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Idle Hands: BMW Z4 3.0si Coupé
1 year ago
The 'concept' was pretty much production-ready
When the company announced UK pricing in January 2006, the E86 Z4 3.0si Coupé started at £31,375, in SE specification, and £32,900 in Sport trim. The premium for the latter netting you 18-inch wheels instead of 17s, along with M Sports suspension, desirable M Sports seats, an anthracite headlining and a leather M steering wheel. Canny buyers, those defaulting to tall sidewalls and softer suspension for the sake of their spines and wheel insurance claims, will be keen to note that many Sport features, trim-specific alloys and steering wheel aside, were available as options on the SE.
Either was admittedly more expensive than some contemporaries, such as the Nissan 350Z, which started at £26,495, and the £28,960 Audi TT Coupé 3.2 quattro. But a Porsche Cayman, well, even in less powerful 2.7-litre form, it’d set you back an extra £3320 over the BMW, at best. And the BMW didn’t disappoint in group tests, either, although the Porsche and Nissan would often trump the Z4 in outright driver satisfaction and ride quality. One element that never drew criticism, however, was its engine: the proverbial jewel at the heart of the BMW, that N52 3-litre.
This naturally aspirated straight-six engine was no humdrum affair: it featured a magnesium-alloy block, which helped bring its weight down to 121kg, some 10kg less than the preceding M54 engine. Its aluminium cylinder head was also stuffed with BMW’s variable valve timing and valve lift systems, VANOS and VALVETRONIC, and the engine further benefitted from lightweight hydroformed camshafts, exhaust manifolds, and intake manifold, as well as an efficiency-boosting electric water pump.
"Thanks in part to its plethora of technologies, it put out a stout 261bhp at 6600rpm, and 232lb ft at 2750rpm, and would spin willingly to its 7000rpm limiter. That aided the Z4 in dispatching the 0-62mph sprint in 5.7 seconds"
At the time, the 24-valve engine was claimed to be the lightest six-cylinder production unit in the world. And, thanks in part to its plethora of technologies, it put out a stout 261bhp at 6600rpm, and 232lb ft at 2750rpm, and would spin willingly to its 7000rpm limiter. That aided the Z4 in dispatching the 0-62mph sprint in 5.7 seconds, or 6.0 flat in automatic form, putting it on a par with the 3.5-litre Nissan and between the 2.7- and 3.4-litre variants of the 987-generation Cayman. And you’ve probably already guessed the BMW’s top speed: yes, limited to 155mph. Quelle surprise.
Not that the engine and performance were the only technical elements of note. The rear-wheel drive Z4 Roadster was already a stiff car, but the Coupé’s fixed roof boosted the torsional rigidity of its structure by just over a factor of two. The rest was fairly conventional: MacPherson struts up front, multi-link suspension at the back, front and rear anti-roll bars, and vented discs all round. There was also the choice of a close-ratio six-speed manual transmission or a torque converter-based Sport automatic gearbox with wheel-mounted shift paddles.
Another appealing factor, for those who wanted to rack up some miles, was decent fuel economy. The car wasn’t featherweight, clocking in at 1395kg (which only sounds light by modern standards), but in manual form it was claimed to average 31.7mpg. With a 55-litre tank, that granted a range of some 380 miles, more if driven gently. And, praise be, no Z4 3.0si Coupé slipped into a teeth-sucking VED band: currently, all cost a tolerable £430 annually. In this area, the BMW comes out on top against the likes of the Nissan 350Z, which can be thirsty and cost up to £760 to tax.
"There was one facet that put some drivers off: the car’s power steering. It used the same electrically assisted Servotronic system as the Roadster, which was the first production BMW to feature electric power steering, saving one litre of fuel every 250 miles and providing variable assistance"
There were other strong points, including the styling, interior, and the 340-litre boot, helping make the BMW more usable. But there was one facet that put some drivers off: the car’s power steering. It used the same electrically assisted Servotronic system as the Roadster, which was the first production BMW to feature electric power steering, saving one litre of fuel every 250 miles and providing variable assistance.
