The 240SX was introduced in 1989 in the United States. It came equipped with the anemic KA24DE, a 2.4 liter SOHC or DOHC (depending on the year) motor. Compared to it’s Japanese equivalent equipped with an SR20DET, it was weak, coming with a mere 155hp and 160wtq, to the Japanese spec’s 205hp and 203tq. While the KA24DE has become popular for aftermarket turbocharging, because of it’s larger displacement, the SR20DET swap still remains a popular alternative, so let’s get started.

SR20 Motor Options

The first step is to determine which SR20DET you will want to swap into your chassis. There are a few different options from different model years.

• S13 Redtop – offered from 1991-1994, this came in S13′s. It’s your base SR20DET motor with a T25 turbocharged at 7PSI clocking in at 205hp and 203tq.
• S13 Blacktop – offered from 1995-1998, these are almost exactly the same as the Redtop S13′s, except for a few small changes in the ECU, o2 sensors and wiring harness. The real benefit of the blacktop over the redtop is that in general they have less mileage.
• S14 Notchtop – offered in S14′s from 1995-1998, this version has a few upgrades over the S13 variants. It comes with a slightly larger, ball-bearing (Japanese spec) T28 turbocharger and variable valve timing on the intake cam. At 7PSI this motor comes in around 217hp and 203tq.
• S15 Notchtop – Some more changes here including larger injectors and a redesigned intake manifold let this monster put down 245hp and 202tq.

When considering which motor to go with, ask yourself “how far do I want to go?”. If you’re just looking to increase your horsepower with a stock SR20 swap, an S15 blacktop might not be a bad investment for the extra power over the redtop. Conversely, if you’re planning a full build, consisting of new camshafts, a sleeved block and forged internals, the extra spent on an S15 blacktop will be a waste.

Emissions Considerations
Anytime you’re performing a swap you’ll need to understand how emissions testing can come into play. To generalize the different laws, there are three “levels” of emissions.

1. Easiest – States such as Florida have no emissions laws. Swap what you want, any motor, any year, any model. Essentially there are no restrictions against swaps.
2. Middle of the Road – States like Connecticut and Rhode Island have emissions testing. However, it’s not quite as strict as CARB certification states. Using Connecticut as the example, any car that is more at least 25 years old is exempt. So, as of writing this, all S13′s are required to pass emissions. Since S13′s never came as OBDII, you’ll be subject to a “tailpipe sniffer test”. You’ll have to hit certain o2 and NOX limits. This usually means a good catalytic converter is necessary.
3. Hardest – Without a doubt, CARB certification states are the hardest. I won’t try to delve into the details of getting a swapped car to pass BAR and CARB certification. Though I will say going through legal channels can be an annoying and lengthy process.

Keep in mind this is a simple list and the laws vary, state to state. It’s generally always difficult if you live in a state that requires emissions testing. Most states have websites dedicated to their emissions process that can be of some help.

Stock Parts List

• SR20DET complete wiring harness
• SR20DET igniter chip
• SR20DET aftermarket radiator
• SR20DET SOHC MAF
• SR20DET downpipe
• SR20DET ECU
• Don’t forget the complete motor and transmission

You’ll need to consider other non-stock parts such as a front mount or side mount intercooler, although there are stock options available for those parts. As with any motor swap guide that we write, it’s smart to consider replacing the clutch, pressure plate and flywheel with a stronger, aftermarket unit. The same goes for the water and oil pump. Also consider placing the battery in the trunk with a quality relocation kit, or buying a smaller size battery. It’ll save space and generally better distribute the weight.

To Clip or Not to Clip?

It’s common with S13 swaps to simply buy what’s called a “front clip”. A front clip is essentially a shell, chopped at the a-pillar. You’ll receive the whole motor swap, ECU, harness and all the accessories unharmed. It’s a great route to go if you have no spare parts laying around. The cost difference between a longblock and a clip is usually $400-$500. If someone asked my opinion, I would go with the clip, it saves a lot of headaches. Keep in mind, once you’re done with the clip, it will have to go to the junkyard.

SR20DET S13 Swap

I won’t go into the whole process of doing an SR20DET swap, step by step, since it’s been done over and over. Browse through these sites for some really nice walkthroughs of the whole process.

• Zilvia has a great post on the necessary items for the swap.
• Need a DIY wiring harness guide for your swap? FRSport published a great one.
• ninja323 published a nice, simple guide for S13 swappers.
• SuperStreet has a walkthrough with some photos available.
• Tune2Win published what I would consider the best SR20DET swap guide yet, definitely worth a look.

S13 SR20DET Swap Kits

There’s plenty of aftermarket support for the S13 swaps. However, since there isn’t a need for custom mounts or crossmembers, there aren’t any “kits” available. There are wiring harnesses available that will make your swap go by that much easier though.