Modern Hemi Engines

By SRT-Tom · May 11, 2020 · ·
  1. SRT-Tom
    Modern Hemi production began in June 2002 at the Saltillo plant in Mexico. The first-generation 5.7 liter produced up to 350 horsepower at 5,600 rpm and 375 lb-ft of torque (4,400 rpm)- one horsepower per cubic inch- just like the legendary 426 Hemi. It was smaller, more powerful, and cheaper to build than the LA-series 360 V8 and the "Next Generation" 4.7 liter V8 it replaced, but produced more power and torque. It hooked up to the Mercedes 5-speed automatic, Chrysler's 5 and 6-speed truck transmissions and, later, the ZF 8-speed.


    5.7 Hemi (345 cubic inches)- Eagle

    The 5.7 Hemi was released 17 years ago, for model year 2003, on the Dodge Ram1500, 2500, and 3500pick-up trucks to complement the Magnum 5.9 engine.


    The 5.7 Hemi in the Ram delivered 345 hp. and 375 lb-ft , but 340 hp and 390 lb-ft for the 300C and Magnum R/T, which was exactly 100 hp. more than the old 5.9 engine.

    Chrysler made various revisions to the 5.7 for the 2009 model year. In the Challenger R/T it produced 372 hp., 400 lb/ft (automatic) and 375 hp., 410 lb-ft (6-speed manual). The first revision was Variable Camshaft Timing or VCT. VCT used a valve that controlled oil flow to a unique camshaft sprocket which contained a phasing device. This device, depending on the operation of the oil control valve, either advanced or retarded camshaft timing. It allowed for improved engine performance, reduced emissions, and increased fuel efficiency compared to engines with fixed camshafts. Cylinder heads were also revised to increase flow, as was the intake manifold. Other changes were a higher compression ratio, better-flowing heads, intake, and exhaust, and an active intake manifold.

    6.1 Hemi (370 cubic inches)

    The 6.1 Hemi first made its appearance in the 2005 Chrysler 300C SRT8 and was quickly adopted for the debut of the new 2008 Challenger SRT8. The engine block was different from the 5.7. It had a 4.06 inch bore and a 3.58 inch stroke and produced 425 hp. and 420 lb-ft of torque, with a 10.3:1 compression ratio.


    The SRT engine included numerous modifications from the standard 5.7 Hemi, such as:

    *Reinforced bulkheads.
    *Larger cylinder bores (by 3.5 millimeters).
    *Oil squirters.
    *Modified oil pan and windage tray.
    *Larger-diameter, high-load, flat-top pistons.
    *Revised connecting rods using higher-strength powder metal material.
    *New floating piston pins.
    *Crankshaft forged from micro-alloy steel, in tri-metal main bearings.
    *Head ports designed with larger high-flow cross-sectional area.
    *A billet steel, high-strength camshaft with more overlap and lift.
    *Intake valves (2.08 inches) featured sodium-filled hollow stems and 2 mm larger heads.
    *Specially designed intake and exhaust manifolds.
    *Cast aluminum intake manifold with shorter, larger-diameter and tapered runners for high-speed tuning. *Core-dipped internal runners for improved air flow.
    *14% higher fuel injector flow capacity.
    *Stainless steel clamshell exhaust headers.
    *Dual knock sensors with premium fuel.

    6.4 Hemi (392 cubic inches)- Apache

    The 392 Hemi replaced the 6.1 Hemi in the SRT line, in 2011. It had variable camshaft timing, as well as MDS in cars with automatic transmissions. Code named "Apache," it was based on a bored and stroked version of the third-generation 5.7 Hemi. Output was 470 hp. and 470 lb-ft. For 2015, power in the Charger and Challenger versions of the 392 was boosted from 470 to 485 hp., with torque climbing from 470 to 475 lb-ft. A new, expensive but sturdy ZF 8-speed automatic transmission was paired with the 6.4 Hemi, along with the 3.6 V6 and 5.7 Hemi. (Note- The engine is different from the one in the Challenger Drag Pack (the Mopar crate engine); for one, the standard 392 shuts off four cylinders when they are not needed, to increase gas mileage. The crate and production engines have a different bore, stroke, cam, heads, compression, and intake).


