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    Bob BMW
    A Question of Sport #2016

    / #AC-Schnitzer / #BMW / #AC-Schnitzer-ACZ4-5.0d / #AC-Schnitzer-ACZ4 / #AC-Schnitzer-ACZ4-E89 / #AC-Schnitzer-ACZ4 / #AC-Schnitzer-ACZ4-5.0d-E89 / #BMW-Z4-5.0d / #BMW-Z4 / #BMW-Z4-E89 / #BMW-E89-AC-Schnitzer

    AC Schnitzer endows the #BMW-Z4 with some serious diesel power with a 400hp conversion! A pure sports car with a triple-turbo diesel under the bonnet? Who’d make such a thing? AC Schnitzer – that’s who. And it knows what it’s doing… Words: Auto Bild Sportscars. Photography: Auto Bild Sportscars and AC Schnitzer.

    The ACZ4 5.0d has a bespoke interior and many one-off components such as the exhaust which saves a staggering 19kg.

    Track tester’s notes

    Engine: Because of its nature, it doesn’t rev as sharply as a sporting, normally aspirated petrol engine. The strong torque always leads to a lightning-fast breakaway of the rear end.

    Gearbox: Take everything one gear higher than normal, and shift up at 4500 rpm. Steering: Direct, precise, plenty of feedback.

    Suspension: Perfectly set up for the Sachsenring, almost no roll tendency in alternating curves, just enough spring travel for small bumps. 1.34g transverse acceleration!

    Brakes: Perfectly controllable, no fading, pressure point clear as glass. Brilliant.

    Some of our readers may well remember the AC #Schnitzer 99d that the company built back in 2011 which combined BMW’s ubiquitous 2.0-litre diesel engine tuned to 190hp and 310lb ft of torque with the expensively lightened body of a Z4. Thanks to innumerable carbon components, the eco-sportscar was able to slim down to an unladen weight of around 1300kg. It ran on low rolling resistance tyres and returned, on average, a smidgen over 74mpg which equates to a CO² emissions figures of just 99 grams per kilometre. Sadly this technology platform – costing €149,000, but not for sale – remained a highly regarded one-off.

    It was also regarded – or rather, watched – by a stubborn interested party who was inspired by the concept of a diesel sports car for rather less noble reasons than saving the planet. For him, it was more about torque. The 310lb ft offered by the four-cylinder diesel wasn’t enough for this customer, so he said to Schnitzer: “If you can make a really powerful diesel, I’ll buy the car.”

    So the engine arrived – a freshly donated unit from a M550d. And in a lengthy operation, the AC Schnitzer 99d was transformed into the ACZ4 5.0d. The name is as unwieldy as it is misleading, because the tripleturbo six-cylinder doesn’t have a 5.0-litre capacity – it is, in fact, a 3.0-litre unit. That’s more than enough, though, because straight from the factory this wonder diesel delivers no less than 381hp and 549lb ft of torque and turns the two-ton-plus M550d into a very lively performer.

    But what can this oil-burner add to a lightweight Z4, even when on top of everything it’s tuned by software intervention – an increase in injection quantity and, consequently, a rise in boost pressure – to 430hp and 620lb ft? And it gets better: our performance measurement actually recorded 445hp. Will the engine and chassis separate themselves from the bodywork during the traffic light grand prix? Will the propshaft tie itself in knots? Or will the rear wheels simply spin helplessly in every gear?

    Somewhat surprisingly none of that happens as Schnitzer transplanted the complete rear axle from the E92 M3 (including the limited-slip diff) and fitted 9.5-inch wide forged alloy rims shod in very grippy 265 Michelins. As a result the Z4 actually transmits all that power and torque to the Tarmac remarkably well. Naturally it is possible, with the driving aids turned off, to transform the rear tyres into small black crumbs with a large dose of the throttle. However, anyone with even a hint of feeling in their right foot should be able to get smoothly off the mark (even in the wet), and rapidly shift up through second and third, and only fully press depress the throttle in fourth gear at the earliest.

