Pontiac 389ci Specs: 4.062 x 3.75 in

Pontiac 389ci specs: 4.062 x 3.75 in (103.2 x 95.3 mm) bore and stroke, shared by all 4 versions. Displacement, compression and factory ratings.

At a glance

Displacement	389 ci
Cylinders	8
Bore	4.062"
Stroke	3.750"
Compression	8.6–10.8:1
Advertised power	215–360 hp
Years	1959–1966
Cylinder head data	4 of 4 engines

Engines in this family

Engine	Displacement	Bore × Stroke	CR	HP
Pontiac 389ci · 4.062" × 3.75" · 8.6:1	389 ci	4.062" × 3.75"	8.6:1	215–256
Pontiac 389ci · 4.062" × 3.75" · 10.25:1	389 ci	4.062" × 3.75"	10.25:1	267–313
Pontiac 389ci · 4.062" × 3.75" · 10.75:1	389 ci	4.062" × 3.75"	10.75:1	318–360
Pontiac 389ci · 4.062" × 3.75" · 10.5:1	389 ci	4.062" × 3.75"	10.5:1	267–333

Factory cars with a Pontiac 389ci

• Pontiac Grand Prix: 1962, 230 hp; 1962, 303 hp; 1962, 318 hp; 1962, 333 hp; 1962, 348 hp; 1963, 230 hp; 1963, 303 hp; 1963, 313 hp; 1964, 230 hp; 1964, 303 hp; 1964, 330 hp; 1965, 256 hp; 1965, 325 hp; 1965, 333 hp; 1965, 338 hp; 1966, 256 hp; 1966, 325 hp; 1966, 333 hp
• Pontiac GTO: 1964, 325 hp; 1964, 348 hp; 1965, 335 hp; 1965, 360 hp; 1966, 335 hp; 1966, 360 hp

What varies across the family

Compression spans 8.6:1 to 10.75:1, so fuel requirements differ meaningfully between members — worth checking before assuming parts interchange.

All are oversquare — bore larger than stroke, which favours revs over low-end torque.

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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