performance engine preparation engine realities production engines used as a base designed for wot...
TRANSCRIPT
Performance engine preparation
Engine realities
• Production engines used as a baseDesigned for WOT 10% of the timeRPM limits & improved components are needed
• Cold starts and operationEnrichment & idle speedFuel vaporization
• Street engines require vacuumEFI sensorsPower brakesSpark timing on some engines
Performance engine preparation
Engine realities
• Emission testing
CO & HC must be controlledNOX tested on a chassis dyno
Performance engine preparation
Enhancements for reliability
• Increased bearing clearance for coolingOil volume increases 5x, with double clearance
• High volume oil pumps to maintain pressure• Increased sump capacity & windage trays • Increased spring pressure• Guide plates to stabilize valve trains• Reduced reciprocating weights• High strength fasteners• Engine balance
Performance engine preparation
Improving efficiency
• Increase cylinder filling on intake strokeIncrease volumetric efficiency
• Increase cylinder pressure Increase flow into cylinders
Mean effective pressure on power strokeAvoid detonation
Performance engine preparation
Volumetric efficiency
• Air flow into engine divided by swept volumeDoes not include clearance volumeIncludes air flow lost during overlap
Performance engine preparation
Volumetric efficiency explained
• 90% VE means…The volume of piston displacement plus theclearance volume at low pressure after theintake stroke, is equal to 90% of swept volume onlyat atmospheric pressure.
Performance engine preparation
BMEP
• Brake Mean Effective Pressure Calculated based on measured torque Max pressure occurs at max VE, near peak torque
Performance engine preparation
Formulas
• HP @ peak torque = Torque x RPM 5252
• BMEP @ peak torque = HP x 13,000 Liters x RPM
• BMEP @ peak HP = HP x 13,000 Liters x RPM
Performance engine preparation
Effective compression ratio
• Calculation based on the volume at IVC
• Piston displacement @ IVC + clearance volume Clearance volume
• Limited to about 7:1 with pump gasoline & 100% VE• Can be higher with VE lower than 100%
Performance engine preparation
Effective compression ratio (cont.)
• Why high compression pistons?
To keep intake valves open longerMaintain the same effective compression ratioVolumetric efficiency improves
Performance engine preparation
Effective compression ratio with cam specs
• Use cam specs to determine IVC point• Determine rod ratio = Rod length / stroke length• Determine percent of total cylinder volume at IVC• Multiply percent by total cylinder volume
• Calculate effective compression ratio
Performance engine preparation
Airflow through ports
• Areas of improvementEnlarging valve diametersPortingIncreasing lift & durationReducing restrictionsTuning intake & exhaust runners
Performance engine preparation
Flow testing
• Direction of air flow• Valves are opened at precise increments• Readings are percentages of max flow• Percentages are converted to CFM• Corrections for temperature, humidity, & pressure
• Before & after comparisons
• Flow “under the curve” is most important
Performance engine preparation
Improving airflow
• Check wall thickness in castings• Improvements without increasing port size
Short turn radiusBowl shape
Performance engine preparation
Improving airflow
• Use gasket to match port• Raise roofline of port• Match other three sides
Performance engine preparation
Improving airflow
• Enlarge taper below seat to 85% of valve diameter• All seat angles should remain
Performance engine preparation
Improving airflow
• Reduce restriction around guidesCutting down or rounding
• Reduce other restrictions in ports
Performance engine preparation
Improving airflow
Performance engine preparation
Restrictions at the valves
• Valve lift (for 2 valve heads)Estimate for increased output is . . .Valve curtain area equal to valve area
• Areas are the same when lift is ¼ of valve diameter
• Exhaust lift may not be proportional. Done to get
exhaust valve open as far aspossible near BDC
Performance engine preparation
Restrictions at the valves
• Valve lift (for 4 valve heads)Valve area is greater than 2 valve heads
• Intake flow begins & peaks earlier
Can have less lift & duration
Performance engine preparation
Restrictions at the valves
• Cautions with oversized valvesPiston to valve clearanceShrouding
Performance engine preparation
Restrictions at the valves
• Oversized intakes should be limited to ½ bore dia• Valve reliefs can be machined
Maintain .200” crown thickness
Performance engine preparation
High flow valves
• High flow valves have . . .Small radius at filletBack cut of 20º to 30ºUndercut stem
Performance engine preparation
High flow valves
• Exhaust valves benefit from a smooth radiuson upper edge