351C rocker arms — 1.73 vs 1.8 ratio
within 1% of peak across that whole range
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: 6000 rpm.
Where each one wins
| RPM | stock 1.73 | roller 1.8 | diff |
|---|---|---|---|
| 2000 | 283 | 285 | +2 |
| 2500 | 302 | 305 | +3 |
| 3000 | 326 | 329 | +3 |
| 3500 | 359 | 362 | +3 |
| 4000 | 394 | 397 | +3 |
| 4500 | 422 | 425 | +3 |
| 5000 | 425 | 429 | +4 |
| 5500 | 411 | 419 | +8 |
| 6000 | 390 | 401 | +11 |
Torque, lb-ft, at the flywheel. Everything except the part named is identical between the two runs.
A higher ratio rocker multiplies the lobe you already have — a 1.8 on a .342" lobe gives you what a 1.73 would need a bigger cam to reach. It is real lift, at the top of the curve where lift is worth the most.
Two things to check before you order. Your springs have to clear the new lift, and your pushrod length changes with the rocker geometry. Neither is optional.
This is a top-end change, not a bottom-end one. The extra lift does very little at two thousand rpm and progressively more as the engine comes up on the cam.
The build
| Block | Factory 351C 4-bolt main (Boss/HO) |
|---|---|
| Crank | Eagle forged 4340 — 3.50" stroke / 351 ci (~$700) |
| Rods | Stock I-beam (factory) — builders' guide ~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 XE274H — hyd flat (32-246-4 · 230/236 @.050 · .562"/.565") — Holdener +44 HP vs Boss cam |
| Valve springs | COMP 916-16 dual |
| Rocker arms | Full roller 1.73 — needle bearing |
| 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 |
These numbers assume a proper dyno tune — timing and jetting set on a dyno, not guessed at in a driveway. It is worth 18 hp on this combination, and it is the one line on this page you cannot buy: we build the parts list, you pick the tuner. Leave it untuned and the engine will run, it just will not read what it says up top.
The other one
| Block | Factory 351C 4-bolt main (Boss/HO) |
|---|---|
| Crank | Eagle forged 4340 — 3.50" stroke / 351 ci (~$700) |
| Rods | Aftermarket I-beam forged (Eagle/Scat) — builders' guide ~600 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 XE274H — hyd flat (32-246-4 · 230/236 @.050 · .562"/.565") — Holdener +44 HP vs Boss cam |
| Valve springs | COMP 916-16 dual |
| Rocker arms | Full roller 1.8 — more lift at the valve |
| 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 |
These numbers assume a proper dyno tune — timing and jetting set on a dyno, not guessed at in a driveway. It is worth 18 hp on this combination, and it is the one line on this page you cannot buy: we build the parts list, you pick the tuner. Leave it untuned and the engine will run, it just will not read what it says up top.
Change these numbers yourself