Pontiac 421ci Specs: 4.093 x 4.00 in

Pontiac 421ci specs: 4.093 x 4.00 in (104 x 101.6 mm) bore and stroke, shared by all 3 versions. Displacement, compression and factory ratings.

At a glance

Displacement	421 ci
Cylinders	8
Bore	4.093"
Stroke	4.000"
Compression	10.5–11.0:1
Advertised power	320–405 hp
Years	1962–1966
Cylinder head data	3 of 3 engines

Engines in this family

Engine	Displacement	Bore × Stroke	CR	HP
Pontiac 421ci · 4.093" × 4" · 11:1	421 ci	4.093" × 4"	11:1	405
Pontiac 421ci · 4.093" × 4" · 10.75:1	421 ci	4.093" × 4"	10.75:1	350–376
Pontiac 421ci · 4.093" × 4" · 10.5:1	421 ci	4.093" × 4"	10.5:1	320–338

Factory cars with a Pontiac 421ci

• Pontiac Grand Prix: 1963, 370 hp; 1964, 320 hp; 1964, 350 hp; 1964, 370 hp; 1965, 338 hp; 1965, 356 hp; 1965, 376 hp; 1966, 338 hp; 1966, 356 hp; 1966, 376 hp

Each engine page carries rod ratio, mean piston speed, bore/stroke character and cylinder head specs where published, and links into the calculators with its dimensions already filled in.

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