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.

Adding Inches

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 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.

Power Parts

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.

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."

Dyno Time

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
412-Cubic-Inch Mopar
Hinkle Performance
Tested at Hinkle Performance
RPM TQ HP
2,500 420 200
2,800 443 236
3,100 452 267
3,300 469 297
3,600 483 331
3,900 489 363
4,200 492 394
4,500 513 439
4,800 515 474
5,100 520 506
5,300 517 522
5,600 510 544
5,900 508 571
6,200 496 585
6,500 491 609
7,000 465 618

BY THE NUMBERS
412 Mopar Big-Block
Bore 4.185 inches
Stroke 3.740 inches
Displacement 412 cubic inches
Compression ratio 10.4:1
Camshaft Custom Comp Solid Flat Tappet
Valve lift 0.656/0.642 inch
Rocker and ratio Harland Sharp 1.7/1.65:1
Piston rings BRC 1.1/1.1/3 mm
Piston BRC Forged
Block OEM Production Mopar 361
Crankshaft Stock forged
Rods Eagle 6.657 inches
Cylinder head Edelbrock Victor
Intake valve diameter 2.25 inches
Exhaust valve diameter 1.81 inches
Intake manifold Edelbrock RPM
Carb Holley 1000 HP
Header Schoenfeld 17⁄8- to 2-inch step
Ignition MSD
Damper PRW
Oil AMSOIL 10w-30
Fuel VP-100 Unleaded

SOURCE
PRW
Placentia
CA  92870
866-412-9630
http://www.prwonlinestore.com
Eagle Specialty Products, Inc.
8530 Aaron Lane
Southaven
MS  38671
662-796-7373
http://www.eaglerod.com
VP Racing Fuels
P.O. Box 47878
San Antonio
TX  78265
210-635-7744
http://www.vpracingfuels.com
Hinkle Performance
6358 E. Laurel Rd.
London
KY  40741
606-864-6897
ARP
800-826-3045
http://www.arp-bolts.com
Edelbrock
2700 California St
Torrance
CA  90503
310-781-2222
http://www.edelbrock.com
AMSOIL
925 Tower Ave.
Superior
WI  54880
800-777-8491
http://www.amsoil.com
Mahle/Clevite
888-255-1942
http://www.MahleMotorsports.com
Harland Sharp
19769 Progress Dr.
Strongsville
OH  44149
440-238-3260
http://www.harlandsharp.com
MSD Ignition
915-857-5200
http://www.msdignition.com
Competition Cams
800-999-0853
http://www.compcams.com
Holley Performance Products
1801 Russellville Rd.
Bowling Green
KY  42101
270-782-2900
http://www.holley.com
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