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Thread: cam profile mod gains

  1. #1
    Junior Member Grease Monkey
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    Default cam profile mod gains

    Hi, in terms of performance gains which part of the cam profile is the most crucial? Is it duration, lift, ramp, etc?

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    Front Yard and Backyard Mechanic white_sandshoe's Avatar
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    Default Re: cam profile mod gains

    subscribed... interested in the answers people give to this...

    I'm under the impression it depends what you're after. Power at high rpm, decent torque, wide torque band, and different again for NA vs forced induction...
    Keen to see what people who know about such things have to say.
    "Think of it like customer service, but the customer is *not* always right. And, you'd rather not have their repeat business." - Mullett

    "well I don't know what the world may need, but a V8 engine is a good start for me..."

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    Default Re: cam profile mod gains

    I have a great book that has a breakdown on cams and which part controls what in regards to the cam dimensions. Will get it back and post up some good info

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    Default Re: cam profile mod gains

    let us know the book title please

  5. #5
    Forum Contributor Domestic Engineer
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    Default Re: cam profile mod gains

    Quote Originally Posted by metcap View Post
    let us know the book title please
    Also keen to know book title
    MA71 - 7MGTE - 340RWHP

  6. #6
    Forum Member Grease Monkey
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    Default Re: cam profile mod gains

    Yeah will try and get it back tomorrow. One of the best books i've read on performance upgrades for piston engine. has a chapter on all you could want like compression, cam, valve train, carbys, efi, suspension, intake and exhaust. Probably not help anyone yet by telling you this though

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    Default Re: cam profile mod gains

    How to build horsepower by David Vizard is a good one but it deals mainly with sbc and 2 valve v8's.

    but you pretty much want the highest ramp rate you can get, which is a rectangle but that shape's not going to be nice to the lifter/rocker.

    "Duration" tells you where the engine will make peak torque, doesn't change how much torque it makes, just where it makes it, according to the book.

    For lift, undervalved(valve too small for engine) engines want more lift to make it "breathe" better. To get more lift in the same duration, you need a higher ramp rate, which your lifters/shims might not agree with. The book recommends valve lift to be 0.35 of valve diam for a 2v v8. I don't really agree with this though.

  8. #8
    Junior Member Grease Monkey
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    Default Re: cam profile mod gains

    For lift, undervalved(valve too small for engine) engines want more lift to make it "breathe" better. To get more lift in the same duration, you need a higher ramp rate, which your lifters/shims might not agree with. The book recommends valve lift to be 0.35 of valve diam for a 2v v8. I don't really agree with this though.
    how so? to small?too big?

  9. #9
    Olde mechanic Carport Converter oldeskewltoy's Avatar
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    Default Re: cam profile mod gains

    don't forget the head has to be capable to flow...

    A stock head will often hit a wall where it just stops flowing more... So cams only tell part of the story.

    for example... 4AG head... without proper porting, there is little reason to run lifts much above stock, but with proper porting....
    Information is POWER... learn the facts!!

  10. #10
    Junior Member Backyard Mechanic
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    Default Re: cam profile mod gains

    First understanding what those terms mean help you understand how they work,

    Lift = how much the valve will open

    Duration = how long the valve will stay open

    Lobe center separation = a relation in degrees betwine intake valve and exhaust valve that determine how long these will be open at the same time during a cycle
    These are some of the most important aspects of a cam when is time to choose one for any particular engine

    Note, that same profiles are not suitable for all kinds of engines,
    Each and every diferent engine design is a diferent animal,

    Whaen choosing a cam for your engine you need to have in consideration what your engine is intended for , in what car it will be installed and what type of engine configuration this will be,

    All those factors will play a huge roll on cam choice,
    Last edited by toyota1515; 18-05-2012 at 07:39 AM.

  11. #11
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    Default Re: cam profile mod gains

    Ok so the book is Modern Engine Tuning by A graham Bell and its published by haynes

    its definitely worth getting if you're into your custom modding because when it talks about the each modification the guys actually do the mod to the same engine and dyno it each time to back up what they are saying. So i'll try summarise the cam part and post a couple of tables from the book to try and explain it the best i can.

    Ok we'll start with a single lobe on the cam
    http://postimage.org/image/owyjtwobv/
    So for the most performance orientated cam they will have:
    short ramps - This is where the slack is taken up between the cam and the lifter
    Longer steep flanks - this controls how fast the valves open and how long they are open for

    Cams are usually classed in 5 stages, phase 1 (being a stock) and phase 5 (being a high performance cam) The way most manufacturers measure their cams are the degrees the inlet and outlet values are open for.
    so to better explain this: a cam that opens the inlet value 26 degrees before TDC and closes it 90 degrees after BDC has a duration on 296 degrees inlet (26+90+180 (which is the degrees between TDC and BDC)) then the exhaust is opened 84degrees before BDC and closes 46degrees after TDC as a duration of 310 degrees exhaust.
    Now that we know that we can class the phase cams:
    Phase 1= inlet 208-212 degrees exhaust 210-216
    Phase 2= inlet 216-220 degrees exhaust 214-224
    Phase 3= inlet 224-228 degrees exhaust 218-226
    Phase 4= inlet 230-232 degrees exhaust 220-228
    Phase 5= inlet 236-242 degrees exhaust 224-230

