I recently had the roush i/c kit installed.

I was pulling my boat, cruising about 65 mph at 2500 rpm. In a part throttle condition.I got to thinking about what makes the booost and if it was full boost at these speeds or partial, or ..

What makes the boost? Rpm, or throttle positon or. something else.

 

I believe the supercharger, as long as it's spinning, is capable of making boost. There is a boost by-pass which is another air passage into the manifold plenum, which effectively will not allow you to pressurize air in the intake manifold. That separate air passage has a vacuum operated throttle valve. When the valve is completely closed, the manifold can generate full boost. When the valve is partially closed it is capable of making some boost.

There are two functions that control the valve, one is vacuum, the other is the boost by-pass solenoid which is controlled by the PCM. The solenoid will cut off vacuum to the valve unless the programmed amount of load and rpm level is reached. If you have the Roush tune, you will have to generate quite a bit of load to be able to generate boost at lower rpm. A custom tune, can be written to allow boost to be made under lower engine loads. Something that might not be a good thing when towing a heavy load.

 

the boost by pass valve, is what allows the truck to make boost, and it's based off of vacuum or lack there of

 

if you have the stock roush tune I want to say its around 60% throttle to make boost.

 

You also might wanna get yourself a boost gauge to help monitor the situation.