302 rebuild kit question

Discussion in 'Technical' started by bryson123, Jul 11, 2018.

  1. bryson123

    bryson123 Member

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    yes that’s the other sad thing I was going off my first machinist. As much as I would wanna do the rods I think I’m going to stick with the stock rods since they are all done up and just have it milled unless someone wants to buy some stock 302 rods with arp bolts!!!!
     
  2. groberts101

    groberts101 Member

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    Hopefully he didn't install 3/8th's bolts in those rods or they are weaker now than they were with the stock bolt sizes. Not enough meat around the holes in the little OEM rod to begin with and that's where they usually break. I and many others have used 11/32" chevy bolts but that is about as good as you'll possibly get with stock stuff. Sounds like you have a plan.. good luck with it all!
     
  3. bryson123

    bryson123 Member

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    If I were to get some kB pistons to fix my issue would I have to rebalance if I can get them as close as possible to current weight. I talked to my machinest and he recommended possibly just doing that because in the long run it might be cheaper because of maybe having to get intake manifold milled if I got block decked also because the heads have been milled.
     
  4. groberts101

    groberts101 Member

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    How much milled from the heads? To gauge where you sit we'd need those numbers to calculate current compression ratio. Did you use that Eagle crankshaft compression calculator to see what a piston swap is worth?

    I'm sure dropping 3cc's of valve relief volume will give you around 3/10's point compression increase but you seriously need to consider how much backtracking you're willing to do here? The other important thing that helps the octane tolerance of just about any wedge chambered motor is having minimal piston to head squish heights. I know of no pistons made for 5.09" rod/3" stroke having much more than 1.605" max compression height(pin height).. might get lucky to find a couple 1.608" pin height deals. This is why people generally calculate and spend to achieve a 0 deck height to make parts matching and final compression heights jive with one another. If you decide to leave the pistons .028" in the hole.. even a thinner .027" gasket will only get you down to .055" squish height/piston the head clearance.

    I'm kinda starting to lean towards baddads initial advice to just build it and enjoy it for what it is. Will it be more of a turd under 2,500 rpm with near a full point less compression ratio?.. absolutely. But most people camming up these little short stroke motor should already expect that to be the case anyways. And like you said.. live and learn.. maybe just get your feet wet and build another bullet later on when more funds and a larger more experienced knowledge base permits.

    Oh, and to answer your question.. anything much more than about 20-30 grams of reciprocating mass/piston and pin weight difference would likely need to have the crank re-balanced. Remember ONLY HALF the reciprocating weight gets added to the rotating weight/bobweight.. so half of the above 20-30 grams would actually only be 10-15 grams of bobweight difference. Usually much better to go lighter(overbalanced) rather than heavier(underbalanced) whenever substituting parts after a crank balance.
     
    Last edited: Jan 26, 2019
  5. mojo

    mojo "Everett"- Senior Citizen Supporting Member

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    Since this is your first build and mostly street operated vehicle; I am of the opinion it should be oriented more too reliability than power. I am not being negative, just realistic. With all of the milling, part interchanging/mixing, calculating, etc; I hope you don't wind up going in the oil pan the first time it's started.
    I realize you have a lot of money and time invested in the build and have to make the most of what you have.
    I hope all goes well and following this thread...
     
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  6. groberts101

    groberts101 Member

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    The other thing I would question is if you've ever mocked the manifold up to know where the china wall end gaps and port alignment sits right now? Edelbrock's, and most others, intake manifolds get slightly smaller right at the port exit(primarily for port matching purposes) which allows more wiggle room till a port mismatch occurs on heads with larger ports(which yours should also have).

    Lot's of guys confuse this stuff with Chevy and other makes where the math isn't so easy and milling is required. Not the case here and Ford's are easy to rough calculate due to the heads manifold face being at 90 degrees to the fire deck and the intake manifolds flange being at 45 degrees to that(90 degree V8 with 45 degree manifold). So, however much you lower/mill the head(thinner gaskets included) towards the blocks deck.. you'd simply need to be cut that measurement in half to figure the true amount the manifold will rise up on the heads intake face. Lower everything .090" on each cylinder bank?.. the head rides .045" higher towards the tops of the heads intake ports. This figure also correlates to the bolts moving inwards on each side as well so intake manifold bolts would crowd the inside of each bolt hole another .045" per side. I've cut over .100" away from heads and never needed to do much more than minor clearance work at the most. It helps a lot that most manifold are drilled for 3/8" bolts + wiggle room and these little motors only utilize 5/16" intake flange bolts.
     
  7. baddad457

    baddad457 Member

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    Mill the decks. You'll get more comp gain per thousandths milled. As for the intake bolts moving towards each other, that's going to depend on the individual intake, they're not all alike. I had my Canfields milled .060 and had to open up the holes on the Vic Jr I used them with on a 5.0. But same heads on my 331 and the repop 3x2, everything fit fine. You probably won't need to do anything after milling the decks on that block as it's obviously a mid 70's tall deck block.
     

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