What is the difference between hemi and a normal engine

It is currently a big selling feature throughout their marketing materials and is a big discussion point among auto enthusiasts. First introduced in the s, Chrysler called it the FirePower engine This was quickly followed with the Hemi which really put it on the market. The Hemi was famously used by Richard Petty and helped launch his career. As the story goes, the Daytona had the first three cars with the Hemi in it. With no street version available, the Hemi was sidelined during the season.

This new HEMI has a combustion chamber featuring value and twin spark plug locations markedly different from the previous ci version. It also has a pinched chamber that does not have the true hemispherical combustion chambers. Many say it is more closely resembles the mids polyspherical chamber that Chrysler developed as a low-cost alternative head for their V-8 engine.

The polyspherical head needs less metal and is narrower due to using only one rocker shaft. Ultimately, this saved Chrysler material, space, warranty claims and allowed it to be used in smaller vehicles. Ultimately, this new Hemi is really popular. The take rate the average number of people who buy it versus another Chrysler engine hovers around 50 percent and it is built at a profit. The classic idea for a hemispherical engine is for the top of the combustion chamber to be a hemisphere.

This would minimize heat loss per unit of volume. However, this gives a far too low compression ratio unless you have a very long stroke. Normally, the piston is domed so that it protrudes into the head at top dead centre. This gives it a more of a chamber shape. It was smaller than the Chrysler HEMI and intended for smaller cars, with engine sizes making up to horsepower.

Between and , low-line DeSotos contained the Red Ram as did various Dodges and high-line to Plymouths. Red Rams had displacements of cubic inches, cubic inches, cubic inches and cubic inches. The first generation HEMI , especially the , proved popular among drag racers. This remained the standard and preferred drag racing engine until the s. The coincided with the s era of Chrysler engine innovation.

The Elephant Engine boasted high power, extreme weight, and dimensions. The displaced cubic inches, or 7 liters. Chrysler only produced 11, The current third generation is the one trademarked as HEMI, boasting up to horsepower. This generation commenced in with the 5. Its use in Ram trucks has helped to cement its reputation among not just muscle car lovers but a wider base that appreciates the performance of the HEMI for work and for play.

In fact, there are some tuning products out there with plug-and-play interfaces that make the modern HEMI swap totally doable. Some of the reasons that auto enthusiasts get the feels for HEMI engines are purely technical: HEMIs have bigger valves and offer higher thermal efficiency and higher power output.

And most folks are impressed by its sheer toughness. HEMI is an ongoing concept that continues to evolve. The HEMI name is now synonymous with Chrysler, a maker that repeatedly upgrades the design for efficiency. Newer HEMI engines are 5. HEMI is an engine that is complicated in its simplicity and the many mechanical ways in which it diverges from other engine designs. The ultimate result is that a HEMI setup can produce plenty of power much more effectively, making it a favorite in muscle cars, racing cars, high-powered pickups, and cars for drivers who value power and efficiency under the hood.

Buying Guides Share. All other things being equal, a larger-diameter valve means more air and fuel can get in and more exhaust can exit. If it were possible to just increase the valve diameter by itself, we'd all have engines with bigger valves—except the valves would crash into the cylinder wall, and in many instances, each other as well. The hemi fixes this by tipping them sideways so they open away from the cylinder wall—an effect called unshrouding.

As a valve opens and gas flows past it, flow is limited at low lift values because the open curtain area under the valve is relatively small near the seat. As the valve opens, flow increases up to a point where no additional lift contributes to the overall flow. At or near the seat, however, the valve's proximity to the cylinder bore inhibits its flow, so anything that is done to mitigate the shrouding restriction helps a bunch, and that's what a hemi does really well.

Ford small-block-based Hemi engine with cylinder heads from Hammerhead Performance. Even smaller engines look impossibly large with hemi cylinder heads. So far, everything looks rosy for the hemi combustion chamber, so why didn't every manufacturer use it in quantity? Perhaps the biggest problem initially for Chrysler—the manufacturer known for embracing it the most—was its size and mass.

If you do everything that's needed to place the valves at hemi angles, to redesign the port shapes to avoid interference with the valvetrain, and design a workable valvetrain that lasts, you use up a lot of real estate, which means Hemis are larger, and as a result, heavier.

By way of illustration, a Gen-II Street Hemi from the muscle car era weighs almost a hundred pounds more than a same-sized ci big-block Chrysler wedge, and is several inches wider. Nick Arias, Jr. Beyond the issues of size and mass, hemi engines of all descriptions suffer from elevated emissions of oxides of nitrogen—gases that are created ironically through the Hemi's inherent efficiency.

Without extra steps to mitigate these emissions, today's Gen-III Chrysler Hemi would be an impossibility for a production car. This has a cooling effect on the burning charge, reducing combustion temperatures and the formation of oxides of nitrogen. This is the evil side of the hemi coin; remember how we said the hemi shape promotes a faster pressure rise time?

Elevated NOX shorthand for oxides of nitrogen are a byproduct of that. Perhaps the first hemi cylinder head that hot rodders ever latched onto were the ones Zora Arkus-Duntov designed for the Flathead Ford before he went on to do the Corvette with Chevrolet.

Due to the shape of the hemispherical combustion chamber, it's difficult to raise the compression ratio high enough to fully take advantage of its superior shape, irrespective of the brand on the valve cover.

Raising the compression ratio usually involves machining the block's fire deck, milling the cylinder head deck, substituting a higher-compression piston, or a combination of these. With a hemispherical combustion chamber, however, raising compression with a domed, or pop-up piston has a practical limit, and a down side.

Changing the shape of the piston so that the combustion volume is reduced also has the effect of disrupting the speed and timing of the combustion event itself.

Over the past half century, the road to the perfect hemi has been littered with odd pistons, domes, coatings, and flame slots—all designed to restore the missing performance promised by the hemi's shape.

For this reason, it pays to stay on the modest side when raising the compression of a hemi-headed engine on a naturally aspirated combo.