calculating supercharger or turbo compression

grumpyvette

Administrator
Staff member
the supercharger or turbo is used to pack a larger volume of fuel/air mix into the cylinder to be burnt, the extra power over a N/A engine is generated by the higher cylinder pressures and a bit longer burn cycle in the cylinders, but that increased pressure tends to increase the potential for detonation that can destroy an engine.
it should be obvious that a larger combustion chamber can hold a larger charge of that fuel air mix at any given pressure level.and that larger charge when burnt will produce more power thru its increased pressure.
it should also be obvious the burning more fuel air/ mix will tend to require a larger exhaust to handle the increased volume of burnt gases and the engine will generate more heat!
larger volume can be archived with a lower static compression , or increased cam duration allowing the valves to close later in crankl degrees and that lower compression is generally the result of either a larger combustion chamber or a dished piston or both, or later intake valve timing, but the combo of lower static compression and a cam matching the engines requirements with a wide lsa and extended exhaust duration helps maximize the power potential.
the cam selected will tend to require a wider lsa than a n/a engine cam would,to reduce the amount of pressurized intake charge from forcing a higher percentage of the intake charge out the exhaust port before its trapped as is intended in the cylinder by the exhaust valve closing, and a longer exhaust duration to allow the extra volume to flow out of the cylinder.
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GARRET TURBOS POSTED THIS
http://www.turbobygarrett.com/turbobyga ... ch_vs_lean
GARRETT said:
Why lean makes more power but is dangerous

When discussing engine tuning the 'Air/Fuel Ratio' (AFR) is one of the main topics. Proper AFR calibration is critical to performance and durability of the engine and it's components. The AFR defines the ratio of the amount of air consumed by the engine compared to the amount of fuel.

A 'Stoichiometric' AFR has the correct amount of air and fuel to produce a chemically complete combustion event. For gasoline engines, the stoichiometric, A/F ratio is 14.7:1, which means 14.7 parts of air to one part of fuel. The stoichiometric AFR depends on fuel type-- for alcohol it is 6.4:1 and 14.5:1 for diesel.

So what is meant by a rich or lean AFR? A lower AFR number contains less air than the 14.7:1 stoichiometric AFR, therefore it is a richer mixture. Conversely, a higher AFR number contains more air and therefore it is a leaner mixture.

For Example:
15.0:1 = Lean
14.7:1 = Stoichiometric
13.0:1 = Rich

Leaner AFR results in higher temperatures as the mixture is combusted. Generally, normally-aspirated spark-ignition (SI) gasoline engines produce maximum power just slightly rich of stoichiometric. However, in practice it is kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for variances in fuel quality. This is a realistic full-load AFR on a normally-aspirated engine but can be dangerously lean with a highly-boosted engine.

Let's take a closer look. As the air-fuel mixture is ignited by the spark plug, a flame front propagates from the spark plug. The now-burning mixture raises the cylinder pressure and temperature, peaking at some point in the combustion process.

The turbocharger increases the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of knock. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock. This is why it is imperative to run richer AFR on a boosted engine at full load. Doing so will reduce the likelihood of knock, and will also keep temperatures under control.

There are actually three ways to reduce the probability of knock at full load on a turbocharged engine: reduce boost, adjust the AFR to richer mixture, and retard ignition timing. These three parameters need to be optimized together to yield the highest reliable power.
read thru these links
viewtopic.php?f=86&t=1894

viewtopic.php?f=86&t=1330

http://www.superchargersonline.com/hp_calculator.asp

http://autoapps.eaton.com/Simulator/EngineDetails.aspx

viewtopic.php?f=55&t=2718

viewtopic.php?f=52&t=727

http://www.rbracing-rsr.com/compression.htm

http://performancetrends.com/Compressio ... us_Version

http://www.popularhotrodding.com/engine ... to_06.html

http://www.autocomponenti.com/boosted_t ... d_tech.htm

viewtopic.php?f=56&t=495

http://www.chevyhiperformance.com/tech/ ... index.html

http://www.hi-flow.com/HP4FAQSuper.htm

http://www.gnttype.org/techarea/turbo/turboflow.html

http://www.mg-tabc.org/supercharger/cap ... f%20SC.htm

http://www.hipermath.com/engines/super_charger_cfm
 
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