    The secret of the fundamentally fine controllability and high output of the BMW diesel lies in the complex valve control of the three turbos: a small high-pressure turbo ensures spontaneous response to even the smallest tap on the gas pedal. From around 1500rpm, the large low-pressure turbo joins in and provides plenty of volume and torque. Stage three comes in at around 2700rpm: a bypass line now supplies exhaust gas to a third small high-pressure turbo. From here up to maximum revs at 5400rpm, all three turbos work together to push the huge air masses into the combustion chambers for maximum power. Yet the driver notices nothing of these processes, simply enjoying the lag-free, harmonious but extreme power development up to maximum revs. So on the motorway, eighth gear is enough for all situations. Hectic flips of the shift paddles, kickdown, high revs – why bother? Just engage top gear in manual mode and press the throttle – and enjoy acceleration to a level not experienced before. The speedo needle climbs from 100 to 200km/h (62-124mph) as quickly as it does from zero to 100km/h in other well-powered cars.

    The vehement thrust however ends unexpectedly early at a measured 279km/h (173mph). Is this down to the short-ratio M3 rear axle, which was really intended for a high-revving V8 petrol engine? No, because at top speed in eighth gear you’re only at 4300rpm and the diesel has enough breath for a further 1100 revs. Roman Fenners of AC Schnitzer thinks the cause lies in a protective function of the gearbox software, to prevent overheating.

    But even 279km/h feels very, very fast in the diesel Z4: the solid hard-top of carbon fibre reinforced plastic, which replaces the standard steel folding top and its complex electro-hydraulic folding mechanism, saving 56kg, produces a noticeable interior noise level. And the very low race-style suspension setup with short spring travel, pronounced negative camber and very wide tyres on the front axle, calls for strong arms on bumpy and grooved surfaces.

    When we head off to the track, and specifically the slalom test, what was a disadvantage on the motorway here transforms into an advantage: the slightly nervous agility of the Schnitzer Z4. The pleasantly heavy steering, which feels beautifully taut and extremely precise, gives excellent feedback from the road and allows the coupé to be steered through the cones with millimetric precision. Understeer? Only when the tyres haven’t warmed up. Oversteer? Only when the throttle is used as an on/off switch.

    The nose-heaviness is successfully countered by AC Schnitzer with 265 tyres on the front too – instead of the mixed tyres with considerably narrower format on the front which come on the standard Z4 top model, the sDrive35is. That car, with 340hp, weighs in at 1601kg – 123kg more than the Schnitzer with the heavy diesel unit up front. As well as the solid hard top of carbon fibre reinforced plastic there’s also a CFRP bootlid (minus 34kg), a lightweight rear silencer (minus 19kg), CFRP bucket seats (minus 35kg) and forged alloys (minus 25kg) which all save weight.

    Our race ace, Guide Naumann, now takes over the controls for our hot laps of the Sachsenring to record a lap time. For this we fitted Michelin Cup 1 semislicks which in the cool autumn temperatures, despite several warm-up laps, never quite reach their optimum working temperature. But the Schnitzer still steers excellently into the Coca-Cola Kurve after the start-finish straight without understeer. The suspension is perfectly set up for the Grand Prix circuit, handling the alternating corners without too much body roll, but was still soft enough to swallow the small bumps of the Sachsenring. For the Nürburgring North Loop we reckon this setup would, however, offer too little spring travel.

    When accelerating out of comers, the triple-turbo has too much power especially in conjunction with an only lightly loaded rear axle. If you press the gas on entry to the apex, the rear kicks out suddenly, so you take it in one gear higher than usual, applying the gas late and progressively. But the rear still calls for your full attention, such as in the fast right kink downhill at 180km/h, where it tries to overtake the front! With the diesel roaring loudly at race speed, you can’t hear the rev limiter so you can’t shift based on engine note. Instead you have to keep glancing away from the track and over to the rev counter. The needle, however, should never drift above 4500rpm because higher revs would only cost time and you’ve still got all that solid torque available in the next gear.

