How much horsepower does a 1971 Boss 351 have?
Engine dyno, as configured — flywheel horsepower. Standard test config: stock manifolds through 18" of pipe, air cleaner lid flipped, no accessories driven. Factory SAE net ratings are measured as‑installed and read 15–25% lower. Rev ceiling for this combination: 5800 rpm.
The Boss 351 is the only Cleveland Ford built with solid lifters — D1ZZ-6250-B, advertised 290/290 on a 116 lobe separation, .477" lift, .025" lash. Rated 330 gross, and the one everybody wants.
It is also famously soft below three thousand. That is not a fault, it is the cam: 58 degrees of overlap does nothing for you at idle and everything for you at six thousand. Look at the low end of the curve and you can see it.
If you are chasing Boss numbers with a hydraulic cam you will get close on peak and never match it up top. The lifters are the difference.
The build
| Block | Factory 351C 2-bolt main (stock) |
|---|---|
| Crank | Stock cast iron — 3.50" stroke (351 ci) |
| Rods | Stock I-beam (factory) — to ~450 HP |
| Pistons | Generic flat top (0cc) |
| Head gasket | Fel-Pro .028" MLS — raises CR |
| Cylinder heads | 4V closed chamber (61cc) — the coveted quench head |
| Porting | As-cast / stock |
| Camshaft | Boss 351 — SOLID flat tappet (D1ZZ-6250-B, 290/290 adv · .477" · 116 LSA) |
| Valve springs | Crane single 110 lb |
| Rocker arms | Stock stamped 1.73 rockers |
| Intake manifold | Stock 4V cast iron — factory 4bbl |
| Carburetor | Autolite 4300-D 4bbl — Boss 351 / Cobra Jet (600 cfm) — built 1971-74 only, reman/NOS |
| Exhaust | Stock manifolds + 18" pipe — DYNO STANDARD |
| Ignition | Dual-point distributor (Mallory) — ~6,000 rpm |
| Fuel | Sunoco 260 GT Plus 104 — unleaded, 13% ethanol |
| Air cleaner | Stock air cleaner, LID FLIPPED — DYNO STANDARD |