340 Big-Block Engine Buildup - Giant Slayer

Since its '68 introduction, the 340 Chrysler engine has been a contender. Built around the LA-engine platform introduced with the 273, it was on the street performance map as soon as its A-Body hosts hit the highway. The new engine featured a big-bore/small-stroke combination (4.040-inch x 3.31-inch) and some of the best production heads of the era; durability came from the forged crank, windage tray, bushed 6.123 rods (same length as other A/LA engines), and shaft-mouthed rockers. Wind it up, and unsuspecting Brand X girlie-men got their lunch eaten at the stoplight Gran Prix. The engine became the basis for most of the early small-block race development. Keith Black built examples that ended up on the Trans-Am circuit, and the 340 engines raced competitively in NHRA Stock Eliminator and NASCAR's "baby grand" series soon after its introduction.

The trick to making big power with small cubes in any engine is rpm. A small engine will be limited in peak torque output simply by its displacement. Since horsepower is derived from torque and rpm, moving the torque peak up high into the rpm range and buzzing the engine is the key to making big numbers with limited cubes (the short stroke and big bore helps here). One limiting factor in relation to potential rpm is piston speed. While the casual enthusiast may be keyed to focusing on the top rpm level the engine can endure, engineers and pro engine builders look at piston speed. Consider that at 7,500 rpm, a 340 with its 3.31-inch stroke has an average piston speed of 4,138 ft /min; a 4.000-inch stroker small-block moves the same piston at 5,000 ft./min. at the 7,500 rpm number.

A bigger bore, on the other hand, gives the room required to make efficient use of large, free-flowing valves; high rpm is the domain of high-flowing heads, proportionally large port cross sections, and big cams. Back in the day, the 340 received the T/A heads with offset rockers, making room to carve the large, high-rpm ports required in serious racing. Development later continued with the W-2, and the subsequent W-series heads, eventually evolving to the race hardware of today. That's quite a racing heritage to tap into for the would-be 340 engine builder, and inspired what we were looking to do.

Master Plan
We had Marco the Rooster's street/strip '68 Barracuda already packing a fairly stout but remarkably stock 340. While it was serious enough for the average challenge, when the big dogs came out to play, it was time to head back to the doghouse. Cruising to the Nats last year, the wheels started turning.... What kind of power could we extract from a 340 street/strip mill with some well-selected pieces of serious hardware, but with a budget approach? While 500 hp seemed readily achievable, and would up the ante from the current combo's approximate 400 hp, it probably wouldn't hold off the more dedicated street rats. Realistically, a well-executed 340, with improvement to cam, compression, and airflow, should pull around 1.3 lbs.-ft. of torque per cube, or about 450 lbs.-ft. total. Crunching those numbers, we figured with some great heads, enough cam, upped compression, and a tunnel ram, we could be knocking on the 600hp door with peak power coming in at the mid-to-lower 7,000 rpm range.

Mondo Combo
Bench racing and math are one thing, but turning nuts and bolts and actually spinning a fat number with a real engine is something else. We'd need some heavy-hitting heads, and here was one place where we had to make good. The best bang for the buck would be Mopar's W-2s, and we already knew what could be extracted from them (see "Porting The Magnificent W-2;" Mopar Muscle Nov. '01). We went for the long-valve econo versions, giving them the full porting treatment, and a set of 2.02-inch/1.60-inch long-stem valves. Availability and price steered us towards these bare castings, though in retrospect, a set of closed-chamber W-2s would have been the better choice.