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How To Turbo Your 240sx


93-240SX-COUPE
12-08-2007, 07:13 PM
Reading up a little on past articles and asked myself, "How many people ask this exact same question?". Well, this basically spoon-feeds and holds everyones hand through the entire process and build up of what to do to my setup when I want to turbo it.

Disclaimer: Article written Feb. '06 but still good info.

And whatever, even if its not worth being stickied, it should help out a newb if they ever decide to search for anything. BUT if a big ass label said HOW TO TURBO YOUR 240SX, then that might reduce flaming and re-answering questions over and over.

Enjoy.

http://www.sportcompactcarweb.com/features/0602_sccp_1995_nissan_240sx/index.html

1991-1998 Nissan 240SX - Budget Boost
Budget Boost
By Jay Chen

In an era when front-wheel drive was king, the 1991-1998 Nissan 240SX was one of the last rear-wheel drive sport coupes that combined affordability, reliability and practicality. It was and still is the cheapest offering with a solid roof, reasonable back seats, a reliable engine and an independent multi-link rear suspension.

During the 240's production, Nissan shipped them here by the boatloads-at least the 1991-1994 S13 model. That means you can find an S13 salvage chassis for less than $1,000, while a newer '95-'98 chassis, the S14, will start at around $7,000 (everyone wants one for drifting).

The big advantage of the 240SX is the number of O.E. and aftermarket parts made for the chassis. Nissan's cookie-cutter method of vehicle design means that the 240SX shares interchangeable components among different generation chassis (from the S13 to JDM S15s). Parts from other 240SXs or more expensive rear-drive Nissan/Infiniti platforms like the 300ZX and Skyline offer cheap, reliable upgrades that can be had for a fraction of the cost of new aftermarket parts.

The biggest gripe with the 240SX, however, is the U.S.-market S13 and S14 engine. The underpowered DOHC 2.4-liter iron block KA24DE-forever known as a truck motor by American enthusiasts-is often discarded in favor of the Japanese market SR20DET turbo 2.0-liter engine.

There's an easier and less expensive alternative: strap a turbo onto the stock KA24. Few realize the power potential available from this setup, not to mention the boost in chassis twisting torque the KA24 is best known for. And because everyone is throwing away their KA24s, there are limitless motors to pick from for pocket change (The KA24DE is also used in some Nissan trucks and Altimas).

Turbocharging a KA24 can be as simple as buying a bolt-on kit from reliable sources like XS Engineering, GReddy, FMAX or Turbonetics. If you have the time and resources though, a boost-it-yourself solution can be easily done for less than $2000.

The KA24DE is a direct descendant of the L16 engine originally found in Datsun 510s, which means that the old cast-iron bottom end of the KA24 is able to withstand tremendous punishment. The same applies for the transmission and R200 rear end.

A stock KA24, which has a 9.5:1 compression ratio, can handle up to 12 psi of boost on pump gas if properly managed. On a larger turbo, this means about 300-wheel hp. Even with just the stock fuel system and a rising rate fuel pressure regulator, the KA24 will run happily on 7 psi of boost, which will get you roughly 225-wheel hp. That's almost 100 more than stock (127-wheel hp) and more than any stock SR swap will get you. The 2.4-liter displacement also means more exhaust gas and less lag. The combination of low-end torque and mid-range boost makes for an incredibly fun street car. Throwing on a turbo also stretches the powerband well past 5000 rpm, where the stock KA24 runs out of breath.

The KA24DE's biggest problem is high piston speeds; it can't spin reliably past 7000 rpm on account of the rod-to-stroke ratio, limitations of the timing chain and half-counterweighted crank. Even Nissan's fully built KA24 race motors redline at just 8500 rpm.

(Pg.2) 1991-1998 Nissan 240SX - Budget Boost

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.

(Pg.3) 1991-1998 Nissan 240SX - Budget Boost

Do's and Do Nots
Here are a couple of things to look out for if you do turbocharge your KA24 240SX.

* Do Not get greedy and turn up the boost past 10 psi unless you're absolutely sure of your tuning.

* Do look into colder and more capable spark plugs.

* Do Not skimp on the fuel management; the more shortcuts you take, the more likely your engine will blow up.

* Do change the stock exhaust or your turbo will be fighting excessive backpressure.

* Do upgrade to a 255-lph fuel pump and larger side-feed injectors.

* Do think about a larger radiator. The turbo adds a lot of heat to the engine and pushes the stock cooling system to its limits.

* Do Not buy the super cheap tubular exhaust manifolds found online. These tend to break and crack easily.

* Do plan on putting in a stronger clutch and limited-slip differential because all this torque will smoke the clutch or the one tire that is spinning.

