Like the 454 and the 502 big-blocks, the 8.1 (RPO L18) is founded on a 9.800-inch-tall deck cylinder block though it deviates from the other two powerplants via a 4.225-inch bore x a 4.370-inch stroke (the 454 and 502 maintain a 4.00-inch stroke).

There are three versions of the 8.1 marine engine: HP 1 (375hp/490lb-ft), HP2 (425hp/505lb-ft) and HP3 (525hp/560lb-ft). There is also a truck version of the 8.1 rated at 340hp and 455lb-ft of torque. All engines are equipped with 4-bolt nodular iron main bearing caps, nodular crankshaft and forged steel 1141 connecting rods that are magnafluxed and fitted with 9mm connecting rod cap bolts.

Unlike the GM piston, which is a cast aluminum hypereutectic construction, the Diamond offering is a forging with side reliefs (notches at either side of the skirt that accommodate a shorter, lighter piston pin, said to increase stability under high load). The forging is hewn from 4032 alloy, weighs 515 grams, and incorporates a single 0.107-inch-deep pocket for the 2.19-inch diameter intake valve. Like the factory casting, the new Diamond forging retains a 9.1:1 compression ratio and the standard ring pack: 1/16-inch (top), 1/16-inch (second) and 3/16-inch (oiler). Premium 8620 case hardened chrome molybdenum wrist pins (1.040 x 2.930-inch) are supplied. Optional 9310 endurance alloy pins are also available as are H13 Tool Steel pins, which are recommended for drag racing applications, notably those with power adders.

For quieter cold starting, the wrist pins are offset by .030 inch. This bias is directed toward the thrust side of the bore, inducing positive thrust. On race motors with open headers, this benefit is irrelevant but in the more tranquil setting of marine life, quieter cold starting leaves a most favorable impression. To avoid incorrect installation, Diamond denotes each piston with the letter F, indicating front.

As the Diamond 8.1-liter piston is a shelf-stock item, it is available for immediate delivery. For more information visit www.DiamondRacing.net.

NEW - 1964-1972 GM A Body TigerCage

The TigerCage is constructed entirey from 304 stainless steel and requires absolutely no welding of fabricating. In fact it installs in a matter of hours with simple hand tools and without altering your current interior.


  1. Increases chassis rigidity
  2. Patent pending TigerClamp system allows for easy installation
  3. Engineered to conform tightly to interior panels
  4. No welding or fabrication required
  5. No need to alter or disassemble interior
  6. All 304 stainless construction

For more information, go here.