Trying to figure out something new to me while dialing in my TPI setup on the rebuilt engine. At idle (850 RPM), vacuum is reading a stable 16 inches. When I crack the throttle open and increase RPMs to a steady 2000, vacuum increases to over 20. I always assumed that vacuum is highest at lower RPMs, such as at idle. I'd appreciate any education on this.

I'm breaking in the engine, so brought RPMs to 2000 by screwing in the throttle stop screw on the throttle body. That way it could idle up without me holding the blades open.

 

Target idle speed vs coolant temp but the iac might max out to achieve such a high rpm. Stick something between throttle arm and stop.

 

I used the throttle stop screw on the driver side of the TB to bring up the idle, that seemed to accomplish bringing the idle up.

Would IAC activity allow for higher vacuum levels at higher idle RPM? That was the only mechanical piece I could think of that would change based off computer commands.

I'm also having a valve tapping issue, so resetting the ARP rocker lock nuts to 1/2 turn past zero lash. At least one was a little loose after my first attempt to set.