    The Schnitzer braking system, with six-pots on the front, remains unmoved lap after lap – no fading, no lengthening pedal travel, just a pressure point set in stone, combined with perfect controllability. Naumann’s summed up the ACZ4 5.0d on track thus: “Race-style suspension with very high and correspondingly narrow limit zone. Overall high grip level but the huge torque proves a killer for perfect lines. With a slightly higher exterior temperature or a softer tyre compound, certainly another second could have been squeezed out.”

    The comparison with the Schnitzer Z4 99d mentioned initially, which we thrashed around the Sachsenring in spring 2013, is interesting: the 200kg lighter car, which also had 255 less hp, took over five seconds longer. A good time in itself, on a par with a current Audi S4 with 333hp. Or expressed in other words: the six-cylinder diesel is a real powerhouse. For the record the ACZ4 5.0d recorded a time of 1:37.27 on a cold track… a F82 M4 DCT Coupé managed a 1:37.74 under warmer conditions. And that makes the ACZ4 5.0d the fastest diesel we’ve ever driven around the Sachsenring.

    And how does the Schnitzer feel in comparison with a standard Z4 35is? Another world away. The softly set up standard BMW, trimmed for comfort and ‘safe’ understeer, feels almost stolid, almost unsporting. Today’s standard, forgiving car sadly can’t offer the sharp handling which you associate with the first generation Z4 (E85).

    Overall we’re left with an impression of a machine that really does stir one’s emotions. Emotions? In a diesel? Which occasionally breathes a hint of diesel oil into the interior? Which on starting rattles like the neighbour’s rep-mobile? Which growls darkly at the front but can’t sing melodiously from the exhaust? Yes! Because the baffled looks of a few car nerds who notice that the engine note and car don’t go together, are pure gold. And then there’s the fab feeling of driving something unique, special and exotic.

    This unique, special, exotic car could, however, make you curse in everyday use. For example, in the supermarket car park when you have to unlock the carbon fibre bootlid in two places, then take it off completely and put it to one side before loading your shopping. Then there’s the short-travel suspension which the driver has got used to but passengers will never take to. Add to that the always high interior noise level (yes, even the sound insulation has been scrimped on) and that when reverse parking it’s very hard to see the rear extremities… and the former Roadster has now become a year-round closed top coupé. Oh well, you can’t have everything!

    It’s not a cheap conversion, though, even if using a secondhand Z4 as a basis. Almost all the internals have been thrown out and the new engine and eightspeed automatic alone cost nearly €50,000. Then it goes without saying that the suspension and brakes have to be uprated to match the huge power gain. The interested party could save a few euros though by skipping the lightweight components.

    Either way, AC Schnitzer has come up with a cracking package for this car. A heavy, extremely powerful diesel in a delicate lightweight coupé? We were sceptical, but our scepticism gradually developed into unalloyed enthusiasm during the test – AC Schnitzer has successfully pulled out all the stops to create this extraordinary concept.

    Schnitzer has stripped a huge amount of weight from the Z4 thanks to the extensive use of carbon fibre such as these front wings and the new roof.

    TECHNICAL DATA #BMW-AC-Schnitzer ACZ4 5.0d
    ENGINE: Six-cylinder, triple-turbo diesel, 24-valve / #N57S / #BMW-N57S / #N57S / #BMW-N57 / #N57 / #N57-AC-Schnitzer /
    CAPACITY: 2993cc
    BORE/STROKE: 90.0 x 84.0mm
    MAX POWER: 430hp @ 4400rpm
    MAX TORQUE: 620lb ft @ 2000-2400rpm
    0-62MPH: 4.0 seconds
    0-124MPH: 12.9 seconds
    QUARTER-MILE TIME: 12.31 seconds
    TOP SPEED: 173mph
    ECONOMY: 20.6-39.8mpg (27.2mpg on test)


