Mopar 360 Small Block

If you want to build affordable small block Mopar power, the Mopar 360 is your best choice. Parts and information are easy to find, and since it's a fairly popular engine, parts are not too expensive. Why is the 360 the best choice for a high performance small block Mopar? Size and availability. The Mopar 318 is a great engine, but it gives up too many cubic inches in a purely performance application. The Mopar 340 makes an excellent performance engine, but it is rare (thus hard to find) and expensive. That leaves the 360.

In spite of the 340's better performance reputation, the Mopar 360 is a pretty good choice. It offers 10 more cubic inches than the popular 350 Chevy, along with shaft mounted rocker arms and a better rod ratio. 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.

How To Build Big-Inch Mopar Small Blocks

There is 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 Mopar 360 needs to be reground, it's almost just as cheap to by 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 of 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 about building large displacement small block Mopars, all the way up to 476 cubic inches. If you're interested in building a "large" small block Mopar, I highly recommend this book.

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 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.

(Image: Scat Crankshafts)

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).

(Image: Scat Crankshafts)

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 after market pistons with close to zero deck height. Use hyperuetetic or forged, depending on 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 horse power. 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.

(Image: KB Pistons)

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 you 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. After market 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 lifter preload.

Unless you're building an economy engine, Edelbock's Performer RPM manifold is better than the Performer. It's also taller so you should check hood clearance. I like it with a Holley 750 vacuum secondary carburetor (3310 with secondary metering block installed). If your 360 came with a factory 4 barrel manifold, it's actually a very good choice. The only downsides are the heavier weight compared to an aluminum manifold and the fact that parts for the factory Thermoquad carburetor are hard to find since it's been out of production for so long. Of course, the ultimate setup would be a factory Six Pack - they are available brand new as a complete package for around $2000.

The 360's stock intake manifold and Thermoquad carburetor are surprisingly good. In fact I doubt the Performer RPM/Holley combo offers much if any performance improvement over the stock setup. 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 street car, and a huge batch of re-manufactured TQ's just surfaced in Texas for only $120. That's an outstanding deal so I just ordered one for the 360 build I have planned this summer.

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.