Somewhat belated entry into this discussion... I have a fully cleaned up M54B30 IM sitting on my coffee table complete with DISA and adapter plate... From the previous posts here it seems that the only fundamental difference in modification for £1000 was the throttle body was bored out and a larger butterfly fitted. Although the IM was also "machined" - by which I assume the runners were machined at the cylinder head ends to assume the same "D" shape.
Having just recently spent 3 days cleaning up the M54 IM, the "D" shape on the M54 manifold ends aproximately 65mm into the runners and thereafter they are oval heading back to the throttle body side of the IM.
What does this mean with regards to improved airflow / intake other than that the flow into the cylinder head ports is matched.
I have read conflicting comments about the length of the M54 runners being shorter than the M52TU runners and some comments that they are longer... Until I take my TU IM off I can't verify what is true or if there is any difference in length at all.
But if anyone also has an M54 IM uninstalled, you can put a finger inside the runner at the square corner of the "D" and follow it inwards. You will find it tapers off just as the bend begins and thereafter the runner walls become oval.
Notwithstanding, it must be an improvement otherwise BMW would not have bothered.. But is this "D" only a requirement for the 3.0 plus size motors since they require more air ??
I have only seen one set of comparative dyno logs of before and after the swap. This showed a 13 HP gain at the crank. I'm not sure what that means HP at the crank or the wheels is Greek to me - what's the difference??
Is 13HP at the crank 5 or 20 HP at the wheels??
Anyhow, I had planned an early start tomorrow to strip out the OEM IM and fit the M54b30 IM... now I'm not sure if it's worth the effort or not.
I do know that
@Antm72 mentioned to me of "someone" on the forum who had done this mod, but that he had had the OEM TB Bored larger.
I assume that would be
@Portmyster who makes reference to it above.
@Antm72 also tells me there's a fella on eBay that offers the "larger bore" M52TU throttle body - I did an eBay search but found nothing in that regard...
Having looked at my OEM throttle body, it doesn't really look like one can bore it out more than 2mm in total diameter increase. That would mean very little gain, or perhaps not ??
I would be interested to hear from any and all what their experiences are or if they can add any verifiable information about this modification.