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2004 BMW Z4 3.0 Roadster vs Mercedes-Benz SLK350 comparison review: classic MOTOR

By Jesse Taylor | Photos: Cristian Brunelli, 05 Nov 2018 Car Comparisons

2004 BMW Z4 Roadster vs Mercedes-Benz SLK350 comparison review classic MOTOR

There’s $20,000 between them, but the sparks fly when these two roadsters square up – stand back!

Our new long term BMW Z4 3.0 is up against it this month. You can read all about it’s welcome to the family on the December 2004 issue, but right here right now, the flame-surfaced Z4’s got bigger problems to deal with than having to live with MOTOR for the next few months. For one, the new SLK 350 from Mercedes-Benz has it firmly fixed in its crosshairs.

This feature was originally published in MOTOR’s December 2004 issue

Quickfanged in the November 2004 issue in seven-speed auto guise, we’ve nabbed the six-speed manual version of the SLK to go up against our resident six-speed Z4. The auto is a delete option on the Merc and drops the asking price from $112,900 to $109,400, but it’s still a big step up from the $92,000 Bimmer drop-top.

The muscular-looking SLK flexes harder than the BMW with its 3.5-litre DOHC V6 turning out 200kW and 350Nm. By comparison, the propeller head musters 170kW and 300Nm from it’s long-lived, but still sensationally-smooth 3.0-litre straight six.

So, on paper the Benz has already got this race run, right? Not so fast, Cletus. While the $86,900 SLK 200 is a better match to the Z4 on price alone, its supercharged four-potter musters a piddling 120kW and is a closer real world sparring partner to the 2.5-litre BMW Z4.

MOTOR used car advice: Z4 now a better-value MX-5

But factor in the Z4 3.0’s lighter weighbridge ticket (1290kg to the SLK 350’s portly 1465kg) and you’re looking at weight-to-power ratios in the same seven-point-something bracket. Game on, then.

The new Merc roadster comes from a position of sales strength with more than 308,000 of the previous generation sold since its 1996 launch. But despite drawing from the same gene pool and wearing the familiar nameplate, the new SLK brings with it a paradigm shift in design philosophy.

It is a far more masculine design, with cues taken from both the McLaren F1 racecar and the SLR McLaren supercar. In fact, the SLK has been accurately described as a mini-SLR.

The Benz does a good job of polarising opinions, but nothing can touch the Z4’s design for love-it-or-loathe-it reactions. After initially cocking an eyebrow, we’ve grown used to the design, and some of us really dig it. There are still question marks over the nose treatment and some of us will never get the Zorro slash down the flank, but the Z4 has those classic roadster traits of a long bonnet and a short bobtail.

The Benz feels big and luxurious on the inside and the SLK represents a huge leap in interior design for Mercedes – it almost feels Audi-like in quality and detail. The interior detailing of the Mercedes highlights, better than any other area, the price gap between the two cars.

There’s more buttons to poke and gadgets to play with (not that everyone agreed that was a good thing), and include Merc’s debut of Airscarf. What? Aside from seat heaters, the SLK’s pews feature a nozzle in the base of the headrest which directs a jet of warm air around your neck and scone. Perfect for those topless winter nights.

The Z4’s cabin, while still featuring all the good gear (satnav, CD, seat heaters) and leather trim, is a more basic affair. It does feature the better seats, though. Proper ones you sit in and not on.

Aside from the muscular looks, Mercedes-Benz endowed the SLK 350 with some serious mechanical heft. The new DOHC V6 is 200cc smaller than the 3.7-litre SOHC unit found in various Benz’s, including the vastly more expensive SL 350, but matches it on peak power and torque, but with a bigger and smoother spread of revs. It is also surprisingly close in spec and feel to the V6 engine in our Nissan 350Z longtermer.

Classic MOTOR: Z4 M v SLK55 AMG comparison

Both V6s displace 3.5-litres and produce similar on-paper numbers – 200kW at 6000rpm and 350Nm between 2400-5000 revs for the SLK, with the Nissan’s mill turning 206kW at 6200rpm and a fitter 363Nm at 4800. Both engines prefer to grunt out their power rather than rev to the rafters, although the Mercedes V6 sounds awesome under load.

The Merc’s six-speed gearbox is heavily sprung toward the centre plane which means lazy one-two shifts can easily become lumbering one-four mis-shifts, and attempts at four-to-five can worryingly go four-three. This is the first manual Mercedes, I’ve driven in recent memory and while the stick-shifter keeps you in the game the smooth seven-speed auto better suits the personality of the Merc.

The Z4’s the complete opposite, with a delicate but direct shift and six tightly-packed ratios keeping the 3.0-litre straight six on the boil. The clutch, too, is a lighter and more precise match than the SLK’s. But with a smaller capacity engine you will need to row the gearbox more often.

Neither car hits a home run with its steering. The SLK’s is heavy but consistently weighted and linear but it lacks any real feedback. That said, the increased weighting is an improvement over most Mercs and the nose grips well under the direction of the heavy tiller. The Bimmer’s electronically-assisted steering is numb and weirdly weighted and takes plenty of familiarisation miles to get up to speed with it.

Overall, though, it’s lightness makes it feel livelier than the Benz, and you’re more willing to throw it around. Sitting so far back in the chassis, however, does exaggerate any flicks of oversteer. At Bang For Your Bucks back in 2003, the Z4 lapped Wakefield Park just a tenth of a second slower than the M3 SMG – seriously impressive stuff given it’s shy 82kW.

