a TBI intake in the garage. Want me to measure the runners?
     
  3. Sledge

    Sledge Registered Member

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    David Vizard has some pretty good stuff about helmholtz resonance in his intake manifolds book. I don't know what you're looking for, but that might be worth checking out.
     
  4. Twiz

    Twiz 1/2 ton status

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    [ QUOTE ]
    David Vizard has some pretty good stuff about helmholtz resonance in his intake manifolds book. I don't know what you're looking for, but that might be worth checking out.

    [/ QUOTE ]

    Agreed
    David Vizard goes into detail on the subject in a couple of books, I might add, for anyone interested, VERY excelent reading. I've also found a "Desk Top Dyno" book that allso goes into detail. But, unfortunetly, no formulas.

    So far, an artical by David Vizard is all I've been able to find that actualy inculdes formulas for figureing out the intake runner length.
    Intake Pulse Tuning

    Thats what I'm looking for, but I'd really like to find as much information as I can get, formulas, design, funtion - anything !

    Thanks guys.
     
  5. Donovan

    Donovan 1/2 ton status

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    I have done alot of reading on this subject. Here is what I am told. You need to know what lift your cam is and the valve size? You get the valve curtain in square inch area. The inlet to the manifold should be the same square inch area as your valve curtain. Next you should find the smallest square inch area of the intake port. On a hemi that should be at the mounting surface where the manifold bolts to the heads. Now the runner should taper from the smallest square inch area to the largest at a 1.5-3 degree taper. That should answer your question. Let me know if you need anything else.
     
  6. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    8 carbs? He also wears black leathers and frequently says, "yes mistress" right? /forums/images/graemlins/rotfl.gif

    I nearly pulled my hair out running 3 dueces on a 455 '66 GTO daily driver just trying to keep them all running right, and that was depending on one as a primary! /forums/images/graemlins/tongue.gif Course they were old patched up rebuilds, but still, 8 carbs? I would tell him to just stick to seeing a 'trix... /forums/images/graemlins/rotfl.gif

    Sorry, no help here, way over my head...
     
  7. Sledge

    Sledge Registered Member

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    Twiz,

    That article looks to be the same as is in his "carbs and intake manifolds" book. I like his explainations, but I think he falls back on "wet thumb" engineering at times -- too many generalizations/hueristics instead of formulae. It is good stuff though! He's certainly the most "scientific" author I've read outside of SAE papers.

    Have you seen is book on the British Leyland A-series engine? It is motor-specific but has a lot of good generally-applicable theory.

    Once upon a time we were starting to a custom intake manifold. We planned to build it in 3 pieces: mounting flanges at the top and bottom with a removable velocity-stack-thing in the middle. That way we could get "close" with the formulae and fine-tune it by swapping in different length stacks w/ the engine on the dyno.

    This was an all-out effort with a very narrow target RPM range. I don't know if it would be worth the effort in your application. It's always fun to play though! /forums/images/graemlins/smile.gif
     

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