Manifold bolts should not be over- or under-tightened, so use this type of wrench with a foot/pound scale
[DOC] [TLE] How to Use a Torque Wrench - Auto Diagnosis Repair Help [PAR] You need a torque wrench to accurately tighten nuts and bolts, especially those 
that must be tightened to a specific load so they do not stretch ... A typical 
automotive torque wrench will have a scale that reads up to about 200 to 250 ft. 
lbs.