Forced Induction Ramair Superchargers Turbochargers and Nitrous Oxide

Forced Induction Ram-air, Superchargers, Turbochargers and Nitrous Oxide

Forced Induction Theory An average normally aspirated engine will achieve approximately 85% volumetric efficiency n With forced induction, a volumetric efficiency well in excess of 100% can be achieved n By increasing the amount of air entering the engine, more fuel can be burned which creates more cylinder pressure and more power n

Ram-air Induction May use forward facing hood scoop, cowl induction, or a forward facing air inlet tube exposed to a higher than ambient pressure area n Uses the speed of the vehicle to pressurize the intake system n

Superchargers Engine driven air compressor capable of pressurizing the intake of an engine n Types n – Roots – Screw – Centrifugal – Axial flow

Roots Supercharger n n Positive displacement type Acts as an air pump Constant boost pressure across the full RPM range Numbering System (example 6 -71) – 6 cylinder – 71 CID per cylinder

Screw Type Internal compression type n Similar to roots style n Lobes interlock and compress the air along the way n More efficient than roots style n

Centrifugal Similar to a turbocharger except it is driven by the engine n Uses an impeller to compress air n May be connected to engine by hoses n May be mounted in more convenient positions n

Axial Supercharger Not widely used n Similar in operation to a jet engine n Multiple compressor rotors progressively compress air n

Supercharger Efficiency n n Volumetric efficiency – Ratio of theoretical airflow and actual airflow – Example: one revolution of the supercharger should displace 5 CFM but in operation only 4 CFM are displaced per revolution - 80% VE Adbiatic efficiency – Ratio of how much engine power is used to run the supercharger to how much air is compressed (air heating has a negative impact on adbiatic efficiency) » » » Roots – 50% Screw – 65% Centrifugal – 75%

Turbochargers n n Exhaust gas spins the turbine wheel which then drives the compressor wheel Disadvantages – Increased backpressure – Turbo lag n A wastegate causes exhaust gas to bypass turbine wheel when boost pressure reaches a pre-determined level – it is operated by an actuator which senses induction system pressure

Turbochargers Rotational speeds may exceed 10, 000 RPM n Turbo charger bearings are oiled with engine oil (oil starvation a major cause of turbo failure) n Manufacturer’s suggest allowing engine to idle 30 – 90 seconds before shutting engine off n

Nitrous Oxide Nitrous oxide increases engine horsepower by supplying more oxygen to the combustion process which allows more fuel to be added n With nitrous the engine is supplied with more oxygen than it could draw through the induction system normally n

Nitrous Oxide Chemistry n n N 20 = nitrous oxide (2 nitrogen atoms and 1 oxygen atom) – The nitrogen acts as a buffer and slows the combustion process – This prevents major cylinder pressure spikes which would cause part failure Nitrous is 36% oxygen by weight – Atmosphere is 21% oxygen Boiling point of nitrous at sea level is 128 degrees When N 20 reaches 572 degrees Fahrenheit it separates into one oxygen atom and two nitrogen atoms – At this point the oxygen is available to the combustion process

Nitrous Oxide Use The number one concern when using nitrous oxide is “going lean” n Nitrous oxide is stored in a bottle at approx 900 PSI n Engine components must be selected to withstand the increased cylinder pressures n

Nitrous Oxide Systems - N O S + Arming Switch Nitrous Solenoid Throttle Switch Carburetor Fuel Pump Fuel Solenoid Nitrous Plate

Nitrous Use 100 – 150 horsepower systems are generally safe for a stock V-8 engine in good mechanical condition n Limiting factor is cylinder pressure. n – More nitrous, more cylinder pressure – More cylinder pressure, more power – More cylinder pressure, more likely that stuff breaks