Camshaft 101 and Regrind Information

Discussion in 'Parts and Accessories For Sale' started by 6A13TT TYPE S, Jul 23, 2016.

  1. 6A13TT TYPE S

    6A13TT TYPE S 3 AYC Bars Lifetime Member

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    As many of you may know I work for a company called Kennelly Cams.
    Figured Id make this thread as a FAQ about camshaft stuff and any other questions in an attempt to not completly derail other threads


    What is a camshaft regrind you say?
    Well by grinding away only selected parts of the existing lobes we can turn a stock profile into a performace profile.

    Before I go explaining how all this works Ill cover some camshaft basics for those interested.

    BASE CIRCLE
    the perfectly round section of the cam lobe. when the roller of the rocker arms is riding on this part of the cam the valve is fully shut.
    FLANKS
    the steep sides of the lobe, this is the part of the cam lobe which starts pushing the valves open on one side of the lobe and helps steadily and safely close the valve on the opposite side of the lobe
    NOSE
    This is the tip of the lobe, the point at which maximum lift is acheived, if you measure a camshaft from the tip of the nose to the opposite side of the base circle and then subtract the base circle diameter that gives you your cam lift value

    LIFT
    this is the height of the lobe above the base circle, in essence how far it will open your valves. the 6A13TT has a 1.7:1 rocker cam follower. this multiplies the lift by 1.7
    for example if you measure your cam lobe lift to be 5mm, the valves will have a maximum lift of 8.5mm
    5 * 1.7 = 8.5
    DURATION
    Camshaft duration, this is a number given in degrees of crankshaft rotation for how long your camshaft will keep the valves open.
    keep in mind that for every one turn a camshaft makes the crankshaft rotates twice.
    there are two ways of describing duration,
    1 - "Advertised" duration which is the number in degrees of crank rotation from the instant the valve starts to open to the instant it becomes closed again this is how most places market their cams to the general public HKS 272. Tomei 264, etc etc
    2 - "Duration @ 0.050"" (50 thousanths of an inch valve lift.) this is the duration in degrees of crank rotation from the instant the valve passes the 0.050" open point until it is 0.050" away from being closed again. this is what most people like me or engine builders talk in as valves don't generally flow any appreciable ammount of air until the valve is at least 0.050" open. (some places use 0.040" which is 1mm this all depends on the cam maufacturer) obviously this number will be lower than "Advertised duration" because it starts after the instantanous opening point and ends before the final closing point.
    for example a HKS cam for an RB26 may have an advertised duration of 272 but its @0.050" duration will be 230ish
    A stock VR4 camshaft has about 240 degrees of advertised duration. so that means the angle between the opening point on the camshaft to the closing point will be 120 degrees apart
    CENTER LINES
    this is where the middle of the camshafts duration occurs in the engines cycle. exactly halfway between the opening and closing points. this is often the point of maximum lift too.
    this is measured in degrees of crankshaft rotation.
    for example if your cams are set up at 105 intake 110 exhaust it means the centerline of the intake camshaft occurs 110 degrees after TDC and the centerline of the exhaust occurs 110 degrees before TDC
    given that a stock cam is 240 degrees (120 either side of the centerline) on these theoretical centerlines 105/110 the intake valves will start opening 15 crank degrees before the piston reaches TDC and the exhaust valves close 10 degrees after TDC this means the intake an exhaust valves are open at the same time for 25 degrees in the time leading upto and shortly after TDC. this is whats called overlap and this is directly effected by the camshaft centerlines. Centerlines and overlap is what you change when you have adjustable cam gears. and is had massive effects on how an engine behaves and where and how it makes its power.
    I don't know what the stock centerlines are on a VR4 as I have yet to measure that.


    Hopefully that all makes sense so far!
    Now I can start to explain how I reprofile a stock camshaft to have extra duration and more lift without actually adding any extra material onto the lobes.
    well a picture speaks a thousand words so here's one I whipped up on trusty microsoft paint

    Capture.JPG

    the black circles represent the base circles of the cam lobes and the blue and red lines represent the lobe profiles. the larger circle and blue profile represents the stock lobe before regrinding. and the smaller one with red profile represends the reground lobes base circle (Not to scale of course)

    as I said before the stock advertised duration is ~240 degrees which means that the total internal angle of the blue lines which intersect at the center and connect to the opening and closing points of the stock lobe is 120 degrees. and the lift from the top of the stock base circle to the tip of the nose of the lobe is 5mm.

    Now what I do is grind away all the material that isn't enscribed inside the red lines and smaller base circle. As you can see, by grinding away only material from the flanks and base circle and not removing much or any from the nose of the lobe the red lobe is noticably larger compared to the blue lobe. if no material is removed from the nose of the lobe, the ammount of material removed off the radius of the base circle is what the increase in lift will be.
    you can also see that it has allowed the opening point of the red lobe has been brought further down the base circle, the same story with the closing point, meaning the internal angle between the red lines is larger than the angle between the blue lines, this is the increase in duration.

    because our engines have hydraulic lifters (HLA's, lash adjusters, lifters whatever you call them in your part of the world) this is what makes a cam regrind a affordable option. I grind the material off the base circle but the lifters just pump up with more oil like a tiny hydraulic ram to take up this extra clearance. some cars have mechanical lifters (RB26, 2JZ, 4AGE) so when you grind the camshafts you need to manually adjust them or make precision shims to attain the correct lash/valve clearance which can be very time consuming and expensive.


    any questions feel free to ask ill try my best to answer
     
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  2. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    Interesting. So basically by making the "closed" part of the lobe smaller, the lifter pumps up to meet it, therefore the valve lift is increased without adding material to the cam.

    Is there any risk with regrinds of the lifter over extending and causing the roller to pop off under high rpm?
     
  3. 6A13TT TYPE S

    6A13TT TYPE S 3 AYC Bars Lifetime Member

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    Thats correct.

    If you grind too much off the base circle yes you can loose lifter preload and it wil become noisy and risk throwing rockers off.
    thats why we limit the regrind to 264° as going bigger means grinding more off which risks running out of lifter preload.
    You can grind more off but then you have to shim the lifters and going too far puts the rocker geometry all out of whack.
     
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  4. lateshow

    lateshow Leaving Skid Marks

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    And if the lifters are already in bad shape they should be renewed when installing bigger cams?
     
  5. 6A13TT TYPE S

    6A13TT TYPE S 3 AYC Bars Lifetime Member

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    Yes. If your lifters are noisy at all then you should give them a through cleanout.
     
  6. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    What's kinda funny is they're technically smaller cams!
     
  7. 6A13TT TYPE S

    6A13TT TYPE S 3 AYC Bars Lifetime Member

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    It's not the size that matters! Its how you use it....
     
  8. lateshow

    lateshow Leaving Skid Marks

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    Isnt it good to gain weight reduction from rotating mass??? Am I right?
     
  9. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    Yeah but rather offset by the stiffer valve springs and more lift. :D
     

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