* Do periodically check for intake and exhaust leaks from loose bolts and fittings. Also look for excess blow-by oil.

* Do Not forget to get an oil cooler and oil-catch tank if you want to prolong the life of your hardware.

Nissan 240SX Turbo
Engine Code: KA24DE
Type: Inline four, iron block, aluminum head, turbocharged and intercooled

External Modifications:
Holset HX35W diesel turbo, custom welded log manifold, Tial 38mm wastegate, 3-in. downpipe and exhaust, Magnaflow titanium muffler, modified Dodge Ram front-mount intercooler, Bosch (OEM VW) blow-off valve (recirculated system)

Engine Management Modifications:
Walbro 255-lph fuel pump, modified AEM Honda fuel rail, 440 cc/min RC injectors (top feed), Vortec 4:1 FMU, D-tec piggyback fuel controller

Drivetrain
Layout: Longitudinal front engine, rear-wheel drive

External
Wheels: 17x8-in. 5Zigen FN01R-C
Tires: 215/45-17 (F) and 235/45-17 (R) Falken RT-215

Penny pinching with a diesel turboNic Cheek's primary goal was to keep his KA24 turbo setup cheap, but not to cut corners where it really mattered. Emphasis was placed on three main areas: the fuel system, the engine management system and the turbo manifold. As we've said, scouring your local junkyard for a turbo is usually much cheaper than buying the usual T3/T04. But why not the turbo from a diesel truck? Sure, it's big, but when the Holset HX35W from an early 90s 5.9-liter Cummins Turbo Diesel can be had for $100, who cares?

These turbos tend to be readily available and have a T-3 flange. As an added bonus, Nic was able to grab an intercooler core while he was under the hood, too.

To make the custom log manifold, the outline of the stock exhaust flange was traced onto a slab of half-inch steel and cut out. The runners are pieces of stainless steel Weld-Els and straight tube welded together to fit in the space available. Another piece of half-inch steel was used to make the flange for the turbine housing. To properly manage exhaust gases, pipes branch off to a Tial external wastegate. Hot air is then channeled through a 3-inch downpipe to a Titanium Magnaflow muffler that Nic bought used.

On the charge side, it's pre-bent 2-inch elbows and straight pipe from the turbo to intercooler, and from intercooler to throttle body. The Dodge intercooler would never fit unmodified, it's nearly 18 inches tall. Cut horizontally into 3 pieces, two sections are used, one behind the other. The hand-made end tanks are plate aluminum; $30 from a metal scrap yard bought a big sheet.

(Pg.4)1991-1998 Nissan 240SX - Budget Boost

An FMU (Fuel Management Unit) delivers the extra fuel the engine needs under boost. While this is a common item in aftermarket turbo kits, it's generally only good for 6-8 psi of boost before the stock injectors max out. Wanting more than that, Nic needed bigger injectors, but they're expensive and hard to find for the side-fed KA fuel rail. A simple swap to an AEM fuel rail designed for the Accord and everyday top-feed RC Engineering 440cc injectors worked with minimal modifications.

The 240SX has a perfectly good MAF that works fine off boost, so why not use it? The trick was to keep it from seeing its 5-volt max, at which time the ECU will do unpredictable things. For larger injectors, the idea is to increase the MAF tube area by the same percentage that the injector size increases. Because it's not an exact science, the car was carefully tuned on a wideband-equipped dyno.

Those modifications left Nic with just the engine management to sort out, and the Turbo XS DTEC-FC fuel controller worked perfectly. Aftermarket kits tend to go lean during part throttle or as the turbo starts to spool up. To adjust for this, a MAP sensor from a Dodge SRT-4 (any linear 5 volt, 2 bar sensor will work) was used in place of the throttle position signal input on the DTEC. This adds fuel much quicker than the actual TPS signal. Unfortunately, there is no control of ignition timing, which makes this setup "safe" for only 8-10 pounds of boost without race fuel. - Tim Kelly

Space limitations in the engine bay make inconspicuously mounting larger turbos impossible.

The tight elbow restriction on the Holset HX35W turbo just adds to the pumping resistance on the compressor.

The stock fuel rail and side fed injector setup was replaced with an AEM fuel rail for Honda-style top-fed injectors and 440 cc/min RC injectors. A rising rate fuel regulator or FMU was also added.

Custom aluminum plate end tanks were welded onto two intercooler core sections from a diesel truck to make a smaller-two row intercooler.

Even with just the stock fuel system and a rising rate fuel pressure regulator, the KA24 will run happily on 7 psi of boost, which will get you roughly 225-wheel hp.

Sticking with a turbo that has 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.

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