Pontiac Laurentian: which version to buy (1955–1957 specs compared)
If you are choosing a Pontiac Laurentian from this catalogue, the decision is inside one generation (1955-01-01 to 1957-12-31), one body (Sedan), and six named versions: 3.9 MT, 3.9 AT, 4.3 MT, 4.3 AT, 4.6 MT, 4.6 AT.
If you are choosing a Pontiac Laurentian from this catalogue, the decision is inside one generation (1955-01-01 to 1957-12-31), one body (Sedan), and six named versions: 3.9 MT, 3.9 AT, 4.3 MT, 4.3 AT, 4.6 MT, 4.6 AT. There is no second generation here to “step up” into, so the buy is an engine-and-gearbox pick: 3859 / 4344 / 4638 cm³, Manual 3-speed or Automatic 2-speed, all Gasoline, all RWD, all naturally aspirated (No boost), all carburetor, all drum/drum with dependent leaf-spring suspension both ends.
Power in this set is 142 hp (both 3.9s), 165 hp (4.3 MT), 173 hp (4.3 AT), and 223 hp (both 4.6s). Kerb mass is 1560–1610 kg. 0–100, top speed, and fuel consumption are not measured on every version, so the ranking below uses only power, torque, displacement, compression, kerb mass, and the arithmetic those numbers allow.
Pontiac Laurentian specs: the six versions at a glance
| Version | hp | Nm | cm³ | Fuel | Cylinders | Layout | Boost | Gearbox | Drive | Kerb kg |
|---|---|---|---|---|---|---|---|---|---|---|
| 3.9 MT | 142 | 285 | 3859 | Gasoline | 6 | Inline | No | Manual (3) | RWD | 1570 |
| 3.9 AT | 142 | 285 | 3859 | Gasoline | 6 | Inline | No | Automatic (2) | RWD | 1610 |
| 4.3 MT | 165 | 348 | 4344 | Gasoline | 8 | V-shaped | No | Manual (3) | RWD | 1570 |
| 4.3 AT | 173 | 348 | 4344 | Gasoline | 8 | V-shaped | No | Automatic (2) | RWD | 1600 |
| 4.6 MT | 223 | 407 | 4638 | Gasoline | 8 | V-shaped | No | Manual (3) | RWD | 1560 |
| 4.6 AT | 223 | 407 | 4638 | Gasoline | 8 | V-shaped | No | Automatic (2) | RWD | 1600 |
Peak power rpm: 4200 on both 3.9s, 4400 on both 4.3s, 4800 on both 4.6s. Peak torque rpm: 2400 on 3.9 MT / 3.9 AT and on 4.3 AT; 2200 on 4.3 MT; 3000 on both 4.6s. Compression is 8 on the 3.9 and 4.3 pair, 9.5 on the 4.6 pair. Bore × stroke: 88.9 × 95.25 (3.9), 95.25 × 76.2 (4.3), 98.42 × 76.2 (4.6). Fuel grade in the data is 76. Tank is 60 L on all six. Front engine placement is Front, longitudinal on all six. Valves per cylinder: 2.
Which generation to buy
There is 1 generation in the data (2 generation in the catalogue key, years 1955–1957, Sedan, 6 modifications). Restyling is not listed as a separate generation. Buying “a later Laurentian” inside this file does not exist: start and stop dates are the same on every version. The whole comparison is therefore version vs version, not generation vs generation.
What does not change between versions: RWD, Gasoline, No boost, carburetor, 60 L tank, drum front and drum rear, dependent leaf spring front and rear, 2 valves per cylinder, Front, longitudinal. What does change: displacement (+485 cm³ from 3.9 to 4.3, +294 cm³ from 4.3 to 4.6, +779 cm³ from 3.9 to 4.6), cylinder count (6 Inline vs 8 V-shaped), peak power, torque, compression (8 vs 9.5), gearbox type and gear count, and kerb mass (40 kg between the two 3.9s, 30 kg between the two 4.3s, 40 kg between the two 4.6s).
Engine: power per litre and what the extra displacement buys
3.9 MT and 3.9 AT: 142 hp from 3859 cm³ = 36.8 hp per litre. Torque 285 Nm. This is the lowest specific output in the set.
