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  • #16
    Just to be clear for the rest of the folks. Cam duration is usually defined at 0.050" lift. So, my earlier claim of 272 is actually 224 at 0.050". I am not sure what Jochems means by 280. Another aspect of longer duration cams is lobe separation, engine application displacement and intended use. A larger displacement engine can tolerate speed density/single TB even with a long duration cam (240 @ 0.050") , typical would be a LS1 motor. Increased lobe separation has yielded greater power (and torque). Intended use, track and drag motors spend most of the time near WOT or WOT or closed in usually a fairly narrow RPM band. In these cases, having a MAP signal isn't important, and therefore ITB works good, AlphaN works good. The downside is that spark advance is basically no different than a dizzy, RPM based only. A street car will spend a lot of time at various partial throttle settings over a wide RPM band. If we want maximum power at the various operating points (load & RPM) that means optimizing the torque at each point [HP= (Torque * RPM)/5252]. That is done with timing [spark hook tests]. That means a good MAP signal perhaps augmented with a MAF signal to determine load. A single TB with properly sized plenum and individual runners will give give a good MAP signal. If time and money is unlimited, the larger tables are better, say 16x16 and up [or multiple tables]. It's difficult to get a good MAP signal with ITB's, but not impossible. I think the biggest criteria is what's the intended use, not just a simple 280 = ITB's.

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    • #17
      Thanks, that clarified it!

      I'll be sticking with my '60s era DCOEs 'til the cows come home. If I'm leaving power/performance on the table it's got to be very precious little, indeed.

      Tom

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      • #18
        Originally posted by ima68tr View Post
        Thanks, that clarified it!

        I'll be sticking with my '60s era DCOEs 'til the cows come home. If I'm leaving power/performance on the table it's got to be very precious little, indeed.

        Tom
        And you don't need a computer to dial them in Tom.
        CF1634U+O Pimento/Chestnut
        2nd owner, since 1975
        Soon to be in Fair Oaks, CA

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        • #19
          cam duration as defined by its timing.
          Kent TH5-6 = 37/63 73/27
          Intake 280
          Exhaust 280

          I agree, what is the intended use....my input was rather a guide as a rule....there is still a big debate going on between (1) single TB or 6 TBs. Current EFI conversion with a more aggressiv cam seem to run best with 6 TBs....

          Jochem
          Flying Dutchman drives: TR6 - 1973 - 56/11 - CF1xxxxUO - J-OD - Kent 270° - 2x ZS - Phoenix - Pierburg - 123Tune - 205/70 on 7x15

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          • #20
            https://www.jegs.com/s/tech-articles...Specifications Camshaft Duration

            Camshaft Duration is the measurement of the time one valve begins to open until it finishes closing. Duration is measured in degrees of crankshaft rotation, not camshaft rotation. You'll see duration specifications at .050 inches. Cam manufacturers agreed on a standard to measure duration so all cams are measured the same way. The idea is to measure duration starting at .050 inches of tappet (lifter) movement. As the lobe lifts the tappet up, when the tappet moves .050 inches, the duration is measured from that point.

            Intake Duration at .050 inch Lift - The number of degrees the crankshaft moves while the intake valve is open. Cam manufacturers agreed to measure and give camshaft duration based on the lifter moving .050 inches. This made duration numbers easier to compare between different cam manufacturers.

            Exhaust Duration at .050 inch Lift - The number of degrees the crankshaft moves while the exhaust valve is open. Cam manufacturers agreed to measure and give camshaft duration based on the lifter moving .050 inches. This made duration numbers easier to compare between the different cam manufacturers. Camshaft Lobe Separation (in degrees)

            Cam Lobe DiagramCamshaft lobes on standard V8's, like the small block Chevy, are arranged in pairs: One intake lobe, one exhaust lobe. Those pairs of lobes are phased to each other. Cam lobe separation is the angle in degrees between maximum lift of a pair of cam lobes. To picture cam lobe separation a little better, look at the end of a traditional V8 camshaft. Draw a line through the center of the cam out through the point of maximum lift on each cam lobe on a pair of lobes. You'll usually find the measurement between 104 and 115 degrees. It's important to note that Lobe Separation describes how the intake valve reacts in relationship to the exhaust valve in the same cylinder. Where cam lift and duration describe the effect of each lobe on a valve. Cam Lobe Separation is an important performance characteristic because it times the intake and exhaust valves. If the Lobe Separation angle was 0 degrees, both intake and exhaust valves would be opened and closed at the same time. That obviously won't work, but it may help us understand what happens as the separation angle decreases or increases on a cam.

            From the Kent Catalog, see description of duration at 1mm. Which is 0.039" Duration at that lift is 243. Duration at 0.050" would be less. See description of duration measurement in catalog at
            http://www.kentcams.com/documents/do...%202016(7).pdf

            TH5-6 FAST ROAD 2200-7000 .293” .423” .421” 280° 37/63 73/27 243° 103° .022” .024” .112” N/A CF25 VS17 - - - S75 BEB15-12

            Furthermore, reference 6-Pack Magazine Fall 2012 "Camshaft Installation - Part 2" it compares Kent cam with WBC 518 cam.

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            • #21

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              • #22
                The WBC cam has the steepest curve shown in the graph, as expected given its lift/duration ratio. This unequivocally translates to higher valve train forces. Until significant mileage ( 50K+ in my book ) is done on one of these I wouldn't consider fitting it nor recommending it ( quite apart from the, er, speckled reputation of the proprietor ) as cams and followers have a bloody track record since TRIUMPHs were in production. A look at contemporary cams fitted to Porsches for example makes the point rather emphatically - they are not nearly as wild that way, and TRIUMPH must have known quite well the practical limitations. The CP cam will go much more than 100K miles as its lift/duration ratio is relatively low. Likewise the KENT TH2; even more so.

                Tom

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                • #23
                  I think we are loosing track of the actual topic....
                  Flying Dutchman drives: TR6 - 1973 - 56/11 - CF1xxxxUO - J-OD - Kent 270° - 2x ZS - Phoenix - Pierburg - 123Tune - 205/70 on 7x15

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