Yes!!! HTHS is even more importaqnt in a turbocharged application. In addition to the obvious stress's a turbo puts on an oil you also have increased loading on all the engine parts. Most turbo's use piston squirters adn some use airators onthe head above 6000 RPM. A HTHS of 2.6 is the minimum for N/A engines for good valvetrain and timeing chain life at speeds typicaly seen iin the USA. My personel minimum is 2.9 for a N/A engine driven at USA HWY speeds. In a turbo application I would want at least HTHS of 3.5 as a minimum and would prefer 4.5 or higher. Redlines 5W40 has an HTHS of 4.8 so you can still get good cold pumping oils with plenty of protection! Their 5W20 has an HTHS of 3.3 so my personel minimums are easy to meet.
