Build Some Power With a '92-'96 Gen II LT1

Geardriven Water Pump
The Gen II's water pump is a unique design. It looks like an electric pump, but it's actually geardriven, using the camshaft sprocket. It was designed this way to be more reliable throughout its service life by eliminating the bearing failures caused by accessory drivebelt tension. The thermostat housing is on top of the pump housing on the inlet side of the system. Placing the thermostat on the inlet eliminates thermal shock, because cold water from the radiator can be gradually mixed with warm coolant already circulating through the engine. Also, the pump is designed to maintain full coolant flow through the engine and heater core even with the thermostat closed. This reduces the possibility of impeller damage by cavitation and allows the engine to warm up more quickly.

There are currently no aftermarket performance mechanical water pumps available, but Meziere and CSR sell electric pumps that replace the impeller section of the stock housing. Flow rates range from a near-stock 35 gallons per minute to 50 gpm. You need access to a hydraulic press to perform this conversion because the driveshaft bearing assembly must be pressed out.

Opti-Spark
Another big change from the traditional small-block design was the Opti-Spark ignition system, which incorporates two functions in one unit: It's a crank-angle sensor as well as a distributor. An optical sensor made of matched pairs of LEDs and phototransistors resides in the distributor housing. Light from the LEDs excites the transistors, causing them to generate a voltage. The light is broken up by a disc sandwiched between the two. The disc has two tracks of slots or windows cut into its perimeter. The outer track has 360 windows; the inner has only eight windows, but these eight windows are all of differing widths. The disc is driven by the cam, so as it turns with the engine, the phototransistor reads the "on and off" of each window as it breaks the beam of light and generates a voltage for each event-a total of 720 pulses per camshaft revolution, which corresponds to one revolution of the crankshaft. At the same time, the inner phototransistor is generating a signal for the eight windows that correspond to the top dead center of each piston. A processor called the EBT reads both signals and determines the exact position of the crankshaft, accurate to 1 degree. The ECM then uses this information to determine the proper ignition timing per cylinder on an individual basis.

Of course, the Opti-Spark performs its duties as a distributor, too. Spark energy comes via a remote-mount coil, like later HEI systems, but through a series of paths embedded in the cap, the plug wire terminals exit the cap according to which side of the engine the cylinder is located on.

Continue of image 9. Figure...        read full caption Continue of image 9. Figure 39 OPTI-SPARK PULSE TRAIN. Courtesy SAE International

The pin that drives the distributor...        read full caption The pin that drives the distributor is mounted on the camshaft timing gear.

The Opti-Spark has earned a bad reputation as an unreliable unit. But those claims are largely unwarranted. The early units, of 1992 and 1993, had problems with carbon tracking and ozone and moisture collecting inside, but improvements were made in the 1994 (or 1995 depending on application) and later units. The bodies were sealed and vented via ported vacuum drawing filtered air from the intake ductwork. No Opti-Spark likes moisture, though, and a water-pump leak can kill it. Since the water pump must be removed to replace an Opti-Spark, it's prudent to replace both parts together if one or the other fails. Chad Golen recommends using an MSD cap and rotor. He says the MSD parts are made of better materials than the GM pieces were. They are less expensive, too.