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TALES OF THE UNEXPECTED: MERCEDES OM605 ENGINED BMW E36

Posted by Glenn Rowswell on 15th July 2020

Just when we think we’ve seen it all before, one of the coolest and fastest diesels we’ve ever seen appears…

Tuned cars are never exactly what people expect them to be at first glance, especially to people who aren’t into modified cars. But this car, Scott Smith’s awesome E36 BMW coupé, takes the usual clichéd expression of ‘with a twist’ and seriously maxes it out, as almost nothing is like you’d expect.

It’s a very fast E36, but is it an M3? Nope, it’s a diesel. So a 330d engine? Nope, it’s not even a BMW engine; it’s a Mercedes. So it’s got the famous OM606 6cyl engine? No, the 5cyl OM605. It can’t be that powerful though, can it, it’s a diesel!? It’s 450bhp! But diesel’s don’t rev. Well this one pulls hard all the way to 6500rpm thanks to a big BorgWarner S366SX turbo. So it’s laggy then with that massive turbo? No, it spools up super fast. Okay, we think you get the idea now. This thing blows all the typical misconceptions out the water in style, and we’re here to show you how it’s done.

The project started almost accidentally, as it wasn’t Scott Smith, the current owner and builder of this beast, that kick-started this awesome car into reality. A friend of his fitted the Mercedes OM605 2.5ltr 20V turbo diesel engine and Mercedes six speed manual box to what was otherwise a pretty much standard base model 316i BMW, mostly to see how hard it would be to get the combination running and driving. The answer to that question was ‘quite hard’, and it was far from the easiest engine to swap in, but once it was done, Scott could see the huge potential in the car, so bought it, and quite rapidly turned it into the absolute beast you can see before you on these pages.

While the big brother to this engine, the 3ltr 6cyl OM606, has almost legendary status in diesel tuning, the OM605 is less famous, so why use the 605? In fact, why not use a BMW diesel engine? Well, the 606 is great, but it’s also huge, and while the BMW 3ltr turbo diesel engines are fantastic too, the electronics mean they’re far more complex to install, and to be honest, they just don’t rev and make the power like these engines do when tuned properly. And besides, highly tuned OM605s sound awesome; the big turbo 5cyl breathing through a 4-inch exhaust sounds like a mix between an ‘80s Audi Quattro rally car and a huge American big rig!

It’s not just the engine choice which is unexpected, but how the engine behaves too. Diesels, they make lots of torque but don’t rev, right? Well, normally yes, but in this case, hell no! This thing revs like a typical 2.5ltr petrol lump, pulling all the way to the 6500rpm rev limit – almost 2000rpm further than most diesels usually pull hard to. But why is that? Special fuel? Some high tech trickery? Black magic? Nope. In fact, as diesels go, this engine is pretty low tech; it’s all about good old tuning…

You see, most diesels don’t rev simply because they’ve been designed that way. They’re intended to make good grunt from almost idle, and have great fuel economy, so generally have a tiny little turbo that strangles power as the revs rise, as well as a fuel system and engine design only really intended for low rpm use. Even tuned diesels with uprated turbos still run relatively tiny turbos for the capacity compared to petrol engines, but this one? Well, this one has a beast of a turbo: a BorgWarner S366 with a twin scroll T4 turbine housing. And the exhaust is just as manly too, with a 4inch diameter from the turbo right to the tailpipe. This, combined with the fact the OM605 has an amazingly well-flowing head and cam set-up for a diesel, means from an airflow point of view, this 5cyl diesel can seriously rev if needed. But what about fuel? A big part of the reason diesels don’t tend to rev high or make big power is the fuel systems are generally not capable of that. But this OM605 has taken a step back in technology to take a huge leap forward in performance, as Scott has binned off the factory electronic diesel injection set-up for a fully adjustable mechanical injection system, and a seriously beefy one too. While a race spec mechanical set-up isn’t exactly the last word in refinement and economy, it can supply the massive amounts of fuel needed to be revving like a petrol engine would and making 450bhp at a hefty 2.3bar boost, which soon could be turned up to 3bar!

A BorgWarner S366 T4 turbo is a big turbo even in petrol engine terms, and it’s pretty gigantic in the diesel world, so this thing must be a laggy dog at low rpm, right? Well, no. While it sure isn’t spooling from idle like most factory diesels do these days, considering this thing pulls way harder for way longer than any normal diesel, it spools up very well, and that’s thanks to a relatively simple but ingenious addiction: the quick spool valve. What this does, under 1bar boost, is block off one of the two exhaust ports on the inlet of the turbos twin scroll turbine housing; effectively halving its size, and making it behave like a much smaller, faster spooling turbo. But, unlike a much smaller turbo which would normally choke performance as the revs rise, the quick spool valve opens once boost pressure goes over 1bar, giving full flow to both sides of the turbine housing, and allowing the engine to be the 450bhp 6500rpm diesel ripper it is.

