The Hidden Gem of Small Displacement Diesels

It’s an engine that is tough as nails, extremely efficient on fuel, and highly affordable at the present time, yet some of you never knew it existed—until now. It’s the 3.0L M57 inline-six diesel from BMW, and it’s arguably as chock-full of performance potential as a common-rail Cummins. When it debuted stateside back in 2008 (as an ’09 model available in the 335d), it packed a unique sequential turbo arrangement (compounds) and boasted 265 hp and 425 lb-ft of twist—numbers that would prove to be underrated. Tremendous drivability is on tap thanks to a responsive high-pressure turbo, and these sporty sedans can go from 0-to-60 mph in 5.7 seconds, as well as scoot through the quarter-mile in low-14-second intervals, stock.

Capitalizing on the M57’s I-6 architecture and beefy internals, the engine’s true potential was eventually realized when the aftermarket got ahold of them. With emissions system shortcomings and a few other weak links addressed, the platform has proven capable of supporting north of 700 hp at the wheels without the need for bottom-end upgrades. To get the full scoop on what the M57 is capable of, we checked in with Santjer Performance, home of the world’s most powerful 335d, and S&S Diesel Motorsport, the common-rail experts who build larger piezo injectors for them. We quickly learned that for way less than $20,000 (including the purchase price of the car), you can make Hellcat-like power without even having to upgrade the factory transmission. And you can have your fun in a car that’s capable of nearly 40-mpg on the highway.

