When the subject of most powerful Mopar engines of all time is discussed, the awesome hemi power plants are sure to be the first ones mentioned. From there, the dialogue generally turns to the torque laden 440cid 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 360cid) were under-rated at the factory and were the last of the big three small blocks to be 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 did not 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 build up we started with a 1972 360cid 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. While the factory 360cid small block was rated at 255 horsepower, we knew that we could certainly beat that target. And although this is not a huge horsepower LA engine, it definitely is a great combination for an everyday driver with good power. Follow along as we show you how to rebuild your small block Mopar for improved performance and durability.
1. The 340 had a six-year production run and was complemented in 1971 by the introduction of the 360cid engine. While 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.
2. Since the 360cid engine had a production run of 30 years, it is easy to find original rebuildable blocks in wrecking yard. It is also easy to determine the block you have by looking at the casting number on the side of the block.3. One nice advantage to the 318, 340 and 360cid 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.4. This 360 engine is going together with mostly original components to keep the cost down. This cast crank was standard in all 360cid engines and has a 3.580-inch stroke. These crankshafts were externally balanced and proven to be plenty strong for most performance applications including Super Stock level drag racing competition.5. The pistons for the 360cid engine are also cast and these forged connecting rods, which measure 6.123-inch center-to-center, are the same length for the 360 as was used in the 318 and 340cid engines.6. The difference in engine displacement for the 318cid, 340cid and 360cid engines is not in the bore or stroke but in the piston height. The piston in the 360cid 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.
7. Our 360cid 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 valve train?
8. The oil is fed through the number 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.
9. The Summit Racing camshaft is a direct replacement hydraulic flat tappet camshaft with an operating range of 2000 to 4500rpm. 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.10. 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.11. The LA engines used two different cylinder heads – the small port style that was used on the 318cid engine and the large port that was used 340 and 360cid 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.12. The cylinder heads are dropped in place and bolted up torquing the heads down by starting in the center of the head and working to the outside edges of the head.13. The solid pushrods are installed in the normal way making sure to lubricate the tips as you would any engine. Engine start up mode requires plenty of lubrication or excessive wear will result.14. 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 are not 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.
15. 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 are headed to the dyno for some testing, a block off plate is installed instead.
16. For budget and performance reasons, we installed this Weiand Stealth High Rise aluminum intake manifold. This intake has a broad power band for great performance from idle through 6800 rpm. On the installation bolts we added some anti-seize compound to prevent stripping.17. This gap in the cylinder head allows some of the heat around the intake manifold’s EGR boss to escape.18. To handle the oiling duties, we used the original style Mopar stock oil pump, pickup and pan.
19. As with all of our engine build ups, and 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.20. Keeping the budget build in mind, we went with this Summit Racing 600cfm 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.
21. The stock 360cid engine was rated at 255 horsepower. During out initial test, the engine cranked out 370 ft. lbs of torque and 295 horsepower. Time for some tuning.22. With a slight reduction in crankshaft timing and a few other tuning tricks, we picked up 12 horsepower and 11 more ft. lbs of torque at 3800 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 horsepower, plenty impressive for the Stage 1 version of the cool small block Mopar.
