BMW 745i turbos were sold from year 1979 to 1986. Up to 1983 cars had 3.2L M102 engine featuring L-Jetronic management. This meant electronic fuel injection and vacuum spark timing. Late cars from 1984 had digital Motronic management for turbo, fuel injection and spark timing. This combined with advanced transmission made improvement in fuel economy and driveability. There were also visual changes to bodywork through years, but power plant can be seen as biggest change. Most notable visual changes were metal nose and chrome mirrors on early cars.
Look for late car with Motronic management. Prices start from a few thousand euros up to tens of thousands euros. Most expensive cars have low mileage and mint condition. A good 745i turbo can be bought above ten thousand euros. It is recommended to skip cars with low price and condition unless buyer is committed to put extra effort on car. Overhauls take vast money and time. Owning a 30-year old car is going to take effort even though being in good condition to begin with. Many spare parts are fit for other BMW models, meaning reasonable running costs.
Most important is history of car and how it was maintained. High mileage car with good documentation is better than non-serviced low mileage one. Costly repairs as new radiator do not always mean there is something wrong, it also shows care take of previous owner. Beside history bodywork should be inspected for rust. Though being from eighties there are minor defects always. Wheel arches, doors, tail lights, side skirts and body underside are places to check. Cars with sunroof are more prone to have rusted side skirts, water is ran trough skirts to ground.
Owning a 745i turbo is most rewarding while driving it. As a collectible item it has less value. Eighties motorsport BMW’s are sold for completely different sums of money. Rare models like Highline and Executive are usually priced higher though. Not many of these were made and after 30-years not many left. For comparison on 1986 you could almost have bought two M3’s for a price of Highline. Total of 17000 cars were sold before moving to naturally aspirated engine. It was last gasoline turbocharged BMW manufactured until twinturbo 335i was introduced year 2006.
Unfortunately low prices of 745i turbos have led to modified, lowly maintained examples. Many cars have lost M106 power plant for another chassis, like E28 during the years and are out of picture. Replacing auto transmission for 5-speed manual seems popular task on several cars due to problems with original transmission. Performance wise there is little to no sense going between auto and manual box on M106 based car. Auto box with Motronic management is way up for task and locking converter downplays economy benefits on highway.
In general try to look for a stock one and carry on from there. Though when cars is modified, it always goes away from original experience. Like serious overboost gives more power output from engine, but makes power curve steep and transforms to light-switch-like behaviour. For all work done to car if not visible or not documented it should mean nothing on sale. Like owners can have very different views of what engine rebuild means. Always try to verify origins for work carried on. When considering getting a 745i turbo, if possible go to see more than one car.
Example prices (average 11100 euros) collected from mobile.de on February 2017: