VALVE TIMING

1
VALVE TIMING

• Intake open before TDC
• Intake stays open long after BDC
• Exhaust opens long before BDC
• Exhaust stays open after TDC
• Page 194

2
VALVE OVERLAP

• End of Exhaust , Begining of Intake strokes
• Longer overlap produces more power at high RPM
• Longer overlap produces poor vacuum at idle
• Long overlap, (late exhaust closing) causes
  Lope
• Long overlap cause valve to piston clearance
  problems
• Page 196

3
CHECKING CAM TIMING

• Degreeing in the cam
• Dial Indicator
• Degree Wheel
• Use Intake centerline Method

4
ROCKER ARM RATIO

• Standard Ratio is 1.51
• 1.61 and 1.751 are also common ratios
• .300 lift at cam would be .450 at valve with
  1.5 ratio rocker

5
MEASURING VALVE LIFT

• Must use a solid lifter and Dial Indicator
• Or special tool
• Net Valve Lift - measured at cam
• Gross Valve Lift - measured at valve

6
PERFORMANCE CAMSHAFTS

• Camshafts are a compromise
• Preformance - Economy
• Low RPM Torque - High RPM Horsepower

7
PERFORMANCE CAMSHAFTS

• Coil Bind
• Valve Springs
• Retainer to Valve Guide Clearance
• Rocker arm slot length

8
LIFT

• High Lift Cams increases all valve train wear
• Minumum .125 clearance between
• valve stem seal and retainer.
• Limited by valve to piston clearance

9
DURATION

• Longer duration increases RPM for Max Horsepower
• Shorter duration produces more low and mid range
  Power
• SAE at .006
• Performance manufactures (SAE) at .050
• High compression can offset for long duration