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Cam timing

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Leadfoot, Oct 5, 2001.

  1. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Does anybody know the advantages/disadvantages of running the cam (at least with aftermarket timing chains or gears) advanced or retarded? I know most timing chains come with an A, O, and R keyways on them. First I'm assuming A is for advanced, O is for straight up, and R is for retarded. Is this assumption correct? Also what are the advantages of running in each of these positions, and also (more importantly) what are the disadvantages of each position. I'm assuming cam profiles and compression play a role, but does anyone know the correlation?
    Thanks


    Learning something new everyday......that's the CK5 way!

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  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I wouldn't consider this gospel, but retarding the timing, at least on the spreadsheet I'm looking at, costs you on the bottom end, and benefits you up high.

    Looking at some 307 (Olds) charts here, and every motor is going to be different, but with about 308hp/366tq max on this motor, at 5500RPM, retarded 6* gives you 34 more hp. At 3000, you've lost 6. Torque, 3000 you've lost 16ft lbs, 5500, you've gained 33. These numbers are based against a 4* advance. So the loss at either end would be slightly less, it stands to reason, if the cam were straight up.

    if that held true on your motor, I'd stick with straight up. Those are pretty large gains up high, but everyday use, the big heavy truck is going to be benefited from middle of the road numbers, "equal" power down low to get started, and in the middle of the RPM band for cruising.

    Again, thats only using one motor as an example, every one will vary in numbers.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
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  3. Zepplin

    Zepplin 1/2 ton status

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    LeadFoot,

    I just passed this along to our Cam expert here at work. I will post his explanation to you when I get it.

    74 Blazer
    Zepplin
    Check out my Blazer<a target="_blank" href=http://community.webshots.com/user/zepplin1976>http://community.webshots.com/user/zepplin1976</a>
     
  4. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Thank you both.

    See my rig at <a target="_blank" href=http://coloradok5.com/gallery/Leadfoot>http://coloradok5.com/gallery/Leadfoot</a>
     
  5. solowookie

    solowookie 1/2 ton status

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    awe come on I thought Dorian was our resident expert at most stuff??? (go Dorian!) I was suppose to advance my cam 5 degree's (according the crane), and they guy at fastchip.com told me he would do it on the chip... well I'm sitting here looking through this post, and realizing I screwed up... [​IMG] well next time I gotta tear it down I will advance my cam that 5 degree's.

    <font color=blue> Jeff - may the force be with you</font color=blue>
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  6. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Basically think of cam timing as a way to move your torque curve up or down. It doesn't change the shape of the curve, just moves it up or down. Advancing makes more low end, retarding makes more top end, and depending on the amount, it could move the curve 500 RPM or more.

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     
  7. solowookie

    solowookie 1/2 ton status

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    that is exactly what I wanted to do... I wanted to move the curve to lower RPM's. the compu cam (by crane cam's) with the specs I wanted won't work for 350's (don't ask me why, made for 305's) so they told me to use the cam I got, and advance it 5 degree's... well I least now I know what they were talking about... LOL

    <font color=blue> Jeff - may the force be with you</font color=blue>
    <a target="_blank" href=http://coloradok5.com/gallery/Jeffs-Stuff>link to k5's</a>
     

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