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.
What a Boss 351 makes today depends on what you put it on. Richard Holdener built a Boss replica for Westech — 11.0:1, factory 4V closed-chamber iron, the factory cast-iron 4V intake, a Schneider copy of the factory solid grind — and pulled 383 hp at about 6,100 and 391 lb-ft at about 4,000, STD corrected, with long-tube dyno headers and a Holley 750 in place of the Autolite 4300D. The number up top, for the as-built car with stock manifolds and the 600-cfm Autolite, sits where it should against that: the headers and the carb are worth roughly the difference.
Ford's own number was 330 gross. Nobody who has dynoed one has got 330; the 1971 rating was measured on a different standard, with the engine bare, and the modern STD correction reads higher than 1971 gross. If you have a survivor and want the real figure, the parts that decide it are the three the replica changed: manifolds, carb, and how much of the factory total timing the distributor is actually delivering.
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) — builders' guide ~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 |
With the dual-point set to the factory total-timing spec on today's fuel, the tune is worth about 9 hp over the as-delivered setting — the smallest gain of any page here, because the factory already did most of the work. Source: Richard Holdener, Boss 351 replica at Westech (STD).
Change these numbers yourself