What’s different between the BMW 435 and BMW 440? From the outside, there are not many differences but, as we learned in school, it’s what’s on the inside that counts. That being said, let’s talk about engines. BMW’s 435i houses a 3.0L Twin Turbo charged 6-cylinder engine. The BMW 440i also houses a 3.0L Twin Turbo charged 6-cylinder engine. The engine in the 435 is an N55 yielding 300hp at 300 lb-ft torque. The engine in the 440 is a B58 yielding 320 horsepower at 330 lb-ft torque. When comparing miles per gallon, both vehicles come in around the same place with the 435 getting 31 highway, 20 city, 24 combined and, the 440 getting 31 high, 21 city, and 25 highway.

               The N55 engine is an open deck engine meaning that there is an open path in the engine block going around along the sides of the cylinders. Because it has an open design, a more efficient cooling process is possible. In the open block engine, the supports are at the ends of the row of cylinders. Being supported in just two places means that this engine block design is not the best option for high pressure. 

The B58 is a closed deck meaning that a different casting meant for for this design, what would be the ‘pathways’ around the cylinders would be closed off. That made the B58 heavier and a little more expensive to manufacture. However, with this design, the blocks have the most support to the cylinders, which will allow the ability to run the highest amount of pressure through the engine.  

One of the other big changes from the N55 to the B58 engine is that the N55 uses an air to air intercooler while the B58 uses an air to liquid intercooler. The air to air intercooler is generally place in the front of the vehicle, funneling air through the intercooler, which lowers the intake air temperature through a process called heat exchange While air to air intercoolers do lower the intake temperatures, they are not nearly as efficient as air to liquid intercoolers. An air to air intercooler is only as efficient as it’s air flow.  A liquid to air intercooler is one where the exchange of heat happens between water and air. The water is pumped through the intercooler so the hot air within the charge pipe is cooled using head exchange with water. This system can essentially be mounted anywhere in your engine as long as a water pump, reservoir, and heat exchanger can be mounted so that it receives sufficient air flow. Overall this is the most efficient option for an engine.  

The B58 engine causes more restricted coolant flow, creating a higher demand for the engine’s cooling system. As a result of the, BMW uses a ‘heat management module’ in the B58. This module is powered mechanically by a crankshaft through the serpentine belt. In the heat management module, the coolant flow rate is adjusted by a rotary valve. To manage cooling the turbo itself, BMW added an extra dedicated electric pump.

In addition to the intercooler systems, BMW has also weighted the B58 engine differently than it’s predecessor, N55. The weight distribution places the oil filter and it’s radiator, along with the timing chain to the back of the engine. In the N55, the alternator, AC compressor, timing chain, and engine oil assembly are positioned towards the front of the engine, which also brings the engine’s center of gravity forward.

The B58 has continued on with a twin-scroll type turbo charger. It is similar to the one in the N55, just with a larger dimension. The B58 has a 6% larger turbine with the compressor wheel diameter being 10% larger. These adjustments give the B58 a 20% boost in pressure compared to the N55.

All in all, the B58 showcases BMW’s latest technology and approaches. The closed deck engine design and air-to-liquid intercooler give this engine clear advantages over the previous, N55. Thanks for reading, see you soon!

Photo Sources:

Water to Air Intercooler. N.d. Http://dsportmag.com/the-tech/bolt-on-basics-cooling-systems/. Web.

Open Deck. N.d. Web. http://youwheel.com/home/2016/03/27/detailed-analysis-the-bmw-b58-inline-6-cylinder-engine/

Carr. Closed Deck . N.d. Web. <http://youwheel.com/home/2016/03/27/detailed-analysis-the-bmw-b58-inline-6-cylinder-engine/>