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Definition - Big Block vs Small Block

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  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15685

    #16
    Re: Definition - Big Block vs Small Block

    Yup, now that you mention it, 331 CI for the '49 Caddy sounds right.

    Duke

    Comment

    • Grant M.
      Very Frequent User
      • August 31, 1995
      • 448

      #17
      Re: Definition - Big Block vs Small Block

      Duke,

      Interesting. Thanks! By the way, can you (briefly) explain the term "over-square" as it pertains to engines? I take it that it refers to bore/stroke ratio, one dimension being larger than the other.

      Thanks again,

      grant

      Comment

      • Verne Frantz

        #18
        Re: It's real simple...

        Duke,
        With all due respect, the W motor didn't "migrate" from a truck motor to passenger car use. It was designed from the git-go for both applications, and with future performance capabilities in place in it's first design.
        I can post the original design objectives that Chevy published in '58 if you'd like. Or you can dig up the Sept. '88 issue of Musclecars magazine and read the article I wrote on the W development.
        It's no more or less of a truck motor than a MKIV, although it's obvious that the MKIV benefited greatly from the cylinder head design of the MKII, and was a performance motor right from the beginning, as you said.

        Verne

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15685

          #19
          Re: Definition - Big Block vs Small Block

          Oversquare is bore/stroke ratio greater than 1 and undersqaure is less than 1.

          Years ago the English and many states in the US taxed cars based on the bore size and there was a formula for "taxable horsepower" that continued to be specified for many year after taxing by this method ended.

          This led to many "undersquare" designs, but as "taxable horsepower" was abandoned by most tax jurisdictions, especially in the US, new designs went oversqaure as they will make more power at high revs and due to larger valves and lower mean piston speed at a given RPM.

          For various technical reasons, undersquare engines generate lower engine out emissions, so there are now some undersquare designs out there, particularly four cylinder engines because transverse installation places a practical limit of overall engine length, so displacement can only be increased with longer strokes.

          Duke

          Comment

          • Duke W.
            Beyond Control Poster
            • January 1, 1993
            • 15685

            #20
            Re: It's real simple...

            Since you've researched it I'll defer to your expertise. I'm certainly not an expert on the W-block, but it was always my understanding that its primary application was trucks. It first showed up in passenger cars in '58. When did it first show up as a truck engine.

            Duke

            Comment

            • Mike M.
              NCRS Past President
              • May 31, 1974
              • 8396

              #21
              Re: It's real simple...

              duke: my 57 chevy truck shop manual lists 2 different v-8's for 57, the small block we all love , and a Loadmaster V-8 that displaced 322 ci. the shop manual doesn't show clear pics of the engine but it doesn't look like the 348-409 W engines. seem to recall Pontiac or GMC having a 322 ci engine. the loadmaster wasn't available in the pickups, just the big boy trucks of 57. perhaps others can answer the ? more specificaly. mike

              Comment

              • Verne Frantz

                #22
                Re: It's real simple...

                As far as I can determine, the W made it's debut in the '58 model year in both trucks and passenger cars at about the same time.
                One of the 5 primary design objectives (#2) was "Overall dimensions compatible with anticipated space limitations of passenger car design". And as it turned out, the W was just 2.6" wider and 1.5" longer than the 283. It was also 0.8" lower.
                If anyone's interested, the complete report of it's development is in the July-August-Sept 1958 issue of General Motors Engineering Journal (Vol.5 #3). The explanations for it's "out of square with the world" deck, staggered valve arrangement and water jacket design make for interesting reading.
                None-the-less, it's an obsolete motor (but with character).

                Verne

                Comment

                • Verne Frantz

                  #23
                  Re: It's real simple...