4.3 MT: 165 hp from 4344 cm³ = 38.0 hp per litre. Versus 3.9 MT that is +23 hp (+16%) and +63 Nm (+22%) for +485 cm³ (+13%). Kerb mass is the same 1570 kg as 3.9 MT, so the step up in engine is not paid for in listed kerb mass.
4.3 AT: 173 hp from 4344 cm³ = 39.8 hp per litre. Versus 4.3 MT that is +8 hp at the same 348 Nm (torque peak 2400 rpm vs 2200 on the MT). Versus 3.9 AT (same Automatic 2-speed idea): +31 hp and +63 Nm, kerb 1600 vs 1610 kg (−10 kg).
4.6 MT and 4.6 AT: 223 hp from 4638 cm³ = 48.1 hp per litre — the densest engine in the file, +11.3 hp/L versus the 3.9s. Versus 3.9 MT: +81 hp (+57%) and +122 Nm (+43%) from +779 cm³ (+20%). Versus 4.3 MT: +58 hp (+35%) and +59 Nm (+17%) from +294 cm³ (+7%). Versus 4.3 AT: +50 hp (+29%) and +59 Nm. Compression 9.5 vs 8 on the smaller engines is the other measured difference on the 4.6 pair.
If the question is “what does the larger engine buy in numbers,” the 4.6 pair is the only step that both raises compression and raises specific output by a wide margin. The 4.3 step mainly adds displacement, two extra cylinders in V-shaped layout, and 23–31 hp depending on gearbox.
Weight per horsepower (kg/hp)
This is the cleanest ranking when 0–100 is not measured:
- 4.6 MT: 1560 / 223 = 7.0 kg/hp (best)
- 4.6 AT: 1600 / 223 = 7.2 kg/hp
- 4.3 AT: 1600 / 173 = 9.2 kg/hp
- 4.3 MT: 1570 / 165 = 9.5 kg/hp
- 3.9 MT: 1570 / 142 = 11.1 kg/hp
- 3.9 AT: 1610 / 142 = 11.3 kg/hp (worst)
4.6 MT is 4.1 kg/hp lighter per horsepower than 3.9 MT (7.0 vs 11.1). It is also the lightest kerb in the set (1560 kg), 10 kg under 3.9 MT / 4.3 MT and 50 kg under 3.9 AT. 4.6 AT matches 4.3 AT at 1600 kg but with 50 more hp, so mass per hp drops from 9.2 to 7.2.
Automatic versions are heavier than their Manual twins: +40 kg on 3.9 (1610 vs 1570), +30 kg on 4.3 (1600 vs 1570), +40 kg on 4.6 (1600 vs 1560). On the 3.9 pair that extra mass buys no extra hp (both 142). On the 4.3 pair the Automatic is the one with +8 hp, so you pay 30 kg and gain 8 hp. On the 4.6 pair you pay 40 kg and keep the same 223 hp.
Pontiac Laurentian mpg, 0–100, and top speed
For 3.9 MT, 3.9 AT, 4.3 MT, 4.3 AT, 4.6 MT, and 4.6 AT: 0–100 is not measured, maximum speed is not measured, city / highway / combined consumption is not measured, CO2 is not measured, eco class is not measured.
Do not treat a missing figure as “this car has no top speed.” The catalogue simply does not list it. Economy cannot be ranked between versions from this file. The only consumption-adjacent facts that are listed: Gasoline, fuel grade 76, tank 60 L on all six, no turbo (No).
Dimensions, weight, tank, wheels
- Kerb: 1560 kg (4.6 MT), 1570 kg (3.9 MT, 4.3 MT), 1600 kg (4.3 AT, 4.6 AT), 1610 kg (3.9 AT). Spread = 50 kg from lightest to heaviest.
- Gross weight: not measured on all six.
- Ground clearance: not measured on all six.
- Wheel size: not measured on all six.
- Tank: 60 L on all six — no version has a larger tank to buy.
Chassis specification does not differentiate a “better riding” or “better braking” version in this data: every row is dependent leaf spring front, dependent leaf spring rear, drum front, drum rear.
