Rotary Car Club - View Single Post - Forced Induction for Dummies (Turbo, Supercharger, Nitrous)

Kane · 10-17-2008, 04:29 PM

Turbocharger / Turbo / Snail – this raises the pressure of the air (boost) by using the exhaust gases exiting the engine to power a compressor that pressurizes the incoming air.
Supercharger / Blower – this raises the pressure of the air (boost) by using the eccentric shaft / crankshaft to power a compressor that pressurizes the incoming air.
Nitrous / Spray / Bottle – this raises the oxygen CONTENT or partial pressure by injecting nitrous oxide into the incoming air. A partial pressure of oxygen (pp O2) of .42 or 42% would be equal to the partial pressure of oxygen in air at 2 ATA, or roughly 14.7 PSI of boost. Oxygen at sea level is pp O2 = .21 or 21% of the total volume of air.

Turbo Advantages: can be installed anywhere in the exhaust stream. Usually smaller than a supercharger. Uses energy that is already being wasted anyway; low parasitic loss. Modern turbos can be highly reliable and provide boost at a wide range of engine speeds (RPM). Modular, you can build or buy some or all the parts to make your own system or get a kit. Boost can be increased to the system without mechanical changes.

Turbo Disadvantages: Can be difficult to install. Compressor is not linear meaning it does not provide a specific pressure at a certain RPM, may cause tuning difficulty. It is an obstruction in the exhaust stream lowering the flow of the exhaust gases and therefore lowering overall VE. Adds heat to the oil and or coolant (in order to cool the central housing of the turbo.

Supercharger Advantages: Can provide pressurized air as soon as the engine is running. May also provide a linear increase in pressure due to it being tied to the engine RPM. Tuning may be easier than a turbo.

Supercharger Disadvantages: Limited location area since it is physically powered by the eccentric / crankshaft of the engine. Uses some engine power to power compressor causing parasitic loss. Typically not modular. Boost cannot be increased without mechanical changes (decreasing the size of the pulley).

Nitrous Oxide Advantages: Inexpensive to purchase and easy to install. Does not cause any additional heat of the intake air (intake charge). Can be installed in numerous locations depending on the size of the bottle. Easier to maintain.

Nitrous Oxide Disadvantages: Must refill bottle. Typically only on during wide open throttle and or a button is pushed. To reach any significant power levels, some expense must be added for engine management.

Special note about temperature and air – when air is compressed regardless of how, it creates heat due to the friction of the air molecules being squished together. Intercoolers and other modifications have been invented to cool this charge air, but the reality is that 1 cubic foot of air compressed into 1⁄2 cubic foot area will become hotter, thus is the nature of gas. So both a supercharger and a turbo will create more heat than a naturally aspirated engine of the same size and design. This does not account for heating of the exhaust gas due higher fuel volume in the chamber, all FI will cause a hotter “burn”, this is a good thing when properly managed. See General Gas Law ^^^

Special note about exhaust temperature- all FI systems will raise exhaust temperatures due to the increase of air and fuel being burned in the combustion chamber. In most cases this is not a great concern. If you get an EGT or exhaust gas temperature monitor you can monitor changes from normal (assuming you know what your normal EGT is). You can also use EGT as a tuning aid.

Special note about fuel systems- Once you go FI, your max ability to boost will likely be limited by your ability to deliver fuel. You must work your FI system and fuel system together. If your FI application requires 30 lb/hr of fuel but you can only deliver 25 lb/hr, you will run lean and cause engine damage. Our injectors are typically rated in cc/min or lb/hr. The time it takes to deliver the rated fuel (the injector is open) is called duration. If a .44 lb/min injector needs to deliver .44 lb/min of fuel, it will be at 100% Duty Cycle AKA Maxed Out. Based on RPM, the duration available will be shorter in high RPMs and longer in low RPMs, all of this affects the total volume of fuel you can flow.

Special note about tuning - your non-factory FI-ed engine is designed to provide fuel in a variety of engine situations, none of which cover forced induction. With all of the extra air the engines “brain” will not add enough fuel causing you to run lean and destroy your engine. Therefore aftermarket forced induction kits have or will need an aftermarket computer to address this shortcoming. Setting this aftermarket computer up and refining the air fuel mixtures and timing is called tuning. All forced induction systems need to be tuned to your engine. If you car came factory with a turbocharger or supercharger; then tuning while still required if you make major VE changes - is usually better supported by the factory PCM.

