Volumetric effieciency?
- Thread starter Bayrunner
- Start date
8) volumetric efficiency indicates how full the cylinder gets during its normal operation. for example, if the cylinder displaces 10 cubic inches, and when it goes through its intake cycle, and you get 9 cubic inches of air/fuel into the cylinder, you have a volumetric efficiency of 90%. the typical stock street engine runs at about 75% volumetric efficiency, high performance engines these days get up between 85-92% efficiency, and race engines can get up to around 110% efficiency, essentially supercharging themselves. this applies to normally aspirated engines only, since forced induction engines will always get higher than 100% efficiency due to the turbo/supercharger when under boost.
Howdy:
In addition to Rbohm's definition, please note that VE is a moving target. Peak VE only occurs at a specific rpm under specific criteria- such as wide open throttle (WOT). In general, VE is a reflection of how well an engine can get A/F in, utilizes it, and gets exhaust out. A stock 200 street engine will seldom, if ever, see peak VE. A well tuned, stock, OEM 200 from the sixties may see 70% VE while a similar 260 or 289 bent eight may achieve 75%.
Improvements to an inline six in induction and flow characteristics, compression, ignition, cam timing and exhaust will frequently show a higher VE gain than on a V8, simply because most American inline sixes are so crude/basic from the factory.
At idle, a 200s VE may be as low as 10%, at cruise maybe 50%. Anything less than WOT, at peak HP rpm will be something less than peak VE. For the purposes of our calculator, the VE percentage is an estimate of performance enhancers moving away from a stock, factory engines rated HP. improvements in compression, intake, ignition timing and exhaust can be reflected in the VE percentage. Cam timing is reflected in the rpm setting. Amount of carburetion in CFM, (cubic feet per minute) is an outcome estimation along with HP.
For estimation purposes, a one point increase in CR will be roughly equal to a 4 to 7 % increase in Peak HP. But the increase will be noticeable across the rpm range, from idle to WOT. Is is less reliable of a predictor of increases of VE because anything less than WOT negates the effect of increased CR. Increased CR is at work at idle, making for a more efficient use of available A/F. VE is not very relevent at idle. So, to answer your question, as it relates to CR- It is best to determine your goal CR and then use it, along with other efficiency improvers to estimate an engines VE.
There! Probably as clear as mud.
Adios, David
In addition to Rbohm's definition, please note that VE is a moving target. Peak VE only occurs at a specific rpm under specific criteria- such as wide open throttle (WOT). In general, VE is a reflection of how well an engine can get A/F in, utilizes it, and gets exhaust out. A stock 200 street engine will seldom, if ever, see peak VE. A well tuned, stock, OEM 200 from the sixties may see 70% VE while a similar 260 or 289 bent eight may achieve 75%.
Improvements to an inline six in induction and flow characteristics, compression, ignition, cam timing and exhaust will frequently show a higher VE gain than on a V8, simply because most American inline sixes are so crude/basic from the factory.
At idle, a 200s VE may be as low as 10%, at cruise maybe 50%. Anything less than WOT, at peak HP rpm will be something less than peak VE. For the purposes of our calculator, the VE percentage is an estimate of performance enhancers moving away from a stock, factory engines rated HP. improvements in compression, intake, ignition timing and exhaust can be reflected in the VE percentage. Cam timing is reflected in the rpm setting. Amount of carburetion in CFM, (cubic feet per minute) is an outcome estimation along with HP.
For estimation purposes, a one point increase in CR will be roughly equal to a 4 to 7 % increase in Peak HP. But the increase will be noticeable across the rpm range, from idle to WOT. Is is less reliable of a predictor of increases of VE because anything less than WOT negates the effect of increased CR. Increased CR is at work at idle, making for a more efficient use of available A/F. VE is not very relevent at idle. So, to answer your question, as it relates to CR- It is best to determine your goal CR and then use it, along with other efficiency improvers to estimate an engines VE.
There! Probably as clear as mud.
Adios, David
Bayrunner":pg5xc0ml said:
8) nah, them rocket scientists aint ready for internal combustion engines
one more thing about VE, peak VE will always be at the peak torque rpm. also there are engine combinations that will have two torque peaks strange as that might seem. they are oddballs though.
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