Manual vs Automatic on the same engine
3.9 MT vs 3.9 AT. Same 142 hp, 104 kW, 285 Nm, 3859 cm³, 6 Inline, compression 8. Difference: Manual 3 vs Automatic 2, and 1570 vs 1610 kg. If you want this engine, 3.9 MT is the lighter, closer-ratio-count gearbox. 3.9 AT is the heavier two-speed Automatic with identical listed power.
4.3 MT vs 4.3 AT. Same 4344 cm³, 348 Nm, 8 V-shaped, compression 8. 4.3 AT is the only pair where Automatic is stronger: 173 hp vs 165 hp (+8 hp, +6 kW), torque peak 2400 vs 2200 rpm. Mass 1600 vs 1570 kg (+30 kg). kg/hp still favors 4.3 AT (9.2 vs 9.5). If you want Automatic and the 4.3 displacement, 4.3 AT is the stronger of the two 4.3s, not a detune.
4.6 MT vs 4.6 AT. Same 223 hp, 164 kW, 407 Nm, 4638 cm³, compression 9.5, 8 V-shaped. Difference is gearbox and 40 kg. 4.6 MT wins kg/hp (7.0 vs 7.2) and is the lightest car in the catalogue row. 4.6 AT keeps the same peak power with Automatic 2.
Gear count is consistent: every Manual here is 3 speeds; every Automatic is 2 speeds. There is no 3-speed Automatic in this model’s data.
Which version to choose
Choose 4.6 MT if the ranking is power and mass per power. It is 223 hp, 407 Nm, 48.1 hp/L, 1560 kg, 7.0 kg/hp. Versus 3.9 MT it is +81 hp and −10 kg. Versus 4.3 MT it is +58 hp and −10 kg. Same Manual 3 and RWD. This is the strongest and lightest combination in the file.
Choose 4.6 AT if you want that same 223 hp / 407 Nm with Automatic 2. You give up 40 kg versus 4.6 MT and still beat every smaller engine on kg/hp (7.2 vs 9.2 on 4.3 AT and 11.3 on 3.9 AT). Power is identical to 4.6 MT; you are not losing listed horsepower by taking Automatic on this displacement.
Choose 4.3 AT if you want Automatic but not the 4.6. It is the peak of the 4.3 pair (173 hp), +8 hp over 4.3 MT, +31 hp over 3.9 AT, and 10 kg lighter than 3.9 AT. You give up 50 hp versus 4.6 AT at the same 1600 kg kerb.
Choose 4.3 MT if you want Manual 3 and the middle engine: 165 hp, 348 Nm, 1570 kg, same kerb as 3.9 MT with +23 hp and +63 Nm. You give up 8 hp versus 4.3 AT and 58 hp versus 4.6 MT. Specific output (38.0 hp/L) sits only slightly above the 3.9s.
Choose 3.9 MT if the goal is the 6 Inline, smallest displacement (3859 cm³), and lowest listed power (142 hp) with the lighter of the two 3.9 kerbs (1570 kg). Versus 4.6 MT you give up 81 hp and accept 11.1 kg/hp. There is no economy figure to claim this version uses less fuel — consumption is not measured.
Choose 3.9 AT only if you specifically want Automatic 2 on the 3859 cm³ engine. It is the heaviest Laurentian in this set (1610 kg) with the weakest kg/hp (11.3), and it does not gain horsepower over 3.9 MT. Versus 4.3 AT you give up 31 hp and carry 10 kg more.
Short decision map
- Strongest Manual: 4.6 MT (223 hp, 1560 kg).
- Strongest Automatic: 4.6 AT (223 hp, 1600 kg).
- Automatic with a power bump vs its Manual twin: 4.3 AT (173 vs 165 hp).
- Same power, lighter gearbox: 3.9 MT over 3.9 AT; 4.6 MT over 4.6 AT.
- Smallest engine, Inline 6: 3.9 MT or 3.9 AT.
- Middle 8 V-shaped: 4.3 MT or 4.3 AT.
- Highest compression (9.5 vs 8): 4.6 MT and 4.6 AT only.
Problems and reliability are not measured in this dataset; this article does not invent failure rates. Prices are not in the data. The buy, from the numbers given, is 4.6 MT for the best mass-to-power, 4.6 AT if the gearbox must be Automatic, and 4.3 AT only if you are capping displacement at 4344 cm³ while still wanting Automatic.