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.
|Cylinder Heads||Free with swap meet parts|
|Comp flat-tappet camshaft and lifters||$139.39|
|Comp PN 925-16 valve springs||$116.95|
|Comp Ultra-Pro Magnum rockers||$696.95|
|Edelbrock 383 Victor intake||$259.95|
|Bore and Hone block with torque plates||$200|
|Cylinder Head Work||$250|
|Balance Rotating Assembly||$200|
|Resize/True Rods and install bolts||$200|
|Dyno Time||Varies by Shop and Region, $600-800 per day|
7 On its first measured dyno...
7 On its first measured dyno pull, our 383 made 360 horsepower and 379 lb-ft of torque. Not a bad starting point, considering we'd already beaten the factory rating by some 25 horsepower. Knowing there was more in our little big-block, we bumped the ignition timing to 35 degrees and installed a Holley 750 HP double-pumper, which resulted in an improvement in both horsepower and torque.
8 We tested six different...
8 We tested six different carburetors during our dyno session, as well as two types of air cleaners, and the details of those tests will be shown in a future issue of Mopar Muscle. Our 383 seemed to like the Holley 850 double-pumper we tested best, so we concentrated our efforts on tuning that carburetor for this article.
9 We tested several carb...
9 We tested several carb spacers as well, and our engine seemed to like a two-inch open spacer best. Of course, once the engine is in the car, hood clearance can become an issue unless your car is equipped with a hoodscoop or factory bulge hood.
10 Equipped with the Holley...
10 Equipped with the Holley 850 and two-inch spacer, our engine made its best pull yet with the factory electronic distributor set for 40 degrees total advance. Using an oxygen sensor and monitor from Innovate Motorsports to monitor the air/fuel ratio, we jetted the carburetor with size 87 jets front and rear.
Power and torque numbers were...
Power and torque numbers were each now above the 400 benchmark, but we had a couple of tricks left to attempt.
11 Removing the pulleys,...
11 Removing the pulleys, we installed an electric motor to drive the water pump on our 383. The engine only picked up one horsepower, but did improve by 6 lb-ft of torque.
12 At 80 psi this 383 had...
12 At 80 psi this 383 had an abundance of oil pressure, so we decided to drain the 20W50 weight oil in favor of 5W30. The thinner oil will be easier to pump, and should free up some power. Of course, we wouldn't recommend this for an engine that has marginal oil pressure, but we only lost 5 psi which lowered our oil pressure to 75 psi. It worked, as we gained 16 horesepower.
13 The best dyno pull on...
13 The best dyno pull on our 383 netted 418 horsepower at 5,900 rpm, for a gain of 58 horsepower over the first pull on this engine, and 83 horsepower more than it was rated for at the factory. Torque was up as well, making this a powerful, economical combination. We're not sure what we'll install this in yet, but it will certainly be a fun street car.