Any time an engineer is thrown into competition, there's bound to be some ingenious solutions and results. Rob Symonds is an engineer with Honeywell's Garrett turbo division, no less. He knows a thing or two when it comes to making power on his 1993 Nissan 240SX, built as a NASA Time Trial-class racer. And even if racecars aren't your cup of tea, this gutted-out KA-powered 240SX might just shed some light on the potential of a turbocharged truck engine in a street car.
Despite its pedigree as a purist sports coupe, the S13 240SX never found much acclaim in professional or amateur racing. Instead, it became the default choice for drifting on account of its ideal rear suspension geometry and the common high-revving SR20DET engine swap. But drifting isn't really racing and engineers like winning by the numbers. So Symonds took his track underdog into the ultra-competitive field of NASA Time Trial (TT) racers at his home track of Mid-Ohio.
To keep a level playing field in TT, NASA implements a base power-to-weight ratio for the upper (TTS and TTU) classes. Closed-wheel/fendered, production-based cars are allowed in TTS and TTU, with TTS governing an adjusted power-to-weight ratio equal to-or greater than-8.7:1. TTU uses 5.5:1. Adjustments come in the form of additions or subtractions based on body type, transmission, drivetrain, tires and competition weight. For Symonds, keeping his PWR as low as possible (more power or less weight), while just fitting into TTS, was ideal, as it kept the 240SX from competing in the TTU class with modern, big-power, all-wheel-drive track dominators like stripped-down race Evos or flyweight prototypes.
Symonds pulled the stock twin-cam KA24DE motor, undressed it and sent it to AMS in Chicago for machining and assembly before starting on the chassis. For race duty, the entire interior was pulled and cleaned. Most of the insulation was stripped out (with the exception of the transmission tunnel) before the chassis was sent to McMahan Autosport in Akron, Ohio, for custom cage work. Per NASA TT rules, a 12-point DOM cage with full door bars, hoop and rear cross braces, as well as a front crossbar, was custom-built. The cage adds side impact and rollover protection, as well as strengthening the soft rear suspension mounts of the open-cabin fastback.
While McMahan Autosport fabricated the cage, AMS was busy building the appropriate long block. The KA24DE motor, although robust, has had little exposure in racing, mostly because of its long stroke and the limited revs it can pull. Much of Nissan's own factory racing effort with the motor, in naturally aspirated form, faced revving limitations. Knowing better, Symonds went for a turbocharged alternative, which the KA seemed almost destined for. The long stoke, oil squirters and cast iron construction meant the block had all the right turbo DNA, like more famous factory turbo motors such as the 4G63 and RB26DETT. The weakness was in the stock rods and 9.5:1 dished pistons.
Based on its significant experience with building boosted KA bottom ends, AMS bored the stock 140,000-mile block ten-thousandths over and installed coated JE 8.5:1 forged pistons and AMS Sportsman H-beam forged 4340 steel connecting rods. The Sportsman rods were picked for their light weight, for reduced bearing loads and inertia. They're good for up to 500 wheel-hp: more than enough for Symonds' power-to-weight target. AMS balanced the entire rotating assembly, as well as polished the stock steel crank, before assembling the short block with Clevite main and rod bearings and ARP studs.