Performance is good for an old automatic executive car, M3 1986 numbers are in brackets. All values are from AMS:
- 0-100 km/h 7.8s (7.1s)
- 0-160 km/h 18.7s (17.5s)
- 0-1000m 28.3s (27.5s)
- Top speed 231 km/h (239 km/h)
Engine power output is 252 hp@4900 rpm and 380 Nm@2200 rpm. There is room for upgrades on intake, exhaust, engine management, boost pressure, turbocharger, suspension, brakes and wheels. Before performance items, taking care of general maintenance is important. Upgrade for intake is simple, stock filter is replaced with a K&N filter (no 33-2005). Performance improvements are subtle but upgraded filter is washable and reusable. There are some downsides, like lesser filtration and filter oil sticking to air flow meter.
Exhaust modifications generate notable improvement in performance and sound. Well constructed stainless steel exhaust with turbo in-line six sounds fantastic. Simply put on turbo engine bigger the pipe the better. Three-inch pipe with single muffler should be plenty performance wise but you should be prepared for loud exhaust note. Leaving stock downpipe untouched might be good idea, not to affect too much on turbine back pressure and response. Upgraded exhaust system may trigger engine protection.
Motronic II engine management which included boost and detonation control and four-speed programmable automatic transmission got praise in press at eighties. Engine management with air flow meter is obsolete technology by today’s standards. Replacing it with fully adjustable system with mass air sensor is attractive but laborious. This most likely means converting auto to manual transmission, discarding EH-transmission electronics. Original equipment can run really well when all adjusted and maintained.
Boost pressure over factory 0.4 bar is best way to make big improvement in 745i performance. Engine is over engineered and bullet proof. There are several steps to take: engine maintenance, boost and fuel mixture monitoring, modifying control unit, securing fuel supply and modifying or replacing wastegate. Bypass valve is gone in late 745i turbo due wastegate solenoid control circuit. High boost levels may cause compressor surge and stress turbo. At 0.7 bar power increases to 300 hp / 500 Nm, similar to E28 ALPINA B7 TURBO.
Turbocharger upgrade should help with faster spool up, more air flow and higher boost pressure. Upgrade usually means replacing compressor wheel to one with larger diameter and better flow charesteristics. This kind of upgrade is called a K27 hybrid. Turbo flange in M102/M106 manifold is no good for just directly bolting another type of charger. In general best results are gained remapping engine management for new setup. This is rather difficult with 745i turbo, details are sparse.
Suspension can be upgraded with quality parts. H&R lowering springs (-40mm) are good choice for better handling when paired with Bilstein sport shocks. Springs are widely available, but Bilsteins are harder to come by. When ordering H&R springs (no 29547-1) there are several diameters related to equipment and national version of car. Always measure old ones before ordering. Replacing rear shocks and springs means also eliminating original self leveling suspension.
Front brakes are 280mm ventilated discs with fixed four piston calibers. Rear brakes are 282mm solid discs with floating single pistons. Last model year 1986 had ABS brakes from factory. Unfortunately front spring struts are different from other BMW series at time. There are no drop-in replacements for a brake upgrade. Rear brakes can be replaced from other series. At close to stock power levels brakes are well up to task. Brakes are equipped with hydraulic booster and pedal feel is different over ones with vacuum booster.
Factory wheel size is 14-inch equipped with 205/70R14 tires. Wheels from other BMW series can be used with or without spacers when 5×120 bolt pattern is available. Upgrade over factory wheels are newer E32 7-series wheels. These wheels include 15-inch size equipped with 225/60R15 tires. Alpina wheels in 16-inch or 17-inch size are most desirable. With wheels same rules do apply as for other performance upgrades, increasing performance will decrease comfort in some content.