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De-stroked KA (~2289cc @ 90mm bore)

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  • De-stroked KA (~2289cc @ 90mm bore)

    What would you guys think about de-stroking a KA with a custom FCW crank?

    Thoughts are this: 90mm stroke with a 90mm bore yields a square motor, Nissan Motorsports GT3 rods almost allow the use of OTS pistons (have to contact piston manufacturer to cut smaller pin diameter), and designing the crank counterweights based on the lightweight rod/piston combo

    The combination of a free flowing head and the increase in R/S ratio (1.719 stock to 1.904) could result in a very rev-happy motor.


  • #2
    This is something I was somewhat interested in. Sort of a pipe dream really, but I thought it could be an interesting concept. I believe I thought I could make the l20b crank fit at 86mm stroke making 2188cc. And if I remember correctly the l20b crank is FCW. I never went further than looking at dimensions and never acquired a crank to test it though. If you do go ahead with it I would be very interested in the results.

    Also look at this. L18 bottom end with KA24DE head.
    98 240SX SCCA STUish


    • #3
      Joe - That's pretty cool! I know it said 282bhp, but I'm curious about the torque curve too. (Edit: just watched the rest of the video and saw the dyno. Not a terrible high rpm dropoff)

      I've seen where a few people have considered L/Z cranks to destroke the KA, but my idea is a one-off. I'm in school for mechanical engineering, so it'll be a project I slowly work on throughout school.....everywhere from the material/alloy side (actual crankshaft manufacturers will also be consulted) to the CAD design and dynamic equations so it makes a ready to go kit when manufactured. The hardest part will be getting the rod weights from Nissan Motorsports, then the custom pistons will have to be ordered before I could go through with the dynamic portion to design the counterweights. I may even have to buy the rods before that too, in case they don't want to reveal info.


      • #4
        I don't see how it could really make more power than a 2.4L KA. It would have a different powerband, but ultimately I don't think you're going to make any more.

        Extensive headwork and dialing in big cams would be money better spent.

        That said, tossing a simple T28 setup on the KA would yield way more torque and power than you'll ever make NA.
        '18 Chevrolet Volt - Electric fun hatch for DD duty!

        DefSport Koni Sleeve and Spring Perch Buy!!!


        • #5
          The stock 1.7 r/s ratio isn't bad. The issue with reving the ka24de is

          1. the crank only being half counterweighted and unable to be dynamically balanced. The solution for that is Brian crowers (I think it's them) fully counterweighted crank shaft for the ka24de. It only weighs an extra 8 or 9 lbs if I remember correctly

          2. Your cams. The cams really decide where your powerband will be. The ka24de don't Rev because the stock cams only make power at that low rpm

          3. The amount of air your head is able to flow. That will be determined by your port job, valve size, valve stem diameter, and of course cam.

          Building an all motor ka24de would definitely be fun but like Def said slapping a turbo would be the best bang for buck. You could daily it with no idle issues, cold start issues, or anything of the sort.

          Once you go all motor to that extent where you have a huge cam and port work, your idle and cold start won't be as great. And then don't forget about high compression pistons, depending on how high of a compression they are you may need race gas which can cost atleast $9/gal. Unless you go e85 which is $2/gal out here


          • #6
            My NA KA24DE made ~260bhp with 10:1 compression, stock size valves and a crappy ebay header..........and for a ton less money. But yes, with a 5.5" clutch, no IACV, 1900rpm idle and 0.500" lift cams, it wasn't streetable.
            NASA Time Trials TT3

            BTW I work for Garrett


            • #7
              The head will be entirely Nissan Motorsports, so I would assume that a head designed for GT3 class racing should flow. By no means is this meant to be a streetable car, it'll be purely a toy. I also understand that a turbo would make more power, but the idea here is throttle response and high revs. The other reason I'm looking at this idea vs the BC FCW crank is that with proper design, I should be able to keep the piston squirters. BC requires removal and block off of them.

              I completely understand how these motors work, there's already been one ITB build under my belt. Unfortunately, the car was stolen if you guys recall. This new build (which will take many years and countless hours of research), is just a continuation of that one with no holds barred this time. Budget isn't in the picture either since it'll take so long too.

              (Posted with my phone, so sorry if there are any errors)


              • #8
                You still won't be able to rev high enough to make up for the ~8% lower displacement IMO. Is a 90 mm stroke KA still going to be happy at 8k RPM? I'd venture to say probably not.

                With lots of work it might make about 220 rwhp... which is what a bolt-on F22 S2000 engine would make. Maybe swap one of those in? The trans is better geared for a highly strung NA setup too.

                Or you can toss in some streetable ~264/264 cams and a small turbo and make way more. I also don't get the throttle response argument, a T28 setup on a 2.4L will have "instant" response above 3k RPM. On my SR with a T25, above 3k RPM the MAP would perfectly follow TPS signal.

                Even on a toy, I think it's important to go with a reliable setup unless you have class rules pushing towards one specific way (like 240sxTTC had to do on his build).
                '18 Chevrolet Volt - Electric fun hatch for DD duty!

                DefSport Koni Sleeve and Spring Perch Buy!!!


                • #9
                  FWIW, I spoke with Dave Rebello the other day and he wasn't a fan of the Nissan Motorsports head. Claimed his hand ported head will flow better.

                  Also, I believe Sonny Bryant made a FCW crankshaft for the GT3 engines. I'm sure it will not be anywhere near cheap, but it might be worth looking into.
                  98 240SX SCCA STUish