When it comes to unpopular engines, the Mopar 361 is one of the kings of the ugly contest. Packing small-block cubes in a big-block envelope, the 361 was introduced in 1958 with a bore of 4.125 inches and a stroke of 3.375 inches. Production continued in truck and industrial applications through to Chrysler terminating big-block production in 1978. In all fairness, in the early to mid-1960s, notable performance versions of the 361 were available. However, in today's world of big-inch big-blocks, the 361 is an orphan abandoned by even the most dedicated Mopar fans as the basis for a performance build. To most enthusiasts, the Mopar 361 is considered a throwaway big-block.
Buck and Clark Hinkle of Hinkle Performance took the unlikely step of considering the 361 as the basis for a true performance street build. Why? As Buck tells us, "I had a few of these lying around, and I just like doing things that are a little bit different." Looking at the basic configuration, Buck recognized the unseen potential. With a 4.125-inch bore, the cylinders are as big as a Chevy 400 small-block, while the 9.98-inch deck height allowed plenty of room for the stroke to grow from its short factory specification. Buck and Clark could see the possibility for building a low-buck performer out of Chrysler's neglected big-block. Hinkle Performance's approach to building this low-deck Mopar was anything but conventional.
The mains use the stock caps, but machined for a custom cross-bolted upper cap fabricated
With the aim of adding displacement, the obvious first step was to increase the crankshaft stroke. While there are plenty of off-the-shelf stroker cranks available for the low-deck Mopar B-series big-block, Buck once again went in an unexpected direction. Eyeing the factory forged crankshaft, he determined that the low-buck approach would be to offset-grind the factory 'shaft, taking the original 2.375-inch journal diameter all the way down to the 2.00-inch small-journal small-block Chevy size. As Buck explains, "I was shooting for a stroke of 3.75-inch, looking for the bore and stroke of a 400 Chevy small-block. I figured I could get very close to that using the original crankshaft and ended up at 3.74-inch, which is pretty close." Buck didn't stop there; he went on to grind the main journals down to the 2.45-inch small-block Chevy spec. Buck's clever crankshaft machining created something from nothing—in the best hot rodding tradition. The result is a forged crank providing dramatically reduced bearing diameters for lower bearing speed and friction while achieving the targeted stroke increase.
Back to the block, Buck line-bored a set of Mopar bearings to serve as bearing spacers to use small-block Chevy Clevite main bearings. The modifications in the mains went further, with Buck designing and machining his own cross-bolted main bearing arrangement using the factory 361 caps as the basis. Buck flat-milled the caps and fabricated bridge supports precision-machined to fit across the Mopar block's deep-skirted crankcase. Again, Buck's machining skills and innovative thinking dramatically increased the bottom end rigidity for the cost of a few hunks of steel bar stock and the bolts. The one-off cross-bolted bottom end is the way Chrysler should have built it.
While the engine could actually use off-the-shelf Chevy 400 pistons, these are custom unit
While the small-block Chevy rod journals might suggest that Buck would use aftermarket small-block Chevy rods, he actually went with an Eagle rod manufactured to fit the Ford 5.4 mod motor. He explains, "I wanted a long rod to keep the compression height of the piston down, so I made these Ford rods work. They are 6.657 inches long, which is about perfect. I took a set of the Ford bearings and made them into spacers to take the small-block Chevy bearings; the machining here is critical to maintain the correct fit and crush. On the small end, I took out the pin bushings and ran the pin steel on steel. Without the bushings, the pin hole just needed a small amount of honing to take a small-block Chevy 0.927-inch pin."
Although the engine could actually be built with very low-cost, off-the-shelf Chevy 400 pistons, Buck had custom pistons made by BRC at 0.060 inch oversize. This puts the bore at 4.185 inches, resulting in a displacement of 412 ci. The custom pistons feature low-drag metric 1.1mm compression rings and 3mm oil rings. Buck's 361 was now looking like a thoroughbred with a very low-friction bottom end, respectable displacement, and the added strength to go the distance.
