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    Built over 13 years, this twin-turbo, M106-engined, 580whp E24 635 is a seriously incredible machine.

    Owned for 29 years, modified over 13 years and delivering 580whp from its twin-turbo M106, this incredible E24 is pure motoring madness.

    Here at we are most definitely not into making assumptions but even we must admit that we did not expect this utterly insane twin-turbo 580whp E24 635 to be owned by a 68-yearold psychiatrist. Pretty much every number in that sentence is eyebrow-raising but all we can say is that we hope when we get to that age we’re driving something as spectacular as this.

    So, 580whp – that’s a lot, especially in a car as devoid of weight and bulk as the E24 and using twin-turbos to achieve that monstrous figure is just wholly unnecessary and utterly wonderful in equal measure. This car is nothing short of an engineering masterpiece; a car owned and built by a man who is as big a petrolhead as they come; a car built without compromise or the constraints of practicality or budget. It’s the 6 Series you’d build if you could.

    While we’re sure Rob Behrends would have loved to invite us to lie down on a couch and ask us about our mother and why we’re scared of bread, this time it was our turn to delve into the mind of the man who made this monster and see just what makes him tick… “I’ve been interested in cars for as long as I can remember,” says Rob. “I collected automobile cards and brochures as a kid, and had several large picture book compilations of European and exotic cars.”

    His personal car ownership took the form of a varied array of American muscle that you might expect a young motor-mad man growing up in the ‘60s to drive, with V8s across the board, but the first spark that would lead him on the journey to building this 6 Series was ignited when, in 1977, he saw an advert in a car magazine for the 633CSi: “It was a two-page side view of the car at speed. The caption read: ‘Cruise all day at 125 miles per hour.’ I was in love. Long story short, in October of 1986 I took possession of a one-year-old Euro-spec 635CSi in Diamond Schwartz with colourmatching centre Style 5s that I imported from Germany. It had a five-speed ‘box, M-Tech side skirts, headlight wipers and E9- style BMW emblems on the C-pillars. It was breathtaking! The drive home was magical. It was a unique and rare car in this area at the time. A phenomenal highway cruiser and no slouch with 218hp. I drove, loved and cherished it for 17 years. In 2002 [interesting number coincidence], I began to think about increasing its power as a project with my son Justin who had come of driving age.”

    Rob looked into various options – including an S88 swap – but the costs involved were prohibitive so he decided to go down the forced-induction route instead. “There was nothing off-the-shelf at the time: some companies were installing superchargers on E36s and some were casting log exhaust manifolds for turbo applications. I chose to go with a turbo for efficiency and because BMW had done so with the 745i however, in a twist of fate, the factory casting the turbo manifolds burned to the ground so I was stymied.

    “Some weeks later my son and I were roaming a local junkyard looking for BMW parts and he came upon a 745i with a cracked head. It had large iridescent red Ss sprayed all over it, indicating ‘save’ by the yard, knowing this was something not to be crushed. My dream was suddenly alive again.” Rob rescued the 745i for $500 and brought it to My Garage, which specialises in Euro cars. The precious engine was removed, along with numerous necessary supporting components, and the process of rebuilding it began. At the same time, the M30 was removed from the 635 and sold, and the six went off to Sports Car Restoration (SCR), which specialises in 2002s, for some serious custom work. “I had worked with SCR for small rust repairs and paint projects on the Six in the past. Initially I wanted bodywork, paint, sport seats, a rear valence and a lower front spoiler. I had bought an Alpina spoiler, a Fittipaldi steering wheel (at a swap meet), Sparco seats, a titanium gear knob, and mounts for the six-way power seats,” says Rob. “A key issue for the metal body fabrication was tyre size. The motor was going to be fitted with a Garret T5, so there would be a lot of power.

    I had already purchased Fikse FM-10s; 9.5” with 265s for the back, 8.5” with 235s for the front. That was as big as I could go, even with the max offset to the inside so I had to make an executive decision to extend the flares! I was then able to widen the wheels and tyres by another inch. At that point I was like a kid in a candy shop. Anything was possible. My sense of practicality and future responsibility were gone. Roll-cage? Sure! Metal fab side sills to replace the M-Techs? Why not? We needed two front arches anyway…”

    With the bodywork complete it was time for the engine to be re-inserted and tuned. After a lot of work and some delays, Rob picked up his completed car in July of 2005. He badged it ‘666 CSi’ and his numberplate reads ‘MENTAL’.