It’s during moments like this, or on smooth flowing public roads, that the suspension firmness fades from memory and you appreciate the Z4’s body control and inherent balance. The Bimmer lets you dance up to the limit and even allows you to dangle a couple of toes over the edge, all the while reminding you how much talent is left in the bag.

While the SLK doesn’t have that kind of reputation-bruising squirt around a track, it can still keep the BMW honest on a winding road and take chunks out of the Z4’s lead on the straights. You can use the torque advantage of the V6 – remember, it’s 50Nm fitter in the twist department – and shift earlier or hang on to a higher gear in places where the BMW has you fishing for the right ratio.

Over the same mix of roads the first thing that strikes you is the Merc’s compliance. It’s still firm over broken ground, but the Z4 is seriously stiff, especially in the rear. With the lids closed, the hard top SLK feels stiffer in the body, but drop the tops and it’s hard to split the difference.

Classic MOTOR: Z4 v Boxster v TT Roadster comparison

Before we hand out the gong on this comparo though, it would be remiss of us not to mention the other great German roadster. We were tempted to throw a current model Porsche Boxster into this mix, but we’ve got a drive of the 2005 model.

It’s hard to ignore the price gulf between the two, but the Mercedes does negate some of that difference with higher equipment levels, a bigger engine and the folding hardtop. With the auto, the SLK is seriously impressive, but either way, it represents a better bang than the previous model. The fact it wears a three-pointed star on its nose will be the deciding factor for plenty of buyers and no amount of BMW magic will sway them.

Still, the Bimmer is $18k cheaper and more fun despite the lack of power. And for out and out dynamics, the Bimmer has the SLK cold. Perhaps the Z4’s biggest accomplishment is not that it bested the SLK here, but that it has banished forever, the bad taste left by the undercooked Z3.

We’ll answer the question of the Boxster early next year.

Blast from the past on classic MOTOR

Fast Facts

  BMW Z4 3.0 Mercedes-Benz SLK350
Body two-door roadster
Drive rear-wheel
Engine  3.0-litre, DOHC 24-valve inline six 3.5-litre, DOHC 24-valve V6
Bore x Stroke 84.0mm x 89.6mm 92.9mm x 86.0mm
Compression 10.2:1 10.7:1
Power 170kW @ 5900rpm 200kW @ 6000rpm
Torque 300Nm @ 3500rpm 350Nm @ 2400-5000rpm
Transmission six-speed manual
Weight 1290kg  1465kg
Power/Weight 132kW/tonne 137kW/tonne
Suspension MacPherson struts, coil springs, anti-roll bar (f), 
multi-link, coil springs, anti-roll bar (r)
L/W/h 4091/1781/1299mm 4082/1788/1298mm
Wheelbase 2495mm 2430mm
Tracks 1473mm (f); 1523mm (r) 1526mm (f); 1549mm (r)
Brakes (f) 300mm ventilated discs,
single-piston calipers
330mm cross-drilled & ventilated discs,
two-piston calipers
Brakes (r) 294mm ventilated discs,
single-piston calipers
290mm cross-drilled & ventilated discs,
single-piston calipers
Wheels 18 x 8.0-inch (f & r), alloy 17 x 7.5-inch (f), 17 x 8.5-inch (r); alloy
Tyres Michelin Pilot Sport;
225/40 ZR18 (f), 255/35 ZR18 (r)
Bridgestone Potenza;
225/45 ZR18 (f), 245/40 ZR18 (r)
Fuel 55 litres, PULP 70 litres, PULP
Price $92,000 $109,400

Two cents worth

"Through the twisty stuff, the Z4 has the Merc covered. Feeling hunkered down it seems to have an endless supply of grip, turning in quickly, settling and then steaming out of a corner. On the other hand, the SLK 350 tends to lean into corners, particularly on long flowing corners where it loads up. But what ground it loses to the Z4 through the twists and turns it makes up for on the straight, able to race away from the Bimmer with ease. But for its on-road dynamics and more involving nature, the Z4 gets my money (if I had $92k, that is). Sure it’s quick, but the Merc just doesn’t have the finesse."
– Isaac Bober

Little brother worth the bother?

If you can’t quite stretch the budget to the $100k-plus ask of the SLK 350, but still want a drop-top roadster with that pointy badge on the key fob? Well, the bean-counters at Mercedes have you covered with the $86,900 SLK 200. The new SLK 200 packs a 120kW, and 240Nm punch from a 1.8-litre four-potter with supercharger.

You get a choice of a five-speed manual or a five-cog auto to stir it along. The torque-laden nature of the supercharged engine is a great complement to the slush ’box, so that’s the pick.

But if you’re a Bimmer fan and can’t shell out 92 large on the 3.0-litre Z4, there’s always the $78,500 Z4 2.5. The lower rung Z4 runs a 2.5-litre straight six for 141kW at 6000rpm and 245Nm on song from 3250rpm. Like the bigger engine, the 2.5-litre is a real smoothy and loves to rev – if anything, even more so than the 3.0-litre. 

Matched to the engine is a choice of a five-speed manual or a slick-shifting five-speed auto, but the manual is the way to go if you have any quick driving in mind.

This match-up is somewhat similar to the main story, as the Mercedes is the torque king (though the peak number drops 5Nm to the propeller head, it flat-lines from 3000-4000rpm) and the Z4 boasts all the handling party tricks.

Again, it’s horses for courses, but like the main event, the price advantage is to the BMW making it hard to beat. Again, though, that advantage is somewhat offset by the longer list of standard equipment in the Mercedes.