CHI 3V 225 vs stock iron 4V on 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: 6000 rpm.
Where each one wins
| RPM | stock iron 4V | CHI 3V 225 | diff |
|---|---|---|---|
| 2000 | 246 | 286 | +40 |
| 2500 | 259 | 303 | +44 |
| 3000 | 281 | 330 | +48 |
| 3500 | 311 | 367 | +55 |
| 4000 | 345 | 408 | +63 |
| 4500 | 374 | 441 | +67 |
| 5000 | 390 | 452 | +63 |
| 5500 | 378 | 444 | +67 |
| 6000 | 358 | 431 | +73 |
Torque, lb-ft, at the flywheel. Everything except the part named is identical between the two runs.
CHI is the Australian outfit that kept the Cleveland aftermarket alive. Their 3V 225 flows 331 cfm against the iron 4V's 273 and — this is the part that matters — it does it without giving up the low-lift numbers.
That is the difference between a modern CNC head and an old big-port casting. The iron 4V trades bottom end for top end. The CHI just adds top end.
It is also several times the money and it comes from Australia. Whether that is worth it depends on whether you are building for a number or building something to drive.
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) — to ~450 HP |
| Pistons | Generic flat top (0cc) |
| Head gasket | OEM compressed (.040") — neutral |
| Cylinder heads | 4V open chamber (75.6cc) — 70s CJ/Q-code |
| 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 | Pump 93 octane |
| Air cleaner | Stock air cleaner, LID FLIPPED — DYNO STANDARD |
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) — to ~600 HP |
| Pistons | Generic flat top (0cc) |
| Head gasket | OEM compressed (.040") — neutral |
| Cylinder heads | CHI 3V 225cc — the modern Cleveland 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 | Pump 93 octane |
| Air cleaner | Stock air cleaner, LID FLIPPED — DYNO STANDARD |