    For a while all was well but unfortunately not for long. The ceramic-coated cast log exhaust manifold cracked and the manifold that Rob purchased to replace it also cracked, taking the turbo with it, as he found out when the setup was dismantled by Steve Sarafini at Fab U This (FUT), whom the garage doing the engine work had used for exhaust work on the car. One option would have been to simply opt for a new, stronger manifold and a fresh turbo but, having come so far with this build, Rob decided to take things that little bit further.

    “At that point I engaged Sarafini in what turned out to be a three-year-plus project of completely redesigning the engine bay (and more) based largely on my making the decision to have two turbos.” The car was dropped off with FUT and work began on the massive new stage in the project in January of #2010 . “He’s a one-man-shop. He also had his bread and butter work to do. This was a complex, close tolerance project of epic proportions. It came together beautifully but slowly, over about three years, essentially redesigning the entire air flow from filters to exhaust tips and properly aligning and securing the engine, transmission and driveshaft.

    “The last stage, when the 666 came home to me, was another frontier. I had no idea what was required for it to run. I looked to my son for direction, and one of his friends, Brian Hoehne of New Directions Performance, stepped up. He picked up on my passion to forge ahead and jumped onboard.

    He knew people where he had grown up a few towns away and brought together Steve Cohen, Brian Hall, my son, and James Moran of Backfire Fab. Brian organised and scheduled the guys and researched and sourced materials and parts. Steve Cohen, with my son Justin’s help, rewired the entire car over several months. Everything original and everything new worked. I was amazed! James (Bopper as he is affectionately known), is a true custom car wizard. Of course, there were numerous hurdles and he had a huge amount of work to do. He plumbed the turbos, installed sensors for the ECU, connected the wastegates and blowoff valve, designed a cam position sensor, tightened and marked every bolt and nut, found and eliminated leaks (oil, water, air), revamped the breather tubing, installed the Ground Control coilovers, problem-solved the turbos, fuel pump, and ECU, tuned the engine, and much, much more… but it was all worth it.”

    Building the 666CSi has been a bigger project than Rob could ever have envisaged when he first start looking at options for more power 13 years ago. Few of us have ever even owned car for that long, let alone spent that sort of time building a project. In a world dominated by people chasing showready build deadlines and hopping from project car to project car, it’s pretty incredible to come across someone who has spent this long reaching his personal version of motoring nirvana.

    As for the car itself, well, this 6 Series doesn’t disappoint. From top to bottom, inside and out, on every level Rob has addressed every aspect of the car and created an incredible build. The car has undergone a lot of body work but the changes have all been subtle and don’t spoil the irresistible E24 styling. The extensive metal fabrication for the widened arches, side skirts and rear valence is blink-andyou’ll- miss-it subtle and elsewhere Rob has had the fuel filler flap, antenna hole, rear bumper spacer and second wiper hole shaved, as well as having the arch and panel seams welded and filled. An Alpina front spoiler has been grafted on up front and there’s also an unpainted carbon bonnet and custom carbon fibre spoiler intake surround, while at the back a Racing Dynamics spoiler perches on the bootlid. It all works so well, and we have to give Rob’s choice of wheels a huge thumbs-up too. We’re going to go out on a limb here and say that most of you probably haven’t come across Fikse wheels before, but this American firm has been producing some extremely stylish designs for a long time now and the forged 18” cross-spoke FM-10s that have been fitted here, their 9.5” and 10.5” widths the reason behind the arch widening, look fantastic. They have a classic design that really suits the shape of the Six – nothing too outrageous and with a healthy dose of dish.

    Inside, it’s a blend of the familiar and extremely alien: classic E24 elements sitting next to necessary additions for a car pushing out this much power. There’s no missing the three-quarter roll-cage, which is attached to the frame rails at the firewall and rear shock towers, or the extremely sexy Sparco Milano seats with six-way electric adjustment and custom Pearl beige leather trim to match the rest of the interior.