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If you’re in the market for a daily driver that sips fuel, rides comfortably, and has 12-second potential with nothing more than a tune, an ’09-’11 BMW 335d should be on your list. These cars are one of the best kept secrets in the diesel industry. Right now, you can pick them up for $8,000 to $12,000 with reasonably low miles on them and instantly make your commute to work more entertaining or your road trips more economical.
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Beneath the composite intake, the BMW M57 engine in this ’09 BMW 335d conceals an aluminum block and head (earlier versions of the M57 used a cast-iron block). Within the crankcase, you’ll find a forged-steel crankshaft, secured by 2-bolt main caps. The rods are forged-steel and the pistons are cast-aluminum pieces with steel ring lands.
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The beam size of the M57’s factory forged-steel connecting rod is impressive, and helps explain why these engines can withstand 1,000 lb-ft of torque at the wheels. Here, it’s being compared side-by-side with a rod out of the BMW N54, a twin-turbo, aluminum block and head inline-six gasoline engine that turned out 402 hp and 398 lb-ft of torque in its most potent factory form.
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A 3.31-inch bore and a 3.54-inch stroke provide for a total displacement of 182.6 cubic inches (or 3.0L). That’s roughly half the size of the 5.9L Cummins and less than half the displacement of the 6.7L Cummins we celebrate so much in the diesel industry. Despite being half (or less than half) the size of those I-6 power plants, pound-for-pound the M57 produced more power. The ’09 version of the M57 that came in the 335d was rated at 265 hp at 4,200 rpm and 425 lb-ft of torque at 1,750 rpm. However, baseline chassis dyno testing would prove those numbers to be considerably underrated (they are achievable at the wheels).
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Unlike most overhead cam diesels you come across, they are chain driven rather than belt-driven in the M57. The cylinder head features four valves per cylinder, and relies on four head bolts per cylinder (with sharing) to fasten the head to the block. While we in the truck world are used to seeing six head bolts per cylinder, in the BMW’s case the lower fastener count does not affect its durability (more on that later).
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It’s unlike any compound arrangement you’ve likely seen before, but the factory sequential turbo system on the M57 hangs both turbochargers from the exhaust manifold. Internal bypass valves limit flow to one turbo or the other at the appropriate time. To get things moving, the low-pressure charger, a BorgWarner K26, sees nearly zero exhaust flow so that the high-pressure unit, a BorgWarner K39, can bring everything to life quickly. At higher rpm, a bypass valve diverts flow to the low-pressure unit without cutting the high-pressure turbo out of the loop completely (the high-pressure charger remains operating at or near 100-percent). The low-pressure charger is also wastegated to avoid possible overspeed.
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Although the factory hardware is stout on the M57 engine, its parts do have their limits. Throughout the past five years, Matt Santjer of Santjer Performance Development has bent plenty of connecting rods and melted a few pistons while testing the limits of the M57 platform—but as a result he now knows what parameters need to remain in check in order to keep a factory M57 alive. “If we really pushed it down low we could make 1,500 lb-ft, but it might come apart,” he told us. “So we try to keep torque in check.”
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While 1,500 lb-ft of torque might be out of the question for the M57, Santjer’s relentless testing of the 3.0L BMW has shown that he can get away with running 600 to 700 hp at the wheels and 1,000 lb-ft on the stock bottom end without issue. “Now that we’ve gathered so much data, we’re more comfortable with what we can get away with,” he said.
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Despite having just four head bolts per cylinder (14 total), Santjer Performance Development has proven that the factory head bolts can keep the head gasket alive at 75-psi of boost. The folks at Santjer believe it has more to do with the bolts’ length and their engagement in the block than their 12mm diameter. After all, the head bolts extend almost to the mains.
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If you must, there are aftermarket head studs for the BMW M57. So far however, Santjer Performance hasn’t felt the need to run them—not even with its triple-turbo 335d turning out 75-psi of boost and more than 1,000 lb-ft of torque! Still, should the company ever find the limit for the factory head bolts, it’s nice to know this option is out there.
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The only real internal weak-link that’s been exposed so far are the factory valve springs. To rule out boost creep and valve float at high rpm and elevated boost, Santjer Performance worked closely with Hamilton Cams in developing stiffer replacement springs. These direct drop-in replacements are good to 6,000 rpm and 75-psi of boost. They’re recommended any time you tune an M57 engine. The rest of the head and valvetrain has remained 100-percent stock throughout all of Santjer’s horsepower pursuits.
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A high-pressure common-rail injection system from Bosch is employed on the M57. In it, a CP3 high-pressure fuel pump provides the rail with as much as 1600 bar (or roughly 23,200 psi) worth of pressure for the injectors to use. The injectors themselves are Bosch piezo electric units. Not unlike larger engines that use piezo injectors (such as the 6.7L Power Stroke), the injectors flow much more than the OEM high-pressure fuel pump can keep up with.
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The factory piezo injectors can support a tune-only, 360 rwhp. Add another CP3 to the equation and they can support as much as 425 rwhp. Then, with a second high-pressure fuel pump in the mix a much larger injector can be utilized. As we go to press, these are the largest injectors built to date for the M57. Built, benched, and balanced by S&S Diesel Motorsport, they are equipped with 100-percent larger nozzles and flow 2,250 cc/min. They are believed to be capable of supporting more than 1,000 rwhp.
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Many of you are familiar with the Bosch CP3, but some aren’t aware that many different versions were produced for a wide array of applications. In the BMW M57’s case, an R70 model CP3 is used. The R70 is different from the larger version of the CP3 you’d find on a Duramax due to no pump gears being present on the backside of the pump. In BMW 335d applications, the R70 gets its low-pressure fuel supply from an in-tank lift pump.
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To get around the volume imitations of the R70 CP3, Santjer Performance came up with a dual CP3 kit. The second CP3 (which is sourced by the customer), is driven independent of the serpentine belt via a Poly-V drive belt. Due to the pulley ratio it’s also overdriven, which means that more than twice the fuel volume is on tap. Here, you can see the billet-aluminum CP3 support mount, but that’s only the tip of the iceberg. Santjer’s comprehensive bolt-on kit also comes with the plug-and-play PWM controller, billet belt tensioner, upper and lower drive pulleys, high-pressure fuel lines, high-flow CP3 fittings, and expansion tank coolant hose you need to install it.