                  Mike,
                  The W was never produced in a 322cid form. I have no clue where that engine came from, but I seriously doubt it was a Chevy.
                  Before the W was worked on, there were two verions of the 265 that were tried. One designated the X increased the displacement to 300cid by using a 4.0" bore with the standard 3.0" stroke (the father of the Z-28?). The other was the Y design which obtained the same 300cid by lengthening the stroke to 3.3" and increasing the bore from 3.75" to 3.8128". That work was all done in 1955 when the engineers realized a larger displacement motor was necessary for both big trucks and the anticipated larger, heavier passenger cars with their trend toward automatic transmissions. It was 1956 when work began on the W design.

                  Verne

                  Comment

                  • Michael H.
                    Expired
                    • January 29, 2008
                    • 7477

                    #24
                    348-409 Ring Compressor

                    As long as we're on the famous "W" motor, has anyone ever wondered just exactly how you're supposed to get the piston rings compressed and installed in these motors if they've been bored .060" or more? This will probably be answered by someone that has actually been there (I have) because most won't understand the problem. You can't use a standard ring compressor.

                    Comment

                    • Grant M.
                      Very Frequent User
                      • August 31, 1995
                      • 448

                      #25
                      Re: Definition - Big Block vs Small Block

                      Thanks again, Duke!

                      grant

                      Comment

                      • Verne Frantz

                        #26
                        Re: 348-409 Ring Compressor

                        Mike,
                        I've heard that the method is to "walk" the rings around with your fingers, squeezing them in from top to bottom of the deck as the piston goes in. I've heard it works fine, but I've never dealt with one overbored that much to require that. On a motor that's not over-bored so much, there's a shoulder at the top of the bore. I've used a standard ring compressor and rested it on that shoulder and had no problems. I just tap it down until it rests square on the top of the bore, then........whoooosh!

                        Verne

                        Comment

                        • Michael H.
                          Expired
                          • January 29, 2008
                          • 7477

                          #27
                          Re: 348-409 Ring Compressor

                          Yes, exactly right Verne. With standard bore, there was a relief that allowed the ring compressor to sit square to the bore C/L but when bored at least .060 or more, the relief was gone. I've installed rings using the exact method that you describe and it works, although I never knew if this was actually the proper way to do it. The oil ring was especially difficult to install. Wonder what an old GM overhaul manual has to say about this?

                          Comment

                          • John H.
                            Beyond Control Poster
                            • December 1, 1997
                            • 16513

                            #28
                            Re: Definition - Big Block vs Small Block

                            Duke -

                            Recalling many of the development meetings I was involved in back in the late 60's (after emissions regulations started, but long before catalytic converter technology arrived), the engine guys spent a lot of time haggling about S/V (surface-to-volume) ratios in terms of HC and NOX production, which manifested itself in the many varieties of reduced-bore size small-blocks (262, 307, 305, etc.). Large bores relative to stroke were considered as the wrong direction in terms of engine-out emissions back in the days of crude emission systems.

                            Comment

                            • Dick W.
                              Former NCRS Director Region IV
                              • June 30, 1985
                              • 10483

                              #29
                              Re: It's real simple...

                              Loadmaster 322 was a nailhead Buick engine. Had a couple of 10000 series trucks with that engine.
                              Dick Whittington

                              Comment

                              • Duke W.
                                Beyond Control Poster
                                • January 1, 1993
                                • 15685

                                #30
                                Re: Definition - Big Block vs Small Block

                                There are some theoretical arguments on bore/stoke ratios and S/V ratios that are legitimate, and maybe were of real merit back when the OEs were stuggling to meet standards with the crude "add-on" emission control systems.

                                I think the advent of modern stoichiometric burn with three-way catalysts has made all those arguments moot, and I think the reason why many modern "large" (over two liters) fours have undersquare ratios is a matter of packaging, especially in transverse applications, which is the majority of fitments.

                                The current generation of SBs are back to oversquare, with the LS7 just making the cut as an increase in stroke to 4" is all that's left to achieve seven liters. A 4.125" bore on a 4" center is probably a practical limit, especially with GM's choice to use a liner.

                                I think they're still smarting from the Vega engine.

                                Duke

                                Comment

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