    The Fittipaldi steering wheel has been combined with a set of AC Schnitzer pedals and handbrake lever, while there’s also a weighted titanium gear knob attached to a much-needed short-shift kit. Finally, there’s a custom instrument pod that houses an array of essential fuel meter gauges.

    So, we should probably talk about the engine because it’s a little bit special. As you might expect from a project spanning 13 years, an insane amount of work has been carried out on this M106 and it looks like some kind of thermonuclear device rather than a mere six-cylinder engine. It has been blueprinted and balanced and built with Ross forged pistons, Pauter billet rods, Total Seal rings, race bearings, and a Metric Mechanic dual profile asymmetrical sport cam. The head has been milled, pocket and chamber ported and sodium-filled over-sized valves have been fitted along with new guides, titanium retainers and F1-1000lb springs, along with a steel head gasket and stud kit, with the compression ratio reduced to 7.7:1. Somewhere deep within the bowels of the bay sit the turbos: a pair of Comp CT3B ceramic ball bearing items mounted on twin ceramic-coated manifolds, mated to twin Turbosmart 40mm wastegates with custom stainless steel lines and Turbosmart 50mm blow-off valve. The fuel system needed some serious upgrading and is now running Injector Dynamics ID1300 injectors with fuel by Marren Injection Systems, ATL fuel cell, dual pumps, lines and a custom fuel rail. There’s also a Snow Performance water/methanol injection system with a custom stainless steel tank. A custom air box has been fabbed in the right frame rail and there’s aluminium intake piping to the air-to-air intercooler and radiator with custom aluminium plenum and runners.

    Look further and you’ll find a custom aluminium coolant expansion tank, a hydraulic fluid tank and a condensation tank. A custom aluminium valve cover with hidden plug wires is a nice touch, while there’s also an oil cooler with a puller fan in the left frame rail and custom aluminium water tubes at the water pump jacket. The icing on the cake is the AEM Infinity 10 ECU with an awesome array of functions including traction control, adjustable boost per gear, no-lift shift, and six dial-in tunes.

    This incredible list of engine mods all play their part in helping the car make that aforementioned figure of 580whp along with 540lb ft of torque at the rear wheels at 1.5bar on MS109 fuel with the water/meth running. All that power makes its way to the Tarmac via a Getrag S6S 420G six-speed gearbox from a Euro E34 M5, SPEC Stage 5 clutch and a pair of 295 Michelin Pilot Super Sports.

    Due to the vast amount of power and torque that the E24 now has to deal with the chassis has undergone some serious strengthening to help it cope. The diff is reinforced by a 1/4” steel, C-shaped bolted bracket welded to a 1/4” steel plate on the boot floor and bolted to cross members which go to the rear shock towers/roll-cage. There’s a custom rear strut brace, the engine and transmission are solid mounted along with most of the rear suspension, with some components mounted on polybushes, and the whole front has also been fully polybushed. Ground Control coilovers offer a gentle drop and a massive improvement in handling while the standard brakes are long gone, replaced by a custom UUC BBK with four-pot calipers front and rear and 355mm two-piece grooved discs up front with 350mm items out back. There are also thicker anti-roll bars and a line lock kit has been fitted on the front brakes, making those all important burnouts a breeze.

    The story of Rob’s 635 is one of highs and lows and while there were moments when the end seemed like it would never be in sight, 13 years on from that great decision to get some more power from his Six, here we stand with one of the most incredible builds we’ve ever come across. “It has been a long and winding road; not easy at times,” muses Rob. “Overall, I’m relieved and happy it’s together and working. A lot of time, effort, creativity, passion and money has been invested in this car. I’m still totally crazy [mental?] about it.” Looking at that numberplate, whoever said Americans don’t get irony? And as for the moniker on the back of the car, well, we’ll let Rob explain: “666CSi has a double meaning. With the 745i, and, of course, the newer models, #BMW has taken a liberty with the displacement representation related to forced induction, and 6.6-litres isn’t that outlandish, I thought.”

