How much horsepower will a cam swap add to a 351 Cleveland?
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.
Where each one wins
| RPM | stock CJ cam | COMP XE284H | diff |
|---|---|---|---|
| 2000 | 315 | 264 | -52 |
| 2500 | 339 | 278 | -60 |
| 3000 | 361 | 302 | -60 |
| 3500 | 389 | 334 | -55 |
| 4000 | 405 | 370 | -36 |
| 4500 | 398 | 401 | +4 |
| 5000 | 380 | 418 | +38 |
| 5500 | 358 | 405 | +47 |
| 6000 | 265 | 384 | +119 |
Torque, lb-ft, at the flywheel. Everything except the part named is identical between the two runs.
The camshaft is the biggest single lever on this engine and the one people are most afraid of. Going from the factory Cobra Jet hydraulic grind to a COMP XE284H is a genuinely large change: 206/221 at .050 up to 240/246, and .481" of lift up to .584".
You pay for it at the bottom. More duration holds the intake valve open later past bottom dead centre, and at low rpm the piston is moving slowly enough to push part of the charge back out. That is the lope, and it is also the lost torque.
And you must change the springs. The factory springs will not clear .584" of lift, and a cam the valvetrain cannot follow makes less power than the one you took out.
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 | OEM compressed (.040") — neutral |
| Cylinder heads | 4V closed chamber (61cc) — the coveted quench head |
| Porting | As-cast / stock |
| Camshaft | 351 Cobra Jet (Q-code, D1ZZ/D2ZZ-6250) — 270/290 adv · 206/221 @.050 · .481"/.490" |
| Valve springs | Crane single 110 lb |
| Rocker arms | Stock stamped 1.73 rockers |
| Intake manifold | Edelbrock RPM Air-Gap |
| Carburetor | Holley 750 cfm — street/strip sweet spot |
| Exhaust | Long tube 1-3/4" — hot street |
| Ignition | MSD Pro Billet distributor + 6AL box — ~8,000 rpm |
| Fuel | Sunoco 260 GT 100 — unleaded, street legal, cat/O₂ safe |
| Air cleaner | Stock air cleaner, LID FLIPPED — DYNO STANDARD |
The other one
| Block | Factory 351C 2-bolt main (stock) |
|---|---|
| Crank | Eagle forged 4340 — 3.50" stroke / 351 ci (~$700) |
| Rods | Stock I-beam (factory) — to ~450 HP |
| Pistons | Generic flat top (0cc) |
| Head gasket | OEM compressed (.040") — neutral |
| Cylinder heads | 4V closed chamber (61cc) — the coveted quench head |
| Porting | As-cast / stock |
| Camshaft | COMP XE284H — hyd flat (32-250-4 · 240/246 @.050 · .584"/.588") |
| Valve springs | COMP 916-16 dual |
| Rocker arms | Stock stamped 1.73 rockers |
| Intake manifold | Edelbrock RPM Air-Gap |
| Carburetor | Holley 750 cfm — street/strip sweet spot |
| Exhaust | Long tube 1-3/4" — hot street |
| Ignition | MSD Pro Billet distributor + 6AL box — ~8,000 rpm |
| Fuel | Sunoco 260 GT 100 — unleaded, street legal, cat/O₂ safe |
| Air cleaner | Stock air cleaner, LID FLIPPED — DYNO STANDARD |