6,000rpm. All six pistons are covering 18 meters per second but the car is travelling significantly faster. At this point, most engines are begging for the clutch to take the strain away before starting the assault all over again, but not the CSL, because it's just getting into its stride. This marks the moment the straight-six comes on cam and stampedes towards 8,000 revolutions and 355 rampant horsepower, that glorious carbon fibre echo chamber emitting its siren call.

The pitch climaxes, the reverb intensifies, the hairs on the back of your neck begin to rise and the world around morphs into a blur. It’s a song so full of motorsport mojo every single one of those combustion cycles is seared onto your psyche, the good vibrations fizzing along the structure into your fingertips, filtered through a cocktail of Alcantara, aluminium and composites. I’ve no idea about the acoustic properties of weaved carbon but from where I’m sitting the Sydney Opera House should be lined in the stuff.

Snap the upshift paddle to attention - keep the foot in, don’t lift - and receive a Jean Claude Van Damme to the back of the neck. The oft-derided SMG gearbox drops me right back into the 6-8 land of milk and honey. Right now I’m not craving three pedals - at this speed it’s prudent to have both hands on the wheel…

CSL. Three innocent, unassuming letters individually, but once combined they take on an almost mythical status, especially in BMW folklore. It’s a Bavarian acronym reserved for very special vehicles, ones designed to compete at the absolute sharp end of the performance car envelope. It stands for Coupe, Sport, Lightweight, and it’s only been rolled out twice in the company’s 108-year history. Once adorned, the manufacturer of ‘the ultimate driving machine’ is projecting a level of confidence and bravado that dwarfs even its famous tagline. That’s because a CSL is all about winning, and to hell with the profit margins.

The key letter in the trio is the L, because nothing is a greater enemy to performance and dynamics than excess kilograms. When it comes to upping the ante, a manufacturer has two choices - increase the horsepower, or decrease the mass. The former is the easiest route, the latter is far more difficult and costly but also purer, because shedding weight improves dynamics in all directions of travel, not just acceleration. It lessens the load on the tyres, the brakes, the suspension and the structure. Every vanquished kilo and luxury promotes a spiral of benefits that leads towards driving nirvana.

The original 1972 CSL was based upon the E9 chassis - specifically the 3.0csi - and was the result of the fledgling M Division homologating the car for touring car racing. Power was upped to 203bhp whilst weight was stripped from the car by using thinner steel, deleting trim and removing soundproofing. You might know it by its more famous later name - Batmobile - due to the wild wings and aero kit added to the car in 1973. So extreme were the additions, they were classified illegal for use on German roads so BMW stuffed them in the boot of the car, instructing owners to fit them post-sale in order to circumvent the regulations.

Going to such lengths paid off for BMW however, as the CSL cleaned up on race tracks around the world, winning the European Touring Car Championship an incredible six times in seven years from 1973-79, whilst also collecting a class win at the Le Mans 24hrs.

Sadly, the 2003 M3 CSL never got to see the chequered flag unless in the hands of privateers, but the competitive spirit remained. That spirit found its epicentre at the Nürburgring, with a key development target of a sub-eight-minute lap - unheard of at the time on a production car, but one the 911 GT3 had breached with a 7.54 time. The standard E46 M3 - itself no slouch and a performance car benchmark - ran an 8.22 against the stopwatch. M had to find 1.7 seconds for every mile of the Green Hell, and the renowned 3.2 straight-six was already making 338bhp. The easy route of turbocharging was not an option. Gerhard Richter was still in charge and his rule and purity of vision were absolute - M cars had to be naturally aspirated. Harder, faster, stronger was the only solution.

BMW returned to Colin Chapman’s guiding philosophy of ‘just add lightness’ with a Germanic twist of ruthless efficiency. Not only is the car lighter, it's targeted mass saving in important places - up on high and at the extremes of the car, lowering the centre of gravity and moving the heft inwards. Take the carbon fibre roof, the first of its kind and one of the great engineering statements killing two birds with one stone - more strength for less weight.

Another but no less trivial benefit is it looks Bruce Lee cool and was a hugely expensive manufacturing endeavour just to save 6kg. This utilization of composites and elements flows across all of the CSL’s surfaces. Low down we have aircraft grade glass fibre thermoplastic bumpers bonded to dual carbon splitters at the front and a carbon diffuser at the rear. The boot lid with its beautifully integrated ducktail is moulded from the same material. The bonnet is formed from Aluminium and the rear glass is thinner.

