bridrive55

There are many reasons to swap out your KA. Some of us want big turbo power, others have broken motors, and still others want to be rid of their SOHC headache. I had all three, but regardless of your condition, if you are a 240SX owner, you have probably considered an engine swap. The KA to KA swap is the most viable engine swap option for the 240SX because the motors can be affordably acquired, the KA24's are readily available all across North America, the KA's are great candidates for turbo, the KA has a broad base of aftermarket and OE parts, and the KA to KA swap can be the easiest of the engine swaps. If you learn anything from bridrive55, let it be that any KA24 can be swapped into any 240SX, quite easily.

I'm not going to say that the KA24E is a bad engine. I'm also not going to try to convince 1989-1990 240SX drivers to dump their KA24E's and toss in a DOHC KA. I can tell you that I am very happy that I did, however. The bottom line of 240SX engine swaps is: If you want a DOHC motor, the KA24DE is your cheapest and easiest option.
The KA24DE engines came in 2 distinct 240SX flavors: S13 and S14. The S13 KA24DE came from the 1991-1994 240SX's. The S13 KA24DE featured some of the same style pieces as the KA24E powerplant that Nissan discarded for the 1991 model year; the spark system being more or less similar between the two S13 motors. The S13 KA24DE features an external ignition coil, like the KA24E. The S13 manual ECU's also had a speed governor. The MAF is new for the S13B, however, and very few parts are compatible between the single- and dual-cam KA's. The S14 KA24DE had a wee bit more compression, a different upper intake runner design, slightly less agressive cam durations, an internal ignition coil, and a new valve cover design. OBD-II diagnostic system hit the KA24DE during the S14 production run as well.
Both KA24DE's are good for turbo. The cam duration and compression differences between the S13 and S14 KA24DE's are not, in my opinion, drastic enough to make one vastly preferrable over the other. S13 KA24DE's are generally cheaper, and S14 KA24DE's generally have fewer miles. Buyers on the market for a KA24DE platform generally tend to seek the motor with the least wear on it; one that will be more reliable under boost.
Putting the S13 KA24DE engine into your S13A is easy. All you need is the harness, ECU, and complete motor with subsystems. Power steering lines, radiator, and radiator piping from the S13B will be needed to make the swap direct. Most of the A/C system will need to be taken from the S13B donor car as well. You can fabricate coolant hoses, of course, to fit any radiator. The interior harness connection is plug and play with the S13A interior harness clip, and the DOHC harness fits into the 2 harness clips by the battery tray.
You can keep your old transmission. The lower wiring harness is compatible with the new S13B wiring harness. In fact, any 240SX transmission from any year is fully compatible with any KA engine, from any year. If you are bolting a manual transmission onto a KA24 that had an automatic transmission on it, you will need the manual flywheel, transmission metal gasket, and engine block transmission mount brackets. Do not use the auto tranny flywheel bolts on the manual transmission.
You will also need a gauge cluster from a 1991-1994 240SX, with the cluster wiring harness. It's neat to get the gauge cluster from the same car that your engine came from, so that you know the milage of the motor, but it doesn't always work that way. Some people keep the S13A guage cluster, but many functions will not work, including the tachometer. The tachometer signal on the S13A and S13B is different.
The S14 motor is more complicated. Everything is similar to the S13 KA24DE, except the interior harness connection, which is drastically different. Using the S14 ECU with the S14 harness creates a wiring nightmare behind the dash. Every single wire on the S13 interior harness will need to be soldered into a new position on the S14 harness, and many functions still will not work, including the tachometer. The easiest way (the only easy way) to swap an S14 KA24DE motor into an S13 is to use the S13B wiring harness, with the S13 KA24DE distributor, external coil, MAF, and ECU. This is $200 of parts that will save you 50 hours and a huge headache. WIth these parts, the wiring is plug and play like the S13 KA24DE, and you have an external coil, which is easier to attach an MSD box to. This is what everyone who has swapped an S14 KA into an S13 and I would recommend.

I would really love to see a KA24E in an S14, but I haven't seen one yet. You can also swap an S13 KA24DE into the S14, but doing the reverse of the opposite swap; use the S14 harness, MAF, and sparksystem. Whatever your engine swap choice, once you bolt in and wire up the motor, it is my advice to drive the engine around for a few days before going turbo. You will get a chance to notice any problems the engine has, and get a feel for the new motor. I would recommend swapping in a beefier fuel pump and filter (300ZX TT fuel pump and filter work great and are affordable) with any engine swap, especially the SOHC to DOHC swap.

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StreetTech S13
KA24DET, .70A/R T04E, FMIC, VLSD, SAFC-II, 550cc's, Q45 MAF.