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Performance engine preparation. Valve events. What are they?. How are they measured?. Which cam lobe leads the other?. Performance engine preparation. Valve events. IVC (Intake valve closing). Determines effective compression ratio. Piston direction @ IVC ?.

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Presentation Transcript
slide1

Performance engine preparation

  • Valve events

What are they?

How are they measured?

Which cam lobe leads the other?

slide2

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
slide3

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
slide4

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
slide5

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
slide6

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

slide7

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

slide8

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
slide9

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
slide10

Performance engine preparation

  • Cam selection considerations
  • Lobe centers
  • Narrow lobe centers . . .
  • Increase overlap
  • Improve VE at high speeds
  • Increase intake reversion (lope)
  • Reduce vacuum
slide11

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)
slide12

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