Many have forgotten the 6.1 Hemi now, but it was an almost impossibly powerful engine when it came out—with the same 425 hp rating (net) as the legendary 426 Hemi (gross). It was launched in 2005, but in just a few years, Chrysler had a more powerful replacement. Most know the new 6.4 liter SRT engine as the 392—it was 392 cubic inches in displacement, the same as the biggest of the first generation of Hemi V8s—which came out in the 2011 SRT8 series.
The SRT 6.1 used a special deep-skirt, cast iron block, springs, cam, valves, manifolds, air paths, and exhausts, with oil squirters to cool the pistons and heavy-duty cooling; not to mention hollow intake valve stems and sodium-filled exhaust valve stems. The recommended fuel was premium—91 octane.
The 392 had all these design features as well as the 5.7 V8’s cylinder cutoff, which shut down half the cylinders when they weren’t needed, putting them back into play in a fraction of a second when they were. Given the high power of the 392, it could spend quite a bit of time as a four-cylinder without owners ever being the wiser; as a result, it had better mileage than the 6.1 despite its greater output and displacement. (This feature was not used with the manual transmission.)
The original 392 was rated at 475 hp and 460 lb-ft of torque on the Grand Cherokee and Challenger, and 465 hp with 465 lb-ft of torque on the Charger, showing slightly different tuning. The 2015 Charger and Challenger both went to 485 horsepower and 475 pound-feet, while the Grand Cherokee version was unchanged.
As with the standard Hemi, both spark plugs fired at top dead center, and one fired just beforehand to burn off the hydrocarbons. That emissions move meant SRT could use less restrictive catalytic converters. As with any engine of its time, it had sequential fuel injection (each piston got its fuel only as needed); as with any Chrysler engine, it had returnless fuel injection, with fuel metered at the tank.
The valves were operated by pushrods and a single overhead cam in each cylinder bank, as with all Hemis from the 331 to the 426, 5.7 to 6.2 Hellcat. A design breakthrough in the 1940s was still handy. There were two valves per cylinder; the exhaust valves were sodium filled to handle heat, and the intake valves had hollow stems. The lifters were all hydraulic, with roller tips
When the 392 was launched, Chrysler was still using Mercedes five-speed automatics; but they later switched to ZF eight-speed automatics which improved gas mileage further.
SRT engine design supervisor Kraig Courtney told Mopar magazine (March/April 2011) that the engine could have gone past 500 hp, but that would have come at the cost of low-end torque; the first tune, set for peak power, didn’t feel as strong as it should have. Switching to intakes similar to the Ram V8, which let the computer choose either a short runner and a long runner to maximize power or torque respectively, fixed the problem. There was less peak horsepower, but the area under the torque curve was much larger, giving the “instant-on” feel the 392 was known and loved for.
cid |
370 cid |
392 |
|---|---|---|
| cc | 6059 | 6417 |
Bore x Stroke |
4.06 x 3.58 |
4.09 x 3.72 |
Compression Ratio |
10.3:1 |
10.9:1 |
Power |
425 bhp @ |
470 then 485@6100 |
Torque |
420 lb.-ft. @ |
460 then 475@4100 |
Redline |
6400 rpm |
6400 rpm |
Fuel |
91 octane (premium) |
|
Oil Capacity |
7 qt. (6.6L) |
7 qt. (6.6L) 0W-40 |
Coolant Capacity |
14 quarts |
15 quarts |
MPG* |
14 /19 |
15 /25 |
* Challenger automatic.
Information from press books, Motales, and Mopar Action. 392 specs from 2019.
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