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Thread: X-303 Cam

  1. #1

    Default X-303 Cam

    will going to 1.7 rockers wake up the X-303 cam without piston-valve inter...?
    Thanks,
    Ed

  2. #2
    Moderator wraithracing's Avatar
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    Which Engine? What year? What pistons? What head gasket? Which heads? Are the heads milled?

    Too many unknowns for that question to be a simple answer. Even then it may not be a simple answer and you might have to physically measure the piston to valve clearance to be 100% sure.

    I believe the cam is 0.542 lift with stock rockers, and that is already pushing it on many stock 5.0, so I am guessing you will need to actually verify clearance.
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  3. #3

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    1987 5.0 pistons are flat top w/valve reliefs, 351W 58cc heads, ported, screw in studs, guide plates, 1.6 roller rockers, .041 head gaskets...
    Thanks,
    Ed
    Last edited by ThunderStruck; 10-30-2018 at 02:11 PM.

  4. #4
    FEP Super Member erratic50's Avatar
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    Intake valve diameter?

  5. #5

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    1.90 in 1.60ex

  6. #6
    FEP Super Member erratic50's Avatar
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    X303
    286° intake duration at.050"
    286° exhaust duration at .050"
    0.542" intake lift with 1.6 rockers (therefore cam lobe is 0.33875)

    It appears to me that your question is what will happen if you go up to 1.7:1 rockers.

    Two things will happen
    1 -- your max valve lift will increase to 0.575875" with 1.7 rockers.
    2 - actual valve duration at or above 0.50" will increase by several degrees.

    I am going to run a 1.9 range intake valve on an Edelbrock head with a custom cam from FTI. Combustion chambers and valve placement are similar to stock. My valve springs are NOTHING like stock.... they are actually an LS part.

    My particular cam goes
    224
    ° intake duration at.050"
    230° exhaust duration at.050"
    0.606, 0.603 lift with 1.6:1 rockers (therefore lob is .3790 intake, .3770 exhaust)

    With a normal Felpro gasket and a normal stock style stroker piston assumed by FTI -- mine models out that you really can't add all that much more lift or duration on either side without PV clearance problems or rather violent valve events. FTI lobes are not at all similar to the lobes of yester-year though either.

    In my case I could get away with a little more if I abandoned the more modern lobe style or went to a twisted wedge head and a piston designed for TW. That's about it.

    You haven't said if you've shaved your heads or if you've had your block decked or anything like that.

    I would not have very much trepidation about running a 1.7:1 on the exhaust side of the house based upon the smaller valve provided the springs are up to the task. That's bind range for a lot of valve springs.

    I would have serious concerns about running any more lift and duration on the intake side without spending a lot of time with clay and a micrometer modeling it out

    Some guys DO report having it work with their combo and even a 1.72:1 rocker, but you are rapidly running out of room for more lift and duration.

    Check P/V clearance is what my gut is telling me looking at numbers vs what I've seen gotten away with consistently.

    Good luck.

    Let us know what you find as you look at this in more detail.
    Last edited by erratic50; 11-01-2018 at 04:15 PM.

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