Most turbos (whether aftermarket or O.E.) floating around the sport compact world will work well for the KA24. Anything from an aftermarket T3/T4 hybrid to a T25 from a Japanese S13 can work. Using a factory turbo from a 2.0-liter engine will give the KA24 neck-snapping response, which is great for the street, while larger turbos like T3/T4 hybrids provide full boost only 3000-rpm short of redline. However, it takes a T3/T4 turbo to get near the 300-wheel hp mark. We recommend choosing a turbo that offers good mid-range boost, because that's where it's used most. You'll probably have to use an external wastegate if you choose the T3/T4.
Ideally, a T28 from a Japanese S15 or a GT28RS would give the best balance of power and response if you had $450 to $1000 to spend on a turbo.
The easiest way to supply oil for the turbo is to tee off the factory oil pressure sender with AN fittings. Depending on the size of the tee fitting and type of turbo, a restrictor (a fitting with a smaller orifice) for the oil supply might be needed so that too much oil doesn't go to the turbo and out the exhaust. If you really want to do it right, you should also plumb in coolant lines for the turbo, but this will add significantly to complexity and effort involved.
Sticking with a turbo with a T3 or T2 turbine inlet flange will prevent a huge headache, since most off-the-shelf turbo manifolds for the KA24 come with such a flange. Durable-cast manifolds are preferable for the street. If you choose to use a tubular manifold, plan on using a flex-pipe joint in the downpipe to avoid cracking the manifold.
If you can't find a KA24 manifold to your liking, some rear-wheel drive SR20DET manifolds will work with the KA24 but will require re-drilling, or cutting and re-welding, depending on the flange design. Welding up a log type manifold may be the cheapest option for those with the skills and equipment.
Making an intercooler for the 240SX couldn't be easier. Since the Japanese models came turbocharged, all the holes for the intercooler plumbing are already pre-cut into the sheetmetal. Intercoolers even come conveniently sized as "Silvia" cores from most Japanese tuners. Modifying a bolt-on Silvia intercooler kit for the SR20 is the easiest option, since it will mount up to the existing factory bolts and mounting tabs. These kits only require a little modification to fit your specific turbo setup.
Fuel management on a turbocharged KA24 has to be addressed. At the bare minimum, you'll need a rising-rate fuel pressure regulator. A Walbro 255-lph fuel pump is also good insurance against fuel starvation. The next step up is to use larger injectors, like the 370 cc/min side-fed units from the Japanese SR20 engine or injectors from a '95-and-up 300ZX.
New injectors will require a reflashed ECU or some form of fuel trim adjustment like that offered by an A'PEXi AFC. If you want to do it right the first time, spill for the NISMO 615 cc/min injectors, a larger MAF, and a retuned ECU like one from Jim Wolf Technologies and get ready for 300 wheel-hp. Proper fuel management will make the difference between a fun driveable car and a dyno queen that can't idle.
When you break it down, the cost of plopping a turbo onto your KA24 doesn't even come close to the cost of installing a SR20 and then modifying it to make anywhere near the power of the KA-T.
By Henry Z. Dekuyper
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