383 Big-Block Engine Build, Part Two

The first change we made to our tune-up was to install a 750-cfm Holley HP double-pumper carburetor, and pull the engine from 3,500 rpm to 5,800 rpm with the ignition timing at 35 degrees. This pull resulted in a noticeable increase in torque, up by 9 lb-ft and 15 additional horsepower. Adding five degrees of ignition timing for a total advance of 40 degrees, we raised the upper rpm limit to 6,200 and another pull was made on the 383, netting 391 lb-ft of torque and 388 horsepower at 6,100 rpm. Thinking our little 383 might want more carburetor, we decided a change was in order.

During our dyno time, we actually tested six different carburetors on our 383, and will give you the details of that testing in an upcoming issue of Mopar Muscle. What that testing revealed is that this engine liked the Holley 850 double-pumper best, so we concentrated our efforts on tuning that carburetor. Also testing multiple carb spacers on our engine, we discovered our best power came with 87 jets in the Holley, a two-inch open spacer, and the ignition timing set at 42 degrees total advance. In this configuration, our big-block made 402 lb-ft of torque at 4,600 rpm, and 402 horsepower at 6,100 rpm, acting a little bigger than its 383 inches.

Having a couple of additional tricks up our sleeve, we decided to really optimize power by installing an electric drive on the water pump to get rid of the engine driven belt. While it isn't likely this modification would be performed on a street car, our engine did make an additional six lb-ft of torque, but horsepower wasn't changed. Next, we drained the 20W50 weight conventional oil from the engine and replaced it with 5W30 conventional motor oil. Since our 383 had oil pressure to spare (80 psi), running lighter oil is a good way to free up horsepower without sacrificing protection. The results of our next pull proved this theory, as the engine made its best numbers of 414 lb-ft of torque and 418.5 peak horsepower at a leisurely 5,900 rpm.

So, was our dyno time at Auto Performance Engines worth the expense and effort? In our case we found an additional 35 lb-ft of torque and an impressive 59 additional horsepower by tuning our 383 on the engine dyno. And while we may have been able to accomplish some of this with the engine in the car, it certainly would have made the work more difficult, and would have taken considerably more time. Additionally, we wouldn't have any measureable results without doing all of our testing under very controlled track conditions. Best of all, our engine is ready to be put in the car with confidence, knowing that at the turn of the key we'll have nearly 420 dyno-tuned horsepower at our disposal and ready to run.

Costs