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n00b question

This is a discussion on n00b question within the General Help forums, part of the LSx Technical Help Section category; Can anyone explain the difference between our pushrod engines and over head cam engines? Pictures would be great too....

  1. #1
    Member Eric1987's Avatar
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    n00b question

    Can anyone explain the difference between our pushrod engines and over head cam engines? Pictures would be great too.

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    James Bond Spikito's Avatar
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    on ours the cam sits under the intake manifold, between the two halves of the motor. the lobs push up on the push rods, which rotate the rockers arms, which in turn, push down the valves. An OHC motor has the cam(s) over the heads and the lobs push directly down onto the valves.

    They have less moving parts (no rocker arms or pushrods) but we only have 1 cam to deal with, that includes modifying, and the power used to turn them/it over.

    Some motors, like the one in 03-04 Cobras i think, has 4 cams total, DOHC on each side. 1 for intake valves, 1 for exhaust valves. So if they want to cam their motor, they have to buy 4 of them.

    heres a link for DOHC, if you go to google images and type in LS1 cam, you can find some good pics, but you cant open the link, you can only view the thumbnail, but you should get the idea

    http://blogs.mysanantonio.com/weblog...shaft-dohc.jpg

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    Veteran 0rion's Avatar
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    This is of a 265 chevy small block. In the cutaway you can see the cam dead center in the belly of the block above the crank. Then you see the lifter which pushes the pushrod which then pushes the rocker and opens the valve.



    this is a cut away of a dohc setup

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    Life in the Fast lane sunsetorangess's Avatar
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    Quote Originally Posted by 0rion View Post
    This is of a 265 chevy small block. In the cutaway you can see the cam dead center in the belly of the block above the crank. Then you see the lifter which pushes the pushrod which then pushes the rocker and opens the valve.

    Click for full size

    this is a cut away of a dohc setup
    Click for full size
    Great pics...
    J
    2001 SS, Its not the car its the Driver that matters....

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    This might be a good place to ask an opinion question(s).

    I've thought for years that someone would eventually delete cams altogether and use solenoids or perhaps DC motors and integrate those the same as you do injector pulsing pretty much.

    Anyone else think this will happen?

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    Veteran 0rion's Avatar
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    I'm sure at some point someone will come up with a different/more efficient way of doing it but right now I think cost effectiveness and simplicity will keep the cam around a while.

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    Yeah...it is always pricing that keeps things around well past "what could be done."

    But you could sure get rid of a bunch of moving mass and friction...and simplify the block a bit. I'd think with cam weight + inertia, push rods, and lifters you got a enough moving mass elimination that the solenoid x alternator x modulator efficiency would be more efficient.

    Last I checked (about 5 years ago) the chief problems of concern for an all electrical valve system (responsiveness, torque, endurance) put it just out of reasonable limits. Torque being at odds with both response and endurance.

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