25MPG highway is within reach. My 745 with LT1 and T56 (3.31axle) turns a bit over 1600 at 70MPH and gets between 25-26 at a steady 70. The engine has around 150k mi, I believe, and has occasional driveability issues, so there may be room for improvement once I get the injectors cleaned and balanced, fresh plugs, etc.

The original Optispark ignition has been heavily modified so that the OE distributor now only handles primary voltage (timing signals to the ECU/PCM) and the secondary consists of a 4-dual-coil setup from a Cadillac Northstar V8.

Per GM recommendation, I use 5W30 oil (Mobil-1 synthetic).

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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)