The 1969 Boss 429 had two versions of it’s potent 429 c.i. hemi. The first 279 Bosses off the line received the Nascar version, also known as the “S” motor. The remaining 580 units were referred to as “T” motors, or street engines. The T engine used a 429 Cobra Jet crankshaft and rods, as opposed to the S engine that had Nascar rods and crankshaft.
These beasts were only produced to satisfy Nascar’s homolagation rules, meaning manufacturers in the day were required to produce 500 units available to the public before an engine was “legal” for racing the circuit.