What advantages does a hemispherical combustion chamber offer?

[Chaotic42]

Everyone's all hyped up about the hemi. Commercials everywhere, people talking about it, etc.

What advantages does it provide?

 

[geno]

Searching is fun

And it's more of a buzz name nowadays since so many motors have copied the design since the inception of Chrysler's HEMI motors. The motor still stays true to it's design, but it's not the be-all-end-all advantage over other V8s

 

[Chaotic42]

So the pent-roof hemi engine is the best one to use?

 

[daveshel]

The shape of the chamber allowed a hotter burn. powerful but inefficient. Later there were other designs that manipulated the shape and design of the combustion chamber - one if the coolest was Honda's stratified multi-lobe chambers from the CVCC engine.

 

[StageLeft]

HSW says that the pent roof is the best, and hemi is old. The 300c and dodge magnum are nice cars with great bang for buck, but really it seems that the hemi could be better if was not in fact a hemi.

 

[imported_Sasha]

True, but how else would you market to the rednecks?

 

[MikeMike]

who introduced the hemispherical engine first?

from what i once read it was not DC, but someone else and DC just put it to mass use. can anyone find the info?

MIKE

 

[iamwiz82]

This is marketing, like any other product (VVTI, VVT, etc)

 

[C'DaleRider]

Originally posted by: nourdmrolNMT1
who introduced the hemispherical engine first?

from what i once read it was not DC, but someone else and DC just put it to mass use. can anyone find the info?

MIKE

Hemispherical combustion chambers first appeared in the 1904 Welch touring car, and Chrysler built its first hemi-head engine during World War II-a prototype V-16 aircraft powerplant. By that time, hemi chambers (shaped like half of a tennis ball) had already proven themselves in air-cooled radial aero engines, in motorcycles, and in racing and production cars. The design could accommodate larger valves, which gave it excellent breathing potential. Its low surface-to-volume ratio gave it superior thermal efficiency. And the hemi chamber worked well with the higher compression ratios now made possible with new high-octane gasoline.

In 1951, Chrysler made it a standard feature. The original 331 cu. in. Hemi V-8 developed more horsepower (180 at 4,000 rpm)than the V-8s of either Cadillac or Oldsmobile. The company fielded a vast family of Hemi V-8s for Dodge, DeSoto and Chrysler vehicles in 11 different displacements, with up to 375 hp. Chrysler discontinued the first-generation Hemi series after the 1958 model year. With its double rocker shafts and elaborate spark plug sealing, the engine had become too expensive to produce, compared with other V-8s. That same year, across the Pacific, Honda was rediscovering the pentroof four-valve combustion chamber, first raced by Peugeot in 1913. Honda's engineers needed four-valve heads to fill the cylinders of fast-rewing Grand Prix motorcycle engines, some of which turned over 20,000 rpm.

Others improved on Honda's work. They realized that a pentroof four-valve chamber gave greater flexibility than the old hemi head. Chrysler's second-generation 426 Hemi ruled the streets from 1966 through 1971, but again fell victim to high costs and the looming Clean Air Act. About 12,000 were fitted to various Dodge and Plymouth muscle cars.

The four-valve head, now the auto industry's standard, often suffers from weak low-rpm torque, unless complex, multi-stage intake systems are added. Enter the 21st century Hemi- still simple, powerful and now, clean.