mike-wsm
Heat Exchanger, Scimitar Engine (Not-Classified)
Page 2 discusses the temperature changes encountered. From what it seems, the pre-cooler takes the temperature from 1,250 K down to 665 K (Truthfully those temperatures seem a touch high for Mach 5 flight as skin temperatures usually just come out to 600 C or 873.15 K), not down to -150 C/123.15 K regardless of mach number (I think the SABRE did operate this way though). This would probably eliminate the turbine-inlet temperature issue I was mentioning earlier (I don't know what the solution for the SABRE was, but it would explain why at around Mach 6, they switched over to rocket propulsion -- that fuel would be awfully hot)