I will leave the short answer to the end of this entry. Before that, several technical deviations.
And before that – disclaimer. As usual, many engine “upgraders” will not like what I wrote.
Offtopic No.1. If we had asked any engineer twenty years ago, how to build a “street” car with a turbo engine with 2+ bar boost pressure and 1:11.0 compression, he would say – it is not possible! Why? With such a high compression ratio, the fuel will self-ignite; the combustion will be accompanied by harsh knocking.
Why do BM engines not blow up? The answer is DI or Direct Injection. And not only, specifically, exactly the Injection strategy of these engines. This strategy involves starting to inject fuel a short moment before ignition. For almost the entire duration of the compression cycle, in the combustion chamber, there is either pure air or a very lean fuel mixture. It solves the problem of fuel self-ignition. Even when the fuel is injected in the combustion chamber, it does not have enough time to mix with the air; the mixture that is able to combust (rich enough) is only in the “vicinity” of the spark plug. That’s why this Injection strategy/fuel mixture is called “layer”, not “homogeneous”, although the average Lambda is 1.00, as in homogenous mode – in the old-school engine.
Off-topic No.2. As we know, B-series engines are manufactured on the basis of the same platform, both for petrol engines and diesel engines. And this is not without a reason or because “it is cheaper”. BMW manufactures hundreds of thousands of these engines each year. If they were able to save even 1 EUR on a lighter crankshaft or pistons, BMW would save because it would be many millions of EUR during the lifecycle of these engines. Obviously, there is no option to save.
If you would listen to how the B series engines “sound” on the go, most probably, the first association would be: the engine is damaged! It’s knocking harshly! And for the second part, you would be right. In B-series petrol engines, the combustion process is very “hard” – it is similar to the diesel combustion process. Also, the torque for this petrol engine in the “street” version is close to the diesel version: 500Nm (F LCI series versions with Performance and Sound kit or Mx40i G series first releases) to even 550Nm (from year 2023, outside the EU) and even 570Nm for the Toyota Supra for export. And all of this – in the name of fuel economy and performance.
Not taking into account the impressive torque/power curve, the stock B58 is “not sick” with any piston problems. In my opinion, it is an indicator of excellent quality, safety, and longevity. There are millions of these engines cruising the roads of the World. Imagine, even if each 100th has had some failure, the number of defective engines would be tens of thousands. No, completely serious – there are no such massive failures!
Until recently, engines of this performance were installed in sports cars. Teams of professionals were working to tune them; each parameter was controlled.
The next breakthrough – the engines of such power were tuned by the best tuning companies. And again – professionals tested, adjusted, measured.
Today’s situation – we send DME to the company, who unlocks it, without our own/local tool, download the “megaturboperformance” management map versions, and the job is done. Without any check of the basic parameters. Even without readapting the engine. Even not knowing if the engine has any problems (I’m not even talking of the fuel hunger, but, for example, worn spark plugs or partially damaged ignition coils).
If a bunch of error messages appear, EML lights up, the owner posts the list of the “codes” in the internet forum/Meta with a question, “What went wrong?” In the forum, there are 99% the same users, who would recommend the most unimaginable “solutions”.
And finally. Are these companies that perform B58 “tuning” car modifications equipped with the appropriate lab and test equipment to test the combustion process fully? Of course, not. What is done during this “tuning”? With an external device (for example, in the case of JB4) – in DME, lowered boost pressure and air mass indications are sent – as a result, DME tries to “push” larger boost pressure than previously. In case of modification of DME maps, a larger boost pressure is required.
In both cases, logically, if you manage to “squeeze” more air out of the stock turbo (and up to a certain point you can: when you don’t, you get a “Christmas tree” as a “bonus”), you need to inject more fuel. Does this process take more time? It does. Does the risk of self-combustion increase? Significantly increases. Does the risk of knocking increase? Significantly increases. Have the tuners considered these aspects? Unfortunately, no. More precisely, they offer a “solution” at your own risk. To develop modified Ignition/Injection strategies, a completely different amount of knowledge, equipment, and budget is required. My belief: you cannot inject 20 .. 30% more fuel based on the previous fuel maps and expect a stable/safe result!
Such (I would use the term – unprofessional/amateurish work) “tuned” engines to “catch” knocking – simpler than simple. There is a range of reasons! As previously mentioned, Injection maps – the story is both for an adequate/correct amount of injected fuel and a timing strategy. Next story – is the current vehicle able to accomplish this task: is its fuel system in a perfect condition? Or – is the fuel mixture controlled after the modifications and during regular maintenance? The answer – of course, not!
In addition to the previously mentioned, even harsher situations – for example, in the case of external equipment: additional fuel amount injection is “intended” at the expense of DME adaptations. Is the adaptation corridor wide enough? Nobody knows that. Even the ones who offer the “solution” do not talk about the “installer”. Accordingly, when external conditions change (for example, weather becomes cooler or more moist), the turbo “blows” a little more air than previously adapted by DME (and can correct STFT), and a leaner fuel mixture/knocking is guaranteed!
In my opinion, if we take into account the level of these “tuning” solutions, the qualifications of installers/customers, you have to wonder why so few pistons are alloyed. No, the Pistons are not the ones to blame. Pistons (unfortunately for them) are the components most directly exposed to the sadistic exploits of all these “tuning” procedures.
My belief says – specialists whose level of technical knowledge matches the level of development of engines and their controls, seeing how 400+ hp engines are “obtained” nowadays, “quietly smoke in the corner” with a “wtf is going on” inside.
p.s. I invite you to pay attention to the compression ratio of the B58 engine vs the S58 engine. For S58, it is 9.3 (not 11.0 as for B58). However, the torque is only 10 .. 15% higher than for the most powerful B58 release. A tricky question – why was the compression ratio reduced in the case of the S58 engine, instead of simply “pouring in” a “more powerful” fuel map?
