EGR Valve Exhaust gas recirculation Used to reduce Nox (oxides of nitrogen) The EGR system mixes spent exhaust gasses with the fresh A/F mixture. The inert exhaust gas displaces some of the A/F mixture (5–10 %), thus reducing combustion temperature. High temperatures are the main cause of Nox.
Carburetors and TBI -The carb/TBI unit delivers an air/fuel charge -Most of the fuel in this charge will evaporate by the time it reaches the combustion chamber (up to 60%)
Carburetors and TBI The remaining fuel droplets will be carried to the combustion chamber at high velocities (300 ft/sec). Swirling aids in the atomization of fuel Guide vanes Abrupt bends Rough inner walls What about golf balls?
Carburetors and TBI At low velocities (under 50 ft/sec) the fuel droplets will separate from the charge and form on the runners of the manifold. This is known as separation A/F mixtures must be richer at idle to compensate for this
Carburetors and TBI Manifold runner cross-sections must be large enough to flow sufficient charge at high RPM but … small enough to maintain a sufficient velocity for fuel droplet suspension. This is one reason why racing engines have a high idle.
Carburetors and TBI V-? Design On a dual-plane or 180 degree manifold one half of the carb. or TBI unit feeds half of the cylinders. Runners may be tuned On a single-plane or 360 degree manifold all cylinders are fed from one open plenum. The intake runners are therefore split into two separate passages at different heights.
Closed Manifolds Open – the bottom of the manifold is separated from the lifter valley. Benefit – the bottom of the manifold does not contact the hot oil. Cooler temp = denser charge
Closed Manifolds Closed – the bottom of the manifold is the top of the lifter valley. Benefit – the bottom of the manifold contacts the hot oil. Better atomization of fuel at cold temps. Coking may occur on a closed type manifold if a heat shield is not used. Thermo-barrier paints are also used.
Port Injection Manifolds The fuel injector is located approximately 3” from the intake valve. Therefore: Runners are for air flow only Swirling is not as necessary Plastic manifolds
Exhaust Manifolds Generally cast iron May be annealed (heat-treated) May be tubular steel Will generally house an o2 sensor Cracks Leaks
Headers Runners Collectors
Headers Reduce restriction for better high RPM power Tuned headers – designed to combine individual pulses into one large pulse. The pressure behind this pulse is lower than atmospheric pressure. Thus – a pulsing vacuum is present called: Scavenging
Headers Low to medium RPM power and torque Long runners (34-38”) Long collectors (12-15”) High RPM power and torque Increased diameter runners Shorter runners and collectors Benefits are measurable above 3500 RPM
Headers Ceramic coating Properly working headers should make a rapping sound between 3500 to 5000 RPM.
All recent automotive oiling systems are of a full-pressure design. Typically driven by the Camshaft Distributor shaft (one-half engine speed) Crankshaft (full engine speed)
Oil Pumps All production oil pumps are positive displacement pumps. All oil that enters must exit May be gear or rotor type. Pumps are sized so that approximately 10psi of pressure is available at idle. Pressure increases by approx. 10psi per 1000 rpm
Gear-Type Oil Pump
Rotor-Type Oil Pump
Oil Pumps The oil pump is the only component of an oiling system that receives unfiltered oil. On all oiling systems oil exiting the pump will feed directly into the oil filter. The screen on the pickup is the only method of debris stoppage.
Oil Pumps Oil pump pick-up screens utilize metal covers to prevent cavitation (aeration). Cavitation is caused by Oil being exited out of the pump faster than it can push it. Air being sucked into the pump via a sudden stop.
Oil Pressure Regulation All full-pressure oiling systems utilize a pressure relief valve Generally spring regulated The higher the spring tension the greater the oil pressure Excessive oil is bled back into the inlet side of the pump.
Oil Pressure Regulation 3 to 6 gallons of oil per minute are required to properly lubricate an engine. Excessive oil pressure does not lubricate an engine better and requires more horse-power to maintain.