The new 2020 Toyota Supra gets a lot of internet bashing for “being a BMW.” It’s almost as if people believe Toyota is still good at building sports cars on their own. The last “Toyota only” sports car was the MR-2 Spyder of almost 20 years ago. By partnering with BMW Toyota not only inherited a ton of free chassis R&D, but they also got to take advantage of BMW’s wonderful inline 6 cylinder engines.
BMW’s M division has always made special engines. They have also always been designated with an S in the engine code. The famous E46 M3 used the equally famous S54. The E92 M3 debuted with an amazing 4.0 V8 dubbed the S65, which was based off the M5’s S85 V10. Ask any E30 owner what engine they wish powered their car and the S50 or S52 from the E36 M3 would be on the top of their lists. The BMW M2 debuted in 2015 with the N55 engine, not a “true” M engine. But in 2017 the M2 became available in competition trim which included the M3 and M4’s S55 drivetrain. The true M engine everyone thought would find its way into the new Supra.
We now know the Supra did not get an S55, but rather the B58 engine which is found in non-M “40i” trims of the 2, 3 and 4 series models of BMW. It may not be an M engine, but in this case that may not be a bad thing.
The S55 engine was first introduced in 2013 in the current generation BMW M3 and now resides in the BMW M2 Competiton as well. It is a 3.0L twin-turbo in-line 6 cylinder engine rated at approximately 405hp depending on the trim. The B58 engine found in the Supra is rated at only 335hp. Despite being down 70hp on paper the B58 shares a lot of similarities with the S55, and even has some benefits over its motorsport derived sibling. Both engines displace 3 liters and have six cylinders. Both engines sport dual overhead camshafts with variable valve timing on both camshafts and variable lift on the intake camshaft. Both are turbocharged and both utilize water to air inter cooling. Both are chain-driven engines and are clad with plastic intake manifolds that house electronic throttles. Both are closed deck designs and employ direct injection and coil on plug ignition systems. With all that said, why would BMW bother making two engines if there were no important differences?
The S55 uses 89.6mm bore with a short 80mm stroke to get to 3 liters and revs to 7,500rpm. The decidedly less motorsport inspired B58 creates 3.0 liters by way of an 82mm bore and a much longer 94.6mm stroke and only manages 7,000rpm. The B58’s smaller bore allows the engine to be shorter in overall length resulting in a stronger crankshaft, and the considerably longer stroke means longer connecting rods for reduced friction. The B58 is part of BMW’s new modular engine design. The engine block is identical to the diesel B57. Diesel’s don’t have short strokes.
The S55 uses tried and true twin turbocharging for fast response and big power. There are two separate exhaust manifolds using a 3:1 design that feed into their respective turbochargers. Both turbochargers then expel their compressed air into a single water to air heat exchanger mounted atop the cam cover area. After intercooling, the air enters the engine through the electronic throttle body. The B58, however, has a much different cylinder head that incorporates an ‘internal’ exhaust manifold into the cylinder head casting. The head has only 2 exhaust ports, one for each scroll of the twin-scroll single turbocharger used on the B58. Integrated exhaust manifolds are becoming common as they allow for faster heater of catalytic converters resulting in lower tailpipe emissions. As emission standards become stricter, this will probably become a more ubiquitous design. After the intake air is compressed by the turbocharger it travels directly to the electronic throttle and then enters the water to air heat exchanger. The heat exchanger is molded inside the plastic intake manifold. This makes for excellent use of space and keeps charge air piping routing very short for good response, but also means that any upgraded intercooler will require a new intake manifold as well (the current manifold is molded as one piece without a way to remove the heat exchanger separately). Both engines use the exhaust camshaft to drive the mechanical high-pressure direct injection fuel pump. Both engines have their camshafts driven by chains. The S55 has its timing chain mounted traditionally, in the front of the engine. The B58 moves the camshaft chain, oil pump drive gear, and chain to the rear of the engine. This is done to make the overall engine length shorter so that belt-driven accessories can reside by themselves at the front.