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 _at_ 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 _at_ 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 _at_ 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 _at_ 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 71 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