Nissan 240SX Fuel Management- Sport Compact Car Magazine

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.