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.