Lets look at original and after market transmissions for your beloved Triumph classic!
Engine changes for 4-cylinder engines as TR4A migrated to TR3B and TR4(A). While the bore, stroke, and displacement remained the same, changes to the cylinder head and manifolds raised net power to 104 bhp (78 kW) and torque to 132 lb⋅ft (179 N⋅m), an increase of 10 percent. The TSF series were identical to the last run of TR3As, so with a two-litre engine and non-synchronized 1st gear transmission. The TCF series has the 2.138-litre TR4 engine. The engine is a straight-four, push rod, three-bearing, with wet liners. It has 9:1 compression and is very rigid. It was fitted with two H6 SU carburetors. It has 105 hp (78 kW) at 4,650 rpm and 172 N⋅m (127 lbf⋅ft) of torque at 3,350 rpm. It gets around 20 miles per US gallon (12 L/100 km; 24 mpg‑imp) to 30 miles per US gallon (7.8 L/100 km; 36 mpg‑imp). The top speed is limited to about 110 mph (177 km/h) by the gear ratio, unless it has overdrive. Electrically triggered overdrive (Laycock-de-Normanville Type A) was available as an option and operates on second, third, and fourth gears.
After market options still exist for TR2 – TR4A 4-cylinder driven Triumphs. The first is the British adaptation of the Ford Motor company type 9 transmission. Several LBC part companies offer this kit to install a helical geared, quiet 5 speed transmission with drop in installation.
The Type 9 was Ford's first five-speed, rear-wheel-drive gearbox, and it is based on the four-speed Type E gearbox. The fifth, or overdrive gear, was added to the four-speed gearbox by placing it in the extension housing or tailshaft housing. This made production easier and cheaper but effectively limited torque capacity to 200 lb. ft. or so. Early Triumphs were around 130 lb. ft.
The Type 9 is a popular choice for five-speed conversions of older Ford cars such as the Cortina and rear wheel drive Escorts, and also for kit car builders, since it comes with a separate bell housing so it can be easily swapped around. Engines that were originally in FWD layouts are fitted to these transmissions so that they can go into a RWD layout, as in a hot rod engine swap or kit car. The gearbox has a 1-inch-diameter (25 mm) 23-spline input shaft, and the main gear housing is cast iron with a cast aluminum tailshaft housing.
Overall, the T-9 is an excellent transmission for vehicles with lower power levels and lighter weight. However, in applications that require more power, the T-9 is frequently replaced with the stronger Borg-Warner T-5 transmission.
The second option is a Mazda MX-5 5 Speed Transmission. This conversion kit for all Triumphs 1952-67 TR2-4As with a fully assembled gearbox with a cast bell housing and casing built to fit directly to the Triumph's engine back plate. The bell housing flange has been designed to resemble the standard gearbox, preserving engine bay originality. The all-alloy casing of TR2/TR4A gearbox conversion kit provides weight savings over cast iron original or type 9 transmissions.