Glenbrook is an online mechanics writer, who enjoys rebuilding and modding classic Chrysler cars.
Affordable Small-Block Mopar Power
The Mopar 360 is the easiest and cheapest way to build a fast small-block Mopar. It makes more power than the 318 and it's a lot cheaper to build than a 340. It's also the easiest to find. Aftermarket support for the 360 is great, and with the right parts, it can easily make 450 horsepower and still have great street manners. If you need more inches, it's easy to drop in a stroker crank and get 406 cubic inches.
Why Build a Mopar 360?
If you want an affordable high-performance small-block Mopar, the 360 small block is your best choice. Parts and information are easy to find, and since it's a fairly popular engine, they are not too expensive.
Why is the 360 the best choice for a high-performance small-block Mopar? Size and availability. The 318 is a great engine, but it gives up too many cubic inches in a purely performance application. The 340 makes an awesome performance engine, but it's rare, hard to find, and expensive. That leaves the 360.
The 340 does have a better performance reputation, but the 360 is actually a pretty good choice too. It has 10 more cubic inches than the popular 350 Chevy, along with a better rod ratio and shaft mounted rocker arms (at least on the LA version). Parts availability is almost as good as the small-block Chevy, if a little more expensive. It's pretty easy to get 400 HP from a Mopar 360 using mostly stock-type parts. With the right modifications, you can get up to 500 HP on pump gas without nitrous or other power adders.
If you've never rebuilt a small block Mopar, How to Rebuild the Small-Block Mopar from SA Design has all the info you'll need. This book covers both the earlier LA series and later Magnum small blocks so it doesn't matter what style 360 you have. If you are only interested in the LA series engines, I actually prefer How to Rebuild Small-Block Mopar Engines from HP Books, but it's sometimes hard to find a copy at a reasonable price.
The Most Cost-Effective Modification
There's an old racing proverb that says, "there's no replacement for displacement." The easiest way to go faster is to build a bigger engine. In the past, this could be very expensive. However, with the proliferation of low-cost, semi-custom parts, this is no longer always true. For example, if the crankshaft in your 360 needs to be reground, it's almost just as cheap to buy a new (cast) one from Eagle or Scat. Or maybe your stock crank is OK, but you want to upgrade to a forged crank. You can do so for only around $700.
In both cases, the stock stroke (3.58") crankshaft costs almost exactly the same as a stroked (4") crank that will turn your 360 into a 408 (assuming a 0.030 overbore). Besides the extra 48 cubic inches, the longer stroke pushes the pin further up on the piston. This gives you a couple of advantages. First, it reduces piston rock. This makes your engine quieter at start-up and helps reduce friction, making your engine last longer and helping it produce more power. Second, it shaves about 1/4" of solid aluminum off the top of the piston, making it lighter. For example, if you're using Keith Black pistons, the 408 package (piston and pin) is at least 23 grams lighter (almost 1 oz.) than the equivalent 360 package. This is dependent on application, in some instances, the difference is substantially more.
About the only extra work you need to do to gain these advantages is a little block clearancing on the bottom end. That's it. Any competent machine shop should be able to do this for you. If you want more information about building big-inch small-block Mopars, you should check out How to Build Big-Inch Mopar Small Blocks. This book tells you everything you need to know.
360 vs. 340
In stock form, the 340 is a better performance engine. If built to the same specs though, the 360 will make at least as much power as the 340 at a lower RPM. The 360 is also easier (and a lot cheaper) to find. For racing, the 340 has more potential, but for street use the 360 is a better choice.
Hotrodding the 360
Like most American V8 engines, the Mopar 360 can make decent power using mostly stock parts. If you're serious about making lots of power with decent reliability though, there are some areas that should be tended to.