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Not wanting to increase the risk of timing chain failure by placing more stress on it, Santjer’s belt-driven dual CP3 kit reduces the load on the factory timing chain by 50-percent. Thanks to the second CP3 being overdriven, Santjer believes that—in conjunction with S&S Diesel Motorsport’s 100-percent over injectors and BRR Tuning’s ECM calibrating—1,000 rwhp is possible on fuel with the M57 platform.
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Every dual CP3 kit Santjer sells also comes with the support you need on the low-pressure fuel side of things. To help the in-tank lift pump supply the high-pressure fuel pumps, a Bosch turbine fuel pump is run in line with the factory pump. At idle, supply pressure being sent to the CP3’s is 50 psi. At higher rpm, it increases to 60 psi. A supplied wiring harness provides for the lift pump to be integrated with the factory PWM-controlled fuel pump circuit.
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Matt Santjer will be the first to tell you that making an M57 perform at its peak begins and ends with sound tuning. None of the injector, high-pressure fuel pump, and turbo mods he’s tried would’ve mattered without someone writing the perfect files for the ECM. Working closely with BRR Tuning and sticking with the factory Bosch EDC17, the results are undeniable. Santjer owns the most powerful 335d in the world according to his dyno sheets. Soon, he’ll be gunning for the honor of owning the fastest 335d in the world as well.
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Building on the factory bypass-style compound turbo arrangement, Santjer has added a third turbo to his purpose-built drag racer. The custom, Holset-based charger serves as a second atmosphere unit and boasts a compressor wheel that’s somewhere in the 64mm to 70mm range (the sizing has been kept proprietary for now). So far, the three-stage, triple-turbo configuration has produced 75-psi of boost—a far cry from the 26-27 psi the original system produced from the factory!
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He may not own the record for the world’s fastest BMW 335d yet, but Matt Santjer won’t rest until he does. And even though he’s still campaigning a full weight car (3,900 pounds), he still believes he can top the current best E.T. in Europe—a gutted race car in the 9.20’s in the quarter-mile. After all, the triple-turbo system, 100-percent over injectors, and dual CP3’s have already produced a timeslip with a trap speed of almost 140 mph. On that pass, Santjer was attempting to get the 335d on the 100-200 KPH super car’s list (it did it in 5.3 seconds), and left the line with zero boost on tap and with power limited to 600-rwhp before fourth gear in order to maintain traction.
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Perhaps the craziest part in all of Matt Santjer’s M57 madness is the fact that the factory six-speed automatic has survived without modification. The ZF 6HP transmission is of the Lepelletier epicyclic/planetary gearset variety and in Santjer’s case has held up to the aforementioned 9-second pass and 140 mph trap speed. Beyond that, we’re told the differential and axles are tough-as-nails, too.
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Just when you thought the M57 was invincible, we have to remind you that no engine is perfect. One of the primary weak links on the M57 engine is the swirl flap design on the intake manifold. Each port is graced with a plastic flap that is intended to help engine efficiency, most notably fuel economy. However, over time the plastic degrades and the material breaks down, often sending debris into the head and causing big problems. For both reliability and performance purposes, it’s wise for anyone pursuing horsepower to remove them early on in the process.
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As with any modern diesel engine, exhaust gas recirculation along with a closed crankcase ventilation system produces a carbon and soot buildup that soon cakes walls throughout the intake tract. And as is the case here, sometimes the carbon buildup seals off a passageway completely. This photo comes courtesy of Andrew Rodriguez of Tune My Euro, a household name in the M57 performance world, but also a shop that regularly cleans clogged intake manifolds. In fact, the problem is so common that Tune My Euro offers an exchange program where customers receive a clean intake and send their plugged up version back.
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Also not unlike the issues we’ve all faced with our own late-model trucks, the M57’s diesel particulate filter and selective catalytic reduction system have common failure points. In particular, the DPF’s tend to clog up quickly and the DEF system heater is prone to quit working, which can be a major problem, especially in cold weather.
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One thing the M57 is fairly notorious for is harmonic balancer failure. It can happen in as little as 30,000 miles or as many as 150,000 miles, and it has no bearing on whether or not the engine has been modified. It’s simply the luck of the draw. In a worst case scenario, a failed balancer can cause a number 1 main bearing failure—but thankfully that isn’t very common. Hints that your harmonic balancer is on its way out are: a non-functioning A/C system, a battery that won’t charge, weak power steering, and the obvious visual inspection. For any new owner, it’s good advice to go ahead and replace it when you first buy the car.
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Even with their few faults, the ’09-’11 BMW 335d sedans make awesome daily drivers. Torque is instant, the transmission is virtually unbreakable, you’re in the 12’s with a tune, and you can knock down upward of 35-mpg even with spirited driving. Take it from Matt Santjer, who might be slightly addicted to these cars. “I have four of these things. My daily driver only has a BRR tune and dual CP3’s, but traps 116 to 117 mph in quarter.” To you and me, that’s 425-rwhp and mid 11’s for just $3,500 to $4,000 in mods. No wonder there’s a growing market for a car that’s been out of production for a decade. Don’t wait! Get yours before prices skyrocket.
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For years, Hot Shot’s Secret has been sponsoring a BMW 335d in the 7.70 Index class within the Outlaw Diesel Super Series. Driver Trey Sikes even set a North American record for the 335d in 2018. The M57 under the hood benefits from custom hybrid turbos, methanol-injection, and proprietary tuning. Wearing a full Hot Shot’s Secret wrap, it’s impossible to miss at a diesel event—and also has zero problem going rounds with 700-plus horsepower diesel trucks.

SOURCES

Hamilton Cams
512.355.9101
hamiltoncams.com

Hot Shot’s Secret
800.341.6516
hotshotsecret.com

S&S Diesel Motorsport
ssdiesel.com

Santjer Performance
santjerperformance.com

Tune My Euro
678.535.7172
tunemyeuro.com

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