In the Mopar world the Hemi revels in superstar status, while the related big-block wedge is the quiet hero providing power to the masses. Built in large numbers from 1958 through 1978, the wedge came in tall-deck and low-deck configurations, in displacements from 350 to 440 ci. While the Hemi's exotic layout deservedly garners attention, it is the very simplicity and commonness of the big-block wedge that makes these engines attractive. Simple, straightforward, and rugged, the Wedge could be found in all manner of Chrysler products, powering everything from factory muscle cars to trucks, boats, motorhomes, and even industrial units.
Though out of production for decades now, the Wedge Mopar is still readily available and remains relatively cheap to build. These days the most popular combinations are built on either the low-deck 400 (B type) or the tall-deck 440 (RB type), the biggest bore versions of their respective series. Jesse Robinson of Robinson Rutters Auto Machine (RRAM) is a long-time Mopar fan, and recognizes the capabilities of the Chrysler Wedge. Building an engine for the 2013 AMSOIL Engine Masters Challenge, Robinson had the ideal venue to showcase the engine's potential, and RRAM's ability to tap into that potential.
Robinson started with a production 400 block, a configuration with a stock bore and stroke of 4.342 by 3.375 inches, and produced from 1972 to 1978. The short-stroke 400 is readily upsized with a bump in crank stroke, with a wide range of aftermarket 'shafts available. Nevertheless, Robinson turned to the popular approach of using a factory 440 crank in the 400 block, which required the main journal diameter to be reduced to the 400 dimension. This alone would up the stroke to 3.75 inches. Taking things one step further, the rod journals were offset ground to the big-block Chevy 2.200-inch dimension, allowing the swing to be increased to 3.900 inches. While diehard Mopar purists may be appalled by the thought of Chevy parts in a Chrysler Wedge, the 2.200-inch rod journal allows use of big-block Chevy rods, which really opens up the rod and bearing selection, and improves crankcase clearance. This modification is such an advantage that many aftermarket crankshafts are built to this specification.
With a clean-up bore to 4.360 inches and the 3.900-inch stroke, the displacement of the engine increased sizably to 466 ci. With the Chevy journals, there are a wide range of rod lengths available. Here Robinson bucked conventional Mopar long-rod wisdom and went with a short-rod arrangement opting for a set of Scat I-beam rods in a 6.135-inch length. Robinson relates: "I have been rethinking the rod length presumptions, and looked to gain the higher piston speeds near TDC with the short rod setup. In an engine like this I see no disadvantages to the short rod, but I did need to cut extra material from the counterweights for piston clearance."
This stroke and rod length combination worked out to allow an off-the-shelf 440 piston from Icon to be used. Robinson explains: "The Chevy rod is so popular these days that many manufacturers are building parts with this in mind. These Icon pistons feature a Chevy spec 0.990-inch pin, so they are compatible at the rod's small end." Although the forged Icon pistons were an off-the-shelf item, to meet the compression ratio limit of 11:1 for the Engine Masters competition, the pistons were heavily modified. Robinson says, "The pistons actually started out as flat tops, but with the small chambers in the heads, we needed to machine them to a dish, and add the large valve relief for volume. I preserved as much of the squish area around the circumference as practical, and brought the volume to where it needed to be to meet the required specification."
A factory block and crank is not what you would normally expect to serve as a foundation for an engine producing north of 750 hp. This factory Mopar 400 Wedge gains considerable beef via RRAM’s custom fabricated girdle arrangement. A factory forged crank from a Mopar 440 provides 3.900 inch of stroke thanks to an offset grind to big-block Chevy journals.
Pistons are Icon units for a 440 Mopar application with a Chevy 0.990-inch pin. These are readily available in-stock units, but the crown was heavily modified to reduce the compression ratio to this dished configuration.
To top the engine, RRAM started with Procomp cylinder head castings, which are manufactured with material to accommodate a Max Wedge sized port, and can accommodate even larger custom port forms.
This detail reveals the magic stack that ties the bottom end together, starting with the stock main caps machined to be topped with a billet aluminum spacer, which in turn mates to a custom 1/2-inch steel girdle, all cinched together by premium ARP fasteners. The deep skirted Mopar block is ideally suited to this kind of reinforcement.
The Icon pistons are made for a common 1/16-1/16-3/16 ring pack, which is handled by a conventional ring set from MAHLE Clevite. Rods are Scat I-beam units measuring 6.135-inch, center to center.
To feed the Wedge, RRAM radically altered the port size and position, going to a wide raised-runner layout. Note the original port size indicated by the epoxy filled area on the floor. The available space between the pushrods is the limitation to port width. The offset intake rockers allow for significant enlargement.