    ENGINE: Triple-turbo straight-six diesel, retuned

    TRANSMISSION: Eight-speed automatic

    FRONT BRAKES: 380 mm, vented and slotted, six-piston callipers

    REAR BRAKES: 370mm, vented

    WHEELS: AC Schnitzer Type VIII lightweight forged wheels ‘BiColor Orange’, 9.5x19 inches

    TYRES: Michelin Pilot Super Sport 265/30 ZR 19 Y

    ROOF: Replacement of the two-piece, electrohydraulically operated, folding steel roof with a CFRP hard-top saves 56kg, the #CFRP bootlid a further 34kg. The roof is now fixed and the bootlid can only be opened by removing it fully.

    GLASS: The rear screen and rear side windows (which can no longer be lowered) are made of lightweight polycarbonate.

    SUSPENSION: AC Schnitzer racing suspension, fully adjustable in compression and rebound stages.

    AERODYNAMICS: AC Schnitzer carbon front spoiler, AC Schnitzer carbon sports wings, AC Schnitzer bonnet vents, AC Schnitzer rear spoiler (two-piece), AC Schnitzer carbon rear skirt insert.

    INTERIOR: Interior trim elements painted, carbon racing seats with #ACZ4 5.0d logo, AC Schnitzer aluminium footrest and pedal set, AC Schnitzer instrument cluster.

    PRICE: €114,000 (one-off build cost)
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    Bob BMW
    Little Zed Riding Good 2015 – Road test #BMW-Z4-E89 / #BMW-Z4-Drive28i-E89 / #BMW-Z4-Drive28i-AC-Schnitzer / #AC-Schnitzer / #BMW-E89 / #BMW-E89-AC-Schnitzer / #BMW-Z4-Drive28i-AC-Schnitzer-E89

    We test the AC Schnitzer-tuned #BMW-Z4-sDrive28i to see what it’s capable of. AC Schnitzer has taken BMW’s Z4 sDrive28i and given it a comprehensive makeover bringing out the sports car that was lurking underneath Words: Bob Harper /// Photography: Max Earey

    On reflection I think I have probably been a little harsh on the second generation #BMW-Z4 over the years, but it’s a car that I’ve never fully gelled with. Conversely I was quite keen on the original Z4 — yes, its electric steering wasn’t the best and its cockpit was a little tight — but it always felt eager and sporty and was always a machine that I looked forward to driving.

    Maybe I’m not really the target audience for the new car as BMW made a conscious decision to make the latest (E89) Z4 more of a cruiser than a bruiser. It said focus groups made up of owners and potential owners brought up the fact that they didn’t want a full-on hardcore sports car. Comfort and refinement seemed to come higher up the list of priorities than the ability to run rings around the Boxster. Perhaps that was the death knell for the overtly sporting Z4 though; BMW tried to make a Boxster-beater with the original Z4 and it failed. Thus the new car is seen more as an Audi TT and Mercedes SLK competitor but I’ve still struggled to get to grips with the E89.

    It is more refined, the cockpit is bigger, the roof is a work of genius… but I still think it could be a little bit more sporting and retain that refinement. Perhaps the biggest disappointment for me was the arrival of the 35iS incarnation. With 340hp on tap this really should have been the answer to my prayers but to me it fell well short of my expectations and showing it a sinuous stretch of Tarmac led to a disjointed and less than satisfying driving experience. The front and rear sections of the chassis seemed to have been designed by two different people who were not allowed to communicate during the process and trying to drive it quickly was a frustrating experience.

    Doubly so as when we went to Germany to sample Schnitzer’s take on the 35iS Seb reported it was an awesome piece of kit with underpinnings to provide a platform for the stunning straight-six under the bonnet. I wasn’t able to make that trip so there was always the nagging doubt that maybe Seb and I have different chassis preferences or that super-smooth German road surfaces had clouded his judgement.