Under the skin are further savings. All sound deadening north of the waistline has been removed and the microfilter housing is a special lightweight design. The battery - as always placed in the boot of a BMW for better weight distribution - is taken from the Mini Cooper S, trimming a useful 5kg. It sends charge down a wiring harness which is stripped of all non-essential loom, saving 1.5kg. The boot floor is not made of cardboard as Jeremy Clarkson’s infamously creative review put it, although given the M3’s propensity to crack its rear subframe it might as well have been.

Inside, the CSL has an interior that oozes DTM swagger. The extensive use of lightweight materials continues, with both the lower centre console and door cars fashioned from glossy carbon fibre. Gone are the heavy, comfortable, electrically operated leather armchairs of the standard M3, replaced by deep-dish bucket seats based upon the Recaro SPG trimmed in Amaretta with glass fibre shells. Unlike the standard car, they’re fixed back, meaning the only way to adjust the upright position is via a set of spanners. The rear seating bench has also been parred back and lightened, whilst the steering wheel has been stripped of all buttons and distractions - the sole remaining one activating the special M track mode for the traction control. It’s also trimmed in Alcantara, complete with the traditional M tricolour stitching.

The sub-eight target also meant early on the decision was made to only supply the CSL with the SMG II transmission, unlike the regular M3 where it was an optional extra over the six-speed manual. Cutting edge technology for the time, the advent of the dual-clutch gearbox has aged SMG in many respects, although not as badly as the internet would have you believe, but more of that later - what wasn’t in doubt is the automated single-clutch transmission was quicker than a professional driver with three pedals.

Underneath the aforementioned aluminium bonnet was the CSL’s signature dish - its three Michelin Star carbon airbox. The M3’s S54 power plant had already won international engine of the year three times on the bounce, and with a specific output of 105.6bhp/litre, six individual throttle bodies and an 8,000rpm redline there was little headroom for improvement. BMW turned to Formula One technology. Fed directly by the asymmetric hole in the front bumper, the carbon airbox acted like a black hole for oxygen before the singularity of ignition.

Such is the volume of the chamber, it bypassed the need for a mass airflow sensor, meaning for the first time in a road car an engine’s ECU had to calculate the amount of air rushing in and mix the fuel accordingly, just like in F1. A beefed-up processor was therefore required - the DME memory is doubled whilst the processing speed is up by 25%. Combined with revised camshafts - 268° inlet compared to 260° of the standard M3 (same lift), and 264° exhaust compared to 260° (same lift), modified exhaust valves and a 200cel catalytic converter, the CSL makes 355bhp at 7,900rpm and 273lb/ft at 4,900rpm - increases of 17bhp and 4lb-ft. The S54 engine had reached its zenith - specific output was now 111bhp/litre with heightened throttle response - but what really mattered was the dramatic shift in character brought about by the new airbox.

To cope with the demands of the Nordschleife, and to account for its lower mass, the CSL’s suspension received some thorough attention. Revised springs cut the ride height by 10mm whilst the Sachs dampers were re-tuned with modified compression and rebound settings attached to new bump stops. A strut bar braces the suspension turrets for sharper turn-in, both anti-roll bars were thickened for greater directional stability and for the first time, the front bar was hollow.

Another component lightened were the rear lower control arms, now crafted from aluminium like their front counterparts, and the new arms were also fitted with uni-ball joints rather than rubber bearings. Bolted to the suspension were new, wider yet lighter BBS alloy wheels - 235/35/R19 at the front with 265/30/R19 at the rear - which widened the track and necessitated factory rolled rear arches to fit. The rack and pinion steering set-up was also enhanced - a new rack with a sharper ratio of 14.5:1 (vs 15.4:1 standard) turned through a new kingpin for improving geometry.

Less thorough was the attention the M division paid the CSL’s stoppers. The regular E46 M3’s brakes were a known track day laughing stock, so it raised eyebrows when the CSL retained the standard cars’ single-piston swing caliper arrangement and rubber lines, even if the discs were 20mm larger in diameter at the front.

The final piece of the puzzle was wrapped around those achingly desirable and oft-imitated alloys - the original specification Michelin Pilot Sport Cup tyres. A far cry from today's Cup 2 Connect, the Ones made a Pirelli Trofeo look like something off a Toyota Prius. Standard M3 tyres were available in the new fatter size, but owners who craved maximum attack famously had to sign a disclaimer due to their poor performance in chilly or slick conditions. Driving with Cup1 in torrential rain must have been akin to the Russian Roulette scene in Deer Hunter, but with an internal combustion engine. On the flip side, if these owners produced evidence of a racing license, BMW would give them the option of deleting the 155mph speed limiter, freeing up the CSL to hit 174mph given enough autobahn or a tailwind down the Dottingher-hohe straight. It was a bold move at the time, but less impactful in a modern world, where even hot hatches offer a Cup tyre from the factory.

