Engine MountingThe K24 goes in as easily as the K20 came out. In fact, you can use all the stock mounts. The K20Z3 oil pan is an integral part of the '06 Si's engine mounting system. It bolts right onto the K24, so you can use the lower mount. Make sure you use the '06 Si oil pump too, the oil pan is deeper and the oil pump pickup extends farther to reach the bottom. The oil pump has to be modified also, so the housing will clear the longer stroked crank of the K24 engine.
Finally you'll need a CR-V right-side engine mount. It's a little shorter. Next, put the engine in from the bottom, install the left and right side motor-mounts, then attach the subframe, along with the rear mount, and install the front mount.
Fuel SystemNo real changes here. The K-series engines all utilize a returnless-style system. The injectors from the K24A2 are the same size (310cc/min) as the Si's and the fuel line is on the same side, so there's really nothing to do but connect the lines. If you're thinking ahead and want to install a big-horsepower engine down the road, you may want to do a return-style system.
Engine AccessorieS & CoolingUnlike older cars that were never designed with the K series engines in mind, all the accessories that came with the Si stay. Since the K24A2 has conventional belt driven power steering, you will need the idler pulley from the Si on your K24. If your K24 came as a stripped long block, all the accessories from the K20 will bolt right on to the K24.
When we had the engine out of the car, we mounted the thermostat housing from the K20Z3 on the TSX engine. The larger engine doesn't require additional cooling capacity beyond the Si's stock hardware and all the hoses from the K20 connect at the same places on the K24. Same for the heater hoses which warm the interior of the car.
Drivetrain HookupWe finally get a limited-slip differential in the Civic, so why use the TSX 6-speed? The TSX has taller (lower numerically) gears to take advantage of the increased torque, but ripping through the gear ratios of the improved Si transmission is too good to resist. Even if we wanted to use it, the K24 transmission mounts differently, making it impossible to use. Unbolt the K20Z3 transmission and add it to your K24.
ExhaustThe good news is that the factory exhaust manifold from the K20 bolts right up to the K24. The bad news that because of increased 2006 emissions restrictions and the Si's ULEV2 rating, that manifold has a close-coupled catalytic converter that keeps a lid on flow. A good 10 horsepower can be had on a K20A2 just by bolting up the JDM Integra header with its longer tube header, which puts the cat under the car instead of near the firewall.
Since the aftermarket got their hands on the new Si early, we were able to get a prototype DC Sports race header. It's not street legal because the catalytic converter was left behind, but what about this swap is CARB legal?
IntakeIn the usual OEM style, the stock intake system uses a series of black plastic boxes and snaking tubes in the engine bay and fender well. The surprising part is that it actually sounds really good. With the stock muffler, the intake is actually pretty burly, especially when the cams switch over to the big lobes.
But it's definitely a restriction and the longer manifold of the K24A2 puts the throttle body where it doesn't exactly match the K20's. On top of that, Honda has switched to a mass-airflow sensor (MAF) to deal with the new, tighter emission regulations. Since we've dumped the stock ECU for a Hondata unit that doesn't require a MAF, the sensor becomes an unnecessary restriction on the intake.
By Tim Kelly
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