Carbs...for what its worth

Discussion in 'Technical' started by cardealer, Jan 26, 2010.

  1. cardealer

    cardealer Member

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    I appreciate the time you put into this post, but I’m not missing the association at all. My initial post was a brief FYI on how I resolved the issue, not asking how to solve it. The overlap of this particular cam is more than double that of a stock cam. The engine was originally built for a different application where street drivability was never a concern. Cam potential is only maximized at a specific moment in the rpm range; throughout the rest of the range it’s just a compromise. In this particular case, the high degree of overlap is fine in a ¼ mile car, but as you correctly stated, it induces a couple of additional problems that are not acceptable on a daily driver. The real solution to the problem is to replace the cam. Not real expensive, but a true PITA. It’s not that I want the hot motor, its what I inherited, and I had to compromise top end performance for acceptable idle quality, mpg, and drivability between idle and 4,000 rpm. If you read the post carefully, maximizing top end power is not one of my objectives. The way the car is now configured its almost perfect for the intended use. In the end it’s all just a big compromise. If I swapped out the cam, all the characteristics that are essential to a daily street driver would be easily achievable, but again, top end performance would suffer. I chose the easy way out – 10 minutes invested in a carb swap vs. 8 hours in a cam swap, and either way you go your top end will suffer. The biggest advantage to the cam swap is mpg, but the gain is not worth the pain. If top end performance were an issue, the only change I might consider would be a spread bore, but the engine doesn’t spend it’s life at the top of the rev scale, and right now it pulls extremely hard in the range in which it’s used.
     
  2. Bluegrass

    Bluegrass Jr. mbr. not really,

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    Very good.
    My reply is more to benifit those who need to undestand some of the relationship on these matters.
    Good luck.
     
  3. baddad457

    baddad457 Member

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    Good stuff but two things................You can have the sound of a hot cam, fuel mileage and a decent idle, plus topend power, all you need here is to use a wide LSA cam........................................................The 289 Hi-po's came with a 600 cfm carb. The Shelby's got a 715, but it was a vacuum sec carb.
     
  4. cardealer

    cardealer Member

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    The top end is compromised, but it is so slight that you would never pick it up without a timed run. Right now, for a street car, it runs extremely well. The other factor is that I built this car for my son. He's not a car guy and drives this like he's in a Taurus going to the grocery store. Also, since he's a student in college, he foots the gas bill on a limited budget. Gearing is also an issue that I'm surprised no one brought up. This one doesn't have a tall ratio (intentially for freeway driving), so maximizing top end is even less important considering what it takes you to get there. If it were mine, I might make a couple of changes, but for him it has worked out fine.
     
  5. baddad457

    baddad457 Member

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    Exactly. (y) The Z cam in mine pulls to 6500-7000 with a 112* LSA. There's no need to run a bigger cam to make it pull to a higher rpm.
     

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