As he was preparing for the 2007 Popular Hot Rodding Engine Masters Challenge, veteran competitor Adney Brown had another challenge when deciding what engine to use. The task was to create an entry for the pump-gas competition that has become the showcase for forward-thinking, yet repeatable, engine combinations. With a 10.5:1 compression ratio limit, 91-octane pump gas, and a mandatory flat-tappet cam, Adney had to find an engine with a good basic foundation to build from. He chose a Mopar 318 engine with a mix of old and new technology. His decision was based in part on the design benefits inherent in the engine. Adney also candidly admitted he thought no one else would build a 318. High-tech and common sense together appeared to be a good combination, as his little 323-cubic-inch engine pounded out 427 foot pounds of torque and 477 horsepower! Big-block numbers from the smallest of small-blocks.
The how's and why's of this engine buildup might not be seen upon a cursory glance. Take a few minutes to sort the wheat from the chaff, the little details start to shine through, and it becomes easier to ask, "Why not build a 318? How could it not make power?"
First, a quick history of the engine in question. At some point as the sun was setting on the 1950s, and America's appetite was growing beyond what the postwar automotive industry was offering, it was clear to the staff at Chrysler that along with the new styling cues of the coming era, a new powerplant would be required-one that was lighter, more powerful, and could take advantage of growing trends in technology. When dawn rose on the 1960s, the engineering team from mother Mopar had completely redesigned the old 318 Polysphere engine into what it referred to as the LA engine. Although sharing several pieces with its predecessor, such as the crank, bearings, connecting rods, and harmonic damper, the new LA engine used a smaller bore, wedge heads, and lighter-weight castings (the "L" in LA stands for lightweight). This resulted in an engine that packaged easily into the smaller cars like Valiants, Darts, and Barracudas, symbolizing Chrysler's entry into the burgeoning high-performance ponycar market. With factory designed full-floating pistons, 18-degree valve angle cylinder heads, large-bore mechanical flat-tappet lifters, and a forged crank, the first LA engine measured up at 273 cubic inches, and appeared to be a perfect platform for some real power upgrades.
The first glimpse into the...
The first glimpse into the engine reveals a lifter valley baffle to keep hot oil from splashing against the bottom of the intake and unnecessarily heating the incoming air/fuel mixture. Here you can also see an oil passage directly above the head bolt between the first two cylinders. This provides oil to the top end on early-style engines. Using the late-model Magnum R/T heads, which oil through the pushrods, this passage was blocked with the head gasket and the head itself.
After receiving the news that he was one of the lucky few invited to participate in the Challenge, Adney and his teammates, Mike Ridings and Randy Malik, picked up a later-model 318 "roller" block as their base, and began their exercise with the usual stuff-torque plate, hone the block, deck it for tight quench, and build sheetmetal block-off plates to keep from draining top-end and camshaft oil onto the crank and creating windage problems. What? Your small-block doesn't have those? OK, maybe that shouldn't be categorized in the "usual" column, but that is just one of the little details that allowed this little engine to make big power.
Adney owns and operates Performance Crankshaft in Roseville, Michigan, not far from Ground Zero of the automotive world: Detroit. Being a crankshaft guy, Adney knows the good and bad of OEM and aftermarket offerings, and chose to use a factory 340 forged crank for this build. The 273, 318, and 340 cranks all shared the same basic dimensions-stroke, rod journal, and main journal size-and he could have used any of them to get his final 323 cubic inches. The 318, and later-model 340 cranks, were cast iron, limiting their use in the high-performance arena, but the '68-72 340 engines use beautiful forged cranks with lightening holes, and Adney had access to a perfect donor. He explained some of his modifications: "It was a 340 crank we lightened up ... bullet-nosed the leading edges, and knifed the trailing edges." This aerodynamic modification allowed the crank to spin through the crankcase with much less resistance, reducing parasitic power losses.
"We took a lot of weight off the throw side," says Adney. "The more weight you take off the throw side, the more you can take off the counterweight side. I guess it probably ended up about 5 pounds lighter than when we started." Often, lightening the rotating and reciprocating weights might not show up on the dyno, but it will be worth its weight in gold at the track.
Even with a small dome, the...
Even with a small dome, the pistons ended with an effective zero cc's of volume when figuring out the compression ratio. Adney applied a water-based antifriction coating on the piston skirts, and a thermal barrier to the crown to keep as much heat in the chamber, thus making power. It also prevents losing the energy through heat transfer into the pistons. Enginetech supplied the rod and main bearings for his engine.
Some more effort into lightening the assembly is seen in the connecting rods. According to Adney, they used a 6.200-inch small-block Chevy rod, an I-beam design from Scat. The small-block Chevy and Mopar rods are very similar, with the Chevy rods just slightly smaller and wider in journal size. With the tools at his disposal, Adney just widened the throws on the rod journals to fit the Chevy rods, and he was able to take advantage of the smaller wrist pin and extra length provided by the budget-priced rods. For a re-creation of this engine, Adney suggested, "the Mopar rod is really totally sufficient for street use. You can bush it for a smaller pin, or even stick with the Chrysler pin and use a thinner wall. I mean, 6.125 inches is nothing to sneeze at," referring to the stock length of the Mopar rods.
At the small end of the rods swings a set of custom Diamond pistons with a lightweight Speed Pro ring pack. "We ran a low-tension oil ring, which we did modify the expander on, crimping it. That lowered the tension on it. We ended up with about an 8-pound pull." Ring tensions that low build great power, but Adney admitted they had a tough time getting the rings to seat during testing. By the time they brought their powerplant to the Challenge, there was no blow-by present.
When asked about engine coatings, Adney states that he is a believer. "The first year I was in it, which was in 2003, I coated everything but the rods. I did the intake, the ports, both sides of the head, everything. And you know that's a ton of work. We've never done any testing before and after, so I can't really tell you, but even if it only gains you four or five points, it's worth it." This year, he and his cronies at Performance Crankshaft did the coatings themselves, using different applications from Tech Line Coatings. Instead of coating everything they came across, however, they concentrated on what they considered key areas, specifically the tops and skirts of the pistons.