383 Big-Block Engine Build, Part Two
Dyno tuning our budget 383
From the June, 2012 issue of Mopar Muscle
By Dave Young
Photography by Dave Young
Last month we built a mild street engine using a factory Chrysler 383 block, crankshaft, rods, and cylinder heads combined with some aftermarket goodies from Comp Cams and Summit Racing Equipment, and put it on the dyno to see what kind of horsepower and torque it could make. And while our numbers were significantly better than the factory rating for the 383 Magnum or Super Commando, we knew there was more to be had through efficient dyno tuning of the big-block. This month we'll show you how we gained 58 horsepower and 35 lb-ft of torque by spending a day on the dyno.
The factory horsepower rating for Mopar's 383 four-barrel varies by car model and year of production, but the highest rating the 383 ever had was 335 horsepower as the base engine of first generation Road Runners. Using a factory '68 block, crankshaft, connecting rods, and .030-inch over cast pistons combined with stock 906 cylinder heads for our engine, we're basically duplicating the '68 Road Runner engine. The only advantages our 10:1 compression 383 has over the factory version are the intake manifold, mild overbore, Comp camshaft, and Comp rocker gear. This is a very economical combination to build, costing less than $2,500 in parts and machine work, and is likely similar to the engine in many of your cars.
One of the questions we're often asked is whether or not dyno time is worth the money when it comes to an engine build. And while the answer to this is somewhat dependent on your budget, and the application, we generally favor dyno testing for a number of reasons. First, it's a lot of work to put an engine in a car, and if you have a leak or mechanical problem with the engine while on the dyno, it makes repairs a lot easier. Next, tuning an engine for peak power and testing multiple bolt-on parts requires accurate measurement, and an engine dyno is the only way to precisely measure changes to horsepower and torque. Sure you can do this at the dragstrip, but most street cars are limited by traction and the results of testing can be somewhat ambiguous. Because an engine dyno is a precise tool and removes the variable of the car from the equation, the results are accurate and replicable.
Another nice feature of dyno time is being able to break in the engine. Even better, a slight load can be placed on the dyno as the rpm is varied, which is a proven way to seat piston rings quickly. We performed the break-in procedure for our 383 on the Superflow engine dynamometer at Auto Performance Engines, checking for leaks or unusual noises, drained the oil and checked the valve lash. With new oil and a new oil filter installed, we were ready to make some dyno pulls on our big-block.
Knowing the parts inside an engine aren't really put under much of a strain until a load is put on them, the first real dyno pull on an engine always makes us the most nervous. It is at this time that any weak link, defect, or substandard part can be exposed, so we're always cautious during the first pull. For our testing we filled the fuel cell with BP 93 octane unleaded fuel, set the acceleration rate of the dyno to 300 rpm/second, and made our first pull from 3,500 to 5,500 rpm. On what was admittedly a conservative tune-up with a 750 vacuum secondary Holley carburetor and only 32 degrees total ignition timing, peak torque was 380 lb-ft at 4,600 rpm with a peak horsepower number of 360 horsepower at 5,500 rpm. Having already beaten the numbers of the factory 383, we were ready to make some tuning changes in the search for more power.
1 We built this 383 from...
1 We built this 383 from a '68 block, 906 heads, forged crankshaft, and factory connecting rods that were sitting around our shop. The 383 was the most widely produced Mopar big-block, and parts like these are plentiful and cheap. Most of this stuff was discarded by others and just given to us.
2 Our plan was to build this...
2 Our plan was to build this engine on a budget, so the 906 heads were simply treated to a valve job and new Comp Cams springs. In an effort to out-power the best factory rating of 335 horsepower, we also installed a new solid lifter flat-tappet camshaft with .502 intake and .511 exhaust lift and a lobe separation of 110 degrees.
3 To accommodate our solid...
3 To accommodate our solid lifter camshaft, we chose a set of Pro Magnum adjustable rocker arms from Comp Cams. These rockers are a great value and come as a complete kit with shafts and hardware. They also utilize ball/ball style pushrods, which are arguably more stable than ball/cup style.
4 Assembled with rings, bearings,...
4 Assembled with rings, bearings, gaskets, seals, and an Edelbrock Victor 383 intake manifold from Summit Racing Equipment, we bolted our big-block to the dyno at Auto Performance Engines to measure its power. We're hoping our mild combination, basically a stock engine with a cam and intake swap, will make significantly more power than the factory 335 horsepower rating.
5 Topped with one of Auto...
5 Topped with one of Auto Performance Engine's Holley 750 break-in carburetors, we fired the 383 up to break in the camshaft and seat the rings. Using Comp's break-in lube and oil, we've never had a problem wiping a lobe off on of their cams. This time was no different, and we were ready for a dyno pull after engine break-in.
6 After break-in we changed...
6 After break-in we changed the oil, set the ignition timing at 35 degrees total advance, and checked and reset valve lash as necessary. With 80 psi of oil pressure and nothing abnormal found, we made our first pull using the shop's 750 carburetor.
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.