The cars used a Rover engine in 4 or 6-cylinder form which came from the 1948 P3 and had overhead valves for inlet and side valves for exhaust. A four-speed manual transmission was used with a column-mounted shifter at first and floor-mounted unit from 1954. At first the gearbox only had synchromesh on third and top but it was added to second gear as well in 1953. A Freewheel clutch, a traditional Rover feature, was fitted to cars without overdrive until mid-1959, when it was removed from the specifications, shortly before the range rearrangements announced for the London Motorshow in October that year.
The cars had a separate chassis with independent suspension by coil springs at the front and a live axle with half-elliptical leaf springs at the rear. The brakes on early cars were operated by a hybrid hydro-mechanical system but became fully hydraulic in 1950. Girling disc brakes replaced drums at the front from 1959.
The complete body shells were made by the Pressed Steel company and featured aluminium/magnesium alloy (Birmabright) doors, boot lid and bonnets until the final 95/110 models, which were all steel to reduce costs. The P4 was one of the last UK cars to incorporate rear-hinged “suicide” doors.
The original P4, the model 75, arrived in 1949. It featured controversial modern styling which contrasted with the outdated Rover P3 which it replaced, and which was heavily based on the bullet-nosed Studebakers of the same era. One particularly unusual feature was the centrally mounted headlight in the grille. Known as the “Cyclops eye”, it was removed after 1952.
Power came from a 2.1 L (2103 cc/128 in³) Rover IOE straight-6 engine. A four-speed manual transmission was used with a column-mounted shifter at first and floor-mounted unit from 1954.
Production of this original model ended in 1954 with 33,267 sold.
A four-cylinder version of the P4 line was introduced in 1953 as the P4 60. Its 2.0 L (1997 cc/121 in³) 60 bhp (45 kW) engine was the same one Rover used in the early Land Rover, with modifications including an SU carburettor. As the block was shorter than that of the 6-cylinder engine, it sat further back in the frame, and this is sometimes held to have resulted in better handling and compensated for the lack of power. It was replaced in 1959 by the P4 80, which used an updated version of the overhead-valve 2286 cc (138 in³) four used in the Land Rover by that time.
In their test of the Sixty in 1954 The Motor magazine recorded a top speed of 76.0 mph (122.3 km/h) and acceleration from 0–60 mph (97 km/h) of 26.5 seconds. A fuel consumption of 25.8 miles per imperial gallon (10.9 L/100 km; 21.5 mpg-US) was recorded. The test car cost £1162 including taxes.
At the same time as the four-cylinder version was introduced, the top-end P4 90 with a more-powerful 2.6 L (2639 cc/161 in³) six appeared. This engine produced a respectable 90 hp (67 kW) and could reach 90 mph (145 km/h). When it was replaced by the P4 100 in 1959, 35,903 had been produced – making it the most popular variant in the series.
Testing the Ninety in 1954 The Motor magazine recorded a top speed of 90.0 mph (144.8 km/h) and acceleration from 0–60 mph (97 km/h) of 18.9 seconds. A fuel consumption of 20.3 miles per imperial gallon (13.9 L/100 km; 16.9 mpg-US) was recorded. The test car cost £1297 including taxes.
P4 75 Mark II:
An updated P4 75 arrived in 1954 with some styling changes. A three-piece wraparound rear window was used, but the 2.1 L (2103 cc/128 in³) IOE engine continued. This model was updated again in 1955 with a larger 2.2 L (2230 cc/136 in³) version of the IOE engine. Overdrive became an option from 1956. In 1957, it was restyled, along with the rest of the P4 line, with a new grille and wings. Production ended in 1959 with the introduction of the P4 100.
P4 105R / 105S:
The P4 90 was not to be the top of the P4 line. Introduced in 1956, the P4 105R and P4 105S used a high-output, 8.5:1 compression (to take advantage of the higher octane fuel that was by then available), version of the 2.6 L (2639 cc/161 in³) engine also used in the 90. This twin-SU carburettor engine produced 108 hp (80 kW). Both 105 models also featured an updated exterior, the 105S featured separate front seats, a cigar lighter, chromed wheel trim rings and twin Lucas SFT 576 spotlamps. To minimise the cost of the 105R, these additional items were not standard, however they were available on the (higher priced) 105R De Luxe.
