Anonymous-0
Well-known Member
At The Old Car Festival sunday there was a 1910 International roadster pick up with a 4 cyl air cooled overhead cam hemi head engine! Very neet and also very rare! Bud.
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Janicholson
Well-known Member
Yo Jimbo, Your statement
"Chrysler's capturing of the comcepts Name was sheer genious"
Is right on. I know manyyyyyyy mechanically challenged folks who brag about owning or how great a HEMI is WHO HAVE NO FREAKING IDEA WHATSOEVER as to what it means....Its just that it sounds cool to say they have a HEMI..
My own brother in law whose son bought a truck with a hemi now says he wishes he had a hemi yet he doesnt even know if his truck is a 6 or 8 cylinder even if you raise the hood, he hasnt a clue butttttttttttt he wishes he had a hemi lol
Oh well, John T (doesnt own a hemi boo hoo)
"Chrysler's capturing of the comcepts Name was sheer genious"
Is right on. I know manyyyyyyy mechanically challenged folks who brag about owning or how great a HEMI is WHO HAVE NO FREAKING IDEA WHATSOEVER as to what it means....Its just that it sounds cool to say they have a HEMI..
My own brother in law whose son bought a truck with a hemi now says he wishes he had a hemi yet he doesnt even know if his truck is a 6 or 8 cylinder even if you raise the hood, he hasnt a clue butttttttttttt he wishes he had a hemi lol
Oh well, John T (doesnt own a hemi boo hoo)
When I was a kid all the hot rodders bought up about all the old 57 Chrysler Hemis....
Still if you think about it seems the exploding expanding gasses are more efficient at pushin the piston down if the head is hemispherical versus flat or wedge shaped??????? but what do I know, thats not electrical stuff lol
John T
Still if you think about it seems the exploding expanding gasses are more efficient at pushin the piston down if the head is hemispherical versus flat or wedge shaped??????? but what do I know, thats not electrical stuff lol
John T
Jim Becker
Well-known Member
Makes absolutely no difference in that respect. The various pressures, amount of surface area, and force directions all balance out. You get the same push as a flat top piston.
Where it does matter is in the quality of the combustion. The coldest part of the combustion chamber is at the surface. Combustion is best where it is hottest. A spherical shape has the greatest ratio of volume to surface area. A hemisphere comes closer to that ratio than most other combustion chamber shapes. The old Chrysler hemis had a more or less spherical shape to the chamber in the head, with flat top pistons, thus the "hemi" name. This idea is somewhat theoretical and other shaped combustion chambers with carefully designed quench areas do quite well.
Bob M
Well-known Member
Hey John T...
Beyond marketing hype - which from an engineering perspective is worthless(!) - the advantages of a hemispherical head are:
1 - Spark plug is centrally located in the combustion chamber. This promotes faster and more thorough combustion with less chance of detonation - especially at higher compression ratios.
2 - Has space for larger diameter valves, hence better engine breathing than other head designs.
Combined these permit slightly more power output per cubic inch - especially at wide open throttle - than other head designs.
The downside is a more complicated (expensive) valve mechanism, and a physically larger rocker box to enclose it. Thus racing hemis were often referred to as the "elephant motors" on account of their large envelope.
Incidentally virtually all large aircraft piston engines after about 1920 employed hemi heads.
Bob M - retired mechanical engineer
Beyond marketing hype - which from an engineering perspective is worthless(!) - the advantages of a hemispherical head are:
1 - Spark plug is centrally located in the combustion chamber. This promotes faster and more thorough combustion with less chance of detonation - especially at higher compression ratios.
2 - Has space for larger diameter valves, hence better engine breathing than other head designs.
Combined these permit slightly more power output per cubic inch - especially at wide open throttle - than other head designs.
The downside is a more complicated (expensive) valve mechanism, and a physically larger rocker box to enclose it. Thus racing hemis were often referred to as the "elephant motors" on account of their large envelope.
Incidentally virtually all large aircraft piston engines after about 1920 employed hemi heads.
Bob M - retired mechanical engineer
Janicholson
Well-known Member
I own a Hemi!!!
Toyota purchased one or more Chrysler Hemis and reverse engineered it into the Corolla 2TC and 3TC 4 cylinder engines.
Exact hemispherical chamber, exact placement of the cam shaft (as high in the block as it would be in a V8).
Exact pushrod configuration and rockers.
Exact bore to block length.
Same wide VC with recessed sparkplug holes down the center. The oil pan parting line was changed to be perpendicular to the deck surface.
Mine is in a Austin Healy sprite which is only 4 times more powerful than the BL engine fitted from the factory and 525CC bigger. Jim
Toyota purchased one or more Chrysler Hemis and reverse engineered it into the Corolla 2TC and 3TC 4 cylinder engines.
Exact hemispherical chamber, exact placement of the cam shaft (as high in the block as it would be in a V8).
Exact pushrod configuration and rockers.
Exact bore to block length.
Same wide VC with recessed sparkplug holes down the center. The oil pan parting line was changed to be perpendicular to the deck surface.
Mine is in a Austin Healy sprite which is only 4 times more powerful than the BL engine fitted from the factory and 525CC bigger. Jim
charles todd
Well-known Member
Now that is a HEMI!
CT
rustyacresnd
Member
Yeah my driver's ed car was a Plymouth Reliant K car with the horibly anemic 2.6 liter Mitsubishi Hemi 4 cyl. So much for the Hemi reputation! The hemis of the 50's through the 70's had a meaning behind them. This was new stuff back then, but a K-car hemi?????????
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