For what it's worth, I believe the RB26DETT head flows 23X -24X CFM Range.
You can see a 380WHP GTR with a 8000RPM Redline go to 600WHP and beyond, including the benefits of headwork. FYI this was on 94oct:
https://dsportmag.com/the-cars/proje...ne-in-the-u-s/
https://dsportmag.com/the-cars/part-...d-part-2-gt-r/
https://dsportmag.com/the-cars/part-...part-3-gt-r/2/
