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Performance engine preparation

Performance engine preparation. Engine realities. Production engines used as a base. Designed for WOT 10% of the time. RPM limits & improved components are needed. Cold starts and operation. Enrichment & idle speed. Fuel vaporization. Street engines require vacuum.

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Performance engine preparation

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  1. Performance engine preparation • Engine realities • Production engines used as a base • Designed for WOT 10% of the time • RPM limits & improved components are needed • Cold starts and operation • Enrichment & idle speed • Fuel vaporization • Street engines require vacuum • EFI sensors • Power brakes • Spark timing on some engines

  2. Performance engine preparation • Engine realities • Emission testing • CO & HC must be controlled • NOX tested on a chassis dyno

  3. Performance engine preparation • Enhancements for reliability • Increased bearing clearance for cooling • Oil 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

  4. Performance engine preparation • Improving efficiency • Increase cylinder filling on intake stroke • Increase volumetric efficiency • Increase flow into cylinders • Increase cylinder pressure • Mean effective pressure on power stroke • Avoid detonation

  5. Performance engine preparation • Volumetric efficiency • Air flow into engine divided by swept volume • Does not include clearance volume • Includes air flow lost during overlap

  6. Performance engine preparation • Volumetric efficiency explained • 90% VE means… • The volume of piston displacement plus the • clearance volume at low pressure after the • intake stroke, is equal to 90% of swept volume only • at atmospheric pressure.

  7. Performance engine preparation • BMEP • Brake Mean Effective Pressure • Calculated based on measured torque • Max pressure occurs at max VE, near peak torque

  8. 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

  9. 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%

  10. Performance engine preparation • Effective compression ratio (cont.) • Why high compression pistons? • To keep intake valves open longer • Maintain the same effective compression ratio • Volumetric efficiency improves

  11. 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

  12. Performance engine preparation • Airflow through ports • Areas of improvement • Enlarging valve diameters • Porting • Increasing lift & duration • Reducing restrictions • Tuning intake & exhaust runners

  13. 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

  14. Performance engine preparation • Improving airflow • Check wall thickness in castings • Improvements without increasing port size • Short turn radius • Bowl shape

  15. Performance engine preparation • Improving airflow • Use gasket to match port • Raise roofline of port • Match other three sides

  16. Performance engine preparation • Improving airflow • Enlarge taper below seat to 85% of valve diameter • All seat angles should remain

  17. Performance engine preparation • Improving airflow • Reduce restriction around guides • Cutting down or rounding • Reduce other restrictions in ports

  18. Performance engine preparation • Improving airflow

  19. 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 as • possible near BDC

  20. Performance engine preparation • Restrictions at the valves • Valve lift (for 4 valve heads) • Valve area is greater than 2 valve heads • Can have less lift & duration • Intake flow begins & peaks earlier

  21. Performance engine preparation • Restrictions at the valves • Cautions with oversized valves • Piston to valve clearance • Shrouding

  22. 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

  23. Performance engine preparation • High flow valves • High flow valves have . . . • Small radius at fillet • Back cut of 20º to 30º • Undercut stem

  24. Performance engine preparation • High flow valves • Exhaust valves benefit from a smooth radius • on upper edge

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