BMW's B58 engine received quite a few important technical updates beginning in 2018. The new variant is dubbed the B58TU1. It is also available in "ML" and "OL" versions. ML represents the "middle output" 335hp version, while OL is the "high output" 382hp engine. Given the B58 is still a new engine, only time will tell how much of an impact the revisions have. Let's break down the B58's technical revisions and discuss the impact of each.
B58 vs B58TU Differences
Often, technical updates are intended to fix design flaws or problems. However, BMW's primary reason behind the B58 technical revision is emissions. Notable B58 updates include:
- Fuel system
- Particulate Filter
- Timing Chain
- Cylinder head/manifold
B58 fuel system, particulate filters, and split-cooling are all intended to improve emissions. The remaining updates assist in supporting the emission improvements. For example, the new B58TU fuel system flows up to 350 bar compared to 200 bar on the original B58 engine. The timing chain was re-designed in order to support the higher pressure fuel flow. Now, let's take a look at each of the revisions individually.
B58TU Fuel System Update
The B58's new fuel system flows at a 75% increased pressure. Maximum fuel pressure on the B58TU1 is a staggering 5,075 psi (350 bar), up from 2,900 psi. Increased fuel pressure assists in reducing soot particles produced during combustion. The B58 receives an updated high pressure fuel pump and injectors to support higher pressure.
B58 Fuel System Performance
The updated fueling should provide some benefits on modded B58 engines. It's higher pressure fuel system will assist in supporting additional horsepower. However, it will be interesting to see how the fuel system holds up. BMW experienced serious troubles with the initial N54 HPFP's. Hopefully BMW got the even higher pressure B58 pumps right on the first go round.
B58TU1 Particulate Filter
For us performance nuts, the B58 particulate filters are a horrible addition. They are similar to catalytic converters, but more restrictive. Fortunately, the filter is located in the downpipe. We always recommend catless downpipes, anyways. You may opt to simply remove the filters from the downpipe. Of course, you may also opt for aftermarket downpipes.
There isn't much else to say here. Particulate filters are good for emissions, but not for performance and sound. Get rid of it!
B58TU Timing Chain Update
BMW re-designed the B58 timing chain to support the fueling changes. The original B58 features a two-part timing chain. However, the B58TU1 converts to one-part timing chain. In turn, the base wheel is eliminated leading to reduced friction. Sounds good, in theory. BMW timing chains have always been excellent, reliable systems. Of course, with the exception of some issues on early N20 models.
We don't expect the timing chain update to mean much. The update is solely intended to support the higher pressure fueling. Otherwise, the timing chains on both B58 versions should be near flawless.
Split-cooling on the B58 is an interesting concept. Again, this update is emissions related. The B58TU1 now features separate cooling circuits for the cylinder head and crankcase. This allows the cylinder wall temperature to remain higher under low loads. At the same time, the cylinder head still receives adequate cooling. Higher cylinder wall temps assist in reducing emissions. Keeping the cylinder head temps down mitigates the chance of engine knock.
With regards to the newer S58 engine, the split-cooling concept was ditched. BMW re-designed the cylinder head of the S58 using different coolant duct routing. It will be interesting to see if BMW does something similar with the B58 in future updates. For now, the split-cooling approach should not have much of an impact apart from reduced emissions.
B58TU Crankcase Update
To facilitate the above updates, the B58TU1 receives a unique re-design of the crankcase. For one, wall thickness optimized alongside additional weight saving measures. This results in weight savings of roughly 4 pounds. Additionally, the B58's forged crankshaft is further optimized. As a result, a few pounds are saved.
Though minor, this is a good update for the B58. Removing weight from the front of the vehicle is always beneficial. Also, lowering the weight of any rotating parts, such as the crankshaft, is a good thing. Of course, assuming strength was not compromised. Nonetheless, this should not be a concern with the B58. It is a forged crankshaft that should not have any issues below 1000hp. Other internals will let go long before the crank.
B58TU1 Cylinder Head/Manifold Update
Integrating the exhaust manifold into the cylinder head housing is, once again, an emissions related update. This allows the engine to warm-up faster and reduces weight and cost. The below image shows the B58 (B) compared to the B58TU1 cylinder head (A).
In image A, you can see the manifold integrated into the cylinder head. Once more B58 owners begin pushing the limits it will be interesting to see how this affects performance. It may cause some complications in larger top-mount single turbo options. Again, the B58 is still a relatively new engine. Especially the B58TU1. Many are still under warranty and, as such, are not being pushed to the limit. Time will tell how this integration affects aftermarket developments.
B58TU Technical Update Summary
It appears BMW is showing their commitment to the new modular B series engines. The N54 was primarily found in 2007-2010 models. And the N55 is 2011-2015 models. It's likely the B58 remains in production for years to come. BMW wanted to stay ahead of the game and improve emissions due to increasingly stricter emission laws. As such, the B58TU1 was introduced.
Of course, BMW also wanted to improve performance. The high output B58TU1 sees a bump in power to 382hp. While the fuel system and cylinder head updates were intended to improve emissions, they may have an impact on performance, too. Higher pressure fueling should enable modded B58's to keep up with the demanding fuel flow. However, the integrated exhaust manifold may create complications in aftermarket turbo setups. The differences should be minimal in the long-run. Though, it's worth monitoring as B58 and B58TU1 engine begin to come out of warranty and are pushed further and further.