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The BMW S65 Is an All Time-Great Engine, but Not Without Flaws or Controversy

A few months ago, we showed you all there is to know about the history behind the BMW M3's first V8, the S65 engine. We highly recommend you go check that out. But it's important to show both sides of the story. The S65 may have been a gem, but people tend to forget how controversial it was at various points and for various reasons. Let's build on what we've already learned about the S65 V8 and the E90 sedan, 92 coupe, and 93 M3 convertibles attached to it, and look at some more details.
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A major source discourse behind whether the E92 M3 was a worthy successor to the E46 has much to do with the engine. As it happens, the BMW S65 V8 has a remarkably interesting story behind it. It silenced critics who claimed at the launch who wrote that a great thumping V8 wasn't necessary for a relatively lightweight sports coupe the likes of the outgoing E46. Or that said V8 would spoil the heritage of past M3s and would turn the E92 into nothing more than a burly muscle car. At least, they did at first.

But at a time when rivals at Mercedes-Benz, Audi, Cadillac, and Lexus were all fitting shockingly good engines in their sport coupes, the E92 M3 coupe just may have been the cream of the crop with biases put aside. At least from a raw performance point of view. All the awards it received from industry media seemed to point in that direction. In truth, the S65 V8's existence has more to do with its association with another BMW engine from the larger M5 than being a bespoke engine model.

So many engines are claimed to be derived from other engines, but with A, the blocks fused, or B, cylinders removed. In reality, it's almost never that cut and dry. Key emphasis on "almost." That's where the BMW S85 V10 from the E60 M5 and the S65 from the smaller M3 throws a monkey wrench into affairs. Why? Because while it's still not as simple as lopping off cylinders with an ax, the S85 and S65 are as closely related internally as a V8 and a V10 could be.

From the crankshaft to the dual-overhead camshafts to the proprietary VANOS variable-valve timing operated at 100 bar (1450.4 psi) of oil pressure. Down to a shared aluminum-silicon alloy die-cast crankcase with a reinforcing steel bedplate. Both engines' cylinder bores were honed using silicone crystal-tipped boring machines to eliminate the need for heavy metal cylinder liners. The bore and stroke are also identical. In all but a few key areas, the S65 and S85 are genetically identical from the bottom up.

Believe it or not, the S65 manages to be around 33 lbs (approx 15 kg) lighter than the straight-six S54 engine it replaces in the E46. The two engines even shared a common ECU system capable of 200 million calculations per second. Not much by modern standards, but it was ten times what the S54 could manage. The biggest difference comes from the wet-sump oil lubrication system instead of the dry-sump system present in the larger V10. Furthermore, the S65 uses only a single air-cleaner box instead of the twin units in the S85. But what does this boil down to in the numbers game?

That'd be 414 horsepower at a screaming 8,300 rpm and 400 N⋅m (295 lb-ft) of torque at just under 4,000 rpm in the inaugural S65B40. This was upped to 444 horsepower at the same rpm with 440 N⋅m (325 lb-ft) of torque in the S65B44 unveiled in 2010. When the first round of E90 M3s made their way to buyers and journalists alike praised the S65 as a world-beating gem of an engine. Winning the International Engine of the Year award from the UKi Media & Events Automotive Magazines in the three to four-liter category four years in a row between 2007 and 2011.

Soon after launch, the racing-focused P65B44 V8 using the S65 architecture made its debut in Group GT2 racing with the 2009 M3 GT2 and in Le Mans racing with the Z4 GTE. At the time, it seemed like the S65 was on a path to all-time great status among sports car V8s. That is until owners started running into a few problems. Starting with the earliest units made from 2007 to autumn 2008, a lack of clearance between connecting rod bearings caused them to wear prematurely.

This problem didn't manifest until a slew of major publications like Car & Driver had finished praising it for being just about perfect. Further snafus came from throttle body actuator failure reported at as few as 31,000 miles (50,000 km) and premature throttle actuator failure at similarly unimpressive time intervals. The culprit? The plastic gears in each actuator mechanism. See? It wasn't just American cars pulling that nonsense in the late 2000s.

The Germans were just as guilty. At least American plastic is usually cheap to fix. Something that can't be said about any aspect of an E90 M3. An aspect of ownership that further adds to the taboo of an otherwise brilliant car and the otherwise iconic car it's attached to. But owners who love them swear by the S65 V8. They claim that as long as you change the oil and filter to the dealer's recommend specifications, and ensure the engine isn't burning oil at regular intervals, these engines can and do last.

It shows that changing the oil is vital in any internal combustion engine. But it's a real-life or death matter with a modern BMW. So please, change your oil, so we can keep revving the snot out of these engines until the world's petroleum reserves are well and truly tapped. Check back soon for more from V8 Month here on autoevolution.

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