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cam retard

  1. #1
    Senior Member vmaxed's Avatar
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    Default cam retard

    Just say and all these numbers are just pulled out of the air. Say your motor makes peak power @ 6000 and then starts falling off. Then say it has a lob separation of 110 and is installed @ 108. If you retard the cam to 110 would it make the same HP @ 6100 then start falling off? Simpler said will retarding the cam just move the power band up RPM scale and make the same HP? HAPPY THANKSGIVING
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    Senior Member wagspe208's Avatar
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    Oh, boy... this is going to be good.
    In theory, maybe, in many cases no...
    See, airflow is not just a cam function, it is also a port size, design function. Maybe the engine is just airflow limited, not cam limited... but you get where this is going.

    So, Theory....yes. ... maybe or maybe not.
    Crappy answer.. I know.
    Wags

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    Senior Member EVILFORCE's Avatar
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    Like Wags said. You could be limited but a advanced cam will lower your peek power rpm and basically lower the whole rpm power band. A retarded cam will raise it but you will loose lower rpm and mid-range as well.
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    Senior Member SoldHondaBoughtHondo's Avatar
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    I went +4 on a stock 455 olds t/r 660's in a v-drive hydro with 40 gears trying to kill off power past 5k so i didn't hurt the motor....it kinda helped and the motor picked up 300 rpm at the hit.I played with cam timing years ago in my car. 6 different cams...ran each one straight up, then +- 4. Like wags said, sometimes yes, a lot of times it didn't make any difference.
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  7. #5
    gn7
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    The intake closing is by far the most important event in the cams timing, and makes the biggest change. 2* is a minimal move. Any change you see will be minimal. Theorically, it will move the peak torque higher on the power band. But I have seen cams moved from 4* advanced to 4* retarded and lose big. It depends on the current cam and engine combo and if the engine WANTS the intake closed later. More times than not, retarding a cam is a looser. I think the whole idea of retarding cams stems from using stock or limited timed camshafts.

    Your talking about running it straight up. Like I said, your advanced a minimum amount, and retarding it back will probably result in a minimum change unless the cam is already to short for the engine.



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    Senior Member Smallblocksperry's Avatar
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    i had a guy tell me that the best way to degree the cam is to check the cranking compression at zero, advanced and retarded, whichever makes the most cranking compression is where you want it, lol dont know how accurate that is, (he was a ford guy)

    i always degree'd mine to whatever the cam card wants the intake centerline at, most of the time ranging from 4 to 6 degrees advanced.

  9. #7
    Senior Member vmaxed's Avatar
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    Default where

    Where is this guy from? That's what I was told by some folks back when I was a kid. After you advanced it till it made the most static comp. and it didn't turn high enough you changed cams. There weren't many custom cam grinders back in those days.
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  10. #8
    gn7
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    Quote Originally Posted by vmaxed View Post
    Where is this guy from? That's what I was told by some folks back when I was a kid. After you advanced it till it made the most static comp. and it didn't turn high enough you changed cams. There weren't many custom cam grinders back in those days.
    The problem with that method is it ignores ram effect. Advanced will always show more cranking compression than retarded or even straight up. Again, because your closing the intake sooner and starting compression instead of blowing back up the intake manifold. Remember, the piston is rising quite awhile before the intake closes. The sooner you close the intake at cranking speed, the more pressure it will make. I cannot imagine how far advanced you could go before it started to drop back.
    I have however, seen some very knowledgable builders time a cam at the maximum DESIRED cranking pressure. Specially if it was running on pump gas. But I will bet you that almost any cam will show MAXIMUM cranking pressure all the way to 95* ABTC intake CL, or better. Or to look at it another way, an intake closing of 0* ABDC will probably make the most cranking compression, but not the most power by a long shot.
    Thats how cams were ground back it the early days of internal combustion engines. But they didn't make power.

    If you want to know where maximum cylinder pressure is taking place, put it on a dyno and see where max torque is. Thats pretty darn close to maximum cylinder pressure. You want maximum cylinder pressure at 200 rpm, or 5500? You can't time a cam for maximum cranking pressure and expect to still be making maximum cylinder pressure at 5500 too.



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    Last edited by gn7; 11-26-2012 at 05:17 PM.

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