what size turbine wheel and housing do you have??

 

Yea it depends on the size of the turbo also.. but! you shouldnt see boost till atleast 35-45% throttle.
ive pulled trailers and could still stay out of boost.

 

nice, the reason i was asking (besides being a complete newb) is because i know on my buddy's cummins, he runs around 12 psi at highway speeds and I KNOW that theyre a completely different beast but i just wasnt sure if wind resistance and rolling resistane at highway speeds would load the engine enough to create some boost. But thanks for all the information, now I know. I only have the theoretical knowledge of turbos, just finished up my mech e degree, and now i finally have money to do my own turbo build.

M&M, havent even calculated my dimensions out yet. Turbo is still a few months out. Trying to do all of the supporting mods first and then tear into the engine performance stage of the build.

 

With the smaller 4.8 engine, the steady state speed at which you'd need boost to maintain the speed is slower than with a bigger engine. Nobody really tests that because it involves too many variables, and probably because nobody really cares since they don't cruise at those speeds anyway lol. But to generalize, I'd say the 4.8 with a small turbo cam, stock form truck and 3.42s, that speed is probably somewhere around 100mph. I doubt you cruise at that speed, so I wouldn't worry about it.

 

Mech E degree eh, well, sounds like we have a project for you! Calculate what jake said no one really cares about

Heres a hint, do it from an energy standpoint. Develop a correlation between energy required and steady state speed...I would start by looking at injector duty cycle at a given speed and back calculate the amount of energy used to maintain that speed (energy rate, actually). Then from there you can infer how much potential energy you are giving the turbine, and using some assumptions about the turbine see how fast it is moving, and from there take the compressor map and find your airflow and wheel speed and see where you would make boost. Should be simple

I should note this is obviously over-simplified since engine VE is changing at every rpm (among other things), but this should get you close!

 

ok lets say i don't set my cruise at 100 to 110 very often anymore(engines wore out) is it possible to set something up to only make boost when you want to? i've heard of boost controllers but to be honest i haven't bothered looking to see what they do. i need to build my new 6.0 first

and yes i used to set my cruise that high when i was traveling alot and knew the highways and cops routines. highest i ever had it set was 120 for about 50 miles....and no i never said i was smart when i was in my 20's

 

Your right foot controls when you go into or out of boost. A boost controller presses harder against the valve in the wastegate, therefore keeping it closed against more boost pressure so you can build higher boost. You start off with a set wastegate spring, and the wastegate would bleed off boost pressure at anything over what that spring can handle, when you put the controller to it, you can increase the pressure against that valve, giving you the ability to increase boost.

 

Even with the most advanced boost controllers, it still takes boost to assist the wastegate in opening. So, you'd have to be in boost before you could vent exhaust around the turbo to prevent it from spooling. Interesting question, though..

 

Smokeshow, you underestimate me HAHA

 

Here is mine boosting at hwy speed with 3.42's
Nick's turbo 5.3 truck - YouTube