The stock Chrysler 360 crankshaft is cast iron and externally balanced. It's OK for moderate performance or light racing use, but if you're planning on making serious power it's better to go with an aftermarket forged crank. Both Eagle and Scat make reasonably priced forged crankshafts for the 360 (the Scat cranks are slightly more expensive but have a better reputation for quality). Besides being stronger than the factory crankshaft, the aftermarket pieces are internally balanced so make sure to get the correct harmonic balancer and torque converter (or flywheel) to go with it.
The stock 360 connecting rods are OK for street use if have them Magnafluxed and checked for straightness, replace the rod bolts, and have them resized. By the time you do all that it's almost as cheap to go with a set of aftermarket connecting rods. The aftermarket rods are made out of better steel and they're also brand new. You know they haven't been abused by a previous owner. For me, it's an easy choice. Up to around 450 horsepower the I beam rods are better (cheaper and lighter). If you're making more than 450 horsepower get the H beam rods (and send me your build recipe).
Pistons and Rings
The Mopar 360 never came from the factory in a high compression version. Factory pistons were cast and could have as much as -0.100 deck height, making for low compression and crappy efficiency. For a performance build, you should go with aftermarket pistons with close to zero deck height. Use hypereutectic or forged, depending on the intended power level. Using a piston design that uses 1/16" rings instead of the stock 5/64" reduces friction and gives you some free horsepower. For pump gas, don't run over 9.5 compression with iron heads or 10.5 with aluminum heads unless you really know what you're doing.
There are almost as many opinions on camshaft selection as there are engine builders. When building a small block Mopar, the main thing to keep in mind is that most cam companies' "stocking" cam designs are likely optimized for the small block Chevy, and are unlikely to be the best choice for your Mopar. Make sure to work with an engine builder or cam grinder who is knowledgeable about what works best with the small block Chryslers.
No matter what cam you run, you should upgrade to adjustable rocker arms. The stock, stamped rocker arms aren't adjustable and they cost you valve lift because they only have about 1.42 lift ratio instead of 1.5 as advertised. Aftermarket adjustable rocker arms have a true 1.5 ratio (they are also available in higher ratios) and offer adjustability. This is important even with a hydraulic can so that you can properly adjust the lifter preload.
Intake Manifold and Carburetor
The Edelbrock Performer RPM Air-Gap is the best intake manifold for the Mopar 360. It's a lot taller than the stock intake, though, so be sure to check hood clearance. It works great with a Holley 750 vacuum secondary carburetor (3310 with secondary metering block installed). The stock 360 4-bbl intake is actually a pretty good piece too so if you're on a tight budget don't feel bad about running it. The only downsides is the weight—cast iron is a lot heavier than aluminum. Also, tuning parts for the factory Thermoquad can be hard to find. Of course, the ultimate setup would be a factory Six Pack—they're available brand new as a complete package for around $2000. In spite of being over 40 years old, the Six Pack runs almost as strong as the performer RPM and looks a lot better.
The 360's stock intake manifold and Thermoquad carburetor are actually a pretty good setup and can save you a lot of money over an aftermarket intake and carb. Back in the 1980s, Bob Lambeck was running 12 seconds in a 360 Duster equipped with the stock intake. The only downsides are the extra weight of the stock cast iron intake manifold and the difficulty of finding a decent Thermoquad carburetor.
Personally, I don't think the weight of the intake is a big deal on a streetcar, and you can find good re-manufactured TQs for as little as $120 with a simple Google search, which is an outstanding deal—in fact, I got one for the 360 build I have planned this summer.
The Final Word
The Mopar 360 can make an excellent performance engine. It was introduced with a 2-bbl carburetor in 1971. Not intended as a performance engine, it also featured a cast crankshaft and low compression ratio (8.5 to 1) cast pistons.
When the 340 was discontinued in 1973, the 4 barrel induction was transferred to the 360 but the cast crank and low compression ratio remained. Quality control was also not exemplary during this time frame. That, combined with overly large main journals, caused the 360 to gain a reputation for spinning bearings.
In spite of this rocky start, the 360 can be built into an excellent street engine. All you need is attention to detail and proper selection of parts.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.