Because there are a few very important misconceptions out there on how engine properties are determined I made the attached spreadsheets. One of the big ones being how CR affects cylinder pressure, which is not a direct multiplication of CR times the pressure at bottom dead center (BDC). It is an exponential relationship and there is a LOT of pressure in there, and heat. Additionally, the aftermarket has dumbed down the very important relationship of air and fuel flow to engine horsepower.
They use cubic feet per minute (CFM) of air and cubic centimeters (cc) of fuel, which are volume flow rates. Volume flow is an inaccurate way to make design choices, but are easier concepts to grasp, because its also how most of the equipment is rated. Most technical desicions should be made based in terms of mass flow, especially when using turbo compressor maps and determining the required boost to a fuel rate. Also, turbochargers do not put out what they are rated for unless the engine flow demands it, dependent on displacement and intake air temp.
So I combined 2 of my updated older calculators with a new Air Flow calculator in one Excel file that is attached.
Sheet 1: Affects of boost, compression ratio (CR), intake air temp (IAT) have on cylinder air pressure and temperature at top dead center (TDC). This can used to compare any engine.
Sheet 2: Air volume and mass flow, and air to fuel ratio (AFR). This can be used with any engine. Has elevation compensation, as well as fuel source (density) and temperature compensation based on user input. Remember the engine is a fixed air pump, boost increases the engine's mass flow, but only RPM and displacement can change an engine's air volume flow. This is why the terms are separated into pre compression (air filter and turbo flow) to post compression (engine and intercoolers).
Sheet 3: 6.5 CR calculator, using shaved or dished pistons or thicker gaskets, or even intake valve closure changes. This was specifically made with the 6.5 diesel engine in mind, but could work closely for other IDI diesels with similar flat top pistons with Ricardo swirl bowls.
These should help give an understanding on design choices when rebuilding an engine, why you would select a lower CR, selecting a turbo, intercooler or air filter, and determing injector pop pressures, boost limits, ect....
Sometimes, knowing these values, can give insight into the design choices that the manufacturer made.
Let me know if you find any issues with the calculations, or have any questions. And let me know if it helps anyone!
They use cubic feet per minute (CFM) of air and cubic centimeters (cc) of fuel, which are volume flow rates. Volume flow is an inaccurate way to make design choices, but are easier concepts to grasp, because its also how most of the equipment is rated. Most technical desicions should be made based in terms of mass flow, especially when using turbo compressor maps and determining the required boost to a fuel rate. Also, turbochargers do not put out what they are rated for unless the engine flow demands it, dependent on displacement and intake air temp.
So I combined 2 of my updated older calculators with a new Air Flow calculator in one Excel file that is attached.
Sheet 1: Affects of boost, compression ratio (CR), intake air temp (IAT) have on cylinder air pressure and temperature at top dead center (TDC). This can used to compare any engine.
Sheet 2: Air volume and mass flow, and air to fuel ratio (AFR). This can be used with any engine. Has elevation compensation, as well as fuel source (density) and temperature compensation based on user input. Remember the engine is a fixed air pump, boost increases the engine's mass flow, but only RPM and displacement can change an engine's air volume flow. This is why the terms are separated into pre compression (air filter and turbo flow) to post compression (engine and intercoolers).
Sheet 3: 6.5 CR calculator, using shaved or dished pistons or thicker gaskets, or even intake valve closure changes. This was specifically made with the 6.5 diesel engine in mind, but could work closely for other IDI diesels with similar flat top pistons with Ricardo swirl bowls.
These should help give an understanding on design choices when rebuilding an engine, why you would select a lower CR, selecting a turbo, intercooler or air filter, and determing injector pop pressures, boost limits, ect....
Sometimes, knowing these values, can give insight into the design choices that the manufacturer made.
Let me know if you find any issues with the calculations, or have any questions. And let me know if it helps anyone!