How to make 450 hp from a 351 Cleveland
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.
Four-fifty on a Cleveland is the XE284H number, and it has been dynoed twice by people who publish their sheets. Speed Secrets: 451 hp / 411 lb-ft on a stock-head 4V with a Performer RPM. Richard Holdener at Westech: 450.4 hp / 411 lb-ft on a .030-over 4V with an RPM Air-Gap and a Holley 750 HP — and in the same session, 450.4 hp again with a Parker Funnelweb single-plane, with the difference showing up as 37 lb-ft less in the midrange, not more peak.
That last result is the one to keep in mind when you are shopping intakes for a street/strip car. The single plane did not make more peak power on a 351-inch engine with this cam; it just moved torque out of the range you drive in. The dual plane is the right call unless the car lives above 5,000.
The rest of the build is what the two test engines had in common: factory 4V iron heads with good springs, a 240-at-.050 hydraulic flat tappet, a 750, long tubes, and a tune. Neither test engine had aftermarket heads, a stroker crank, or a roller cam. Neither needed them for 450.
Four fifty is where the Cleveland starts wanting real parts. Closed-chamber heads for the compression, a bigger hydraulic cam, roller rockers, and rods you trust.
It is still a pump gas engine and still perfectly drivable, but the idle tells you something changed and the bottom of the curve is softer than the 400 build. That is the trade and it is worth understanding before you buy.
Watch the compression readout as you change pistons and gasket. On 93 octane there is a ceiling, and the tool will show you when you have crossed it.
The build
| 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 | Fel-Pro .040" MLS — 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 | 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 |
The tune is worth 19 hp here — more than on the 400 — because the cam is big enough to be fussy about timing. Holdener's Westech pulls on the XE284H were run with total timing set on the dyno, and that is the number the calculator matches. Sources: Speed Secrets 351C cam test; Richard Holdener dual-plane vs single-plane 351C at Westech (dyno date 01/15/21, STD).
Change these numbers yourself