I bought a pair of large port Dart II iron heads with 72 cc chambers and put a hundred or so hours (some of which was learning time) into porting and polishing them. The compression ratio works out to about 10.25:1, which seems to be just below the practical detonation limit for well cooled iron heads and 93 octane premium.
This 418 engine, according to its casting numbers, started life as an early '70s Chevy small block 400 with 2 bolt mains. Speed-O-Motive cleaned it, decked it, bored it 0.030 inches over, and combined it with a stroked 400 crank, 327 rods, and special Ross forged pistons. The rod journals on a stock 400 crank are 2.100 inches in diameter compared to the 327's 2.000 inches. A creative machinist removed 0.100 inches from the crank centerline side of the rod journals, balanced everything, and voila: A stroker small block with 5.7 inch long rods.
The engine in its current form carries ZGS moly first and gapless second rings, Michigan 77 bearings, a Melling high volume oil pump, a Diamond Stripper windage screen, a 245 degree at 0.050 inch custom solid-roller cam with 0.575 inch lift, Melling hardened pushrods, Crane roller rockers on 7/16" (big block) studs, high performance 3 piece 175 lb springs, Manley Severe Duty Pro-Flo undercut 2.02 / 1.60 inch 0.100 inch longer valves set in ported and polished Dart-II 74cc large port angle-plug heads, and a Fluidampr balancer. A Cloyes double roller timing chain with a torrington roller block bearing and a roller button coordinates everything. An Accel HEI Super Coil feeds the spark from the GM distributor to the plugs through Accel 300+ wires. A Weiand Team-G aluminum water pump provides a high coolant flow through a Griffin aluminum radiator mated to a Flex-A-Lite Black Magic fan to keep this beast from overheating. Fel-Pro gaskets and an assorted selection of genuine GM parts, such as a '70s Corvette oil pan and dipstick complete the list.
Cool air induction, a high polish in the combustion chambers and constant vigilance by the car's GM electronic spark timing (EST) system keeps the engine detonation-free on 93 octane pump gas, even though the compression ratio is about 10.25 to 1.
I reverse-engineered the PROM in the GM Electronic Control Module and did quite a bit of tuning of the spark timing tables to run this engine properly...
Click Here to download a 156 KB zip file containing a document describing what I did and some software (including sources) to help interpret the calibration tables from within a 1982 ECM. I don't promise it's perfect, but it runs my car pretty darned well! :-)
All Content Copyright © 1995-2010 Noel Carboni