The cumulative effect of all the changes was extraordinary. Kerb weight without air conditioning or audio? 1,385kg. With? 1,415. The CSL is lighter than a standard E46 M3 to the tune of 110kg, a margin that surely increases once the inevitable optional extras are factored in - indeed German magazine Sport Auto independently verified the CSL at 1,420kg with a full tank of fuel, compared to the regular press M3 at 1,570kg. The grip generated by the high-performance tyres saw the CSL record a peak lateral G of 1.4 during the magazine’s famed Supertest, more than making up for the CSL’s slightly inferior straight-line acceleration against the GT3 - 0-124mph 14.8s v 16.7s - where the CSL recorded a 7.50s Nordschleife lap time in the hands of the same driver. Job done, for £17,000 less and a deficit of nearly 30bhp.

You wouldn't know such drama is to come by twisting the CSL’s key. There is no Shakespearean flare of revs on startup, the S54 just settles into a muted, smooth idle. The car's orange temperature warning lights placed around the circumference of the rev counter in 500 rpm increments have found their voice again whilst pleasantries were exchanged, plans hatched and idiosyncrasies of the car discussed.

Walking around the CSL, it's hard not to fall for the restrained styling - the aggressive stance, beautifully judged flared arches, evocative ducktail spoiler, bonnet power dome and subtle carbon details contrasting with the metallic Silver Grey paintwork - one of only two colours the CSL was offered in, the other being Sapphire Black. Purists might argue a special M car like this deserves its own individual colour traditionally named after a race track, but there’s no denying whatever the hue the CSL is a handsome, timeless design that foregoes attention-seeking wings.

Pottering out of town, the orange segments extinguish one by one as the engine works its way up to temperature - the goal is to turn them into their secondary function as quickly as possible - shift warning lights. The grey-backed dialled are clear and precise, there’s an oil temperature gauge replacing the usual mpg counter, an 8,000rpm redline and a 180mph speedometer. All the information a keen driver needs. It makes a folly of current shapeshifting digital read-outs. Why ‘fix’ things that aren’t broken?

What does appear to be broken is the SMG gearbox. Well, at least the folly of running it in automatic mode whilst I acclimatise leaving town. The CSL’s zealous throttle response and misguided anticipation of my intentions see us pogo-ing around like a learner driver. Best to knock the stubby little gear lever to the right and tell the autopilot to take the rest of the day off. Much better, but the changes still don't come as fast as I’d like from paddle pull to meshing of cogs. Up the little volume control button we go. Another incremental improvement. I’ve been informed the oil in the gearbox takes even longer to thin than what's in the sump.

There’s no holding back the smile though. The slightest pressure on the throttle pedal sees the intake decibels soaring and the car surging forwards as bystanders' heads swivel around in curiosity or disapproval. Even shackled by suburban speed limits, there’s little doubt the CSL possesses a mighty engine. Negotiating junctions the steering is heavy and the ride has little give - this isn’t the cars’ natural environment, but surely if you buy into the ethos of the CSL, you can tolerate the firmness when loping along?

Then it happens - down to the final amber light. Permission for take-off coincides directly with the appearance of a long straight running alongside Llyn Celyn. It would be rude not to. I thumb the Sport button and the CSL is just as eager, the car leaping forwards on its own accord. It might seem like overkill to have such a device on a machine as hardcore as this, but it really does ramp up the throttle response. It also handily wedges the intake flap in the open position from 3,500rpm rather than the regular 6,000rpm. Just don’t try to parallel park whilst it's depressed.

Full throttle is the trigger for a wall of noise to erupt, the bellow first mimicking the deep anger of an early Diablo before evolving into the fury of a McLaren F1. Lighting the blue touch paper in a CSL is one of the great motoring experiences and it's not an overstatement to say so given the inherent links between the F1’s motor and the M power straight-six. The aural assault doesn’t intimidate, however, because the straight-line performance is of the goldilocks variety - just enough to thrill, not so much you can’t enjoy wringing the car out to its full potential without constantly fearing a court summons.

There’s no doubt the S54 does its best work the faster it spins, but the low mass has also effectively massaged the torque output - the CSL has a greater amount of twist per tonne than the 4.0L V8 E92 M3 that followed - 192 plays 178, meaning the newer car will have to be deep into fourth gear before any horsepower advantage is deployed. Sure, a modern turbocharged M power plant might be a lot more bombastic, but in terms of raw emotional pyrotechnics, the CSL is in a completely different dimension.

