LS POWER

Sam Logan June 07, 2022 All Feature Vehicles

Manna for those who understand hot rods

When John Tucker’s company, SPS Engines, began offering LS conversion kits for hot rods in 1999, it was a career-changing act. Now in his 67th year, if his life has a theme beyond developing innovative hot-rod kits and simplifying their installation, it is his penchant for problem solving.

Hot-rod LS power is usually transmitted through a Tremec T56 Magnum 6-speed manual gearbox or GMPP’s 6-speed (6L80E) or 4-speed automatic (GM’s 4L70E) as shown.

The engine and transmission installation kit is powder-coated and fasteners anodized for best appearance and longevity. Mounting bushings are available in black or red.

GMPP’s entry-level hot-rod power unit. Displacing 6.2 liters and generating 430 hp, the LS3 will record mid-20s fuel consumption, depending upon gearing and tire size.

Although not unusual among engineers, Tucker has a reassuring eye and a bright, adaptive mind that seems to overcome every technical obstacle that emerges. Inevitably, transforming the hot rod from the pristine simplicity of a small-block Chevrolet power unit to the sophistication of the LS presented numerous complications. Nonetheless, it was this auspicious backdrop that spurred the dramatic introduction of the SPS LS kits that overcame many of the hurdles that inhibited the hot-rodder.

Gear ratios for the 4L70E are as follows: 1st 3.06, 2nd 1.62, 3rd 1.00 and 4th 0.70 (overdrive). Compared with the 4L60E this 4L70E transmits greater torque.

SPS crossmember is a direct fit. Once installed, shims position the engine and transmission to the correct angle: 3 to 5 degrees from horizontal.

Cooling lines and fittings (No. 6) connect the transmission to a heat exchanger built into the radiator. Notice heat-resistant sleeves that insulate the lines from the exhaust header.

All battery cables are constructed of No. 2 gauge, full-flex 100-percent copper containing three times the normal strand count. Doubled sleeved, they allow greater amp draw without overheating.

Not the least of these is the computer, which is often concealed under a seat or in the glovebox. A universal system with a blank memory, this GM computer is purchased separately. SPS re-flashes the unit and inserts a file, usually from a 2011 or 2012 Corvette. From there, they modify the file during dynamometer tuning. The computer consists of the ECM (engine control module) and a TCM (transmission control module). It also includes a fuse block as well as a diagnostic connection operated by Tech 2 or Snap-On scanners.

If the knock sensor detects vibrations caused by engine knock, it retards the ignition timing and protects the engine from damaging pre-ignition.

The SPS harness, which manages engine and transmission functions, is encased in a heat-protective sleeve and carefully tagged for easy installation. It employs Packard-Bell weather-pack connectors.

The water temperature sensor transmits its information to the gauge. Chief sensors include Manifold Absolute Pressure, Mass Air, throttle position and O2 readings.

Beyond the electronic challenges, Tucker also extends his influence toward the vehicle’s handling characteristics. “The roots of greatness for any hot rod are its power and balance,” he explains. “No one interested in driving ever tires of the pleasure of real steering feel, instantaneous throttle response, an incisive gear change and a properly balanced chassis.” To obtain the latter, Tucker recommends setting the LS engine as far back in the frame as possible, which allows the engine to adopt a more satisfactory rearward stance, thus improving the car’s balance. “Having a hot rod feeling heavy, bloated and uninviting to drive is the last thing the enthusiast wants,” says Tucker.

This double-pass radiator houses a transmission cooler, a steam line connection, an optional bung for external fan control, and two 14-in. electric fans of which each draws 1555 cfm.

The fuel system includes a new tank that incorporates an Aeromotive in-tank pump, which maintains a minimum of 55 psi and supports up to 700 hp.

Just forward of the rear axle is a venting system that eradicates any hint of fuel fumes from hot rods running in pre-emission condition. This is particularly useful when parked indoors.

OEM and aftermarket exhaust headers often leave the LS too wide, striking the frame as a result. But SPS offers modern headers and stainless-steel units if required.

By necessity, hot-rodders will select one of two transmissions: a manual or an automatic. Helpfully, SPS provides several LS conversion kits, the most comprehensive of which is called their Turn-key option. Others include an engine-transmission installation kit, a cooling kit and a fuel system kit ($3295). Once everything is in place, the work can be usually accomplished in about one day. In the following images is the process for installing a GM LS3 6.2-liter engine mated to a 4L70E automatic transmission in a desirable 1969 convertible Chevrolet Camaro.