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  1. #1
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    Tell me about Camshaft

    Title says it all. I'm a noob when it comes to Camshaft and camshaft tuning, but i would like to know more about it.
    Thanks

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    I'm in for this one as well.

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    wiki is honestly your best bet: http://en.wikipedia.org/wiki/Variable_valve_timing
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    I could write a 100 page paper on it, but your best bet is to start google searching camshaft basics. If you have a specific question it would be easier to answer, but understanding exactly how the camshaft affects performance requires a degree on the subject.
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    Boo, give us basics.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Boo, give us basics.
    Camshafts control the timing events of valves.
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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    Camshafts control the timing events of valves.
    Well, it's a start.

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    The reason i ask is because afew days ago when i stopped at light there was a Mustang with really aggressive cams. the car was shaking like nothing else, and the sound reminds me of machine gun. one of my questions ( which really is a dumb one ) is why with aggressive cams the engine rattles so much and also why it sounds like that? why we don't have this problem with factory cams?

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    Here is a great article that explains it: http://www.jdmcars.com/tech/lift_duration.pdf

    Basically more aggressive cams have more overlap between when the intake valve opens and the exhaust valve closes. This improves engine performance at high rpms, and hurts performance at low rpms. It all has to do with momentum and how the exhaust creates a scavenging effect, drawing more air into the cylinder as it leaves.

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    The popping you hear when a car with really aggressive cams is idling, is exhaust gases actually escaping through the intake valves due to the fact that the intake charge doesn't have enough momentum.

    At higher rpms, the intake air is moving fast enough the exhaust has to leave through the exhaust valves, and it can create the scavenging effect.

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    I am assuming there is an electronic version of a camshaft that idles well and then, at higher rpms adjusts accordingly for better performance?
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    ok since my buddies PEI and evolve are out partying I'll take a shot at it.

    What camshafts do:

    What they do is simple, very simple. Just open and close valves, thats it. They open and close the valves at specific times.

    The impact they have on an engine performance is not simple, it is very complex, so complex in fact that we cannot fully simulate the way the air moves due to the nature of valves opening and closing. I will explain.

    I want you to imagine for a second, a long tube. Say 2 inches in diameter, and 20 feet long. This tube is connected to a leaf blower on one end. You turn on the blower and air is going to flow through the tube. Now, imagine that I can push a button and shut the end of the tube instantly with some type of fast action valve. Guess what happens, at the instant in time I do this the leaf blower is still flowing the same amount of air, at that instant.

    A few milliseconds later, the leaf blower is gonna start to flow less until it flows zero. Because it 'got the message from the valve' on the other end. Guess what, that 'message' is going to bounce from the valve end back to the leaf blower and continue to bounce back and forth like a spring would. The pressure wave will do this until it dampens out (it can happen a couple hundred times in a low pressure loss system).

    You intake ports are exactly this. The leaf blower is air rushing into your ports, the valves on your motor are closing much faster than the air can anticipate. So who cares?

    This concept is paramount in understanding how camshafts effect performance. Air does not move as easily and freely as we may think it does, at low speeds it is intuitive but at high air speeds air carries a lot of momentum. Momentum is what wants to keep air moving in one direction.

    The application of this is twofold.

    First, lets talk about the intake valve. When the piston is moving down the bore it is 'sucking in air', actually it isnt, it's just creating a low pressure zone and ambient air is pushing it in (think leafblower). As the piston continues to move down the bore on the intake stroke the air is rushing, at low engine speeds you want to shut that valve right when the piston hits bottom dead center so you capture as much air in that cylinder as possible (this is at engine idle).

    At high engine speeds, the air is moving so fast that when the piston hits bottom dead center in fact air is STILL flowing into the cylinder. Even after the piston stars to move back up the cylinder for the compression stroke, AIR IS STILL FLOWING INTO THE CYLINDER BECAUSE IT IS CARRYING A LOT OF MOMENTUM. The job of the camshaft is to shut the valve at the EXACT INSTANCE in time when air will stop packing itself into the cylinder and youve recovered as much of the fluid momentum as possible. This is called inertial packing.

    Resonance. Remember the leafblower and superfast valve concept? This effect is shows up after the intake valve shuts completely and the air pressure bounces back into the intake plenum. Once it hits the plenum, it wants to bounce back into your intake valve, guess what folks; if you tuned your intake length to the precise length to exploit this phenomena you've just created a 'tuned port intake' and your cylinder will have even more air packed into it.

    Volumetric efficiency, the amount of air that theoretically should fill a cylinder under perfect conditions (such as air being inviscid, that is having no viscosity) versus how much air actually makes it into the cylinder. Most car engines have a VE of less than 90% which means that a 5.0 liter engine at 90% VE is only 'sucking in' as much air as a 4.5 liter engine at 100% VE.

    A very well designed camshaft can actually produce 110 to 120% VE, these cams take advantage of helmholtz resonance and precisely tuned inertial packing. One example is the Honda F20C and the Honda K20Z3, those engines are greater than 100% VE due to hondas amazing VTEC technology.

