Technical Specifications
| Brand | BMW |
| Model | Z4 |
| Generation | Z4 (E85 LCI, facelift 2006) |
| Type (Engine) | 2.5si (218 Hp) |
| Start of production | 2006 |
| End of production | 2008 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Roadster |
| Seats | 2 |
| Doors | 2 |
| Fuel consumption (urban) | 12 l/100 km (19.6 US mpg) |
| Fuel consumption (extra urban) | 6.3 l/100 km (37.3 US mpg) |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 6.5 sec |
| Acceleration 0 – 62 mph | 6.5 sec |
| Acceleration 0 – 60 mph | 6.2 sec |
| Maximum speed | 240 km/h (149.13 mph) |
| Weight-to-power ratio | 5.9 kg/Hp |
| Weight-to-torque ratio | 5.2 kg/Nm |
| Power | 218 Hp @ 6500 rpm |
| Power per litre | 87.3 Hp/l |
| Torque | 250 Nm @ 2750 rpm (184.39 lb.-ft. @ 2750 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | N52B25A |
| Engine displacement | 2497 cm3 (152.38 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 82 mm (3.23 in.) |
| Piston Stroke | 78.8 mm (3.1 in.) |
| Compression ratio | 11:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | DOHC |
| Engine oil capacity | 6.5 l (6.87 US qt | 5.72 UK qt) |
| Kerb Weight | 1290 kg (2843.96 lbs.) |
| Max. weight | 1585 kg (3494.33 lbs.) |
| Max load | 295 kg (650.36 lbs.) |
| Trunk (boot) space – maximum | 260 l (9.18 cu. ft.) |
| Fuel tank capacity | 55 l (14.53 US gal | 12.1 UK gal) |
| Length | 4091 mm (161.06 in.) |
| Width | 1781 mm (70.12 in.) |
| Height | 1299 mm (51.14 in.) |
| Wheelbase | 2495 mm (98.23 in.) |
| Front track | 1473 mm (57.99 in.) |
| Rear (Back) track | 1523 mm (59.96 in.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, manual transmission |
| Front suspension | Independent, type McPherson with coil spring and anti-roll bar |
| Rear suspension | Coil spring |
| Front brakes | Disc |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Tires size | 225/50 R16 |
| Wheel rims size | 16 |
The 2006-2008 BMW Z4 2.5si, part of the E85 LCI (Life Cycle Impulse) update, was a two-seat roadster designed to offer an engaging driving experience with a touch of luxury. Built on the E85 platform, it represented BMW’s continued commitment to the roadster segment. The LCI facelift brought subtle but noticeable improvements to the exterior styling, including revised headlights and taillights, as well as enhancements to the interior. The 2.5si trim level was positioned as a sweet spot in the range, offering a significant power upgrade over the base 2.0i while remaining more accessible than the range-topping 3.0si.
Powertrain & Engine Architecture
At the heart of the 2.5si lies the N52B25A inline-six engine. This 2.5-liter naturally aspirated engine is a hallmark of BMW engineering, known for its smooth power delivery and responsive character. The N52 featured Double-VANOS (variable valve timing on both intake and exhaust camshafts) and a magnesium alloy engine block to reduce weight. Fuel is delivered via multi-port fuel injection, and the engine produces 218 horsepower at 6500 rpm and 184 lb-ft of torque at 2750 rpm. The engine’s architecture emphasizes balance and refinement. The standard transmission for the 2.5si was a precise six-speed manual, though a six-speed automatic transmission was also available. The automatic transmission, while offering convenience, slightly impacted acceleration times compared to the manual.
Driving Characteristics
The Z4 2.5si delivers a distinctly sporty driving experience. The inline-six engine provides ample power for spirited driving, and the rear-wheel-drive configuration contributes to a balanced and engaging feel. Acceleration from 0 to 60 mph takes approximately 6.2 seconds, making it a quick roadster. The manual transmission offers precise shifts and allows the driver to fully exploit the engine’s powerband. The automatic transmission, while smooth, feels less connected to the driving experience. The Z4’s suspension is tuned for a balance between comfort and handling, providing a firm but not overly harsh ride. Steering is precise and well-weighted, offering excellent feedback to the driver.
Equipment & Trim Levels
The 2.5si came reasonably well-equipped as standard. Interior features typically included leatherette upholstery (leather was an option), power windows and locks, air conditioning, and a basic audio system. Optional extras included premium sound systems, navigation, heated seats, and sport packages that added features like sport suspension and upgraded brakes. The interior design was driver-focused, with a clear and intuitive layout. The LCI update brought improved interior materials, giving the cabin a more upscale feel.
Chassis & Braking
The Z4 E85 utilizes a McPherson strut front suspension and a multi-link rear suspension, providing a good balance of handling and ride comfort. The 2.5si typically featured disc brakes on all four wheels, providing ample stopping power. ABS (Anti-lock Braking System) was standard. The chassis was designed to be lightweight and rigid, contributing to the car’s agile handling. The standard tire size was 225/50 R16, providing good grip in most conditions.
Market Reception & Comparison
The Z4 2.5si was generally well-received by automotive critics. It was praised for its engaging driving dynamics, smooth engine, and stylish design. Compared to the base 2.0i, the 2.5si offered a significant performance boost, making it a more rewarding driving experience. Compared to the 3.0si, it offered a more affordable entry point into the Z4 range, albeit with slightly less power. Fuel economy was respectable for a sports car, averaging around 23 mpg combined. Reliability was generally good, although some owners reported issues with the cooling system and oil leaks.
Legacy
The BMW Z4 E85 2.5si remains a popular choice among roadster enthusiasts. The N52 engine is known for its durability and relatively straightforward maintenance. While not as collectible as the 3.0si, the 2.5si offers a compelling combination of performance, style, and affordability. On the used car market, well-maintained examples command reasonable prices. The Z4 E85, in general, is considered a modern classic, representing a high point in BMW’s roadster heritage. The 2.5si variant, with its balanced performance and accessible price point, continues to appeal to drivers seeking an engaging and rewarding roadster experience.
