The numbers 392 and 426 instantly heap on the street cred when fender racing at the local lawn-chair farm or sniffing nitro at the cackle fest. They're Hemis, and unless you have 15 large for a long-block or are lucky enough to have a leftover in the family, the original engines are getting out of reach. But there is another way to have Hemi on the fender and big power underfoot—take a third generation or G3 Hemi from a '03-and-later Dodge Ram or Charger/300C/Magnum, and stroke your way to glory. JMS Racing Engines in El Monte, California, shows us how with their 1971 Dodge Demon.
Dodge Demon - The Rotator
Although the original 426 Hemi from 1964 is a great engine, the reality is that smart guys like legends Keith Black and Don Garlits used the smaller 392 in the early days of drag racing for reliability and low cost. The same can be true today. The 5.7L is the most common G3 Hemi engine and, when combined with a 392 rotator from K1/Wiseco, can be an affordable and reliable way to go racing. A G3 426 requires a more expensive and less common 6.1L block and, depending on who you ask, needs to be sleeved to get the bore up and the stroke down to be reliable when facing big loads of boost or nitrous. The 392 rotator has a thick 0.280-inch top ring land on the forged piston, a 6.125-inch forged H-beam rod with a Chevy 2.00-inch journal, and a forged crankshaft with a 4.080-inch stroke to get the cubes up and handle a power-adder. Using the K1 kit and a pre-2008 85cc cylinder head, the compression ratio is 9.0:1, but with a '09-and-later head, the compression ratio is 11.0:1. If you don't have the bucks for a complete rotator, you can also find a used factory forged 6.1L crank that bolts into place and run a K1 rod and Wiseco piston combo for about half the cost.
Dodge Demon - The Heads
You might say that because the 392 has a 3.93-inch bore, there is no room for big valves and performance heads. On the Hemi, the 18-degree intake and 16.5-degree exhaust valve angles unshroud the relatively large 2.00/1.55-inch valves. The Head Flow sidebar (page 40) illustrates the potential of the pedestrian 5.7L Hemi head with both stock and ported numbers. JMS offers a complete head porting service for $1,200 or will sell you a set of ported heads for $1,600, outright. We sent JMS the stock heads from our eBay Hemi, and the company repaired the problem areas like the intake valve seats, cleaned and inspected the castings, cc-matched the combustion chambers, installed new seals, and pressure-tested, ported, and polished the runners and bowls.
The "Other" 392
You might be wondering why our Dodge Demon doesn't use a factory 392 found in the new Challenger. We spoke to Dave Weber at Modern Muscle in Martinsville, Virginia, who sells the '11-and-later G3 392 crate engine for $7,650 with a core charge. The engine makes 470 hp, has a warranty, and comes with everything, except a starter and the accessories. If you do the math on the 392 build in this article, it will cost more to build one. What you get for the extra cash is ported heads, a custom cam, and a complete forged rotator with enough meat to handle 900 rwhp or about 1,100 at the crank, before the block comes apart. If you are serious about using more than 10 pounds of boost on a regular basis or more than a 200-shot of nitrous, you are going to have to take apart the engine. That's where the 5.7L build becomes the better deal. If you want to swap a 392 into any '03-and-later vehicle, we agree with Weber, go for the new 392, but if you want to go fast and afford a room full of spares, go for the engine in this article.
Dodge Demon - The Turbos
Of course, we want to make 900 hp at the wheels and see if the block explodes, so we had Joe Delgado from Comp Turbo pick us a set of 65mm CT4 turbos with billet compressor wheels and P-trim turbines in 0.81 A/R housings. Even though the compressor wheels are designed to deliver a maximum of 96 pounds of air per minute and support 950 hp each, we were looking for instant boost delivery in a usable rpm range, hence the relatively small A/R ratio on a T4 flange. The triple ceramic bearing system in the CT4 uses a ceramic ball that is perfectly smooth, lowering friction losses and temperature for more speed. We used these turbos to make 978 rwhp a couple of years ago ("The Wrenchrat Twin Turbo Kit," Apr. '09) on Ted Toki's '55 Chevy with a '70s-era 355-inch small-block Chevy. The turbo's roller bearing design, combined with a high-speed billet compressor wheel, allowed the engine to make usable boost (6–8 pounds) as low as 3,100 rpm and make more than 500 lb-ft of torque. In addition, we saw torque gains of 527 lb-ft from 3,100 rpm to the torque peak of 978 lb-ft at 4,314 rpm. The car was a bullet.
We hope to better those numbers using modern Hemi parts in the 1971 Dodge Demon. Our quick air math says with a 3,000-pound race weight and 978 rwhp has the potential to put us in the mid-8s at 160 mph. That would be fun, don't you think?
You do realize that you're committed in print to running 8s in this car? Tall order, my friend… Reality's a b#&@h...