The intake even makes the car totally immersive when you just settle into a rhythm, carving along the A4212, flicking between ratios whilst surfing the mid-range - you don’t have to be a Horst von Saurma to enjoy the CSL. But when you finally turn off onto that writhing B-road that seems to have no destination or purpose other than to entertain and the red mist descends, boy does the CSL respond. There’s zero slack to the handling - it doesn’t dive under hard braking, roll into a turn, or squat during acceleration. Both front and rear axles respond to steering inputs with immediacy, whilst rapid direction changes carry little inertia. The car communicates the precise level of grip via the pressure building in my rib cage, hips and thigh as the racing bucket initiates a Bear hug - for a car nearly two decades old, the CSL generates a deeply impressive level of adhesion. Everything builds in a linear fashion, in fact, on road-biased the CSL flat out refuses to understeer no matter the radius or angle of a turn, and thanks to the dialogue between Amaretta and buttock, you’re aware of the exact moment the rear will transition into oversteer - it’s as if the side bolsters are hardwired into the stability control’s yaw sensors.

Early road tests found the huge grip generated by the Cup tyres resulted in sharp break-away characteristics when the laws of physics were exceeded, but the friendly balance of the M3’s natural 50:50 weight distribution ensured the handling was always faithful once it let go. Today, on more road-biased rubber, that edge is more malleable. You get the feeling the CSL would be happiest with the rear tyres carving an ever so slightly wider line than the fronts, the DCS’s track mode parameters satisfied, the M differential still finding drive, creating a sweet spot to operate in just before the need to apply anything more than a quarter turn of opposite lock. I’m no Keiichi Tsuchiya, and we’re on the public road, so such antics will be kept in check, but my courage runs out long before the CSLs. This is a joyous chassis, and the only time you want to get out of it is to brim the tank with 99 ron and wipe all the bug stains from the windscreen.

The handling is complemented by accurate steering. The E46 M3 was never famed for its steering feel, however, the CSL’s revisions and ten years of exposure to electrically assisted racks means I’m instantly dialled into the feedback being offered. There’s more going on through the steering of this car manoeuvring around a car park than many current sports cars at maximum attack. The lampooned brakes are also never anything but strong at road speeds - although circuit work could be a different matter altogether - whilst the tense low-speed damping morphs into ultimate control and stability once prompted into action.

Onto the elephant in the room - the gearbox. There wasn’t a fence when it came to SMG. The prosecution launched its shells by accusing the uncooperative transmission of being the ruination of a potential all-time great. Manning the trenches was the defence, claiming those who write the car off haven’t spent enough time in one, that it takes a lot more exposure than a short test drive to learn its foibles. In-between sits a No Man’s Land laced with Marmite and internet forum nonsense.

Part of the problem lies with perception – SMG essentially remains a manual gearbox underneath the surface, the operation of swapping cogs has just been delegated to some robotized hydraulics and an electronic processor. Smooth it is not, however, some opinions may be influenced by an experience with the standard M3 and SMG. But the CSL ran revised software and its launch control was also more aggressive – disengage the stability control, hold the stubby little gear-lever forwards, press the brake and floor the throttle, then release. The CSL will catapult forwards and providing you don’t waver in commitment, it will upshift for you bang on the last revolution in each gear, whereas the standard M3 will clatter into the limiter. Given how quickly the straight-six spins, it’s a useful aid.

The gearbox clicks at maximum attack, getting the most out of that possessed engine, but more crucially you still have input with SMG, you have influence on the car’s behaviour, it still engages you in the process of proper driving. Where it suffers is in pottering around, jerking and stuttering between ratios - the trick isn’t a well-timed lift as often purported, but to actually keep your foot in because the SMG processor has a limited capacity to learn your driving habits and adapts itself accordingly. Too much time mooching around will result in a car that likes to slip its clutch, so every now and again performing what’s known as an adaption reset is a wise manoeuvre. The best technique when your hair isn’t on fire is to keep it simple - lock the car into S4 mode, and never, ever lift.

One area SMG is immune to criticism is in the downshifts, which are utterly sublime. Each one is accompanied by a perfectly timed blip of the throttle. It’ll even heel and toe seamlessly into first for you without complaint. SMG still has another party piece to play though. Summon up some confidence to pop a couple of brave pills, turn the stability assistance fully off and a secret Narnia mode is unlocked – S6. The shifts now come hard and fast as every ratio thumps home with the speed and brutality of a Mike Tyson haymaker. Unleash a CSL on track in S6 and suddenly it all makes sense and the criticisms evaporate.

