The 6.5 is an indirect injection engine. Horsepower is not what IDI engines do. They run great, awesome low rpm non turbo reliant grunt, good mpg without turbo help and with a turbo have the ability to push a driver back in the seat with a gleeful yell.
I’m not trying to make this about me. However, I want to relate a 313 mile drive I did yesterday in the Cowdog. 6.5 GEP engine, turbo heads, diamond pre cups, 6.2 intake, 4L80E transmission and Banks Sidewinder turbo. 2,000 rpm is right at 70 mph. I can get up to highway speeds without any boost if I stay out of the power. But, any other car on the road is going to be faster than I. Just a little more right foot gives me 1-2 psi of boost and I am flowing with traffic if not leading. However, in the boost means higher exhaust gas temperature and higher coolant temperatures. The IDI head gets very hot very fast with boost pushed into it.
Cruising at 70-75 mph means 0 to maybe a pound of boost on flat road. Meaning the turbo isn’t even needed for normal driving. Along comes a hill, head wind or even an overpass. Then it is either get slowed down or ride the boost to maintain speed. Sustained boost means coolant temp will start creeping up and up and up. Out of the boost and all the temperatures go back to normal just as fast.
Drive behind a direct injection engine with a turbo and it is a completely different experience. They are for the most part boost dependent. Which is fine since their heads don’t get hot and they have lower compression.
My point is that direct injection engines better in just about every way. That is why all the manufacturers have gone that way for at least the last 15 years. IDI engines do not compare to the DI ones. Except for lighter weight and all mechanical controls.
A turbo on an IDI engine is to be thought of as a supplement. Sure, with lower compression pistons, an intercooler, water or alcohol injection and a few other things IDI engines can get to where DI engines were 10 years ago. But, that is it.
