Cylinder Heads
The bolt-on
We swapped out a set of factory iron cylinder heads for a pair of Holley's aluminum small-block heads, which have 184cc intake runners, 68cc chambers, and 2.02/1.60 valves. $1,226
The mule
355 small-block, 8.3:1 compression, GM production iron heads, 650-cfm Carb Shop-built Holley.
Our take
Even a mild, low-compression small-block can benefit from a good set of high-flow cylinder heads.
Before
Max torque: 365 lb-ft @ 3,500 rpmMax power: 307 hp @ 4,900 rpmAverage torque: 342Average hp: 258
After
Max torque: 407 lb-ft @ 4,200 rpmMax power: 375 hp @ 5,500 rpmAverage torque: 389Average hp: 296
Difference
+42 lb-ft+68 hp
Exhaust
The bolt-on
We replaced a compression-bent, 2 1/2-inch exhaust with a 2-inch balance pipe and big-block Chevelle mufflers in favor of a Flowmaster 2 1/2-inch, mandrel-bent A-body dual exhaust kit with Super 44 mufflers. $386
The mule
355 small-block, 9.5:1 compression, ported L98 heads, Edelbrock Performer RPM intake, 750-cfm Holley carb. Power measured at the flywheel.
Our take
Even with identical pipe diameters, the mandrel-bent system with Flowmaster's new Super 44 mufflers freed up double-digit power gains.
Before
Max torque: 405 lb-ft @ 4,300 rpmMax power: 393 hp @ 5,700 rpmAverage torque: 385 lb-ftAverage power: 334 hp
After
Max torque: 418 lb-ft @ 4,600 rpmMax power: 413 hp @ 5,700 rpmAverage torque: 400Average power: 352
Difference
+13 lb-ft+20 hp