Hemi Tech
- Thread starter Stallion
- Start date
grumpyvette
Well-known member
its mostly an advantage in that you get a more even burn in the cylinder and less chance of detonation.
look, a 427 has the same 4.25" bore as a 426 hemi, the hemi has a centered spark plug location, the chevys spark plug is located much more towards the exhaust side of the cylinder dia.
it takes approximately 40 thousands of a second for the flame from the ignition to cross a 4.25" bore,at low rpms and still takes about 15 milliseconds at high RPM due to the much faster movement of the compressed fuel air mix in the cylinders, lets look at what that means
if the chevy plug is located 4/5ths of the way to one side thats a time of about 32 thousands for the pressure to build as the flame travels 3.4" in the chevy but a hemi, ignitions flame front needs to travel only 2.125" or a complete burn in about 20 thousands of a second. at low rpms, this of course speeds up as the swirl and turbulance increase with increased engine RPMs but the ratios stay similar. this results in more useable energy WORKING on the piston AFTER IT PASSES TOP DEAD CENTER ON THE POWER STROKE. BUT MODERN WEDGE combustion chambers use increased QUENCH to speed the flame front and lower the burn time combined with a smaller combustion chamber and a more centrally located spark plug to get even better results than the older hemi design, even CRYSLERS new (HEMI) is really a very shallow combustion chamber like a modified wedge to better use QUENCH and swirl to speed burn times
http://naca.larc.nasa.gov/reports/1939/naca-tm-914/
http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf
http://www.combustion-net.com/library/articles/PDFs/0210-spark-ignition-engine-cycle.pdf
http://www.nedians.8m.com/Comp_IC.html
http://mb-soft.com/public2/engine.html
http://hpp.primediaautomotive.com/archives/tech/0209hpp_fire.shtml
look, a 427 has the same 4.25" bore as a 426 hemi, the hemi has a centered spark plug location, the chevys spark plug is located much more towards the exhaust side of the cylinder dia.
it takes approximately 40 thousands of a second for the flame from the ignition to cross a 4.25" bore,at low rpms and still takes about 15 milliseconds at high RPM due to the much faster movement of the compressed fuel air mix in the cylinders, lets look at what that means
if the chevy plug is located 4/5ths of the way to one side thats a time of about 32 thousands for the pressure to build as the flame travels 3.4" in the chevy but a hemi, ignitions flame front needs to travel only 2.125" or a complete burn in about 20 thousands of a second. at low rpms, this of course speeds up as the swirl and turbulance increase with increased engine RPMs but the ratios stay similar. this results in more useable energy WORKING on the piston AFTER IT PASSES TOP DEAD CENTER ON THE POWER STROKE. BUT MODERN WEDGE combustion chambers use increased QUENCH to speed the flame front and lower the burn time combined with a smaller combustion chamber and a more centrally located spark plug to get even better results than the older hemi design, even CRYSLERS new (HEMI) is really a very shallow combustion chamber like a modified wedge to better use QUENCH and swirl to speed burn times
http://naca.larc.nasa.gov/reports/1939/naca-tm-914/
http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf
http://www.combustion-net.com/library/articles/PDFs/0210-spark-ignition-engine-cycle.pdf
http://www.nedians.8m.com/Comp_IC.html
http://mb-soft.com/public2/engine.html
http://hpp.primediaautomotive.com/archives/tech/0209hpp_fire.shtml
- Thread starter
- #3
I appreciate it. 
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