1. Performance engine preparation Valve events What are they? How are they measured? Which cam lobe leads the other?

2. Performance engine preparation Valve events IVC (Intake valve closing) Determines effective compression ratio Early – High cylinder pressure, detonation Late – Low cylinder pressure, intake reversion Piston direction @ IVC ? Occurs after BDC to take advantage of inertia

3. Performance engine preparation Valve events EVO (Exhaust valve opening) End of power stroke Early – Shortened power stroke, lower output Late – Incomplete evacuation, more effort required to remove exhaust gas (pumping loss) Piston direction @ EVO ? “Blow down” is between EVO & BDC

4. Performance engine preparation Valve events IVO (Intake valve opening) End of exhaust stroke & beginning of overlap Early – Exhaust gas dilutes intake Late – Reduced intake stroke & efficiency Piston direction @ IVO ? Ideal – Cylinder & manifold pressures are equal

5. Performance engine preparation Valve events EVC (Exhaust valve closing) End of overlap period Early – Pressure rise at end of exhaust stroke Late – Shortened intake stroke Piston direction @ EVC ? Resists piston travel Reduces intake flow Exhaust gas dilutes intake Manifold vacuum drops

6. Performance engine preparation Camshaft terms Duration – Valve open period Lift – Cam lift or valve lift Overlap – End of exhaust stroke, both valves are open Base circle – Time valve is closed Ramp – To take up valve train slack before opening To reduce shock on valve closing Flanks – Determine opening & closing rates Limited by lifter diameter Nose – Transition from opening to closing Lobe centerline – Centerline of the lobe in relation to crank angle Lobe centers – Angle between intake & exhaust lobes

7. Performance engine preparation Camshaft terms Lobe taper – For lifter rotation Symmetrical cam lobes – Same opening & closing contour of lobes Asymmetrical cam lobes – Different contours ground on opening & closing flanks Dual pattern grinds – Intake & exhaust lobes ground to different duration and/or lift

8. Performance engine preparation Cam selection considerations Measure or calculate static compression ratio Choose IVC for 7:1 effective comp ratio Be realistic about RPM range & redline Duration based on centerline Lift based on flow data or ¼ valve diameter Intake

9. Performance engine preparation Cam selection considerations Does exhaust flow 75% (80% for turbo) of intake? Add duration for low percentages Reduce duration for high percentages More duration = more overlap = poor vacuum Exhaust Good port efficiency is preferred to long duration Exhaust valve open as far as possible by BDC

10. Performance engine preparation Cam selection considerations Narrow lobe centers... Lobe centers Increase overlap Improve VE at high speeds Increase intake reversion (lope) Reduce vacuum

11. Performance engine preparation Cam selection considerations (forced induction) For selecting duration, include CR and boost Increase in compression = boost pressure atmospheric pres Final compression ratio = static CR (increase + 1)

12. Performance engine preparation Cam selection considerations (forced induction) Exhaust flow should be higher than NA engine 80% compared to 75% with NA Increased exhaust duration required to deal with higher VE Lobe centers may be spread to reduce overlap