But North Wales isn’t a race track, it's a playground - one that might be better still with three pedals. Understandably, a growing number of CSL owners are taking advantage of Everything M3’s excellent manual conversion package. The Banbury concern sells a DIY kit from £3,500 upwards or can perform a drive-in, drive-out service for a little more. Head honcho Darrah Doyle also recommends fitting a new differential with a shorter final drive. It’s a move we approve of that shows scant regard for obsessive originality, however for those who have gone light headed the conversion is fully reversible.

What really grinds the gears of SMG apologists is feeling the gearbox has been unfairly singled out for criticism, especially when cars like the Ferrari 360 Challenge Stradale receive a free pass from the press despite its near-identical transmission. Could it be down to Ferrari’s infamous PR protection racket? You never hear about anyone complaining about the automated manual in the Lexus LFA either...you’ll be very surprised to learn that SMG’s shift speed has both the Italian and Japanese cars covered. Nevertheless, time and technology always move on, so would a later seven-speed dual-clutch with tighter ratios be the ultimate incarnation? I don’t think so, it would mean most of the hard-won 110kg weight saving over the standard car would be wiped out by a 75kg penalty, and that matters in a car with Leichtbau in its title.

Further criticisms? The exhaust note, which despite the reprofile doesn’t even attempt to be the Hall to the intakes Oates. The emission is still tinged by the tinnitus of the regular E46 - to see a CSL approach at full chat and pass is to be elated and deflated in short order. Anything else is really nit-picking, but some of the modern convenience items we take for granted would be welcome - Bluetooth connectivity, a USB port and a decent sound system. On the other hand, perhaps like the CSL’s scant regard for its secondary ride quality around town, maybe that's enlightening, forcing the occupant behind the wheel to immerse themselves in the business of driving. Still, even that person would bemoan the pathetic Glow-worm headlamps.

Looking back on today's drive, it's difficult to imagine the CSL received mixed press when it launched. Many took umbrage with the list price - at the time the track leaning sports car market was finding its feet and the CSL cost £20,000 more than a regular M3 - which was another 50%, or the equivalent of £95,000 accounting for inflation. For many, that was too much to ask for a paltry return of 17bhp, but in a world where Alfa Romeo can charge an additional £100,000 for a Giulia Quadrifoglio with thirty more BHP and forty fewer kilograms, it appears a bit of a steal. Less reasonable is the cost of replacement CSL parts - today a new bumper will set you back well over £3,000, if BMW will supply you one. A boot lid is £1,500. A genuine airbox? £5,000. A full interior? Try £17,000. An engine? If you have to ask…

Only 1,393 cars were produced over twelve months, with 422 examples coming to the United Kingdom - actually the CSL’s biggest market. According to Howmanyleft, only 297 cars remain of that initial run, and just 152 of them are taxed. Disappointingly, BMW’s support for its heritage is lacking compared to the likes of Porsche - even at its lofty price the CSL was a loss-making exercise thus the appetite isn’t there to maintain parts supply, and what was produced has been swallowed up by regular M3 owners attempting to create a doppelganger.

With each passing year more items are marked NLA - no longer available - on the parts department's computer. It’s a factor in the rapidly rising valuation of the CSL, with the entry point to ownership now heading north of £50,000. By the end of the year expect the very best cars to breach six figures or be prefixed with a £POA, and you only have to look at the value of an E30 M3 Sport Evolution or original CSL to see there’s a much higher ceiling. If you have been considering a CSL, act quickly.

And you should be because the CSL is the GT3’s nemesis. It's kryptonite, and the closest any car has gotten to upsetting the status quo, even if ultimately you would still take the 911. Even patron saint of the Porsche Motorsport religion Andreas Preuninger has gone on record praising the CSL. “There was no serious competition. Then the M3 CSL came along and rushed around the Ring in just 7.50 min. A drumbeat that kept us busy. I liked and enjoyed the CSL very much, it was a good competitor, a very cool car”

Impressively, the CSL did this without resorting to annexing the rear seats - it remained a properly usable car with accommodation for four and all the practical benefits of its three series shell.

If anything, there’s a Porsche Motorsport product the CSL bears a closer resemblance with - at least in terms of its relationship with the motoring press - the 964 RS. Both were underappreciated at birth, both have flourished in later life as the market and shifting tastes came to meet them. Today, the CSL is about more than its list price or lap time. It's a harmony of balance, precision, performance and soul with those six individual throttle bodies putting the trumpets of Jericho to shame.