LT1 Engine Build - Rotating Assembly And OptiSpark

The torque converter loads up the crankshaft in such a way that it causes excessive wear on the thrust bearing and flange. We replaced the crank with a new one from Scat.

After the block was machined and the crank balanced, JMS' Jeff Johnson began reassembly. Here's a look at the new timing set, which includes the water pump drive gear partially hidden behind the cam gear.

JMS handled the assembly, but we had to get it ready to run on the dyno. To speed up the process, we ordered a wiring harness from Painless Performance rather than try to decipher the factory harness. We were impressed with the Painless harness--all the connections were labeled and the kit included this nice, braided loom. We had the engine wired up in just a couple of hours.

Here's the engine wired up and ready to be rolled into the dyno cell. To get an accurate baseline, we decided to run the engine totally stock with the original cam, iron heads, iron exhaust manifolds, and stock catalytic converters.

Unfortunately, our engine wouldn't start. We double-checked all our wiring and even replaced the mass airflow sensor and ECM before finally getting out our factory service manual and tracing the problem to a bad OptiSpark. There was no high-resolution signal from the optical trigger to the ECM, so the plugs wouldn't fire. Though aftermarket OptiSpark units are available, we wanted one from GM--and good luck finding one in stock at your local Chevrolet dealer. We bought ours from LT1 specialist George Bates Automotive in Upland, California. They're not cheap, either.

Bates warned us to pay close attention to this connector. It's the link between the ECM and the OptiSpark, and it often gets melted by engine heat. We checked our factory harness and found that it was, in fact, a little melty looking. It's a good idea to wrap this connector with some sort of heat-insulating sleeve.