Recommended Reading:
Street Turbocharging - Mark Warner
How to Tune and Modify Engine Management Systems - Jeff Hartmen
Turbocharging - Corky Bell
Engine Management: Advanced Tuning - Greg Banish

10-17-2008, 04:29 PM	#2
Kane All about the O2 Join Date: Sep 2008 Posts: 295 Rep Power: 17	Turbocharger / Turbo / Snail – this raises the pressure of the air (boost) by using the exhaust gases exiting the engine to power a compressor that pressurizes the incoming air. Supercharger / Blower – this raises the pressure of the air (boost) by using the eccentric shaft / crankshaft to power a compressor that pressurizes the incoming air. Nitrous / Spray / Bottle – this raises the oxygen CONTENT or partial pressure by injecting nitrous oxide into the incoming air. A partial pressure of oxygen (pp O2) of .42 or 42% would be equal to the partial pressure of oxygen in air at 2 ATA, or roughly 14.7 PSI of boost. Oxygen at sea level is pp O2 = .21 or 21% of the total volume of air. Turbo Advantages: can be installed anywhere in the exhaust stream. Usually smaller than a supercharger. Uses energy that is already being wasted anyway; low parasitic loss. Modern turbos can be highly reliable and provide boost at a wide range of engine speeds (RPM). Modular, you can build or buy some or all the parts to make your own system or get a kit. Boost can be increased to the system without mechanical changes. Turbo Disadvantages: Can be difficult to install. Compressor is not linear meaning it does not provide a specific pressure at a certain RPM, may cause tuning difficulty. It is an obstruction in the exhaust stream lowering the flow of the exhaust gases and therefore lowering overall VE. Adds heat to the oil and or coolant (in order to cool the central housing of the turbo. Supercharger Advantages: Can provide pressurized air as soon as the engine is running. May also provide a linear increase in pressure due to it being tied to the engine RPM. Tuning may be easier than a turbo. Supercharger Disadvantages: Limited location area since it is physically powered by the eccentric / crankshaft of the engine. Uses some engine power to power compressor causing parasitic loss. Typically not modular. Boost cannot be increased without mechanical changes (decreasing the size of the pulley). Nitrous Oxide Advantages: Inexpensive to purchase and easy to install. Does not cause any additional heat of the intake air (intake charge). Can be installed in numerous locations depending on the size of the bottle. Easier to maintain. Nitrous Oxide Disadvantages: Must refill bottle. Typically only on during wide open throttle and or a button is pushed. To reach any significant power levels, some expense must be added for engine management. Special note about temperature and air – when air is compressed regardless of how, it creates heat due to the friction of the air molecules being squished together. Intercoolers and other modifications have been invented to cool this charge air, but the reality is that 1 cubic foot of air compressed into 1⁄2 cubic foot area will become hotter, thus is the nature of gas. So both a supercharger and a turbo will create more heat than a naturally aspirated engine of the same size and design. This does not account for heating of the exhaust gas due higher fuel volume in the chamber, all FI will cause a hotter “burn”, this is a good thing when properly managed. See General Gas Law ^^^ Special note about exhaust temperature- all FI systems will raise exhaust temperatures due to the increase of air and fuel being burned in the combustion chamber. In most cases this is not a great concern. If you get an EGT or exhaust gas temperature monitor you can monitor changes from normal (assuming you know what your normal EGT is). You can also use EGT as a tuning aid. Special note about fuel systems- Once you go FI, your max ability to boost will likely be limited by your ability to deliver fuel. You must work your FI system and fuel system together. If your FI application requires 30 lb/hr of fuel but you can only deliver 25 lb/hr, you will run lean and cause engine damage. Our injectors are typically rated in cc/min or lb/hr. The time it takes to deliver the rated fuel (the injector is open) is called duration. If a .44 lb/min injector needs to deliver .44 lb/min of fuel, it will be at 100% Duty Cycle AKA Maxed Out. Based on RPM, the duration available will be shorter in high RPMs and longer in low RPMs, all of this affects the total volume of fuel you can flow. Special note about tuning - your non-factory FI-ed engine is designed to provide fuel in a variety of engine situations, none of which cover forced induction. With all of the extra air the engines “brain” will not add enough fuel causing you to run lean and destroy your engine. Therefore aftermarket forced induction kits have or will need an aftermarket computer to address this shortcoming. Setting this aftermarket computer up and refining the air fuel mixtures and timing is called tuning. All forced induction systems need to be tuned to your engine. If you car came factory with a turbocharger or supercharger; then tuning while still required if you make major VE changes - is usually better supported by the factory PCM. Recommended Reading: Street Turbocharging - Mark Warner How to Tune and Modify Engine Management Systems - Jeff Hartmen Turbocharging - Corky Bell Engine Management: Advanced Tuning - Greg Banish __________________ My 2007 Turbocharged RX8 Last edited by Kane; 10-21-2008 at 12:38 AM.