While the engine set-up is no doubt the main feature of this car, it’s hard to miss the fact that the car looks almost show quality, and that’s because Scott literally stripped the car right down when he bought it to make it a really immaculate example; something of a rarity in E36s these days! Genuine M3 bumpers and a M3 GT rear spoiler were fitted, and the whole car was repainted. It was just as comprehensive underneath too, with the whole underside made good as new, with everything powder coated or painted, along with fresh bushes and a complete disc brake E36 328i rear end – a big change from the base model drum brakes the car had when he first bought it!

The suspension and brake set-up is well thought out, with M3 hubs, longer E46 front lower arms for wider track and more camber, adjustable HSD coilovers front and rear, and a clever suspension geometry set-up. Rather than the typical negative camber all round, this beast runs very slight positive camber on the rear when static. This means that when the car squats down under hard acceleration, rather than giving huge rear camber and pure wheelspin, the rear tyres sit flat to the road, giving amazing grip from the Toyo R888R tyres.

The brakes are far from typical for a diesel too, with big AP Racing 6pot brakes on the front, meaning it’s more than able to haul itself down from the insane ‘best part of 200mph’ speeds this car has seen on the clock! For what it’s worth, we’ve done the maths, and with the 205/40×17 tyres, the 2.93:1 ratio rear diff, the 0.828:1 ratio 6th gear in the gearbox, and the 6500rpm rev limit, this car’s top speed should actually be a genuine 187mph, which would show as well over 200mph on most cars’ speedos! Not shy for an E36 with an old mechanical diesel engine, eh…

Another thing you don’t expect from a big power diesel E36, with a welded diff and a ridiculously high top speed, are WORK Meister S1 wheels. Normally seen on Japanese-tuned cars, S1s are a classic wheel that look awesome on anything they’re fitted to. And these ones, 8.5-inches wide on the front and 9-inches wide on the rear with a low ET15 offset, are no exception.

So this car is full of surprises, but what the hell is it used for? It looks like a show car, but has a spec like a race car? Well considering how different the whole car is, you’d probably not be surprised even if we told you it was used for off-roading or as an ambulance, but in reality it exists for the reason all modified cars should: fun! “I use it every weekend, driving for fun, taking it to shows and to annoy people in fast, fancy cars, of course!” Scott explains.

The car does a good job of chucking the misconception that highly tuned cars are unreliable, clean out the window. As you can see, it’s all pretty insane and used hard, and Scott’s had no real teething problems; the car has been good as gold. Of course, it helps that he’s a bit of a car wizard himself and runs S&B Motorsport, but for a car this far from standard and this highly tuned, to not spend the first year of its life with issues that need ironing out, is very good going.

Now who’s going build a car to top this on the unexpected-o-meter? It will take some serious doing and some serious imagination and skills, but one thing’s for sure, Fast Car want to see it once it’s complete…

TECH SPEC: BMW E36

Engine
Mercedes OM605 2.5 5cylinder twin cam 20valve engine conversion, Diesel Pump UK 8mm fully adjustable mechanical fuel pump, custom top mount turbo manifold, BorgWarner S366SX turbo with twin scroll T4 0.91 A/R turbine housing, custom turbo back 4inch exhaust with down turned tailpipe, Turbosmart boost controller, 44mm Turbosmart external waste gate with screamer pipe venting out front wing, quick spool valve with 1bar actuator, E36 M3 radiator, 2.5inch thick custom front mount intercooler, custom 2.5inch diameter stainless steel boost pipes powder coated black, custom thermostat housing and coolant pipes, Ramair cone filter.
360hp at 1.8bar boost, 450bhp at 2.3bar boost, capable of 3bar boost, 6500rpm rev limit.

Transmission
Mercedes Sprinter solid flywheel, heavy duty clutch, Mercedes six speed manual gearbox, B2D short shift, medium case 2.93:1 ratio welded diff.
Chassis/suspension
E36 316i coupé non-sunroof shell, HSD coilovers front and rear, E46 lower arms, M3 hubs, front and rear strut braces, poly bushed front lollipop arms, fully poly bushed rear end, front subframe and cross braces.

Brakes
AP racing 6 pot front brakes with 356mm discs and Ferodo DS2500 pads, BMW 328i Sport rear discs and callipers with EBC Yellowstuff pads.

Interior
Full black and red leather interior, black roof lining, AC Schnitzer handbrake lever; volt, boost, and water temp gauges, fuel cut-off switch, E46 M-Sport steering wheel.

Exterior
Front and rear genuine BMW M3 bumpers, tinted windows, rear window louvre, E36 M3 GT rear spoiler, bonnet raisers, Depo smoked rear lights, Depo smoked front corners, smoked side repeaters, black kidney grilles, headlamp air duct.

Wheels and tyres
WORK Meister S1 wheels (front) 8.5×17 ET15 R-disc, (rear) 9×17 ET15 O disc, 205/40×17 Toyo R888R semi-slick tyres front and rear.

Cheers to
S&B Motorsport, PillarFab for the welding. KDKustoms for the paint!

Words Stav Photography Ade Brannan