The 105R featured a “Roverdrive” automatic transmission. This unit was designed and built by Rover and at the time was the only British-built automatic transmission (others had bought in units from American manufacturers such as GM). This unit was actually a two-speed automatic (Emergency Low which can be selected manually and Drive) with an overdrive unit for a total of three forward gears. The 105S made do with a manual transmission with overdrive, but could hit 101 mph (163 km).
The Motor magazine tested a 105R de luxe in 1957 and found it to have a top speed of 93.9 mph (151.1 km/h) and acceleration from 0–60 mph (97 km/h) of 23.1 seconds. A fuel consumption of 23.6 miles per imperial gallon (12.0 L/100 km; 19.7 mpg-US) was recorded. The test car cost £1696 including taxes of £566.
When production of the 105 line ended (in 1958 for the 105R and 1959 for the 105S), 10,781 had been produced, two-thirds with the manual transmission option. For 1959 the manual model was described simply as a 105 and the trim and accessory level was reduced to match the other models.
In 1959/1960 the P4 range was rationalised to two models, the 80 and the 100. The P4 80 was the four-cylinder version. The engine was now a Land Rover-derived straight-4 overhead-valve engine, this time displacing 2.3 L (2286 cc/139 in³); it is entirely different from the units used in all the other models. With 80 hp (59 kW) available, the car could top 85 mph (137 km/h). Girling 10.8 in (274 mm) vacuum servo-assisted disc brakes at the front were new, and the car used wider tyres and had updated styling. Overdrive, operating on top gear only, was standard on the four-speed transmission. Options included a radio, two tone paint schemes, and either a bench or individual front seats. These options also apply to the 100 (see below).
The four-cylinder P4s were never popular, and just 5,900 had been built when the line was cancelled in 1962.
The Motor magazine tested an 80 in 1961 and recorded a top speed of 82.9 mph (133.4 km/h) and acceleration from 0–60 mph (97 km/h) of 22.4 seconds. A fuel consumption of 23.5 miles per imperial gallon (12.0 L/100 km; 19.6 mpg-US) was found. The test car cost £1396 including taxes of £411.
The P4 90 was replaced in 1960 by the more-powerful P4 100. Its similar 2.6 L (2625 cc/160 in³) IOE straight-6 engine was in fact a short-stroke version of the P5 3-Litre unit. The car could now reach 100 mph (161 km/h). The interior was luxurious, with wood and leather accents on traditional English car elements like a curved “Shepherds Crook” handbrake lever. Either a bench or individual front seats could be ordered. A heater was a standard fitting. Like the smaller 80 version, the 100 was fitted with servo-assisted Girling disc brakes at the front, keeping drum brakes at the rear. Overdrive, on top gear only, was a standard fitting.
Production ended in 1962, by which time 16,521 had been produced.
Testing the 100 in 1960, The Motor magazine recorded a top speed of 92.1 mph (148.2 km/h), acceleration from 0–60 mph (97 km/h) of 17.6 seconds and a fuel consumption of 23.9 miles per imperial gallon (11.8 L/100 km; 19.9 mpg-US). The test car cost £1538 including taxes.
The final member of the P4 family was the P4 95 and P4 110 series. Introduced in 1962, the vehicles aptly represented the end of an era. Late in the run, the vehicles were fitted with steel door panels and electric windscreen washers. Although the Roverdrive automatic had been put to rest, overdrive was standard on the 110, whereas the 95 made do with a higher ratio differential (3.9:1).
Both models used the same 2.6 L (2625 cc/160 in³) version of the IOE engine. The wider availability of higher octane fuels permitted an increase in the compression ratio to 8.8:1, and the old unit now produced 123 hp (91 kW) in 110 guise, which used a Weslake cylinder head, and 102 hp (76 kW) in the 95.