Way back when the polyspheric-headed small-block Dodges gave way to the “modern” LA engine in the ’67 Valiant, the Pentastar populous could not have known that their little creation was capable of making over 1.4 hp per cubic inch on plain old pump gas. A team of engine builders from SKMFX Racing Engines in Ontario, Canada, recently did that using cylinder heads designed when the LA was only a couple years old. Though much of the rodding community has moved to the cookie-cutter late-model EFI swap, the guys at SKMFX built this LA engine from old-school parts using new-era thinking. Lead engine builder Jesse Robinson ain’t no newbie when it comes to making power to go. As a two-time competitor in the AMSOIL Engine Masters Challenge, he’s done his share of research into what it takes to make power.
Team leader Jesse Robinson claimed that the number-one factor in the engine performing so
“I always liked the stock stroke deals,” he says. “Everybody’s building 408s and 416s out of the 340s with a 4-inch stroke. I built one for myself about eight years ago, and I didn’t like the power curve. It was all done by about 5,500, and it pounded the mains out of it. The caps like to walk, and it kind of turned me off. I built a real budget 360 about eight months after that 408, and bang for the buck it was about the most fun engine I’ve ever had.”
With those experiences in the back of his mind, Robinson decided that for the 2010 Engine Masters Challenge, he’d build a stock stroke 360 to bring back the fun factor. He rounded up an old 360 block, and after a good cleaning, gave it a short fill of Hard Block to stabilize the cylinders. SKMFX offers full machine shop services in-house so it was no biggie to bore and torque-plate hone the block .040 over. Robinson often leans on team member Joe Rutters to perform the machine work flawlessly, and he made sure that the hone job matched the intended ring package. Leaving the cylinder walls too coarse can prematurely wear the rings while some rings won’t seat quickly if the bores are too smooth.
Running an oil line across the lifter valley to even oil flow is not too uncommon for an L
Another of the techniques the team used to make the lightweight “A” engine scream was to mill the deck to an even 9.588 inches. Using that number as a baseline, subtracting half the stroke and the rod length of 6.123 inches revealed a final piston compression height of 1.675 inches. “Diamond [Racing Products] whipped me up some excellent pistons. That was my first time using an .043 inch with a Napier-tapered hook groove second, and low-tension oil rings, and boy, I specify that Napier second ring in everything now if I can.” Besides offering low tension and surface friction, he noted that the pairing of that Napier with the low-tension oil rings really helps keep the oil out of the chamber. “I think there’s something to be said for that second ring doing a lot of scraping and I think the low-tension oil rings are sealing better.”
Having seen previous issues with the two-bolt main small-blocks exhibiting signs of cap walk, SKMFX installed a set of ARP main studs. The extra pulling power of the studs kept the main caps from moving around as the crank spun through its rpm range. An Eagle forged steel crank was chosen and treated to Eagle’s Armor Shield treatment to reduce friction and shed oil. Since the steel crank was denser than the original cast-iron crank, it allowed them to internally balance the rotating assembly. Mopar engines that are externally balanced use a counterweight on the torque converter instead of the flexplate like the rest of the world. That tends to make balancing the crank with a fake converter “substitute” a real pain. Internally balancing alleviates that problem.