308 deck height & rod length needed

Unknown
Unknown
edited November -1 in HUDSON
NEED, from factory specs or factory stock engine:



rod length, center (pin) to center (crank) = _____ "





distance from top of piston (TDC) to



the lowest point of stock block relief = _____ "



thanks

Comments

  • Unknown
    Unknown
    Think I found the rod length to be 8.125"; if incorrect, pls advise.
  • Unknown
    Unknown
    I'm attempting to calculate the new compression ratio, if I keep a stock 308 head and raise the deck (TOP) 0.125"; and, a new compression ratio looks to calculate to ~ 8.68 (up from 7.00), plus the piston is still below the stock relief. Maybe a Ross or Venolia piston.



    Have any of you guys done this of late?



    Just wondering if this change is worth the trouble; maybe a small improvement in performance and little savings in gas mileage, plus forged v. cast pistons, and cost twice as much for the pistons.



    It's a toss-up. Your ideas welcome.
  • [Deleted User]
    [Deleted User]
    Why don't you work this out using the bore and stroke? you know what the stock bore and stroke so work it out from there.
  • [Deleted User]
    [Deleted User]
    I did measure the deck height on my block, which was an unmolested 1953 308 in terms of deck cutting and/or main bore truing beyond factory original.



    From the center of the main bearings to the deck surface. I did this in 13 locations from the front of the block and each deck surface adjacent to the cylinder bore back to the main centerline. The smallest measurement was 12.376", tallest was 12.379". The smaller reading was at the forward edge of #6 cylinder, the tallest measurement was 12.379 measured at 9 of the 13 locations.



    Conclusion, I'd say the original was supposed to be 12.379" deck height.



    On the pistons, I'd check out Venolia. I posted an answer to your "wrist pin" correction in the "Clifford Header" thread. I'll hunt up my build number and you can just change the diameter to suit you, the ring package you intend to run, and relocate the wrist pin height according to your stroke and finished deck height.



    I was impressed with my pistons, none were more than one gram out and did have the .975" wrist pins.



    Mark
  • Unknown
    Unknown
    I measured the deck height to be 12.375, and 2.25 throw, + rod length and about 2" for center of the wrist pin to ToP comes out to be ~ 12.375; therefore, the top of piston must/may be toping at the block surface, and if so I am REALLY shocked. I have it completely apart and it goes to the shop first thing in the am. I'll talk to the shop foreman and see if that can be true. If so I can't move the pin location down 0.125" as I hoped to do.



    Oh well, better be safe than sorry. I don't plan to race it at Bonneville any way!! hehe
  • [Deleted User]
    [Deleted User]
    One more thing, the rod length is correct. However, I've seen them vary about .010-.015". That is fairly impressive given some more modern rods vary as much as .025".



    If your rod rebuilder is pretty savvy, you can even them up when resizing the big end of the rods. Knowing your true rod lengths prior to resizing the big end and after sizing the wrist pin hole is the key, not a book spec'd number. The goal here is to get them all the same length.



    Mark
  • [Deleted User]
    [Deleted User]
    Stock Relief cuts.



    The same block measured throughout all the cylinders in the relief depth. Some close. I measured them with a deck bridge and a dial indicator, actually searching for the lowest point in the relief cut as measured from the deck surface. I really can't help you on distances from the relief cut to the piston head at TDC or the ring distance, I knew I wasn't going to use stock pistons and just didn't measure that dimention.



    It turned out like this:

    #1 - .150"

    #2 - .142

    #3 - .141

    #4 - .130

    #5 - .130

    #6 - .138



    Mark
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