Port work is extensive, with a hybrid port window configuration designed to work with a mo
Induction duties are handled by an Edelbrock Performer RPM manifold topped with a 1,000-cf
The attractive valve covers are vintage Cal Custom pieces reworked by Buck and fitted with
Teamed with the pistons are Eagle H-beam rods in a 6.657-inch length, actually for a Ford
A flat-tappet cam delivers outstanding results thanks to the rapid lobes possible with Mop
Fully ported Edelbrock Victor cylinder heads deliver the airflow, while Harland Sharp rock
A view of the manifold exits shows the extensive widening done to the runners to match the
To feed the newfound cubes in his one-off 361, Buck wasn't shy about adding airflow capacity. The Edelbrock Victor heads come with large raised ports, which Clark Hinkle reworked and fully ported to a variation of the famous Mopar Max Wedge port. A limitation on the port configuration was the requirement to run a two-plane intake manifold to compete in the '12 AMSOIL Engine Masters Challenge. Buck opted for an Edelbrock Performer RPM manifold, since there is no available two-plane Max Wedge intake for the low-deck Mopar. The complication here is that the Max Wedge port window would be too tall to fit within the fingerprint of a standard port intake.
Buck solved the manifold puzzle by raising and widening the port while filling the port floor, essentially making a short, wide port that could be replicated at the manifold. To mate the intake to the raised port location, he fabricated manifold spacers out of oak plywood. The Victor heads feature Edelbrock valves with generous sizing at 2.25/1.81-inch diameter, admittedly crowded in the small bore of the modified 361. Buck tells us, "You have to be really careful with the small bore and the big valve heads. We notched the bores, helping clearance and airflow, and checked the fit very closely." A Holley 1,000-cfm HP-series carb tops it all to provide the mix.
Up front, Buck used a Mopar Performance beltdriven mechanical water pump arrangement, with
To work those big valves in the Edelbrock heads, Buck went with a Competition Cams solid flat tappet. With Mopar's large 0.904-inch tappet diameter, a very fast rate of lift can be designed into the cam profile. As Buck tells us, "These Mopar flat tappets are very fast and perform just about like a roller. I went with a set of Harland Sharp rockers, using a 1.7:1 ratio on the intake and 1.65:1 on the exhaust. I've been using the Harland Sharps for years, and they never give me any trouble. I did turn a set in to rebuild, and when they saw the rockers they told me they must have been built over 20 years ago, and they actually did them for me for free. The cam and rocker give me 0.656-inch lift on the intake and 0.642 on the exhaust, with the duration at 255 degrees intake and 259 on the exhaust (at 0.050). I had some used NASCAR springs in the shop that I put on and they worked out really good."
With the unusual Mopar's internals assembled, the engine was completed for testing with a set of Schoenfeld 17⁄8- to 2-inch headers and an MSD ignition system. Testing at Hinkle Performance showed numbers that were very encouraging, topping the 600hp level with ease. Buck relates, "We did run the engine with a single-plane intake manifold, and that was quite a bit better as far as top end power. The two-plane did make a lot more torque down low and into the midrange." Looking at the numbers, it's hard to reconcile that the basis here is an old Chrysler 361. Topping out with a torque reading of 520 lb-ft and delivering 618 hp at 7,000 rpm, this Mopar oddity proves that innovative thinking and a mastery of machining talent can pull unexpected power from an unlikely source. Really, isn't that what hot rodding is all about?
|ON THE DYNO
|Tested at Hinkle Performance
|BY THE NUMBERS
|412 Mopar Big-Block
||412 cubic inches
||Custom Comp Solid Flat Tappet
|Rocker and ratio
||Harland Sharp 1.7/1.65:1
||BRC 1.1/1.1/3 mm
||OEM Production Mopar 361
||Eagle 6.657 inches
|Intake valve diameter
|Exhaust valve diameter
||Holley 1000 HP
||Schoenfeld 17⁄8- to 2-inch step
Buck custom-fabricated a valley plate to seal the span between the heads. An oil fill was
Exhaust is expelled via a set of Schoenfeld stepped headers with 17⁄8 to 2-inch primary tu
An interesting detail is the oil pan, a full-length unit that is actually an original Chry