408 Engine Question

[Bob318]

My feelng has always been that it's perfectly okay to make performance/reliability/practicality upgrades, and Bristols are no exception. Based on sheer horsepower per cubic inch, it's hard to beat Mopar's 340. Chrysler's threw everything they had at that engine, which puts out far more than it's rated horsepower (numbers designed to fool the insurance companies!).

That said, it's awfully nice to open the hood and see the engine that's meant to be there. As other commenters have noted, there are loads of 318s around for dirt-cheap. You can keep the stock forged cranks and con rods, or put in the entire bottom end from a 340. Growing interest in this "semi-hemi" V8 also means growing parts and value--another reason to stick with the A-series Poly.

While the dual-quad manifold from '57 and '58 Plymouth Furys looks nice, it's essentially a single-plane log manifold that turns the relatively thrifty 318 into a gas guzzler. And as someone mentioned, the most-common Weiand aluminum four-pot manifold is also a single-plane that reduces the low-end grunt these mills are known for.

Best option: An original, if heavy, cast-iron dual-plane manifold made from '56 thru '62 (on the US 277, 301, and 303 and Canadian 303/313 versions of this engine) with, say, a modern Edelbrock four-barrel or even a plug-and-play throttle-body EFI setup. And while you can go all the way over 400 CU IN, the best compromise seems to be boring the A engine out to 3.95 inches (like the '59-only 326) and, perhaps, stroking it to roughly 3.58 inches to bring nearly 360 cubic inches. Or simply leave the stock bore and stroke and enjoy a pleasant combination of torque and reasonable fuel economy.