I will start with the 845cc engine: it is possible to fit a carburettor with a 32mm intake from an R5 or 6. This gives a useful increase in power and torque. It is also possible to fit a custom, freeflow exhaust and electronic ignition to boost performance.
These modifications are also possible on the 1108cc engine. In addition, the 1108cc cars can be fitted with larger engines from the contemporary Renault range; the 1289cc 54bhp , 1397cc 63bhp, or the 1397cc 93bhp Gordini motor. These all require a custom exhaust system, special throttle linkages, radiators, plus more. It is also possible to fit electronic ignition systems, or a programmable ignition that is set up on a rolling road.
There are several gearbox options available as , unless it is an early 3speed model, the R4 has either a 4speed low ratio ( van) , or 4speed high ratio box. It is possible to fit a 5 speed, though this requires a different cross member and bonnet modification.
With all these modifications a donor vehicle may be required.