Turbo Small-Block Build - Building The Two-Headed Animal

Did You Know?
The cam journals in GM blocks are bored with three different inside diameters so the bearings can be loaded on a stepped tool and installed all at once to speed assembly and reduce cost. Dart bores all the cam journals to the same size so they can line-hone them to a finished dimension. This makes a more precise diameter and ensures true alignment of the journals. It also means all the cam bearings are the same size.

Big Small-Block Piston/Rod Combos
434
9.025 deck height/4.00 stroke
5.70 rod-1.320 piston
5.85 rod-1.170 piston
6.00 rod-1.020 piston
420
9.025 deck height/ 3.875 stroke
5.70-inch rod-1.375 piston
5.85-inch rod-1.225 piston
6.00-inch rod-1.075 piston

Two-Headed Specs
4.155 bore
3.875 stroke
5.850 rod
9.020 deck height
Compression distance: 1.227
-.0055 deck clearance
8.57:1 compression ratio
-31cc inverted dome
68cc combustion chamber volume
Head gasket: 0.061 thickness, 4.200 Bore: 13.9cc volume