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Crankshaft counter weights and harmonic balancers

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  • Crankshaft counter weights and harmonic balancers

    I haven't stirred up any thing here in a while so today seems like a good time!

    The shop that originally freshend my DE block several years ago mainly works on drag and circle-track V-8's, with a few monster street cars mixed in. The owner is from New York but retired to the Georgia countryside a few years ago. His son now runs the shop but he's still active in the business.

    He's a bit of a ride from my house but I was on a trip last week that took me by the shop. I stopped and picked his brain for a while. He's in his 70's and he's been doing this a long time.

    I asked him if he'd had any experience comparing half-weight vs fully counter-weighted crankshafts. He said he'd worked on a number of 4 cylinder engines for various uses and that he had experimented. He said he was never able to identify any differences in horsepower or vibration levels between the two on the dyno. He did say that he found that checking the balance in two planes (weights up/down and side-to-side), just like a V-8, does improve the balance on a 4-cylinder engine. He said that you can also tune to certain RPM ranges by adjusting the "bobweight percentage" values. He said he'd explain it when I bring him one to balance....,

    I also asked him about his experience with harmonic balancers. He said that they can make more horsepower but they have a natural tune that favors certain RPM's and that you need to understand that when selecting one. He said that is true for both rubber/poly and viscous balancers. I asked him about the TCI "rattler" balancers (the ones with bob-weights inside). He said that they were patterned after aircraft engines that had the crank weights attached to the cranks on a pivot so that they could swing and help absorb the acceleration/deceleration forces. He said that they do work well over a wider range than the others.

    TCI's website says that the rattler works "at any RPM". I don't necessarily believe that, but I've researched the physics behind them and they do cover a wider range than rubber/poly or viscous balancers. I mentioned that TCI builds one for a Pontiac 4-cylinder but not for a Nissan. He said that from a balancing standpoint it would work on any similar 4-cylinder if you made your own hub adaptor and the pulley grooves were compatible.

    <flame suit on>
    Don Johnson (really!)
    Just so you know.

  • #2
    You don't need a dynamic vibration absorber on short 4 cylinder cranks. The crank is so short the 2md order harmonic is so high in RPM that very few builds reach it. Its easily 9k+ for our cranks, if not 10k+.
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


    DefSport Koni Sleeve and Spring Perch Buy!!!
    http://www.nissanroadracing.com/showthread.php?t=5902

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    • #3
      According to jwt, they definitely help keep from eating bearings. Even more so on the ka-e, as the block isn't as stiff and the cranks are weaker.... the kade isn't as bad but gains can still be had in longevity with a crank damper.

      However, i think its funny that we spend tons of money on tiny flywheels and clutches only to turn around and add mass to the other end of the crank. I've been revving my kade to 6800all day every day for the last 45k miles, and its held together on light crank pulley, aluminum flywheel and stock size clutch..
      Originally posted by SoSideways
      I don't care what color they are as long as they are LONG AND HARD.
      '04 G35 Sedan 6MT- The DD
      '96 240SX- The Track Toy

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      • #4
        So matt do u attribute a positive gain to having that lighter flywheel mass? Obviously theres an acceleration advantage but you would say it even helps components. I find this thread rly interesting because im so ignorant about it every lil tidbit so far has been exciting


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        • #5
          lowering rotating mass helps performance. unfortunately , the lighter weight hurts longevity of many components in the system by increasing shock loads on everything in the driveline. gears, baulk rings, rod/main bearings, etc.

          those are of course generalities and specifics are hard to describe in layman's terms (which is all I've got), but that's the general idea of what happens. the higher rotating mass absorbs the impulses and shock loads and slows the change in rotational speed (acceleration). lower the rotating mass and the engine accelerates faster, but also has less mass to counteract the shocks placed on it by firing pistons, clutch drops, axle hop, etc.
          Originally posted by SoSideways
          I don't care what color they are as long as they are LONG AND HARD.
          '04 G35 Sedan 6MT- The DD
          '96 240SX- The Track Toy

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          • #6
            I'm running a Fidanza flywheel and an ASP underdrive crank pulley myself but I like to get a conversation started occasionally. ;-) I've seen GT3 240SX's and 350Z's running KA24E's with no pulley at all! I'm just revisiting the subject a little since I've got to do a mod anyway to install a pulley for my blower belt.....,
            Don Johnson (really!)
            Just so you know.

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            • #7
              http://www.youtube.com/watch?v=sqIVtja4qGQ

              If you search Youtube for TCI rattler this is the first hit. An S13 240sx coupe with a Chevy 400ci small block.
              Don Johnson (really!)
              Just so you know.

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              • #8
                Unfortunately, that video doesn't tell you anything you can't get from a marketing brochure...
                Originally posted by SoSideways
                I don't care what color they are as long as they are LONG AND HARD.
                '04 G35 Sedan 6MT- The DD
                '96 240SX- The Track Toy

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                • #9
                  As has been brought up, the greater mass of the OEM reciprocating components is more for longevity and comfort. Most people don't want their to be an vibration in their car.

                  Below is a photo of my current crank, crank pulley and water pump pulley. The difference from stock is over 12 pounds of reciprocating weight.

                  Left: SR20 N2 crank with aftermarket crank and water pump pulleys
                  Right: Stock SR20DET crank, balancer and water pump pulley

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                  • #10
                    More info on the differences between N2 and normal cranks? And are N2 cranks like VE N1 cams, i.e. super hard to find?

                    cheers
                    -Evan

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                    • #11
                      I believe the "N2" crank is just a stock crank from an SR20VE. Needless to say, it has half the counter weights.

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                      • #12
                        Originally posted by Biggie™ View Post
                        I believe the "N2" crank is just a stock crank from an SR20VE. Needless to say, it has half the counter weights.
                        So Brian Crower gets like $3,000 for a KA24DE fully counterweighted crankshaft but all the SR20 kool kids run 8,500rpm with an SR20VE 4-weight crankshaft?
                        Don Johnson (really!)
                        Just so you know.

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                        • #13
                          How many RPM do you run the half counterweight crank to? Supposedly some VEs have had failures and/or bearing failures from high RPM and the half counterweight crank.
                          '18 Chevrolet Volt - Electric fun hatch for DD duty!


                          DefSport Koni Sleeve and Spring Perch Buy!!!
                          http://www.nissanroadracing.com/showthread.php?t=5902

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                          • #14
                            Another big issue is the stroke of the KA being 10mm longer than the SR. it's only 10mm, but that causes you to spin a lot more mass and induces more vibrations. it's 10mm longer than the SR, 13mm longer than the VG30, and 15mm longer than the VQ35.

                            ... and you wonder why the KA rattles like a diesel...
                            Originally posted by SoSideways
                            I don't care what color they are as long as they are LONG AND HARD.
                            '04 G35 Sedan 6MT- The DD
                            '96 240SX- The Track Toy

                            Comment


                            • #15
                              4cw cranks are notorious for bearing destruction and general unreliability on 'hard' useage VE cars. On street cars it's one thing, but asking something to survive at 5000 RPM plus all day is another. You can forget it under boost.
                              'Slicks on a car show me you care - broken axles show me you're trying'
                              [I]Nitrous Rental Cars - Turbo Festivas - Vehicular Lunacy[/I]
                              [SIZE="3"][B][url]www.sloppymechanics.com[/url][/B][/SIZE]

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