Hemi engines aren’t perfect. Sorry. Half-grapefruit-shaped combustion chambers sure do let designers increase valve sizes, and in the larger displacement Hemis, these valves could probably pass golf balls without difficulty. This gives Hemi engines some seriously impressive power figures, especially when combined with supercharging and E85-specific tuning. However, the design has some inherent weaknesses, including production costs, excessive nitrogen oxide emissions, valvetrain limitations, and sheer elephantine weight.
Put your monocle back in place, I’m not saying these engines are bad. But there are solid reasons why Chrysler introduced and killed off hemispherical combustion chambers three times now. Well, kinda. Gen I and II Hemis are true Hemis, but Gen III Hemis aren’t really Hemis, having chambers that are more semi-oblate spheroids. Regardless, the Gen III Hemi died, too, with the “Last Call” Hemis ending the line.
Except no, the Gen III Hemi isn’t dead after all! It’s been Lazarused, baby, and buyers can show their Hemi loyalty with the new Hemi-headed, straight-piped angry Ram logo. Stellantis’ Dodge EVs are selling like cold cakes, and even though the Hurricane inline-6 makes tons of power and isn’t a new thing for Chrysler (looking at you, Australian Hemi Six-Pack), the company’s new leadership knows there’s a contingent of buyers who want Hemi V8s. So, do Hemis have downsides? Sure. But the positives are positive enough, and the Hemi proves we make purchases based on emotional response anyway. Long live the Hemi! Until it doesn’t anymore.
The reason Hemis are super awesome
The main pro of the Hemi design is the “crossflow” hemispherical combustion chambers, where the massive intake and exhaust ports are opposite each other, letting it breathe exceptionally well for a two-valve engine. It’s the reason Corvette-father Zora Arkus Duntov went with hemi-chambers for his Ardun overhead-valve conversion heads, as did the Mitsubishi 2.6, which, yes, did get branded a Hemi for the Dodge Aries.
In hemispherical chambers, the volume of air is massive, but the cylinder-head surface area is small, causing it to absorb less heat. Since this heat stays in the combustion chamber, pressure can rise faster than in other head designs. If the spark plug is close to the center of the chamber, the Hemi engine can take advantage of this quick rise in pressure and ignite the fuel at the perfect moment in the power stroke to give it a mechanical advantage on the crankshaft.
When Chrysler introduced its Hemi-headed FirePower 331-cubic-inch V8 in 1951, it made 180 hp, a brutal figure for the era. Hemi engines then spread to other divisions, from the lowly DeSoto to the scorching Chrysler 300s. Hemis peaked at 390 hp for the final 392-ci range-toppers in 1958, the year Chrysler Old Yeller’d the Hemi (the first time).
When the Hemi came back in 1964, it sported 426 cubes of displacement, and thanks to those Brobdinagian valves and one or two four-barrel carbs, it could breathe like Lance Armstrong giving CPR to an elephant. It was an incredible comeback for the engine, as was the Gen III in 2003. And hey, the new Charger might even get a Hemi, contradicting everything Stellantis originally said was possible.
Where Hemis fall behind
Here’s why the Hemi keeps getting the axe. First, Hemis tend to be expensive, thanks to their relatively complex valvetrain. In 1969, a Hemi cost buyers an extra $700 vs. $119 for the also-powerful 440 Six-Pack. Then there’s size. The Gen II 426 Hemi wasn’t called the Elephant for nothing. Crossflowing valves make for good breathing, but they necessitate domed pistons and make the resulting engine really wide. Plus, without extensive valvetrain magic, two valves per cylinder is your max in a true Hemi.
Unless you make a Hemi out of lightweight materials, it’ll be a porker. Early 331-ci Hemis weigh almost 1,000 pounds. Sure, that includes an integral bellhousing flange, but that’s heavier than a Caterham Seven 170. Gen II 426 Hemis weighed more than 800 pounds from the factory. It was only through copious amounts of lightweight materials like aluminum that the Gen III 5.7-liter Hemi debuted at 560 pounds, fully dressed.
The final problem is emissions. Hemispherical combustion chambered engines release more nitrogen oxides than other engines, which are pretty harmful to biological and environmental health. Gen III Hemis are certainly better in this regard, thanks to quench pads and dual plugs, but towing capacity isn’t the only reason new Hemi Rams will be hybrids. At least the dreaded 5.7 “Hemi tick” is a thing of the past. It remains to be seen how well Stellantis can make the Hemi adhere to emissions regulations moving forward, but in the meantime, you can look for that new logo on the side of a Ram 1500 and ask, like comedian Jon Reep, “Hey! That thing got a Hemi?”