It was late in 1967 when Mopar's 340 first became available in the '68 models. Sure, it may have only been 22 ci larger than its counterpart, the 318, but with performance in mind, the guys at Mopar gave it goodies like a dual-row timing chain, a windage tray, 2.02-inch intake and 1.60-inch exhaust valves, and a high-rise dual plane intake with an AVS carburetor, a steel crankshaft, and high-performance heads. Make no bones about it, the 340 was here to make a statement.
The 340 Six Pack crate engine...
The 340 Six Pack crate engine as delivered. When you get your engine, you'll need to get carburetors, linkage, fuel lines, and a neutral balance flywheel. Other than that, it's ready to rock.
Throughout its life, the 340 was treated to different options and changes. Some maybe not considered performance oriented; a cast-iron crankshaft was utilized starting in 1973. And as for induction, everything from an 850-cfm Thermoquad, all the way up to a Six Pack (Six Barrel for you Plymouth guys), rested on top of the "high performance" heads of the 340.
But we know you guys know all this stuff, so why are we telling you this? Because it's 2009, and some of it may have been forgotten, and would you believe you can now buy an all-new 340 Six Pack directly from Mopar? That's right, Mopar has brought back the 340, and it does its heritage proud. At its peak, the venerable '70 340 boasted 290 hp--this in its Six Pack livery. Now, however, the new 340 Six Pack is rated from Mopar to reach 330 hp, and 330 lb/ft of torque--we prove them wrong, and more on that later.
Proving an engine's worth...
Proving an engine's worth is a lot better if you can physically test it. Saying your engine has 500 hp doesn't mean a thing without the proof, so we hooked up to the Dyno at Automotive Performance Engines in Auburndale, Florida.
As in the old days, the parts list is of stuff designed for durability and performance--to an extent. Our only improvement wish would be to add forged pistons to the mix--currently, the new 340 uses a cast piston. Starting from the bottom, the new 340 replacement block (PN P5007552AB) includes the original 340 production casting part number with an M added at the end to identify it as a Mopar Performance 340 block. The block does have a few cosmetic differences from the original 340 block, but it is machined to work with all 340 production components. Special features include high nickel content for added strength (not a thin wall casting), four-bolt main bearing caps on the center three journals, and a standard 340 journal size. It has a thicker webbing and pan rail (like the 340 T/A), a thicker deck surface, and thicker-bore cylinder walls in major/minor thrust directions. The deck height is approximately 9.600 inches. It also requires the use of Mopar PN 05281090BA oil filter, or equivalent. It is not recommended for use with roller tappets, and may require use of a late '70s 318 motor mount on the left side.
The crankshaft is an internally balanced cast piece with the 340's original 3.31-inch stroke. The rods used in the new 340 are forged I-beam units. We were unable to get part numbers for the crankshaft and rods as of this writing. According to Mopar, altogether, the short-block creates a compression ratio of 10.0:1. Definitely within the realm of using your corner gas station Premium fuel.
Sitting on top of the short-block is a pair of LA-style aluminum Commando heads PN P5153849. This part number head uses 2.020/1.600-inch stainless valves. Since these are LA-style heads, shaft mounted stamped-steel rocker arms are used. We know you're wondering what camshaft is used, so here it is: a hydraulic flat tappet stick, PN P4120233 with .508/.508-inch lift, and a duration at .050 inch of .248/.248 degrees. What can we say other than this camshaft has been around for a long time.