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1967 427 400HP cam

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  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15670

    #31
    Re: 1967 427 400HP cam

    It's built to GM print 390404364, which is the finished camshaft part number with no rear journal groove. Add the pin and you have a 3904359, which is what GM sold over the counter. They only sold camshaft "assemblies" consisting of cam and indexing pin.

    Cut the correct groove in the rear journal and you have a 3883944/3883986.

    The NAPA web site just crosses it to a ...986, even though it's really a ...359.

    The actual nominal blueprint lobe lift values are .27143/.28253".

    Nominal .050" durations/IPOML/EPOML, LSA are 214/218/110/120, 115

    The OE specified nominal big block rocker ratio is 1.70, and sometimes lift is specified at the valve by multiplying lobe lift times this specified rocker ratio.

    The SAE J604d duration values are taken at .006" valve lift, which would be .006/1.70 = .0035294" lobe lift. Looking at the GM data and without interpolating between the lift data points, which are listed every cam degree I get 288/302. If I used linear interpolation, I would probably get closer to the specified 290/303.

    The CS-274, manufactured to the 3893930/3896929 prints, is 194/202/108/116, 112, .26000/.27333", and the SAE J604d duration is about 260/270.

    If you compare the 390/400 HP cam to SB cams it is closest to the L-79 cam, which has .050" durations of 222/222 and about 310 SAE J604d duration, so I consider the 390/400 HP cam to be a true high performance cam. It delivers a very road useable torque curve, and the best thing you can do to these engines is massage the heads, which will improve top end power about ten percent and add at least another 500 useable revs without screwing up the idle quality or low end torque characteristics.

    If you want to trade a little low end torque for some additional top end power and revs, retard this cam 5 degrees from OE indexing along with massaging the heads, and I recommend retarding it this amount on massaged head 4" and longer stroke BB configuations.

    Duke
    Last edited by Duke W.; April 7, 2010, 11:05 AM.

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