    This engine shared the same architecture as the 2009 5.7L HEMI with many performance upgrades, such as:

    *Increased Bore-4.09 in.
    *Increased Stroke- 3.72 in.
    *Increased Valve Sizing.
    *Variable Cam Timing (VCT) Cam Phasing System.
    *Variable Valve
    *Aluminum heads.
    *Increased Maximum RPM Timing (VVT).
    *Multi-Displacement System (MDS) (auto trans only).
    *High Flow Ports..
    *Combustion Chamber Shape.
    *High Compression Ratio- 10.9:1.
    *Heads have splayed valves.
    *Oil cooler was a stack plate design coolant-to-oil heat exchanger.
    *Intake manifold is a composite material with a dual shaft Short Runner Valve (SRV) system.
    *Exhaust manifolds are tube-in-shell air gap design.
    *Connecting rods are made of forged powdered metal with a “fractured cap” design.
    *Four dual-nozzle oil jets are bolted to the cylinder block.
    *Valve guide seals are made of rubber and incorporate an integral steel valve spring seat.
    *High-strength aluminum alloy pistons.

    6.2 Hellcat (376 cubic inches)

    For 2015, Chrysler introduced an all-new high performance supercharged variant of the Hemi engine, called the Hellcat. It featured the same 4.09 in. bore as the 6.4 Hemi and the same 3.578 in stroke as the 5.7. The supercharger was a 145 cu. in. twin-screw IHI unit with integrated charge coolers, capable of producing 11.6 psi of boost.

    This engine was rated at 707 hp. at 6,000 rpm and 650 lb-ft at 4,000 rpm of torque, with a compression ratio of 9.5:1. This engine was the most powerful engine produced by Chrysler, as well as the most powerful production engine ever in a muscle car, until the Dodge Demon was introduced. This engine was not equipped with MDS.

    The drop from the SRT 6.4 liter engine to 6.2 liters was caused by a reduction in stroke, which was done to increase the strength of the camshaft. The Hellcat Hemi, in the Challenger, is hooked up to either a manual transmission or an 8-speed automatic with two power modes activated by choosing either a black (500 hp.) or a red key fob (707 hp.).

    Air came in through the front of the blower, and was compressed upwards, going through runners, making a 180° turn, and going straight down through the four heat exchangers (one for each pair of cylinders), then into the intake ports. The fog lights were replaced by vents for the low-temperature oil/coolant radiators; an opening in the wheel well let the air flow out. One side was an oil cooler, the other side was coolant.

    The supercharger was provided by IHI, which also sells superchargers to AMG (higher-performance Mercedes). They worked with Chrysler to develop the specifications and design of the supercharger. Turbochargers were considered but the supercharger provided better “instant-on” torque. The 2.4L IHI supercharger runs 14,600 RPM, at just over 11psi.


    6.2 Hellcat Redeye Widebody (376 cubic inches)

    Dodge “demonized” the Hellcat by incorporating the Demon's supercharged 6.2 Hemi, 8-speed automatic, and driveline bits- including the line lock and launch control but not the trans brake- into a Hellcat and added the Redeye suffix to differentiate it from lesser 707-hp (and now 717 hp.) Hellcats.

    The Redeye's twin-snorkel hood resulted in its slightly reduced 797 hp. output. Even with the driver's-side headlamp void and an inlet near the front-left wheel liner supplementing the air supply, Dodge had to recalibrate the engine for the reduced airflow.


    6.2 Demon (376 cubic inches)

    The ultimate Hemi- the Demon- featured a number of drag race-inspired improvements over the Hellcat. It was fitted with a larger, 2.7 liter twin-screw supercharger, as well as reinforced reciprocating components, a new camshaft, and several other valve train upgrades.

    With these improvements, the Challenger SRT Demon was rated at 808 hp., at 6,300 rpm, on 91-octane pump gasoline, with 770 lb-ft, and 840 hp., at 6,300 rpm, when running on 100-octane unleaded racing gasoline. Cooling was aided by a functional Air-Grabber hood scoop, as well as a unique charge cooling system which made use of the air-conditioning coolant to lower the intake charge air temperature. High-speed launches were assisted by a factory line-lock system, which allowed the car to perform a burnout to warm the rear tires and a Torque Reserve Launch System.


    Here is an excellent article, From Holley Motor Life, about the Gen III Hemi engines.

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