So I've scoured the internet in search for discussion around the 540i vs 550i, and surprisingly haven't come up with anything.

From research, it's clear that most people have a preference from the 550i to the 545i, mainly due to reliability due to an added oil cooler and lower maintenance costs.

One thing I've never seen people discuss is comparing the 540i and the 550i.

So with that, does anyone have any information regarding the 540 vs 550 in terms of reliability, and features?

This is especially interesting to me as unlike the 545/550, the 540/550 were made in parallel to each other, so in theory they should be the same car with same characteristics and reliability, but different engines.

 

I'm not sure about the rest of the world, but here in the US we never got a '540i' version of the E60.

I'm sure some others from other parts of the world will chime in.

 

the only 540's were e39's. A ton of problems with these V8's so not recommended.
The 550i is a much better car being an e60 with many of the issues resolved from the 545's.

The only issue for me is the gas guzzling aspect of the 550.

 

The engines between the E60 540i & 550i are technically the same. Same N62 block, different bore and stroke.

But an interesting aspect is that the N62B40 bore is much smaller than either the B44 or B48. However the stroke is even longer than the B44.

I would assume the reliability of the B40 might be a little bit better, since it doesn't put out as much power. It is on par with the output of the 535i twin-turbo I6, but at higher revs.

A good comparison between all 3 of these motors is finding dyno graphs of the stock engine to see how they perform (relatively) against each other at matching revs. That would give a good idea to see if there are any benefits to using a smaller bore or longer stroke.

 

According to this website (BMW N62), it appears the N62B40 was only released as a N62TU, just like the N62B48. So the reliability should more closely match the B48.

Also, the N62TU family appears to have had a bump in compression ratio from 10.0 to 10.5.

 

The N62 is an open deck block where the M62 isn't. Both make use of Alusil. Also, the N62 has valvetronic and double-vanos.

 

Ah it seems like there's a little confusion as the US didn't get the 540i with an N62.
It runs an N62B40 as dingolfing mentioned, with same production years as the B48 (550i)

Interesting... From what dingolfing has said my theory might be correct.