Join Date: Apr 2002
Location: Hanover Park, IL
At idle I am measuring 11 inches of vacuum either from manifold or under butterfly vacuum port on Carter 650 cfm carb. Vacuum goes up to 18 to 19 at about 1800 to 2200 rpm. When deaccelerating it spikes up to 22 to 24 inches. 18 inches vacuum is needed to properly operate power brake booster.
I have called the engine builder and the cam company and everyone says that there should be enough vacuum or there is enough vacuum built into the cam.
Here is what I have; 406 SB (.030 over) Compression ratio is either 9.1 :1 or 10.2:1 (I'm not sure on the cc size of the head). The Extreme Energy Comp Cam is an CS XE284H-10 grind (Lobe Seperation 110 Degrees, Lift is .507 Intake/.510 exhaust, Duration 284 intake/296 exhaust. I have 1.5 roller tip rocker arms as well.
What kind of vacuum should I have and if it isn't enough based on these specs any ideas on where to look? I have already ruled out a vacuum leak to the transmission (TH400) vacuum modulator.