Performance engine preparation

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 • Piston direction @ IVC ? • Early – High cylinder pressure, detonation • Late – Low cylinder pressure, intake reversion • Occurs after BDC to take advantage of inertia

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

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

5. Performance engine preparation • Valve events EVC (Exhaust valve closing) • End of overlap period • Piston direction @ EVC ? • Early – Pressure rise at end of exhaust stroke • Resists piston travel • Reduces intake flow • Late – Shortened intake stroke • 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 • Intake • Be realistic about RPM range & redline • Measure or calculate static compression ratio • Choose IVC for 7:1 effective comp ratio • Duration based on centerline • Lift based on flow data or ¼ valve diameter

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

10. Performance engine preparation • Cam selection considerations • Lobe centers • Narrow 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