My thinking is that it does not seem like the m3/m4 guys are having significant trouble with their cars overheating on road courses (not thoroughly researched, I just have not heard of any issues).
While it is true that you are adding another boundary for heat transfer, the thought is that you are more effective at both of those boundaries.
It certainly makes sense to have two large thin radiators sitting in front of each other, instead of having two thick ones sitting in parallel. Because one is low temp and the other high. And you just have more space for larger coolers in general with the A2W setup.
However, while the S55 certainly has better coolant cooling, it is not immune to iat-related power reduction.
From
https://f80.bimmerpost.com/forums/showthread.php?t=1003735
Here's how the S55 performs on dyno if you do consecutive pulls. In its defence though, this is probably a worse scenario than anything you would ever experience on track.
In comparison, my car starts to pull timing above iat 130F as a preventive measure, and in the case of my 7in FMIC (non-HD) it mainly affects the end of very long straights (going from 3rd though 5th) in 25C weather if you look in the log I posted.
Just for fun, I tried comparing the virtual dyno curves of the very first WOT pull on track against the very last. I took out the 4th gear rpm range and deleted everything else. During the first 4th gear pull, the car saw 212F coolant and 111F peak iat. During the last it was 223F coolant and 133F peak iat. Also, during the last pull, timing was down by 2-3 degrees, and boost was up 1psi.
Here's the result - a difference of 0-15hp depending on rpm. However, it should be noted that this track is basically two long straights with some lower speed cornering in between. Other tracks may have a slightly higher percentage of wot per lap and a lower average speed.
Since the S55 cooling system is used in the M4 GT4 (with the exception of the DCT cooler, which is from the dct M5/M6) I think it is fair to say it is track-ready, and great inspiration for those of us (read: me) running similarly low power levels. Another point of reference is the N55 powered M2 which also features upgraded coolant cooling, semi-dry oil sump etc but with a traditional FMIC.
EDIT: I talked to some M4 track-junkies here in China and Im told their coolant temps seem to stay below 95C on track, even in hot weather. I am also told that 106C is not a problem with most newer engines from germany...
bmw.spoolstreet.com
