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Undersquare or Long Stroke Engines

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  • Undersquare or Long Stroke Engines

    I have always heard that Studebaker V8 engines, regardless of displacement, were "Long Stoke" engines, meaning they were "undersquare". A Wikipedia article about engines explains the meaning of an engine being oversquare or undersquare and gives examples of both but it does not include Studebaker V8s in its discussion. The article says the Chevy 283 and Ford 289 are oversquare. The Studebaker V8s are undersquare correct?

  • #2
    A good read on the subject is here....

    http://speedtalk.com/forum/viewtopic.php?f=1&t=37486
    HTIH (Hope The Info Helps)

    Jeff


    Get your facts first, and then you can distort them as much as you please. Mark Twain



    Note: SDC# 070190 (and earlier...)

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    • #3
      The 224 certainly isn't!

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      • #4
        Only the 289" is undersquare. The 232", 224", 259" and 304.5" are oversquare. The 299" is square, equal bore and stroke.

        FWIW, in today's technology, undersquare/oversquare are descriptive only of the bore-to-stroke ratio. It is no longer predictive of the ability/inability to handle high revs. Several of Honda's 8,000 RPM redline engines are undersquare. More than one 10,000 RPM sport bikes are undersquare.

        Back in the day, before reliable oiling, before good bearings, before lightweight pistons, since inertial forces go up with the square of the RPMs, revving a long stroke engine would literally pull the piston or rod apart. Interestingly, the destruction usually occurred on the exhaust stroke, when there was no resistance in the cylinder to cushion the inertial forces. The Jaguar long-stroke (4.2") 6-cyls were known to blow when the driver backed off at the end of the longest straight of the race course.

        jack vines
        PackardV8

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        • #5
          My Acura K20 A2 engine in my dedicated autocross Lotus 7 replica is a square design. We rev it to about 9000 rpm. When it blew it was at the end of a fast run just as it crossed the finish line.

          Yeah, they let go when you back off, its maximum stress on the rod bolts and they break.

          The square configuration with mild cams gives a flat torque curve more or less from 2000 rpm up to 9000. the engine also has variable cam timing on both cams and variable lift on the valves.

          Its pretty stunning technology to me at least and its a 2002 model motor.
          Diesel loving, autocrossing, Coupe express loving, Grandpa Architect.

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          • #6
            anouther issue with long stroke-high RPM back in the day was ring flutter.If I member right about 4000 ft per min.was about the max on piston speed .Anything over and you had ring flutter,with the loss of pressure and oil control.

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            • #7
              Originally posted by Chipmaker View Post
              anouther issue with long stroke-high RPM back in the day was ring flutter.If I member right about 4000 ft per min.was about the max on piston speed .Anything over and you had ring flutter,with the loss of pressure and oil control.
              The thick, heavy old 5/64" cast iron rings have been replaced by incredibly thin (1 mm), incredibly light, incredibly flexible steel top ring with HV385 supersonic thermal spray process rings. No more worries about flutter.

              jack vines
              PackardV8

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              • #8
                Yea, on ring "flutter"...
                Pro Stock engines (long stroke) are running in the 11,000 rpm range, 1000cc motorcycle engines are up into the 14,500 rpm range (even the longer stroke engines are running 11,500rpm. Some Comp. Eliminator engines are running in excess of 10,000 rpm with long stroke cranks.
                Then there's the F1 guys, that I admit I don't know much about their ever changing bore to stroke numbers are spinning pretty tightly.

                All because, like Jack says...VERY light weight rings.
                And now to add to that...Total seal has a new ring that will conform to slightly out of round cylinders, which can be found in some of todays less thAn ideally supported cylinder engines.

                Mike

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                • #9
                  Originally posted by t walgamuth View Post
                  My Acura K20 A2 engine in my dedicated autocross Lotus 7 replica is a square design. We rev it to about 9000 rpm. the engine also has variable cam timing on both cams and variable lift on the valves.

                  Its pretty stunning technology to me at least and its a 2002 model motor.
                  What is this engine in "normal" terms (for example: 2002 3.2 litre V6)?
                  Gary L.
                  Wappinger, NY

                  SDC member since 1968
                  Studebaker enthusiast much longer

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                  • #10
                    Originally posted by studegary View Post
                    What is this engine in "normal" terms (for example: 2002 3.2 litre V6)?
                    Right Gary, what Stude. owner has EVER heard of a K20 A2? Could be a 4 Poper for all I know!
                    StudeRich
                    Second Generation Stude Driver,
                    Proud '54 Starliner Owner

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                    • #11
                      It is a four cylinder 2 liter motor. For moving around a 1250# Lotus seven replica autocrosser with 250 hp it has plenty of grunt for the purpose.
                      Diesel loving, autocrossing, Coupe express loving, Grandpa Architect.

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