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65 Fuelie - 11:1 compression - Octane Booster?

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  • Joe C.
    Expired
    • August 31, 1999
    • 4598

    #61
    Re: 65 Fuelie - 11:1 compression - Octane Booster?

    Originally posted by Timothy Barbieri (6542)
    Joe,

    Is that how you built your 327 with the 12.3 static compression ratio. I sure wish everyone used the J604 valve timing points (.006 lobe/tappet lift) instead of the .050 lobe/tappet lift. With the approx 1.5 rocker ratio, the J604D is probably closer to calculate effective timing and static compression.

    Just a FWIW, on my 327 .060 with flat tops and stock 929 cam the cranking compression pressure is 175 with a thick .038 head gasket and I have often thought how it would act with the steel GM thin head gasket and retarding the camshaft 4*. Idle will probably stay the same with a little extended power up top.
    Using the 0.050" valve events to calculate DCR is meaningless because the piston is still generating significant pressure at that point in the stroke. It is common practice to use SAE J604D (AKA: "advertised" or "seat-to-seat" ) duration because pressure build effectively ends at this valve lift value, although the rate of valve closure will cause some variation in results as well. Durations are never measured at a tappet lift point; they are always measured at a valve lift point and SAE J604D is 0.006" for a mechanical tappet and 0.004" for a hydraulic tappet. To further complicate matters, different manufacturers use different timing points in which to define their cams, and one very popular one is 0.015" valve lift.

    That chart is a guide and is useful in noting the relative intake valve closing points of the more popular vintage SBC cams, especially considering the fact that the rate of closure impacts the rate of pressure build and causes a certain amount of leeway around using SAE J604D as the calculation point. The absolute points must be considered in light of what I mentioned above, especially valve actuation rates at low lift. I built mine with an honest 11.3:1 SCR and have no issues. The engine develops between 230 and 240 psig during a "warm, dry" cranking pressure test. The engine in its present form uses a tight lash/fast ramp solid roller cam of 286/292 (@ 0.015") 248/254 (@ 0.050") and 0.604"/0.608" lift with 1.6:1 full roller trunnion rocker arms.

    In your case, if your block has not been decked then you have a whopping 0.025" +/- 0.010" (nominal deck) + 0.038" gasket = 0.063" +/- 0.010" quench, which will result in much earlier detonation (since detonation begins in the quench zone) than an identical engine built with a more acceptable quench of 0.040. SBC were originally designed with 0.025" (nominal) + .021" = .046" quench. Mine is built with - 0.004" + 0.038" = 0.034" quench. Retarding the cam will NOT affect your engine's idle , at all, since idle vacuum is affected by valve overlap, valve lift and valve actuation speed (solid tappet lash affects both duration and valve lift, as does "zero lashing" your hydraulic cam). I don't recommend retarding your cam unless you compensate by adding more static compression. Retarding the cam by 4 degrees will result in the intake valve closing 4 degrees later, which will decrease your engine's dynamic stroke and thus its DCR. I recommend retarding the cam only in instances where the subject engine suffers from detonation, and decreasing SCR is not an option.
    Last edited by Joe C.; May 5, 2012, 02:50 PM.

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    • Brooks R.
      Expired
      • September 14, 2011
      • 25

      #62
      Re: 65 Fuelie - 11:1 compression - Octane Booster?

      Hi Rick,

      I am pleased with the great work, attention to detail, and the friendly group of folks at both Joe's Engine Shop and Just Joe's Automotive.

      Just Joe's Automotive removed the engine, cleaned up the engine compartment, rebuilt the starter and alternator as well as reinstalled the completed engine repaired my shifting linkage (now short throw).

      Joe's Engine Shop performed all the machine work, balancing, assembly, break-in, and dyne testing.

      Both shops had a constant parade of customers with Corvettes and many other street and drag vehicles. Lots of repeat customers from the conversations i heard while hanging around the shops.

      Joe's Engine Shop
      1303 Galindo St.
      Concord, CA 94520
      925-682-4013

      Just Joe's Automotive
      1110 Erickson Rd.
      Concord, CA 94520
      925-676-6700

      Comment

      • Timothy B.
        Extremely Frequent Poster
        • April 30, 1983
        • 5179

        #63
        Re: 65 Fuelie - 11:1 compression - Octane Booster?

        Joe, Did you change the compression height of the pistons or different rods to bring the piston out of the hole?

        Comment

        • Joe C.
          Expired
          • August 31, 1999
          • 4598

          #64
          Re: 65 Fuelie - 11:1 compression - Octane Booster?

          Originally posted by Timothy Barbieri (6542)
          Joe, Did you change the compression height of the pistons or different rods to bring the piston out of the hole?

          First I had the decks measured and there was variation of 0.015" between all 4 corners, and there was a low spot in the middle on one side, as well. This was unacceptable to me.

          When engineering the build, one of the prime considerations was to keep it as a small displacement engine, with solid tappets. I wanted to maximize horsepower and also wanted a high revving engine with excellent durability. I retained the small journal 3.25 stroke crank, and got in on a group purchase of Crower Sportsman con-rods over on the Forum, which was initiated by Scott Marzahl. The rods involved in the deal were all 5.7 inch, with small journals, with the choice of either full floating or pressed pins. I chose ultralight weight pressed pins. I re used the Speed Pro L2166NF-30 pistons which were pressed on the original GM rods. The compression height of the pistons is still the original spec 1.675". I specified a Total Seal gapless top ring set.

          I decided to use a Comp Cams "nostalgia-plus" version (since been upgraded to a solid roller) of the 30-30. This cam has tighter lobe centers as well as 7 degrees less duration on the intake side than the blueprint 30-30 as well as SIGNIFICANTLY faster ramps, all adding up to far less bleed-off, earlier intake valve closing and a much broader torque curve with higher levels achieved not only earlier, but further up into the rev range. I deduced that 11.3:1 would be reasonable with this cam, by means of engine simulations run on the Engine Analyzer Pro program, which quantifies detonation potential at all RPMs. Had I used a blueprint 30-30 I would have gone with a higher SCR. In light of the uneven decks, I decided to surface grind them. With the decks now at -0.004" (piston crowns 0.004" above the decks) and Mr Gasket 5800G steel/composite 0.038" compressed thickness head gaskets, I achieved my target SCR with a very detonation resistant quench of 0.034".

          There is an excellent online photo, on the Corvette Forum website, of an original engine block whose stamp pad has been preserved after having been "decked" .
          Last edited by Joe C.; May 6, 2012, 06:14 PM.

          Comment

          • Timothy B.
            Extremely Frequent Poster
            • April 30, 1983
            • 5179

            #65
            Re: 65 Fuelie - 11:1 compression - Octane Booster?

            Sounds like a nice build, Joe, I like the roller cam idea.

            Comment

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