    This devilish 6 Series, then, is no longer that comfortable, refined GT that it was back in 1985 but we wager that Rob too is a very different man from the one that started out on this journey 30 years ago. This car, much like its owner, defies convention and expectations and while to the outside observer it might seem plain crazy to have spent so much time and money creating this car, in our world of modified cars where we’re all a little bit crazy he fits right in.

    TECHNICAL DATA FILE #BMW-666CSi-E24 / #M106 / #BMW-635CSi-E24 / #BMW-666Csi / #BMW-E24 /

    ENGINE 3.5-litre straight-six #M106 , solid mounted, blueprinted and balanced, stock crank, Ross forged pistons, Pauter billet rods, Total Seal rings, race bearings, compression 7.7:1, #Metric-Mechanic dual profile asymmetrical sport cam, milled, pocket and chamber ported head, sodium filled over-sized valves, new guides, titanium retainers, F1-1000lb springs, steel head gasket, stud kit, #Injector-Dynamics ID1300 injectors, twin Comp CT3B ceramic ball-bearing turbos, twin-Turbosmart 40mm wastegates with custom stainless steel lines, #Turbosmart 50mm blow-off valve, ATL fuel cell, dual pumps, lines, custom fuel rail, custom cam sensor, custom wheel speed sensors for rear axle for traction control, AEM infinity 10 ECU, custom software elements for adjustable boost per gear, no-lift shift, six dial-in tunes, valet mode and kill switch, Halon fire extinguisher, Snow Performance water/methanol injection system (including custom stainless tank), custom rewiring of engine and complete car, twin ceramic-coated exhaust manifolds, full custom stainless exhaust with twin 2.5” tailpipes, uprated radiator with twin electric radiator fans, custom air box in right frame rail, ceramic-coated intake piping to air-to- air intercooler and radiator, custom aluminium plenum and runners, custom aluminium coolant expansion, hydraulic fluid and condensation tanks, custom aluminium valve cover with hidden plug wires, oil cooler with puller fan in left frame rail, custom aluminium water tubes at water pump jacket, Optima Red Top battery. 580whp and 540lb ft rear wheel torque at 1.5bar with water/meth injection (22-23psi) and MS109.

    TRANSMISSION #Getrag-S6S-420G six-speed gearbox from Euro E34 M5 #Getrag-S6S / #Getrag , solid mounted, SPEC Stage 5 clutch, differential reinforced by a ¼” steel C-shaped bolted bracket welded to a ¼” steel plate on the boot floor and bolted to crossmembers which go to the rear shock towers/roll-cage, custom stainless rear strut brace.

    CHASSIS 9.5x18” (front) and 10.5x18” (rear) #Fikse-FM-10 wheels with 265/35ZR18 (front) and 295/35ZR18 (rear) Michelin Pilot Super Sport tyres, Ground Control coilovers, front suspension fully polybushed, rear suspension solid mounted and polybushed, custom aluminium front strut brace, custom UUC #BBK comprising four-pot calipers with 355mm two-piece grooved discs (front) and four-pot calipers with 350mm grooved disc (rear), 22mm anti-roll bars, line lock on front brakes.

    EXTERIOR Custom metal fabrication by Sports Car Restoration including flared arches, side sills and rear valance with exhaust scallops, shaved fuel filler door, antenna hole, rear bumper spacer, second wiper hole, welded/filled arch and panel seams, #Alpina (lower) front spoiler, PIAA three-way running lights, custom carbon fibre bonnet and spoiler intake surround, Racing Dynamics rear wing.

    INTERIOR Custom instrument pod, fuel gauges, short-shift kit, titanium (weighted) gear knob, #AC-Schnitzer pedals and handbrake lever, six-way power Sparco Milano seats custom covered in Pearl beige, Fittipaldi steering wheel, new tool kit, three-quarter roll-cage attached to the frame rails at firewall and rear shock towers, Escort Passport Max radar detector, Directed SmartStart System.

    THANKS My son Justin, My Garage, Sports Car Restoration, Fab U This, Backfire Fab, New Directions Performance, and European Performance Labs.
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