CAM selection 318

Mopar Performance Issues

  1. Danizanon

    Danizanon Well-Known Member

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    I have a 318 on a dart... with paxton supercharger and a edelbrock 2177 cam
    I want to change my CAM for one that will fit better with the supercharger
    My configuration is stock... the only changes are fuel tech F500 injection ... super victor and short headman exhaust.. changing for A500 tranny
    A friend told me about summit 6901... I want something for street performance use... IMG-20180526-WA0020.jpeg
     
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    • dano

      dano Evil Handy Man

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      I'd call a cam grinder for that one.
       
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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        forget the 6901 for this application
         
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        • roccodart440

          roccodart440 Well-Known Member

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          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            Wide so you don't send your air/fuel charge straight across the piston and out the exhaust, at split overlap.
            the 6901, from my research is;
            276/288/114/54* overlap; and 218/228@.050 as you can see the intake ramps are 58* from .050 to advertised........... but at it's advertised, it is still far from closed. And while that might not matter when normally aspirated, if you add say 7* to the intake opening and 8* to the exhaust closing, then the overlap becomes 69 friggen degrees. That's a big window. I have no problem thinking that cam could be a 291/304 seat closed to seat closed.
            That works at the other end too. Let's say that 6901 was a 291/304 seat closed to seat closed and say you installed it at 111.5 Then your events would be;
            291/302/68.5 overlap/103 compression/92.5 power extraction. The Ica would be77*, which off-boost and below about 3500rpm would make for a very doggie 318, because of the very late closing intake valve, combined with the very low dynamic compression ratio.. At 77* the piston is already quite a ways up on the compression stroke.
            But worse is the power stroke, which opens the exhaust valve at 92.5 degrees down ; in other words the piston is just abut half way down and the exhaust valve is already opening. Such a cam with locked timing, at part throttle/off boost, would be very hard on gas....... not that it would be any better on boost,lol.
             
            Last edited: Nov 7, 2019
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            • Danizanon

              Danizanon Well-Known Member

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              Screenshot_20191107-175642_Adobe Acrobat.jpg
              View attachment 1715420144

              Mine is worst?
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              no, I don't think so. Maybe 62*overlap; And your intake closes sooner. But Really; it's all a guessing game when I work off advertised numbers cuz nobody knows when the valve actually closes, except the guy who grinds it, and the guy who installs it and measures it. And maybe Wormryder.
               
            • roccodart440

              roccodart440 Well-Known Member

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              Keep in mind turbo Vs. Supercharger the sc typically has far less lag.
               
            • yellow rose

              yellow rose Doctor of Thinkology.

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              LOL! Yup. You look at a dyno graph, or better yet a download from a data logger and see that boost from a roots blower goes almost straight up from the hit.

              That's why (one reason) turbos are easier to get hooked. The roots blower makes boost now. The turbo, even with a bump box will never get a boost curve like a roots blower.
               
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