    Thus when Chris Rossiter who is the face of AC Schnitzer in the UK called to say he had a fullyconverted Z4 28i at his Norfolk HQ that I could try, I jumped at the chance. This was a car that was actually built by Chris as a demonstrator over a year ago and just about the first customer who drove it bought it! It returned to Chris to be sold again after the first owner decided to move on and since we went to sample it it’s already found a new owner again. And having put this Z4 through its paces I can confidently say he must have one of the best E89 Z4s in the country.

    The pristine Z4 that greets us at AC Schnitzer UK is certainly a sight for sore eyes and while the Schnitzer enhancements are pretty subtle for the most part it looks very nicely done and visually at least adds some of the pizzazz missing from the standard offering. Normally I’d be having a good look at the spec sheet before driving the car but the weather forecast isn’t the best and with the prospect of more storms on the way we nab the keys and without further ado disappear off to get some pictures in the bag and some driving impressions on relatively dry roads.

    Having carried out a recce before arrival we’ve found a photo location a scant distance from base and in order to keep car cleaning to a minimum we tip-toe our way around the puddles and generally drive the Z4 like your maiden aunt. When I originally spoke with Chris Rossiter he was effusive over the car’s Schnitzer suspension setup but after five minutes behind the wheel I’m beginning to wonder how his idea of a good ride and mine can be so wildly different. Bobbing along at 20-30mph the car feels stiff and fidgety over bumps and ruts and I’m beginning to wonder whether this might be a step too far in terms of setup.

    As usual, though, getting the pictures takes first priority and after we’ve given the car a quick rub down it’s time for Max to work his magic with his Nikons and it gives me a chance to drink in the details and look at the spec sheet. The bottom line for the complete conversion is £12,995 – that’s a saving of nearly £2000 if all the parts were fitted separately – and that includes everything, parts, painting, labour, VAT, the lot. It’s certainly a fair chunk of cash but you can always cherry pick the parts that you like and if you visit the AC Schnitzer UK website you can find prices for each individual item, or what’s involved in the complete conversion.

    As far as the looks are concerned up front there’s a carbon fibre addition to the lower front spoiler that adds just the right amount of visual drama without going over the top, although having said that in my part of London that’s infested with speed bumps I’m not sure how long it would last! There’s a new set of front wings, too, sitting aft of the front wheel and below the bonnet line that feature little cooling grilles and a ’Chromeline’ set of slats, the latter are optional and could be left off if you so desired. I’m not a massive chrome fan at the moment – it suits some cars better than others, and given the rest of the Z4 more or less does away with chrome design elements I’d be inclined to leave them off.

    What does suit the car particularly well are the 19-inch Type VIII AC Schnitzer alloys that are wrapped in Michelin Pilot Super Sport tyres. These wheels can be ordered either in a traditional silver finish or, as you can see here, a silver and black bi-colour combination and they measure 8.5x19-inches at the front and 9.5x19-inches at the rear with 225/35 and 255/30 section rubber respectively. At the rear there are a pair of winglets that adorn the bootlid but other than that, bar a few decals, it’s as it came from the factory as far as styling is concerned.

    One thing that’s most un-factory like is the lowered stance of the Schnitzer Z4 which is a result of the car being fitted with Schnitzer’s fully-adjustable RS Suspension setup. Ride height, compression and rebound damping can all be adjusted to suit your personal taste and I’m itching to give it a proper evaluation and start to wonder if Earey will ever finish with his cameras. The last shot to be done is an underbonnet view and two things strike me as we open up the Zed’s large clamshell. First, the engine really is set back so far in the chassis that it’s not really stretching the truth that much to call it a frontmid-engined setup, and when compared to the sixcylinder machines this must really bring about improvements in handling, especially when you consider that the 28i weighs a useful 105kg less than the six-cylinder 35i. The second thought is that I’ve yet to mention or think about the power upgrade this Z4 has been endowed with. As standard the 28i puts out 245hp and 258lb ft of torque but thanks to the ministrations from Schintzer’s boffins the tuning box that’s fitted to this car those figures have been boosted to 294 and 310 respectively. That’s just down by 12hp on the 35i version but torque’s up by 15lb ft. And if you look at the power-to-weight ratio this Schnitzer Z4 actually beats the Z4 sDrive35i with 199hp per ton compared to 193 for the six-cylinder machine. It should be rapid, too, with Schnitzer quoting a 0-62mph time of 5.5 seconds (an improvement of 0.2 seconds) while a whopping 2.9 seconds has been shaved off the 50-112mph time.