    The S65 is also up in the 90s VE.

    I havent gotten to exhaust valves and scavenging, or boost. Thats going to be another day.
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    awesome man, glad someone like you stepped up. look forward to part 2
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    Camshaft lope.

    When you hear a big honkin' muscle car with a 'big cam' loping, that sound is basically the intake cam closing so late that at idle the car has barely enough air to sustain idle. Also, the overlap of the intake and exhaust valve causes the engine to buck, the engine is basically gasping for air. Think asthma.

    At high engine speeds, this big honkin' V8 has no VTEC, the cam is set for ONE engine speed. And it makes lots and lots of power at that speed. VTEC allows a car to idle like an economy car, smooth as silk, and at high engine speeds the camshaft intake closure is then electronically DELAYED to allow for inertial packing. So, the Honda K20 doesnt lope at idle, and still makes over 100% VE at 8300 RPM because it has multiple cam phase routines that it goes through.

    The 'lope' sound although cool as hell sounding, really means that the cam has a tremendous amount of intake valve retard and also a tight lobe separation angle. Which means, it is meant for very high RPM performance. Engines like the S65, K20 and F20C idle just fine, and also make ridiculous horsepower per liter at high RPM because they can shift the intake cam closure to remain optimal at all engine speeds. No low speed lope.
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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    ok since my buddies PEI and evolve are out partying I'll take a shot at it.

    What camshafts do:

    What they do is simple, very simple. Just open and close valves, thats it. They open and close the valves at specific times.

    The impact they have on an engine performance is not simple, it is very complex, so complex in fact that we cannot fully simulate the way the air moves due to the nature of valves opening and closing. I will explain.

    I want you to imagine for a second, a long tube. Say 2 inches in diameter, and 20 feet long. This tube is connected to a leaf blower on one end. You turn on the blower and air is going to flow through the tube. Now, imagine that I can push a button and shut the end of the tube instantly with some type of fast action valve. Guess what happens, at the instant in time I do this the leaf blower is still flowing the same amount of air, at that instant.

    A few milliseconds later, the leaf blower is gonna start to flow less until it flows zero. Because it 'got the message from the valve' on the other end. Guess what, that 'message' is going to bounce from the valve end back to the leaf blower and continue to bounce back and forth like a spring would. The pressure wave will do this until it dampens out (it can happen a couple hundred times in a low pressure loss system).

    You intake ports are exactly this. The leaf blower is air rushing into your ports, the valves on your motor are closing much faster than the air can anticipate. So who cares?

    This concept is paramount in understanding how camshafts effect performance. Air does not move as easily and freely as we may think it does, at low speeds it is intuitive but at high air speeds air carries a lot of momentum. Momentum is what wants to keep air moving in one direction.

    The application of this is twofold.

    First, lets talk about the intake valve. When the piston is moving down the bore it is 'sucking in air', actually it isnt, it's just creating a low pressure zone and ambient air is pushing it in (think leafblower). As the piston continues to move down the bore on the intake stroke the air is rushing, at low engine speeds you want to shut that valve right when the piston hits bottom dead center so you capture as much air in that cylinder as possible (this is at engine idle).

    At high engine speeds, the air is moving so fast that when the piston hits bottom dead center in fact air is STILL flowing into the cylinder. Even after the piston stars to move back up the cylinder for the compression stroke, AIR IS STILL FLOWING INTO THE CYLINDER BECAUSE IT IS CARRYING A LOT OF MOMENTUM. The job of the camshaft is to shut the valve at the EXACT INSTANCE in time when air will stop packing itself into the cylinder and youve recovered as much of the fluid momentum as possible. This is called inertial packing.

    Resonance. Remember the leafblower and superfast valve concept? This effect is shows up after the intake valve shuts completely and the air pressure bounces back into the intake plenum. Once it hits the plenum, it wants to bounce back into your intake valve, guess what folks; if you tuned your intake length to the precise length to exploit this phenomena you've just created a 'tuned port intake' and your cylinder will have even more air packed into it.

    Volumetric efficiency, the amount of air that theoretically should fill a cylinder under perfect conditions (such as air being inviscid, that is having no viscosity) versus how much air actually makes it into the cylinder. Most car engines have a VE of less than 90% which means that a 5.0 liter engine at 90% VE is only 'sucking in' as much air as a 4.5 liter engine at 100% VE.

    A very well designed camshaft can actually produce 110 to 120% VE, these cams take advantage of helmholtz resonance and precisely tuned inertial packing. One example is the Honda F20C and the Honda K20Z3, those engines are greater than 100% VE due to hondas amazing VTEC technology.

    The S65 is also up in the 90s VE.

    I havent gotten to exhaust valves and scavenging, or boost. Thats going to be another day.
    That wasn't so bad, was it?

  16. #16
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    Awesome man. took time to figure out what you were saying but it was worth it.

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    Yeah this is some incredible info.
    Josh M5 2011

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    I like it.

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    DBFIU,
    you are the man! Thanks for thatClick here to enlarge

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