355 & 383 Chevy Engine Performance Gain

On paper at least, the larger engine has a lot going for it. Naturally, we couldn't end this on sheer speculation, so we devised a test to illustrate just what happens when you increase the displacement of a high-performance small-block. To keep things interesting, we decided that our test subjects would differ only in displacement, meaning every other variable-including compression, cam timing and even the tune up specs-would be identical. Our goal was to run a pair of small-blocks, one displacing 355 ci and the other 383 ci, equipped with all the same components.

The one key element was compression, as the increase in displacement has a decided effect on static compression assuming no change in piston design. To keep the static compression the same, the 355 featured flat-top pistons (with valve reliefs) while the 383 came equipped with 9.8cc dish pistons.

Some might argue the change in piston design might affect power irrespective of the fact that this equalized compression, but the change in flame travel should be minimized and we saw no other way to keep the testing accurate. Thus we had a pair of engines, displacing 355 inches and 383 inches, respectively.

Each engine was set up with a standard volume oil pump (from ProComp), stock oil pan and pick up. Up top, each was configured with a set of AFR 195 aluminum heads, a Comp XE274H cam and ProComp dual-plane (air-gap style) intake manifold.

The two combinations also received the same 750 Holley Street HP carburetor, a ProComp HEI distributor with the ignition timing locked at 34 degrees (where both produced best power) and a set of 1 3/4-inch long-tube headers feeding 18-inch collector extensions. As you'll soon see, both of the small-blocks were rather healthy.

In each case, the carb was jetted to optimize the air/fuel curve under wide open throttle. All power runs were made with 10W-30 non-synthetic Lucas oil.

Both the 355 and 383 were run with the same set of 1.5 ratio roller rockers from Comp Cams.
Both the 355 and 383 were run with the same set of 1.5 ratio roller rockers from Comp Cams
The test subjects were run with a set of long-tube headers feeding 18-inch collector extensions (no mufflers).
The test subjects were run with a set of long-tube headers feeding 18-inch collector exten
Given the street orientation of both combinations, we naturally chose a dual-plane intake. This air-gap style intake from Pro Comp offered both impressive peak and average power numbers. A dual-plane intake is the hot set up for any performance street motor running below 6,500 rpm.
Given the street orientation of both combinations, we naturally chose a dual-plane intake.

Carburetion came in the form of a Holley 750 Street HP. Sure, we may have made a few extra horsepower with an 850 or 950 HP, but the ideal carb size for street use on these small-blocks is definitely the 750.
Carburetion came in the form of a Holley 750 Street HP. Sure, we may have made a few extra
ProComp supplied one of its ready-to-run HEI distributors. All we did was supply 12 volts to the distributor and lock the centrifugal advance (at 34 degrees) and we were off and running. ProComp also supplied a set of its high-performance plug wires.
ProComp supplied one of its ready-to-run HEI distributors. All we did was supply 12 volts
After installing the headers on the 355, we were rewarded with 441 hp at 5,900 rpm and 438 lb-ft of torque at 4,500.
After installing the headers on the 355, we were rewarded with 441 hp at 5,900 rpm and 438

The 383 demonstrated why strokers are so popular by thumping out 480 hp at 5,700 rpm and 495 lb-ft at 4,300 rpm. Torque production from the 383 eclipsed 440 lb-ft (more than the peak torque production from the 355) from 3,000 rpm all the way to 5,700 rpm.
The 383 demonstrated why strokers are so popular by thumping out 480 hp at 5,700 rpm and 4
One look at the graph shows the substantial torque gains offered by the 383 stroker. In fact, the 383 offered more power everywhere, from as low as 3,000 rpm (our lowest load point on the dyno) all the way to 6,000 rpm. Where the 355 produced 438 lb-ft of torque, the 383 managed 497. Is it any wonder why the streets are so full of 383 small-blocks? Eagle-eyed readers will no doubt recognize the fact that the 383 produced both peak torque and power 200 rpm lower than the 355 and that the power fell off quicker past the power peak. What the 383 needs to rev like the 355 is wilder cam timing, but with the same cam, the larger motor will always produce peak power earlier in the rev range. The added bonus is improved idle quality over the 355.
One look at the graph shows the substantial torque gains offered by the 383 stroker. In fa

SOURCES
Comp Cams 3406 Democrat Road Memphis TN 38118 800-999-0853 www.compcams.com	Probe Racing 2555 West 237th Street Torrance CA 90505 310-784-2977 www.probeindustries.com
Holley/Hooker 1801 Russellville Road Bowling Green KY 42101 270-782-2900 www.holley.com	Procomp Electronics 605 S. Milliken Avenue Unit A Ontario CA 91761 909-605-1123 www.procompelectronics.com
Demon Engines Sante Fe Springs CA 562-694-2559 www.demonengines.com	Air Flow Research (AFR) 28611 W. Industry Drive Valencia CA 91335 877-892-8844 www.airflowresearch.com
L&R Automotive 13731 Bora Drive Sante Fe Springs CA 90670 562-802-0443 www.lnrengine.com