    Impressive stuff indeed, and now I can finally have a proper play as Max has competed the static shots and we just need to get some action in the bag. Previously I’ve taken a little time to warm to BMW’s new four-cylinder units but I don’t know whether it’s a result of Schnitzer’s ministrations or perhaps being able to hear it rather better in the Z4 but I’m coming to the conclusion that it’s not a bad little powerplant. It certainly feels every bit as fast as Schnitzer’s figures would suggest and at certain points in the rev range it’s pretty tuneful with almost a flat-four-style warble to it. The ratios in the six-speed manual seem perfectly attuned to the engine’s power characteristics, too, and it’s a joy to either chase down the redline or short-shift and let the ample torque take the strain depending upon your mood.

    Perhaps the biggest revelation is the suspension setup. What felt somewhat uncompromising at really low speeds soon becomes far less intrusive as the speeds rise and by the time you’re up to cruising speed it feels just like a proper sports car – firm but by no means filling-loosening. The real improvement, though, is in the Z4’s handling and Schnitzer’s RS setup really does endow the car with the sort of behaviour you’d expect from a BMW. Even on these slippery, cold, damp roads there’s plenty of grip from the gumball Michelins but there’s a finesse that’s totally lacking from the standard car. There’s a decent level of communication coming back through the steering and any movement at the rear is telegraphed back to the driver through the seat of the pants. It’s as if the standard Z4 is operating on a dial-up system and the Schnitzer one has gone fibre-optic. I’m not feeling brave enough to switch the DSC off on the tight lanes around here, but selecting the halfway house DTC mode allows enough slip from the rear on the greasy surface to let you have a huge amount of fun without risking a car/hedge interface. It’s genuinely exciting to drive and has restored my faith in the Z4.

    As I said at the beginning perhaps I’m not in the right demographic for Z4 ownership, but I love the way the car looks and it now packs the performance to match the style.

    AC Schnitzer UK
    Tel: 01485 542000

    It’s as if the standard #BMW-Z4 is operating on a dial-up system and the Schnitzer one has gone fibre-optic.

    TECH DATA #2015 #BMW #AC-Schnitzer-ACS4-28i
    ENGINE: #N20 four-cylinder,
    16-valve, turbocharged
    CAPACITY: 1995cc
    MAX POWER: 294hp @ 5800rpm
    MAX TORQUE: 310lb ft @ 2500-3000rpm
    0-62MPH: 5.5 seconds
    50-112MPH: 11.9 seconds
    TOP SPEED: 155mph (limited)
    EMISSIONS: 159g/km
    WEIGHT (EU): 1475kg
    ENGINE: 294hp performance upgrade
    WHEELS & TYRES: AC Schnitzer Type VIII alloy wheels (black or silver bi-colour), 8.5x19-inch (front), 9.5x19-inch (rear) with 225/35 and 255/30 Michelin Pilot Supersport tyres
    SUSPENSION: AC Schnitzer RS suspension package (fully adjustable for ride height, compression and rebound damping).
    STYLING: AC Schnitzer carbon front spoiler, Sports front wings with chromeline set, boot spoiler set, decals.
    INTERIOR: AC Schnitzer pedal set
    COST: £12,995 (complete package including all parts, labour and VAT)

    There are plenty of tasty exterior upgrades on the Schnitzer Z4 from new front wings with Chromeline elements to boot spoilers and a carbon front spoiler.
    If you look at the power-to-weight ratio this Schnitzer Z4 actually beats the Z4 sDrive35i.
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