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Technical IR manifold theory

Discussion in 'The Hokey Ass Message Board' started by speed_is_addictive, Jul 29, 2015.

  1. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,355

    falcongeorge
    Member
    from BC

    Just for shits and giggles, I ran the numbers on my combo, rounding down it would call for 42mm venturis, so if the venturi should be ballparkish 80% of the throttle plates 48's mm dellortos would be on the small size. From what I am reading, booster signal deteriorates if the venturi size exceeds 80% of the throttle plate size, you want to be around between 72% and 80% of the throttle plate size.
    56mm Bergs would probably be ideal, but thats BIG $$$
    Metalshapes, you built your intake from a rochester fuel injection base right? You could probably build a decent intake from an Edelbrock TR-1YX or early Weiand tunnel ram.
     
    Last edited: Mar 14, 2016
  2. RichFox
    Joined: Dec 3, 2006
    Posts: 9,541

    RichFox
    ALLIANCE MEMBER

    I built an IR intake for my 320 inch GMC six with a Howard 12 port head. No books. No science. Just a drill press and torch. Had 270 CFM (OEM on Rambler V8) Holley carbs. Then I switched to 500 cfm Holley's. On the dyno it had lots of reversion. Big cloud of fuel above the carbs. Made stacks for it and ran it in my '32 Ford coupe. Got the XXO/VGAlt record in '84. Then I sold the engine to George Cambell and he put it in his Salt Circus roadster. Did very well in his car. Wasn't really fast but it did OK.
     
  3. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,355

    falcongeorge
    Member
    from BC

    Science isnt always a bad thing...;)^^
     
  4. RichFox
    Joined: Dec 3, 2006
    Posts: 9,541

    RichFox
    ALLIANCE MEMBER

    Science is usually a good thing. But you have to be smart enough to interpret it. The rest of us just cut and try.
     
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  5. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,734

    metalshapes
    Tech Editor

    This is my second set of Webers on this engine.
    The first set was home made from a early Vette lower FI intake, Citroen/Maserati DCNF's and adapters & linkage I made myself.
    The second set is a IDA setup that was probably matched for a 302 Formula 5000 or similar.
    I kept the venturi's the same, and they were a nice match for my 400 Cubic Inch Donovan.
    Its a beautifully torque engine that will still rev. ( just over 500/500 both torque and horsepower )

    I've never owned anything like it...

    The one tip I can give that really seems to make a difference, is spend plenty of time on the linkage.
    I made a progressively acting linkage for the IDA setup, and that made a lot of difference.
    ( slowly acting for the first half of travel, and then quickly from 1/2 to WOT ) 7 28 15 b 022.JPG
     
    Last edited: Mar 14, 2016
    Tim and falcongeorge like this.
  6. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,734

    metalshapes
    Tech Editor

    I'll do a build thread about the Morgensen Special when I'm going to restore it.
    Here is a pic of it, taken in 1954. Morgensen 003.jpg
     
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  7. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,734

    metalshapes
    Tech Editor

    George, specs on the cam.

    Lift: .525/.555
    Duration: 288/296
    Lobe center: 106
    Solid.
     
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  8. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,355

    falcongeorge
    Member
    from BC

    Thanks Alex, And further to this, pretty much what I figured...Note Davids comment below that the 383 wanted 1 degree less with IR.
    And David runs 106 in ALL his 383's, so one degree lees means a 105 LSA. I will hazard a guess, that based on my calculations, the 383 wanted 1 degree less because the 48 IDA's actually constituted an inlet restriction on the 383. Typically, an engine with a restricted inlet tract will want a slightly narrower LSA.
    _____________________________________________________
    Re: Vizard's secret '128' cam spec # revealed
    [​IMG]by David Vizard » Mon Mar 14, 2016 2:52 pm

    falcongeorge wrote:Question for David, pretty sure I know what its going to be, does using an IR intake affect the optimum LSA for a typical 2 valve wedge combination?

    Yes but not as much as I had expected. Tried different cam LCA in a Pontiac 455 and a 383 SBC with 48 Dellorto's on. The Pontiac was no different to a single or two plane. The Chevy wanted one degree tighter and the difference in power was only about 7-8 hp. Would like to have done more with IR but ran out of time. However I suspect I may have an opportunity to do a lot more with an IR system on a 289 Ford later this year so we will see what transpires

    DV
    David Vizard
    Member
    [​IMG]
    Posts: 189
    Joined: Thu Jan 15, 2015 9:19 am
    Top
    Re: Vizard's secret '128' cam spec # revealed
    [​IMG]by falcongeorge » Mon Mar 14, 2016 2:57 pm

    David Vizard wrote:falcongeorge wrote:Question for David, pretty sure I know what its going to be, does using an IR intake affect the optimum LSA for a typical 2 valve wedge combination?

    Yes but not as much as I had expected. Tried different cam LCA in a Pontiac 455 and a 383 SBC with 48 Dellorto's on. The Pontiac was no different to a single or two plane. The Chevy wanted one degree tighter and the difference in power was only about 7-8 hp. Would like to have done more with IR but ran out of time. However I suspect I may have an opportunity to do a lot more with an IR system on a 289 Ford later this year so we will see what transpires

    DV
    Thanks David. I was guessing it didnt make any difference.
     
    Last edited: Mar 14, 2016
  9. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,734

    metalshapes
    Tech Editor

    David Visard is still around?
    Cool...:)
     
  10. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,355

    falcongeorge
    Member
    from BC

    Hes on Speedtalk regularly. He has cut way back on the seminars. For those that dont know, David Vizard started his career on Mini-Coopers and Ford Kent motors, so needless to say, he has TON of weber and Dellorto IR experience under his belt.
     
  11. ghornbostel
    Joined: Jan 3, 2012
    Posts: 131

    ghornbostel
    Member


    I had my 3c ida's on a stock 231 Buick v6. It ran better than the 2bbl and gave the same gas mileage. I had to choke them down to 24mm but they ran very well. I then built the engine and when I ordered a cam I was told that reversion was caused by excessive overlap. I ended up with a Crower 282-fdp
    Intake lift .478 duration 282*
    Exhaust lift .486 duration 287*
    LSA 107*
    overlap 26*
    solid lifters
    The engine has seen 6k but with the adjustable pushrods I try to hold revs to 5500 rpm. While chopping the plugs at top end I haven't seen any raw fuel on the tops of the carburators (reversion). The ram tubes are 2'' long and I feel the engine runs better without them but the tubes put the occasional backfire during cold starts above the carbs. Gas mileage is about 20 mpg driving around.
     
    Last edited: Mar 14, 2016

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