However, in part due to it being the brand’s first shot at the technology, not everyone liked the way it behaved and felt, and it could later prove problematic. And BMW’s engineers seemingly concurred, at least with the general preference for pumping a bit of Dexron around a hydraulic rack: the Z4 M Coupé, in which efficiency was less of a concern, got a traditional hydraulic system that was deemed by the brand to offer the ‘correct level of steering feel’ for such a car.
That isn’t to say that you should immediately scrub the idea of buying a Z4. Test a sorted example and, depending on your points of reference and preference, you might find that the steering serves up gratifying weight and response. And improvements are possible: ditching the factory-specified run-flat tyres for conventional ones is an instant way to improve a poorly handling and riding Z4. You can also lubricate the steering system and adjust the tension ring in the column to better its action, while adopting E46 M3 CSL alignment can further enhance the front end’s behaviour.
What you can also do, if you’re set on the car but the steering ultimately sours your experience, is retrofit a hydraulic system. The rack, hoses, cooler line, pump, reservoir, and a few minor pieces, are all available from E46 and E90 generation BMW 3 Series. The only hard-to-source piece is the intermediate steering shaft from the hydraulically steered Z4 M, but an alternative can be fabricated. Otherwise, it’s mostly a bolt-together affair, aside from removing the power steering motor and coding it out. Just don’t forget to discuss the conversion with your insurer beforehand…
There is a long list of other potential upgrades for any Z4 3.0si Coupé, too, ranging from aftermarket spring and damper combinations, and additional bracing, through to limited-slip differentials, weighted gear knobs for the manuals, xHP transmission tuning for the automatics, and improved rear trailing arm bushes. Depending on what you end up with, you might shortlist suspension and tyre changes quite quickly, as some Z4s can be stiff and harsh.
Rightly, though, you might be wondering whether it would be best to pay the premium for a 338bhp Z4 M. After all, it comes with hydraulic steering, and a limited-slip differential, and the rest. But nowadays, usable Z4 3.0si Coupés start at the aforementioned £5000, while around £8000 will get you a smart example. More, and you’re into pristine territory. A Z4 M Coupé, on the other hand, will cost over £15,000. And, in some cases, you might have to spend thousands immediately, on things such as rod bearings and engine mounts, as well as enduring higher running costs across the board.
Those factors might make the M unviable or undesirable to you. And, importantly, the N52 engine in the 3.0si, as opposed to the 3.2-litre S54 in the M, is unlikely to pitch any significant concerns or problems your way. It might occasionally weep oil from a gasket, or burn a bit, and you might have to replace the odd coil pack, intake flap or VANOS solenoid, but that’s about it. It’s a similar story for the rest of the car: buy a sound example and, the occasional trashed bush, broken spring, corroded brake line, or unexpected electronic water pump failure aside, reliability should be good.
But while the N52 is stout, its major limitation is that there’s not much you can do with it should you eventually find its output wanting. Companies such as BDS Motorsport did develop some upgrades, ramping the N52’s power up to over 300bhp, but at a cost. And forced induction is an option, thanks to supercharger kits from brands such as T-21 Industries and ESS Tuning, but prohibitively expensive. Consequently, if you’re seeking power or looking for a car to develop extensively over time, without changing the motor, an N52-engined Z4 probably won’t tick your boxes.
That aside, the Z4 3.0si Coupé has lots in its favour, ranging from its eye-catching looks through to its affordability and compelling, albeit flawed in places, performance. And for some, the car’s soul-filling styling, its character, and that engine, could be enough to disregard its imperfections. For others, those wanting out-of-the-box driving pleasure and precision, a Cayman would prove better, higher costs aside, even alongside the fabled but somewhat wayward Z4 M. But what a choice to have, hey? Just don’t wait too long, lest everyone else work out what they’re missing.
