1. prostreeter9

    prostreeter9 Well-Known Member

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    Hey guys:

    The machine shop is about done with my heads and I'm second guessing my self on the amount of shaving I had them do. I originally had them just do .010 of a cut because I don't want to get into trouble lining up the intake. However I've been doing some reading and it looks like most of you cut them about .030 which I understand will help a little with the compression.

    So my questions are will taking this much off cause any problems lining up the intake, and is it worth the extra $75.00 dollars?

    The heads are 714 casting that have been opened up to 1.88 intakes and 1.6 exhaust. 3 angle valve job, back cut the valves, everything to make them flow.

    Jon
     
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    • 318willrun

      318willrun Utube channel 318willrun

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      I've cut .045 off of small block heads before, never an issue with bolt holes or push rods. I did give some of that back by using the Fel pro head gaskets, though. That's just my experience.
       
    • stroked340

      stroked340 FABO Gold Member FABO Gold Member

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      Got a friend who cut .060 off his heads no problems lining anything up on a (cough) 318..
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      ONE FULL POINT of compression equals about a 3% power difference. So no, IMO it's not worth the cost, because .030" will be about 1/4 of a compression point. That money will be better spent elsewhere, IMO.
       
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      • mderoy340

        mderoy340 Well-Known Member

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        Run them the way they are. 714 is closed chamber and you have to mill a closed chamber head a lot more than an open chamber for a significant compression gain.
         
      • prostreeter9

        prostreeter9 Well-Known Member

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        These heads are going on a 68 318 aren't these a higher compression engine to begin with?
         
      • alpha13

        alpha13 Well-Known Member

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        Like Rusty says. Milling for power isn't very cost efficient. Especially since you have closed chambered heads. Port them nicely and appreciate the gains. Spend your money on nice gaskets. I like to spend money on the reusable gaskets. That's just me.
         
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        • prostreeter9

          prostreeter9 Well-Known Member

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          I assume you are talking about the head gaskets. What kind do you use?

          The heads were already ported some when I got them and then the guy I have doing my work took a little more to dress it up and make the transitions smoother. I would say as far as the heads go I'm not sure there is much left to do. I'm just trying to make sure I'm covering all my bases and not leaving anything out that might be a HP gain.
           
          Last edited: Jun 13, 2016
        • nm9stheham

          nm9stheham Well-Known Member

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          The LA 318's are pretty low compression.

          A comment on the 3% HP thing: that % number applies for peak HP only, and does not tell the whole story. Higher compression ratio translates directly to higher compression pressures, which drives torque. Higher CR gives higher torque values and at lower RPM's, and thus helps to extend the lower usable RPM range. If you are revving all the time, no big benefit. If you are driving on the street, then the added torque down low is a major benefit.

          And higher CR tends to drive better cylinder clearing of spent gasses and thus better cylinder filling. This is always ignored in the 3% statements, which is just looking at thermodynamic power extraction, and totally ignoring other torque/power producing factors. So it is not presenting a complete picture by any means.
           
        • prostreeter9

          prostreeter9 Well-Known Member

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          Well this is a street car only. I do not have any plans on racing this motor, but would like to have a nice running street motor out of the deal. So that being said in the motor will be performing in the lower to mid range most of the time and hardly ever full out. But will another .020 gain me that much?
           
        • mderoy340

          mderoy340 Well-Known Member

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          What pistons do you have? Flat, dish, any valve reliefs? Are they below/ above/ zero deck?
           
        • prostreeter9

          prostreeter9 Well-Known Member

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          The motor appears to have been bored .040 over at least the pistons have a 40 stamped in the top of them. They have four relief cuts and set down in the cylinders.
           
        • nm9stheham

          nm9stheham Well-Known Member

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          With the general description of the pistons, I ran CR numbers on your setup and come up with about 0.2 increase in CR for .020" extra. (Roughly 7.6 to 7.8 CR.) Not a lot. But if you go from standard Felpro head gaksets that are .051" think to MP thin head gaskets that are .028" thick AND add that .020 cut, then you are up to 8.25 CR, roughly a 0.6 points CR increase. You will feel that as a happy improvement in low end torque.
           
        • moper

          moper FABO Gold Member FABO Gold Member

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          I routinely use the thin head gaskets because I'm buying gaskets anyway. Milling causes other issues (or can) so it's best left to a minimum if you can. It's just not enough return on investment.
           
        • prostreeter9

          prostreeter9 Well-Known Member

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          So where do you guys get the thin head gaskets and what brands do you use?
           
        • nm9stheham

          nm9stheham Well-Known Member

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        • prostreeter9

          prostreeter9 Well-Known Member

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          Looks like the Pistons are .75 below the deck. I'm assuming this is good for the compression ratio?
           
        • mderoy340

          mderoy340 Well-Known Member

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          I'll assume you meant .075 below deck. With a 65cc head volume your around 8 - 8.2
           
        • prostreeter9

          prostreeter9 Well-Known Member

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          I'm hoping that the 714 (302) heads have a smaller chamber then 65 cc's. That's why I'm asking about shaving them.
           
        • nm9stheham

          nm9stheham Well-Known Member

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          Better than .100 below the deck with the truck pistons! BTW, the numbers I ran yesterday were with 68 cc heads; I was thinking of the wrong heads. So you numbers will be higher than I listed.
           
        • prostreeter9

          prostreeter9 Well-Known Member

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          I'm hoping to get close to 9 on the CR. Do you think with this without shaving I can do it?
           
        • mderoy340

          mderoy340 Well-Known Member

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          You need to CC your heads anything else is a gueuss. The 714 heads I have are 66cc.
           
        • nm9stheham

          nm9stheham Well-Known Member

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          It'll take some shaving to get to 9:1. Using the 66 cc chamber volume from above minus 1 cc for the .010" shave already, and a .028" thick head gasket, and the pistons .075" down in the hole (the highest in the bore that you will get with stockish pistons) and assuming 5 cc's in the 4 piston eyebrows, I come up with 8.2 SCR.

          You'll have to get to 57 cc's chamber size to get to 9:1 with those thin head gaskets to boot. The core issue with CR here is in the pistons. If you switched to Sealed Power 526AP pistons, that are flat top with no valve reliefs, then you'll get up to around 8.6-8.7 SCR with the thin head gaskets. Another .020" on the heads would get up in the high 8's.

          I agree with the above: If you have the heads right now, it would be good to cc a chamber or 2 to see where that it. This is all just roughing in the numbers at this point.

          Edit to add: And if you change these pistons, you'll have to pay to have the old ones to be pressed off and these new, inexpensive ones to be pressed on. You'll want new rings too, and probably a cylinder hone. It all adds up.
           
          Last edited: Jun 15, 2016
        • MOPAROFFICIAL

          MOPAROFFICIAL FABO Gold Member FABO Gold Member

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          [QUOTE="alpha13, post: 1971284034, member: I like to spend money on the reusable gaskets. That's just me.[/QUOTE]

          I can understand that when you end up pulling back apart to put some cylinder pressure into it. You would be flabbergasted at the throttle response difference between having 130 psi cranking and 150 psi.
           
        • nm9stheham

          nm9stheham Well-Known Member

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          Roger that..... if CR made no difference, we would just all run 5 or 6:1 SCR and not ever have to worry about detonation. I changed my 2.6L Mitsu rally engine from 7.2 to 8.1 SCR, and it was night and day different off the line (before the turbo spooled up).
           
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