225 performance upgrades without pulling engine

Slant 6 Engines

  1. Dan Miller

    Dan Miller VCV666

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    Gday guys, Im from Australia and own a 66 VC Valiant Regal with a completely stock 225 aside from the addition of electronic ignition. Im wanting to know if putting an Aussiespeed Longrunner 2 bbl manifold and perhaps 400cfm 2bbl carb with extractors is overkill? Or would I be better off just using a 2 bbl short runner manifold and smaller carb? Im not wanting to pull the engine out at this stage by the way, Im just after the right advice for a few extra horses with bolt on gear for now, thanks guys
     
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    • RustyRatRod

      RustyRatRod Weenie idiot loser. FABO Gold Member

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      I think the long runner intake and headers would be a good upgrade. One without the other....not so much.
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Breath easy in... breath easy out ...

      Long runners provide more torque.
      Shorter runners provide more top end HP.
      The headers into a 2-1/2 inch exhaust and a long runner intake is what I would do for bolt on performance upgrades. FWIW, a small 4 bbl. carby isn’t a bad idea ether since your driving around on the primary side at approximately 200 if you can find an old Carter @ 400 cfm. A readily available 500 is easy to get and travels around on the primary side at approximately 250 cfm.

      Jet/tune the crab accordingly and you’ll be fine.
       
    • Dan Miller

      Dan Miller VCV666

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      Cheers mate, any suggestions on carb sizes?
      Thanks mate, excellent info. I may look at a 4 bbl longrunner manifold instead of 2bbl then. Cheers
       
    • RustyRatRod

      RustyRatRod Weenie idiot loser. FABO Gold Member

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      I think the 4 barrel would be overkill on an otherwise stock engine. The Holley 350 2 barrel would be good, IMO.
       
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      • Ddaddy

        Ddaddy I'm changing the World... one pixel at a time! FABO Gold Member

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        One of my old tricks to get just a little bit of extra power on a stock 225 was to tighten up the valve clearances a bit.

        Normal is 0.010 intake and 0.020 exhaust. I used to tighten them up to 0.008 intake and 0.016 exhaust. Not so much as to screw things up being too tight, but enough that you could feel the slight power gain.

        Add a header and long tube intake with a 2 bbl and it became a snappy little power plant.
         
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        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          I’m guessing a cam change would not be very easy with the engine in the vehicle.
           
        • Ddaddy

          Ddaddy I'm changing the World... one pixel at a time! FABO Gold Member

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          Yep.

          Ever try to change a cam in a slant in the vehicle?

          Not really possible. Have to take it out. The cam sits at the bottom of the block.
           
        • Ddaddy

          Ddaddy I'm changing the World... one pixel at a time! FABO Gold Member

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          D2F1A606-B4AB-4345-AFC7-BFEA68C51095.jpeg
           
        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          Nope, never tried. I see the problem. Oh yea, that’s down there.
           
        • Fgill

          Fgill Well-Known Member

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          cam change.
          2bbl manifold.
          mopar elct ign conversion - if not done already. orange box.
          headers will help HP but kill low end tq in S6..which it needs all it can get.
          an easy to find carb is the carter BBD off of an early 318 ( i think they are 390cfm)..they can be found much easier than the similar factory 225+2 spec unit and fits super six linkage, man, etc.
          factory 2bbl manifolds came in both alum & cast.
          4bbl is overkill and can cause issues in a all stock 225.
          In a rather low-pro motor like S6, taking weight out of the car can really help get it moving.
           
        • Charrlie_S

          Charrlie_S Well-Known Member

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          If you are up for it, I vote for milling the head. Not a lot of money (best bang for the buck), but kind of labor intensive. Does not require pulling the engine.
           
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          • rumblefish360

            rumblefish360 So close, yet so far away FABO Gold Member

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            A little more compression is a plus.
             
          • RustyRatRod

            RustyRatRod Weenie idiot loser. FABO Gold Member

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            Also, don't forget recurving the distributor. That right there is perhaps the best bang for the buck hands down. That, milling the head, the cam change, better carb, intake and headers and you can really wake one up. Even if you don't want to get into the engine with the head and cam, you'll notice a big difference with everything else.
             
          • white-night

            white-night Well-Known Member

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            I'm also in Australia. The best set of headers available here for the money are Hi-Tech in Melbourne & if you use the std 2 bbl manifold with a Holley 350cfm carb, that will give you the best bang for your $. The Aussie std 2 bbl manifold is a lot better design than the US version. You will also need an adapter plate for the holley.
             
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