I took the Cummins to work today, to try and get the clutch to release correctly, and noticed that when I am going about 65-70 mph I was making about 5psi of boost. I was on Interstate 90 in the river valley, so it was fairly flat, and it was holding right at 5psi and would jump up a couple psi when I would hit a hill. I had the cruise on so I know it wasn't because my foot was in and out of the throttle. Is this normal? I figured once I was up to speed I shouldn't make any boost, since boost means the motor is fueling and with 4.10's and a 5spd I shouldn't have any problems with torque in the top "hole".
DS79

 

im around 10 pounds at 65

 

im running about 10 -12 psi at 65. 5 sounds right for your mods

 

On flat ground with 3:54 I run about 3psi at that speed.

 

Ok, so my milage just sucks that bad then. That sucks, was hoping I could do something to make it better. So, once I do the 16cm housing, and the 3200 spring I should see even more?
DS79

 

You can raise the starwheel to decrease the fueling at your cruising boost levels, which should result in better mileage....there is a chart around which shows the amount of boost needed to start deflection of the afc spring vs. starwheel height...try the search

 

i'm about 4psi at 65 mph with my 3.55's

 

4-5psi @70mph in my truck. about 10-12psi when going up hill or accelerating.

 

The governor tries to keep the engine at a fairly constant speed, so when you hit a small grade change the governor will add some fuel even if you don't push the pedal down.

 

Sounds good, guess I was thinking I shouldn't see any once I' up to speed. Guess I was wrong. I think the AFC has to see 10psi before it starts to add fuel, I remember reading that somewhere. My star wheel is only turned down about 1/4 turn so that shouldn't be an issue. I need to get my speedo accurate before I get to worked up over milage I guess.
DS79