There is a more cost effective route and that is by fitting a higher back axle ratio at 3.31 vs the SP standard unit of 3.54
However, if the Borg Warner T5 is your preferred route the closest set of ratios comparable to the SP is 2:95 (2:933 SP) 1:94 (1:742 SP) 1:34 ( 1.232 SP ) and direct 1.1. then the 5th gear and as Borg Warner offered a number of options for the T5 you can opt for a 5th gear ratio of 0:.85 to 0:63 . The most common in the USA is that fitted to a Mustang from 2.95 to 0: 73.
Whilst here in the UK it’s best to source those fitted to the 4 litre V8 TVR Chimaera.
The other route is the Jaguar option either 4 speeds plus overdrive or the 5 speed unit. In this case you need to buy the bellhousing for a V8 Saloon then some minor welding as the starter motors are in different locations Daimler saloon vs the SP.
Don’t forget you may need a clutch driven plate that will fit those boxes.
All gearboxes can take the torque of a higher tuned SP engine – I think up to 400 BHP (Jaguar might be lower to be on the safe side)
Note Borg Warner develop the T5 then sold the rights to what is now Tremec
Laurence
