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  • #1

    shaving heads

    A few years back I ran an 1970 Olds W-31 Cutlass. For those of you that don't know, they had larger valves, radical, balanced and blueprinted, forged internals, all factory. The stock pistons were 10.5:1 flats. We shaved the heads, IDK how much, but the engine shop came up with a figure of 13.7:1 compression on copper gaskets. The heads were shaved so far the stamping numbers on the bottom of the heads were flattened. We also had to have a good deal taken off the intake to get the ports and bolt holes to line up again.

    My question is, and does anyone know.....

    How much can you take off the 3500 heads and still be safe?

    How much more compression can I get on stocker gaskets, with the .020" over bore diamond pistons with max shave on the heads?

    How much valve clearance am I going to have with those 11.5 pistons?

    1. Car is drag only and I don't expect engine temps above 150 degrees.
    2. Yes I want 13:1+ compression. Don't ask it's an old school thing.

    This is also pending Ben's finding's of flow on a race ported 3500 and his reading above .600" lift. Waiting patiently for his new flow bench!
    sigpicHow to make High performance Emissions:
    A "true" High flow converter, straight pipe.
    Low/No flow EGR valve, block off plate.
    Carbon canister and purge valve mod, place in large 30 Gallon can, cover, and place curbside, the city will do the rest.
    PCV valve and vent tube, reroute to exhaust to dump where it belongs, on the ground. Or add breathers and let it all free.
    Tags: None
  • #2
    Quench on an engine that old was probably terrible, so having room to shave the heads that much was probably somewhat easy. On these heads, the quench area is so small in stock form that you really don't have much room to play with when it comes to shaving heads. In order to get the CR you are looking for, it would seem like a better idea to just get pistons with less of to no dish.
    -Brad-
    89 Mustang : Future 60V6 Power
    sigpic
    Follow the build -> http://www.3x00swap.com/index.php?page=mustang-blog

    Comment

    • #3
      So now I wonder.....Will a .020" over 3400 piston at 13.5:1 comp on a 3500 head be a dome? Will it clear the valves? Actually I should ask, has anyone done this before? I think I'm going to have to do the valve reliefs myself.
      sigpicHow to make High performance Emissions:
      A "true" High flow converter, straight pipe.
      Low/No flow EGR valve, block off plate.
      Carbon canister and purge valve mod, place in large 30 Gallon can, cover, and place curbside, the city will do the rest.
      PCV valve and vent tube, reroute to exhaust to dump where it belongs, on the ground. Or add breathers and let it all free.

      Comment

      • #4
        Stock bore 3.4 pistons and 3500 heads will get you about 11.5 or so, 3.4 DOHC pistons and overbore will get you in the 13:1 range. I think there was someone running 13.x:1 with DOHC pistons and 3500 heads on pump gas and a cam from Ben...
        Links:
        WOT-Tech.com
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        • #5
          OH HEY! forced I wanted to tell you, my uncle just picked up a 1983 Trans Am, with 56k original miles, 305 and a 5-speed. Never seen snow, and with the exception of a small tear in the drivers seat, this car is cherry! She's pitch black with the gold striping. Only thing that shows her age is a little fading on her bird decals.
          sigpicHow to make High performance Emissions:
          A "true" High flow converter, straight pipe.
          Low/No flow EGR valve, block off plate.
          Carbon canister and purge valve mod, place in large 30 Gallon can, cover, and place curbside, the city will do the rest.
          PCV valve and vent tube, reroute to exhaust to dump where it belongs, on the ground. Or add breathers and let it all free.

          Comment

          • #6
            actually, john, there is somebody on the forums thats been trying to get rid of some 3.4DOHC pistons for a while.... i think you may have just made the sale...
            1995 Monte Carlo LS 3100, 4T60E...for now, future plans include driving it until the wheels fall off!
            Latest nAst1 files here!
            Need a wiring diagram for any GM car or truck from 82-06(and 07-08 cars)? PM me!

            Comment

            • #7
              12.4:1 with 3.4 DOHC pistons. Camaro pistons and .040 camaro had gaskets will get you where you wanna be. If you want forged, just get them "custom" for a little more. You can't take enough off the heads to make a significant difference. Not enough bore to the engine and not enough combustion chamber size.
              Ben
              60DegreeV6.com
              WOT-Tech.com

              Comment

              • #8
                Originally posted by bszopi View Post
                Quench on an engine that old was probably terrible, so having room to shave the heads that much was probably somewhat easy. On these heads, the quench area is so small in stock form that you really don't have much room to play with when it comes to shaving heads. In order to get the CR you are looking for, it would seem like a better idea to just get pistons with less of to no dish.

                Actually the Olds was the exception. It had an awsome 6* valve angle with dual quench pads on each side of the cylinder and a centrally located plug. The heads worked so well they passed emissions with a carburetor up to 1990. They were also very fuel efficient.

                Back to the topic. Modern castings are designed primarily for light weightand cost. Hence the large core openings. Milling the heads by huge amounts is not recommended and in this case not even required. Mill them 005 to 010 to clean them up only if it is required and use piston selection to get the compression you want.

                Your Olds head most likely had nearly 1/2" deck thickness and they were iron so milling them did not kill their strength.
                1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                Because... I am, CANADIAN

                Comment

                • #9
                  Originally posted by betterthanyou View Post

                  Back to the topic. Modern castings are designed primarily for light weightand cost. Hence the large core openings. Milling the heads by huge amounts is not recommended and in this case not even required. Mill them 005 to 010 to clean them up only if it is required and use piston selection to get the compression you want.
                  Agreed. You run a real risk with modern castings - you can easily compromise deck strength by taking a cut that would have been routine with old tech cast iron heads.

                  Besides, decking great chuinks off is really a poor but cheap way to get compression. Using the correct pistons is the better way to go and it sounds like you have a couple of options to get up where you want to be.

                  I assume you have an unlimited supply of race fuel....

                  Comment

                  • #10
                    55 gal drum of sunoco blue 260. Dieing to use it.
                    sigpicHow to make High performance Emissions:
                    A "true" High flow converter, straight pipe.
                    Low/No flow EGR valve, block off plate.
                    Carbon canister and purge valve mod, place in large 30 Gallon can, cover, and place curbside, the city will do the rest.
                    PCV valve and vent tube, reroute to exhaust to dump where it belongs, on the ground. Or add breathers and let it all free.

                    Comment

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