Originally Posted by NYC6
You're correct to a certain extent. The aluminum alloy used in the N54/55 blocks contains other elements, Mg included and the Mg block in the N52 contains other elements as well. The fact is, the Al block is mostly Al and the Mg is mostly Mg. The other elements are in small amounts to serve specific function. Im not saying, nor have I said the N54/55 engines are 'better' just that the N52 block are deemed not suitable for F/I power levels by the man who knows best about the engines. Direct from the horses mouth! Explains it quite simply. Some hate to hear the truth. Not too surprising.
I appreciate the technology that BMW used to make this first and one of a kind lightweight engine. Its a marvel of design and execution to marry 2 alloys together and make them work in such a great way to make power and cut a nice chunk of weight off the front of the car. Being the hp freak I am I needed more power for my DD. If not, I could have been quite happy with a 128. Its a fine package indeed.
I posted some information directly from BMW saying why they wont use the Mg/Al block for turbo cars. There are many here that have been chomping at the bitt for F/I to be made available for their cars when I dont think its coming and thats why I posted. Its not something I made up to piss owners off but thought owners would like to know the truth from the real expert in BMW's engineering/ motor building team. Mr Welter knows the exact alloy BMW alloy formulas, wall thicknesses, design criteria and all necessary data..... and concluded from all that, it wont work. Some take that as insulting when that wasnt the intent. So be it.
article mentions forged early in the article but most of it its talking about cast. And we are talking about the overall design of the engines, application(F/I) and powertrains(N54 turbos) so its all very relevant.
No, I'm not correct to a certain extent, I am 100% correct. BMW uses an Al alloy (Aluminum base with added elements, most casting Al alloys are also high in Si for improved wear) and the Mg alloy has added elements as well. Al and Mg are both pretty poor elements to use in a pure state, but when alloyed meet the design characteristics.
Al alloys are typically higher strength than Mg alloys, but strengths can vary greatly by subsequent heat treatment (solution temp, aging temp, etc.), but I believe Mg alloys have a higher strength-to-weight ratio, which is really the key design factor. An Al alloy with a high age temperature could have a lower tensile strength, than a Mg alloy with a low or two stage age heat treatment. BMW's heat treatment temps/time could also be proprietary and not the same as general published heat treat times/temps.
Now why is BMW switching to an all Al alloy block, versus the Mg-Al block? That is question no one has the answer to, and the rest is all pure conjecture. (It could be cost for all we know, which BMW would of course, not officially announce to everyone).