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Thread: Adjustable Cam Gears Vs. Aftermarket Camshafts

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    Arrow Adjustable Cam Gears Vs. Aftermarket Camshafts

    Wierd Topic but I wanted to get an understanding of this. I understand that cam gears that are adjustable can alter the cam timing which in effect changes the camshafts duration/lift...but is it better to do one over the other?

    Would it be best to do both?

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    Senior Citizen Member Array FutureEcotecOwnerAgain's Avatar
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    Cant really answer your question, besides why would you wanna mess with the duration and lift once you have your cams tuned to where you need and want them? And you ask alot of questions, LOL, j/k. I understand you wanna fill your head with knowledge, now that you got rid of the Sunfire, you want even more knowledge. LOL

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    I'm mainly asking for a friend but I'd like to know myself.

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    well the cam gears just adjust cam timing... usually with stock cars you can advance them alittle to gain some power.... best bet is to do both in one swap... get new cams and cam gears so you can dial in the setup right...
    but you really aren't gonna get a significant gain with just the gears... I think this motor is pretty high strung to begin with
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    Senior Citizen Member Array FutureEcotecOwnerAgain's Avatar
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    I'm mainly asking for a friend but I'd like to know myself.

    I'm trying to prepare myself for my next project car....in a year or so.
    Project car, project car, what is it, what is it? LOL. Hopefully I get my project car in my Cavalier and you get yours too. Maybe we could help each other out alittle bit once we get started. :Banane04:

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    They don't change lift or duration. Thats kindda built in to the lobe profile. Only timing. I have them. The idea is I can take advantage of boost that way. I may have to change my cams to get the real advantages, but I can do that anytime without much trouble.
    Last edited by Halfcent; 10-30-2006 at 12:06 PM.

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    They don't change lift or duration. That kindda built in to the lobe profile. Only timing. I have them. The idea is I can take advantage of boost that way. I may have to change my cams to get the real advantages, but I can do that anytime without much trouble.
    Halfcent Quoted Post
    Ok, maybe I'm mis-understanding camshaft timing. Can explain more of how it works?

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    Camshaft timing is different than lift/duration.

    Cam basics: rotating shafts with lobes on them that control the opening and closing of the valves, contributing greatly to the power delivery, total power and running characteristics of the engine.

    Lift:Valve lift;the amount the camshaft allows the valvetrain to open the valve(usually noted as .xxx", sometimes .xx mm.) Lobe lift; the amount the camshaft directly moves the camshaft follower. Lobe lift is an absolute, and cant be changed other than by grinding/replacing cam. Valve lift can be changed by valvetrain (followers/rocker arms) with different actuating ratios.

    Duration: the amount of time expressed in degrees of crankshaft rotation that the valve is held open. Also often expressed in more than one fashion; "duration @ .050" lift" or "total/complete/advertised duration" The difference being when the measurement begins...total duration counts from the exact point the valve moves open til the point it stops closing, this usually gives a longer duration and implies a more aggressive cam and is why its used as "advertised duration" duration @ .050"lift is what it says... duration measurement isnt begun until the valve reaches .050" open and stops when its .050" away from closed. This gives a more realistic idea of the actual cams characteristics because it omits the extremes of operation.
    Duration alone doesnt give a valid indicator of a cams performance capabilites either though because duration doesnt indicate(directly) how quickly the valve opens and closes or how long its actually open fully.

    Overlap is the period of time when both the intake and the exhaust valves are open at the same time, this determines the engines dynamic(running) compression ratio, how well or poorly it responds to a pressurised intake charge, and how it idles to a degree. Overlap is not changeable on a single cam system(either OHV or SOHC) it is adjustable via cam sprockegts/gears on a dual cam system. because you independently change the opening and closing times of the valves(in relation to piston position not the length of time they are open)

    Cam/valve timing: this is expressed as degrees before or after top dead center( ATDC or BTDC) you might see something like "intake opens 25BTDC, closes 185 ATDC" this would indicate a total duration of 210degrees.

    Changing the cam/valve timing would change WHEN the valve is open in relation to the piston, but not for how long or how far. So if we "advanced" the above intake cam by 10deg it would open degrees sooner(35 BTDC) and close 10deg sooner(175 ATDC) but it wouldnt change the fact that its open for 210degrees of crankshaft rotation.

    So you can see if we advanced(open and close sooner) one cam and retarded(open and close later) one cam we would affect how long the valves are open at the same time. "overlap"

    This is what VVT is for. by retarding or advancing one cam or the other the idle quality, emissions output, and power output can be altered to best suit the current needs of the vehicle.

    Quick emissions tutorial, VVT acts as artificial EGR(exhaust ags recirc) and AIR(air injection reaction) for pollution contol.

    Retarding the exhaust cam makes it close later(partially in the intakestroke) meaning incoming fresh air is blocked and the cylinder stays partially filled with exhaust and only partially fills with fresh intake charge. reducing combustion temps and the production of NOx......this strategy is used mostly under cruise type conditions(never at idle)

    Advancing the intake cam(making it open farther in the exhaust stroke) acts like AIR by allowing the exhaust system to scavenge fresh air into the exhaust system and further burn combustion byproducts in the exhaust and improve catalyst efficiency.

    Adjusting cam timing is important for the above reasons(mainly for manufacturers with VVT) but is also highly useful when building an engine because it allows you to fine tune the valve opening and closing times based on your engine combination it also allows you get exactly what you paid for cam wise by allowing you to adjust out any undesirable production tolernaces(this is what is being done when people are "degreeing" their cams)

    ALso important is to note that nearly all degrees are referencing crankshaft degrees of rotation, this of note because all four-stroke piston engines use 720 degrees of crank roation to complete one full cycle (intake, compression, power, exhaust) for all cylinders. Camshafts spin at half engine speed, 360 degrees of rotation for every complete cycle. This why cams always have gears/sprocket twice as big as the crank.

    Hope this helps

    (this took forever....dial up @ my parents house )
    Last edited by maven; 10-29-2006 at 07:34 PM.
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    Thank You, I'll read all of it when I get into work.

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    This should be stickied!!! Awsome write up man. I bet that did take some time. I'm printing it up for a quick reference. Thanx!
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    This should be stickied!!! Awsome write up man. I bet that did take some time. I'm printing it up for a quick reference. Thanx!
    BledRedGaSe Quoted Post
    Done and Done.

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    awesome, it was stickied....btw, im the friend he was askin for, and the newest member! w00t

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