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Discussion Starter · #1 ·
Hey, I gotta question for you all.

I know what a real Hemi is. Chrysler started building them in early 1950s and they were a smaller V8 engine with a "hemispherical" combustion chamber. Then Chrysler jumped into the horsepower wars of the 1960s with a second generation of bigger V8 Hemis, like the famous 426 Elephant.

My question is: do the Hemis of today have hemispherical heads like the previous generations did? From what I read, they don't. Chrysler (FCA, Stellantis) just use the Hemi term as a marketing designation. Are there any true Hemi engines anymore?
 

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Stu
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Emissions is what changed the real Hemi engine. In my opinion, the gen III Hemi engine is as close to a real Hemi engine as it can be with better emissions technology. This could blowup to be an interesting discussion...


 

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Red Trucker
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To quote Robert Lee, director of rear-wheel engine engineering at the time:
"The situation is that we have a true hemispherical chamber except for a few cubic centimeters of material added to each side of the chamber," says Robert Lee, Chrysler group's director of rear-wheel engine engineering. "And that's done to channel the flow and get the burn characteristic we wanted with the dual (spark) plugs. That's the only possible area that people could quibble about."
Engineers could have put the raised areas on the crown of the piston instead of in the cylinder heads, but Lee said that would have meant sacrificing efficiency.
Says Lee: "Everything else, in terms of the valvetrain arrangement, the shape of the chamber, is in fact a true Hemi. It's not as huge as the old Hemi, of course."

So basically a filled chamber but the valve and dual rocker shaft arrangement/layout is virtually identical. The varying 50's versions (Dodge, Chrysler, DeSoto) had their own names for their versions of the engine; none of them were "hemi". That wasn't a common word til the 60's when the elephant was released.
 

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Discussion Starter · #4 ·
Wow, that's fantastic. It's good to hear that some things don't change. I was worried that someone would say that engines today aren't even close to being hemispherical in shape.
 

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Red Trucker
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It works lol. All they did was downsize it a bit, make it more efficient and emissions compliant. When they were coming up with the design prior to 2003, the engineers paid Tom Hoover a visit for some advice. I know one of the things he recommended was raising the cam in the block. The head design and valve size that the Hellcat and 6.4/392's use are probably some of, if not the best heads Mopar has ever released. An Indy prepped set of apache heads on a 6.1 based 426 stroker with a somewhat mild hydraulic roller cam made over 700hp naturally aspirated.......and that was almost 10yrs ago. Some light reading lol:
 

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Hey, I gotta question for you all.

I know what a real Hemi is. Chrysler started building them in early 1950s and they were a smaller V8 engine with a "hemispherical" combustion chamber. Then Chrysler jumped into the horsepower wars of the 1960s with a second generation of bigger V8 Hemis, like the famous 426 Elephant.

My question is: do the Hemis of today have hemispherical heads like the previous generations did? From what I read, they don't. Chrysler (FCA, Stellantis) just use the Hemi term as a marketing designation. Are there any true Hemi engines anymore?
Simple Answer yes..it's Hemi , there's more to it then just Chamber shape, The G3 is a true cross flow head, plugs in the center, Chamber is arched from Valve to valve.


Back in late 96 when Chrysler took over the power tech(4.7) program from Jeep engineers , part of the goal was to build a 4.7(3.66X3.40) and a 5.7(3.86X3.72) out of the program , they knew that with the new Emission standards coming down the pike that the LA/Magnum platform was on borrowed time.
There was a lot of debate going on about doing away with the pushrod V8 and going OHC like Ford was doing, But marketing knew they needed a torqy V8 if they were going to steal the newly disappointed Ford buyer.
Lucky for Mopar enthusiasts everywhere Daimler bought in to Ma Mopar when they did(1998).....see Dieter Zetsche LOVED his 70 Hemi Cuda Clone Loved Loud American V8s and was Impressed with the Team Orca Wins in 97, Dodge's Nascar trucks were running well and were competitive considering the engine tech at the time was 10 years behind GM and FUD ... one of the 1st things Dieter did was dump a pile of capital (CASH) in to the Prostock programs....he wanted to start the ball rolling on a brand new engine platform......Out goes the 5.7 cammer and in comes something new.
Designers were giving one(two) condition(s), the block had to similar to the 4.7 because of the new tooling procedures, and had to have the traditional Small block bell housing pattern . Displacement needed to be 5.7-6.0 liters from the get go....now the block was originally going to be a 4.0 bore and 3.58 stroke so it could be a direct CI replacement for the 5.9(360) but the then current emissions' thinking derailed that and then they wanted to keep the bore to less then 100MM (3.937) because it has proven to be the best bore size for emissions, 3.917 was chosen to allow the engine to be bored and still be with in optimal emissions bore 100m...it's the Goldilocks of bore sizes( go and check out the average bore size of modern engines) now Mr Motor head Dieter made sure they built in room for growth.....Hence the 4.46 bore spacing and not the 4.09 spacing of the Power tech program....the bigger the spacing the bigger the bore potential.

The Heads originally were based on a design by Dale Eicke, then some of DCX and Mclaren head gurus got involved, then Dieter ....who wanted to capitalize on the "HEMI" name said How much of the Hemi 99 Prostock head can we incorporate......(Not much.....but the exhaust ports showed up on the 6.1 head)
Tom Hoover's input was.....do what you can to keep the Exhaust rocker arm the same length as the intake....henc the reason for the raised cam in the block allows for a shallower angle.
Willem Weertman Input was Make the Chamber as shallow as you can, to keep the piston as flat as you can avoid needing a dome, this way the piston is lighter and will be less demanding on the Rods.

the shallow Angle come of the valves came from the Hemi 99 program....

Neat thing to do with the intake off of a G3 hemi is look down at the intake valve....you can see 90% of the valve.....try that with almost any other engine..............
 

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Stu
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Some of my favorites.
 

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Red Trucker
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LOL I still love this part
To achieve a displacement of 426-inches (or 425.67928 to be exact), we utilized a bore size of 4.090 inches and a stroke of 4.050 inches. The 6.1 block can be bored to this dimension with plenty of cylinder wall left,

They must not of sonic tested that block....
 

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Discussion Starter · #12 ·
Awesome article: Thanks guys!

 
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