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Thread: Ok, Explain Cams To Me Please

  1. #1
    Junior Member JOURNEYMAN
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    Ok, Explain Cams To Me Please

    Just the Readers Digest version, not a long dissertation. I know the physical differences between hydraulic, solid, mushroom and the different roller types, what I'd like to know is why one is preferable over the other. Is it basically just the rpm limits?

  2. #2
    Senior Member EXPERT BUILDER
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    Well Kend, in simplest terms, the camshaft is the 'brain' that tells the engine intake and exhaust flow what to do and when.
    It delegates how and when each valve opens and closes, and is a 'science' everyone is looking for to find the optimum efficiency for their component package throughout the entire rpm range.
    Your choice of camshaft should be the most logical design and efficiency for the intended application... do you need low end pulling torque, do you need top end racing speed, do you need a wide range of rpm efficiency across the board, or do you need to putter to the grocery store drivability...? One who finds that 'secret edge' for his/her application will have an advantage over all the others... Jim
    I'm not hatin... I'm just sayin...

  3. #3
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    Flat tappets are limited in the steepness of the 'ramp'. ( how RAPIDLY the valve will begin the opening process). Rollers can use an almost vertical ramp simple because of the design. Example is off road 4X4's going up an almost vertical rock because the tires/rollers are rotating instead of sliding. Rollers have a very small contact 'patch' as opposed to flats which have to have a larger and offset contact to promote rotation of the lifter for lubrication/even wear action.
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  4. #4
    Junior Member JOURNEYMAN
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    Thanks guys but what I'm looking for is.... why would you use a solid instead of a hydraulic? What does a solid do that you can't do with a hydraulic? Why are the factories now using hydraulic rollers, just for the decreased friction? I know the difference in construction and what a roller lifter can do as compared to a flat lifter, just looking for some "why" answers. Thanks

  5. #5
    Senior Member RACING JUNKIE
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    Lessee if we can keep this simple.

    The difference between the Hydraulic lifter and a "Solid" lifter (or camshaft follower) is that the Hydraulic Lifter maintains it's own adjustment through rpm and usage wear. The Solid lifter tends to require maintenance and adjustment, often, frequently when used in racing applications . .

    The advent of the Hydraulic Roller Lifter (or follower) was a normal but late progression of engine technology applied to the mass produced engines for greater efficiency and lower parasitic horsepower loss and, of course, less wear.

    The problem that apparently kept the Roller lifters out of mass produced engines centered around getting the oil to the lifter because of the difference and location of the hydraulic component in the lifter body, along with the additional cost of more moving parts.

    When the Engineers were given the newer casting and machining technologies that enabled them to overcome the oiling problems and the assembly problems that the new lifter created, "Voila!", Roller Cams for the grocery getter.

    However . . Most of the Blown Nitro Engines and the GM Gen IV NASCAR engines all use Flat Tappet (Solid) lifters because of the less reciprocating weight in the valve train. The thought, at least in NASCAR, is to keep the valve train components as light as possible, the cam lobes as small as possible and to use the extended rocker arm ratios (1:8-1:9) to multiply the lift to compensate for the small size of the cam lobe . . Very low valve seat and opening pressures enable all of this . . It makes a large reduction in reciprocating mass, which we all know is one of the major "Engine Killers" . .

    But this is predicated by use of the engine and types of induction. What works in one case, won't in another . .

  6. #6
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Quote Originally Posted by kend
    Thanks guys but what I'm looking for is.... why would you use a solid instead of a hydraulic? What does a solid do that you can't do with a hydraulic? Why are the factories now using hydraulic rollers, just for the decreased friction? I know the difference in construction and what a roller lifter can do as compared to a flat lifter, just looking for some "why" answers. Thanks
    Most of the time to keep increasing hp with the same cubic inch you have to turn more rpm. You will hit a point that the spring will not keep the lifter in contact with the cam, so you have to increase spring pressure. You will then hit a point that the hydraulic lifter can not keep oil in it because of the spring pressure, it will beat itself or other valve train parts to death. The next step in the evolution was to go to a solid lifter at that point. Hope that answers your question.

    Curtis

  7. #7
    Junior Member JOURNEYMAN
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    Perfect, thanks!

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    Administrator RACING JUNKIE bjuice's Avatar
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    These guys did a good job of explaining the science of it.

    Also just to add I do not know if a Hydraulic Roller would act the same as regular hydraulic cam and lifter set up in that its very forgiving if you stay in the gas and twist one tight it will float the valves before turning on up breakiing something. Not so forgiving with a solid flat tappet. I still run a solid flat tappet in a small block 406ci in a 69 camaro. Small but very responsive and effective all the way around .
    Bjuice..

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  9. #9
    Senior Member DYNO OPERATOR bixblk's Avatar
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    cams, we could all use some help now and then

    These guys are sharp !!!! Getting the right combo for application is key . Some of us think were close but always learning $$$$$$$ ,... ;)
    Good luck.... alot of the fun is the journey, but it sure is fun when you get there.

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