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Reliable Power on the Cheap

Building up the 360cid Mopar small-block on a budget

The 340 had a six-year production run and was complemented in 1971 by the introduction of the 360-cu in. engine. Although the 360 shared many of the 340’s performance parts, it never got the respect given the 340 because of the fuel and emissions standards that came about during this time period.
Cam BentyAuthor, Photography

When the subject of most powerful Mopar engines ever is discussed, the awesome hemi powerplants are sure to be the first ones mentioned. From there, the dialogue generally turns to the torque-laden 440-cu in. big-blocks most often featuring the legendary Six Pack carb option. All of these are mighty fine, fire-breathing, axle-twisting engines to be sure.

But in terms of small-block power, the Chrysler LA-series engines are often overlooked despite their ability to make good power on reduced funds. The fact is, the small-block Mopar LA engines (318, 340, and 360-cu in.) were underrated at the factory and were the last of the big three small-blocks offered to the public. Because Mopar engineers could study the errors inherent with other earlier small-block designs, they "corrected" some things with their small-block and blended in some additional design benefits where possible. Remember, the 273 didn't appear until the 1964 model year and the newly designed small-block 318 (that replaced the larger and heavier Poly 318) came along during the 1967 model year.

The most unique engineering change on the small-block Mopar was the use of solid pushrods and rocker arm shafts rather than the hollow pushrods and individual rockers found on Ford and Chevy small-block engines. The result was excellent oiling, better pushrod and rocker arm rigidity, and no need for valve lash adjustment. Simply bolt down the rocker shaft, and the valves are set. And as any racer will tell you, rocker shafts are far less prone to flex, keeping the rocker ratio perfect rocker to rocker and helping head strength as well.

For our buildup, we started with a '72 360-cu in. engine taken from a wrecking yard. After checking the block for soundness, we cleaned and bored it 0.030-inch over and set about selecting parts from Mopar Performance, Summit Racing, Holley, and others. Although the factory 360-cu in. small-block was rated at 255 hp, we knew that we could certainly beat that target. And though this isn't a huge-horsepower LA engine, it definitely is a great combination for an everyday driver with good power.

The 340 had a six-year production run and was complemented in 1971 by the introduction of the 360-cu in. engine. Although the 360 shared many of the 340’s performance parts, it never got the respect given the 340 because of the fuel and emissions standards that came about during this time period.
Even though the 360-cu in. engine had a production run of 30 years, it's easy to find original rebuildable blocks in wrecking yard. It's also easy to determine the block you have by looking at the casting number on the side of the block.
One nice advantage to the 318, 340, and 360-cu in. engine series is that the blocks are made from a high-nickel alloy that made it stronger overall—a material not common with other standard-issue OE-manufactured blocks.
This 360 engine is going together with mostly original components to keep the cost down. This cast crank was standard in all 360-cu in. engines and has a 3.580-inch stroke. These crankshafts were externally balanced and proven to be plenty strong for most performance applications including off-roading or towing with a big, heavy truck/trailer combo.
The pistons for the 360-cu in. engine are also cast, and these forged connecting rods, measuring 6.123-inch center-to-center, are the same length for the 360 as was used in the 318- and 340-cu in. engines.
The difference in engine displacement for the 318-, 340-, and 360-cu in. engines isn't in the bore or stroke, but in the piston height. The piston in the 360-cu in. engine is the smallest and also the lightest of the three allowing for more displacement overall. In addition, these use a press-fit piston pin as opposed to the floating piston design used in the other LA engines.
Our 360-cu in. engine uses a flat-tappet hydraulic camshaft that features an uncommon oiling system. The pushrods are actually solid eliciting the question: How is the oil going to get to the top of the valvetrain?
The oil is fed through the No. 4 main journal on the camshaft, which pumps oil up through the block and through this rocker arm galley hole in the head and into the rocker shaft.
The Summit Racing camshaft is a direct replacement hydraulic flat-tappet camshaft with an operating range of 2,000-4,500 rpm. Duration on this camshaft is 218 degrees intake, 228 degrees exhaust at 0.050-inch lift with a maximum lift of 0.441 inch. This timing chain oil tab attaches to the thrust plate, which keeps the camshaft in place, and a double-roller timing chain will keep the timing right.
The Summit Racing hydraulic lifters were installed after full lubrication of the contact surfaces. Note the pre-lube used on the camshaft lobes as well. This is critical to ensure the camshaft breaks in properly.
The LA engines used two different cylinder heads—the small-port style that was used on the 318-cu in. engine and the large port that was used on 340- and 360-cu in. engines. In addition, there are two different versions of the large-port heads, pre-1972 engines, which used a 2.02-inch intake, and 1.60-inch exhaust valve, and the later 1972 heads used a reduced 1.88-inch intake and 1.60-inch exhaust valve. The intake on these heads is 1.88-inch, meaning these heads are from a 1972 and later engine.
The cylinder heads are dropped in place and bolted up, torqueing the heads down by starting in the center of the head and working to the outside edges of the head.
The solid pushrods are installed in the normal way making sure to lubricate the tips as you would any engine. Engine startup mode requires plenty of lubrication or excessive wear will result.
For this engine, we used the original-style, stamped steel rockers on the hardened steel rocker shaft. These rockers retain the factory 1.5:1 ratio and aren't adjustable. To adjust for any other engine modifications, such as decking of the block or surfacing the head, different length pushrods are used to compensate for this shorter-length requirement.
Now we can bolt up the stock timing chain cover, which incorporates the water pump as part of the assembly. Normally, the fuel pump would be installed at this point, but because we're headed to the dyno for some testing, a block-off plate is installed instead.
For budget and performance reasons, we installed this Weiand Stealth High Rise aluminum intake manifold. This intake has a broad powerband for great performance from idle through 6,800 rpm. On the installation bolts, we added some anti-seize compound to prevent stripping.
This gap in the cylinder head allows some of the heat around the intake manifold's EGR boss to escape.
To handle the oiling duties, we used the original-style Mopar stock oil pump, pickup, and pan.
As with all of our engine buildups, especially flat tappet camshaft-equipped engines, we poured in some Royal Purple Engine Break-In oil. We turned the oil pump using a drill and drive bit through the distributor hole and watched the fresh oil pump up and come through the rocker shafts and into the cylinder head and engine valley.
Keeping the budget build in mind, we went with this Summit Racing 600-cfm Street/Strip carb and one of their electronic Mopar distributors. To evacuate the exhaust gases, we went with a set of Hooker competition headers with 1.5-inch primary tubing and 2.5-inch diameter collectors.
The stock 360-cu in. engine was rated at 255 hp. During out initial test, the engine cranked out 370 lb-ft of torque and 295 hp. Time for some tuning.
With a slight reduction in crankshaft timing and a few other tuning tricks, we picked up 12 hp and 11 lb-ft of torque at 3,800 rpm. Most impressive was the torque curve, which went straight up and then held steady at peak torque. In addition, the power curve was nice and smooth throughout. We further adjusted the timing in small increments until no further power and torque increases occurred. In the end, power peaked at 314 hp, which isn't too shabby for an otherwise-stock rebuild using stock heads, 87-octane-friendly compression, and only a mild cam and intake manifold in the way of performance parts.

Sources:

Mopar Performance
moparperformance.com

Summit Racing
summitracing.com

Weiand Performance
holley.com