    So below is a comparison of stock cam, phase 4, phase 3 and a marine one which is phase 1 sort of cam
    http://postimage.org/image/hjbed96hz/

    You've then got lobe separation which is the overlap of inlet and exhaust open and close. I'll skip the breakdown and just say that they are typically between 108-112 degrees where narrows figures give mid rang whilst wider figures increase the peak power at the expense of low rpm power
    http://postimage.org/image/su68w2qa9/
    The reason this will effect low mid or high and not all three is because with different overlaps you'll effect the intake and exhaust so at various RPM you may force the fuel straight into the exhaust or not completely vent all the exhaust gas before the valves close because of the velocity of the gasses at the different RPM


    So the longer and steeper the flank the better performance you'll get as it allows more fuel in and and a faster speed.
    ramp you want these short so you can extend the length of the flank (ramps are just for a smooth transition from no lift to lifting the valve)
    separation depending on where you want the power increase, a bigger angle will give top speed and a smaller angle will give low speed acceleration

    Hope i's answered your question properly and havent put too much technical crap in :S its just the manufactures may have different definitions of what a phase 1 and 2 cam are so you can compare the different cams the different manufacturers may have

  12. #12
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    Default Re: cam profile mod gains

    great post Davespec, keep all the info

    And helping with the pics:


    Last edited by metcap; 19-05-2012 at 04:38 PM.

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    Default Re: cam profile mod gains

    when doing a long duration, hi lift cam conversion what important details need to be taken to upgrade the valvetrain parts?

  14. #14
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    Default Re: cam profile mod gains

    For high performance engines...
    when upgrading to maximum lift rockers say a 1.25:1 to 1 1.5:1 there will be excess wear in on the value guides. It is recommended to upgrade to roller type rockers (more expense) but designed to produce less engine wear becomes of a less friction designed rocker.
    You can go to the extreme if this is a race engine and get high quality and expensive aluminium arms with needle roller bearings and needle roller tips for best performance.
    ^^ this is from my book
    so in this case upgrading to a long duration hi lift cam, the only real problem you're going to face is the increase in friction amongst the valvetrain parts.
    Rockers:
    So it would be best to use, as above, roller type rockers, if you already have these then it comes down to how much of an increase in lift the cam will produce and if the stock rockers can handle this. To find this out the best way would probably be to find what cams are available for the current engine that are safe to just swap without changin the valvetrain, if you're goin to exceed this cam then you will need lower friction rockers, probably of a higher strength than stock.
    Springs:
    the valve springs would also need to be check if they can handle the hi lift (stock springs are usually fine for a phase 3 cam).
    If you use the wrong springs for this lift then the spring coefficient might be too high meaning you are wasting energy by forcing the springs to compress more than they want to and they will close with more force than necessary causing excessive wear to the value seats or broken valves.
    Valve clearance:
    This needs to be checked with a new cam to ensure that there is at leas a .060in clearance between the collects and the valve guide at full lift. The retainers can be ground down if necessary but only by .040in. You'll also need to adjust all the value clearance to the engine specs after a cam change.
    valves:
    You'll also need to decide if the valves can handle the new cam. Theoretically, with correct springs and value clearance for a new cam, the valves should be fine as as far as they're concerned nothing has really changed as the are still being closed by the same amount of force and this experiencing the same forces as the previous cam, so generally it is unnesary to change the valves to a higher strength type.

    Also one other thing to note with installing a custom cam is that the oil passage should be inspected regularly for Over head cam engines as there may be more friction and heat in after installing a different cam so to prevent any extreme engine damage they should be inspection to ensure they are correctly lubricating.

    There is another section for hydraulic lifts and push rod type, and also a bunch more info on measurements and stuff for rocker lifts. I've only done a quick overview for the moment.

    I've got my uni exams comin up soon so i dont have a lot of free time but i can give you a better breakdown of the valve train in a week probably if you like.

    I'll eventually be doing a breakdown on complete engine tuning for my website so if you've got some interest in customising other parts i should be able to help out

  15. #15
    Junior Member Automotive Encyclopaedia
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    Default Re: cam profile mod gains

    Are your springs and shims capable of the cam's rpm range, rest of the engine & drive train capable of that rpm and power range, does spring guide & seal have clearance at max lift, lobe wiping the follower/shim within its diameter, are intake compression or exhaust restrictive?
    'I've scrapped better.' John stated when asked what he thought about the guy with the silver tipped cowboy boot's car!

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