Performance engine preparation Engine realities Production engines used

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

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

Performance engine preparation Enhancements for reliability • Increased bearing clearance for cooling Oil volume increases 5 x, 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 stroke Increase volumetric efficiency Increase flow into cylinders • Increase cylinder pressure Mean effective pressure on power stroke Avoid detonation

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

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.

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 longer Maintain the same effective compression ratio Volumetric 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 improvement Enlarging valve diameters Porting Increasing lift & duration Reducing restrictions Tuning 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 radius Bowl 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 guides Cutting 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 as possible near BDC

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

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

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 fillet Back cut of 20º to 30º Undercut stem

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