The Mopar 360 engine doesn't exactly have the sense of glory and myth that some of Chrysler's other V-8s have had over the years, and that's not entirely fair. The 360 had the misfortune of debuting in 1971 with a two-barrel carburetor, and spent the next 20 years chugging reluctantly through the smog era in the engine bays of trucks and sedans. While the 360 never got quite the limelight that the 340 did in its heydey, these days, it's every bit as competitive -- if not quite as cheap to build -- as any small-block Ford or Chevy.
This won't come as any great shock to experienced Mopar builders, but Chrysler engine builds can get very expensive, very quickly. Fords and Chevys are dirt cheap to build because they remained fundamentally unchanged for nearly half a century, they were produced by the millions in many applications, and a lot of those applications were high-performance vehicles that people wanted to modify. The early 360 -- not so much. For that reason, building a really strong 360 is as much a matter of how much you're willing to spend and replace as anything else. But one thing you'll need to replace on a 1973 no matter what is the heads. Early heads don't have hardened valve seats for use with unleaded fuel, and it's not worth having new valve seats pressed in when there are better options.
Cylinder heads are a major factor on the 360 -- enough that a good set will make or break your whole build. Early on, factory high-performance 1968-to-1971, 340 -- "X" casting -- heads were the default choice for serious 360 builds. They used 2.02-inch intake and 1.88-inch exhaust valves, which are perfect for a 360. However, these heads are very hard to come by now, expensive when you do find them, and bound to need some valve seat work. Despite what others may tell you, later "J" casting 360 heads had identical port designs, and differed from X heads only in the valve sizes and that the combustion chambers were 3 cc larger after milling. They're also dirt cheap, and were made long after Chrysler went to hardened valve seats, so any junkyard set will work. The smaller 1.88 valves are actually an advantage here, because you can have the seats machined oversize for new 2.02 valves, have a three-angle grind put on them, and then you'll have brand new valves and seats. With minor pocket porting and a little cleanup, these heads are almost as good as aftermarket units casting five times as much.
As Mopar enthusiasts know, 400 horses is no big feat for a 360, especially one with properly prepared heads. Even the woeful little 318 regularly sees numbers surpassing this. Revs Research's crate engine provides a pretty good basis for an easy DIY 400-plus horsepower. The Revs engine starts with late-model Magnum heads, which are more trouble and expense than they're worth if you've got a good set of J heads with 2.02 valves. Revs builds their engines with 10.5-to-1 pistons, and Edelbrock Torquer II or Performaer RPM intake, adjustable roller rocker arms, a windage tray and a single pattern cam with 245 degrees at 0.050-inch lift. If you find yourself a bit short of Rev's 425-horse figure after using J heads and a more street-friendly 9.5-to-1 compression, you should be able to make it up by gasket-matching the heads to the intake.
A good set of ported factor heads should get you to about 450 horsepower, but to hit 500 horses you'll need to step it up a bit. Car Craft Magazine recommended RHS Pro Action 360 X heads, based as you might guess on the old 340 X head. At about $650 unassembled in 2014, they're a good deal, and easily outflow a ported stock head with plenty more room for additional porting. Or, you could go for a set of Performer RPM heads if you have the budget. With the right cam, those and a Performer RPM air gap intake and 750 carb should get you near 500 horsepower. But you'll be revving the 360 to death to do it. You'd likely be better and safer off going with a stroker kit with a 4-inch crank, and boring the engine 0.030 over. This will get you about 402 cubic inches, which will maintain the same horsepower output, but with more torque and at a low engine rpm. At $1,500 to $1,800, a stroker kit isn't the cheapest thing in the world -- but you'll at least have the peace of mind of having a rotating assembly that's up to the task.
