Building an engine or having one built for your Mopar can be one of the most costly, time consuming, and nerve-wracking procedures you'll endure while restoring a car. Unlike years ago when you could simply add a camshaft, headers, intake, and bigger carburetor while overhauling the factory engine, there are so many aftermarket parts available now that it's hard to know which combination will work, and which will leave you disappointed and broke. While the aftermarket is flush with huge displacement big-blocks, stroker kits, and exotic aluminum cylinder heads, the fact is, most of us simply can't afford the parts to build monster stroker engines, so we're left to make the best of the factory parts our car came with. Fortunately, the right combination of factory Mopar parts, combined with a few aftermarket goodies, can still make respectable power without costing a fortune.
In this article, we'll show you some of the ways we've learned to make power, while still operating on a working man's budget.
Go Big Or Go Home
One of the best ways we've found to start off with an advantage is to consider a swap to the largest engine of the same type as is in your car. By this we mean if your car has a 273 or 318, you should consider swapping to a 360. And if your car is equipped with a factory 383 or 400, try to find a 440 to build. While it will cost you a little to get a rebuildable core engine, the extra displacement is usually well worth the price, and the bigger engine will swap right into your vehicle without any major modifications. Since building a 360 will cost about the same as building a smaller displacement LA engine, and building the 440 will cost about the same as the smaller B or RB engine, you'll only be out the cost of the core engine, and you'll be way ahead in terms of potential power.
Of course there are reasons you may want to stay with the original, smaller displacement engine in your car. First, you already have it so it costs nothing. Second, you may want your car to retain its originality, or at least the appearance of originality. In these cases, there are still good options to increase your engine's displacement. Stroker kits consisting of parts like those from Eagle and Scat have really come down in price recently and are available for most popular Mopar applications. Though these parts are typically manufactured in China (that's what keeps the costs down), they are strong enough for a healthy street engine or mild race application, and are far better than the "used" factory stuff your engine came with.
Although stroker kits themselves are fairly inexpensive, remember that most of these kits require at least some additional machining to the block for connecting rod and crankshaft clearance. While this procedure can usually be accomplished with a die-grinder in your home shop, if you aren't equipped to handle it you should expect to pay your machinist a little more in labor to perform this task for you. Typically, stroking a 360 small-block or a 440 big-block requires the least amount of clearancing, thereby making them the easiest engines to install stroker kits in. Even factoring the cost of the machine work and the cost of the parts, a stroker kit is still one of the best ways to improve the power potential of your engine.
Swap Heads
One of the most important considerations when building an engine is which cylinder heads to use. Luckily, Mopar made some great factory heads for their small- and big-block engines, and just swapping on a better factory head can greatly improve power. If you're building a small-block, consider finding a set of J or X castings which contain larger valves, a more efficient combustion chamber, and a better port configuration than other early small-block heads. Even better, a swap to later model swirl-port castings will help power with an improved combustion chamber design. If you really want to wake up your small-block, a Magnum head swap is a great way to improve power, though it requires changing lifters and using Magnum-style, pedestal-mounted rocker arms.
If you're building a big-block, you are fortunate to have some good options when considering factory cylinder heads. Factory 906 and 452 casting cylinder heads are readily available and have big valves, good ports, and decent combustion chambers, but they aren't our favorite factory big-block heads. Our favorites are the 915 and 516 castings that offer a great combustion chamber design with plenty of quench area. In fact, stock and super stock class racers with '68 cars would swap from 906 open-chamber heads to 915 closed-chamber cylinder heads to take advantage of not only the better combustion chamber design, but also to gain more than two points in compression. The only problem with the factory closed-chamber heads is the relatively small exhaust valves. This is easily cured by having the valve seats cut for larger valves while the machine shop is performing the valve job. Bolting a set of these heads on a later, low-compression big-block will improve performance through their better combustion chamber and also by increasing the engine's compression.
Of course, the best cylinder heads for your Mopar-if your budget allows you to consider them-come from the aftermarket. And while the sky certainly is the limit in terms of the potential power and price of aftermarket cylinder heads, there are several manufacturers that make great cylinder heads for the money. Indy Cylinder Head offers several big-block heads, but their SR castings are some of our favorites. The Indy SRs are a true bolt-on head, using factory rocker gear and having a factory exhaust configuration. Edelbrock's Performer RPM cylinder heads are a great choice for either a big-block or small block, and are priced economically enough that it almost doesn't make sense to rebuild your factory heads. Another benefit of aluminum heads is somewhat obvious-they're about 40 pounds lighter than factory cast-iron units, shaving weight from the front of our already nose-heavy Mopars.
The Three Cs
The three Cs-cam, compression, and carburetion-are also important considerations when building an engine. The right combination can be deadly, the wrong combination, disappointing.
While we've jokingly adopted the theory around here that there's no such thing as too much cam, just not enough motor, the fact is, choosing a cam can be nerve wracking. At Mopar Muscle, when we pick a camshaft for one of our engines, we first closely define the purpose of the engine. If it's used for towing, we need a cam that makes great low-end torque and idles reasonably well; if racing, well, the bigger the cam, the more power. Chances are the cam you need for your build is somewhere in-between. Since most applications will have more than one good cam choice, we recommend you do what we often do, which is call up the cam manufacturing company and use their experience and expertise to help pick the cam that's right for your engine. If your budget allows, and you don't mind the clatter and adjusting valve lash occasionally, a solid lifter camshaft will offer more power and better throttle response than a hydraulic cam. As we showed in a previous article, roller cams definitely make more power, but the power comes at significant expense. For most street applications, a hydraulic flat-tappet cam will work just fine, and save the expense of adjustable rocker arms and expensive springs. Whatever your cam choice, remember that the rest of the combination must match. Large cams require stiffer springs and won't be optimized unless compression is also bumped up. Solid lifter cams require adjustable rockers, adding expense and complexity to the engine. A big cam may also require a looser converter and lower ratio rearend gearing, so take our advice and do your homework before selecting a cam for your engine.
One of the parameters that has the most effect on power is the compression ratio of the engine. While the ideal compression ratio has a lot to do with the intended use of the engine, and the octane of the fuel you'll be running, more compression will make more power in nearly every application. The proper compression ratio depends on factors such as combustion chamber and piston design, but even a good street engine should have a minimum of 10:1 compression to make decent power. In our Engine Challenge, we've seen engines with compression ratios as high as 12:1 still run great on pump fuel, but for a street engine limited to 93 octane gasoline, 11:1 is a more reasonable limit.
There are many ways to raise the compression ration of an engine. Generally, Mopar engines produced after 1972 had the compression lowered to meet emissions standards by placing the piston below the deck of the block at top-dead-center. In addition to reducing compression, this also makes the engine more prone to detonation. As a start, we recommend a piston/decking combination to get the piston as close to the top of the cylinder as possible, improving compression and the efficiency of the combustion area. Domed pistons will also improve compression ratio, but are generally not as efficient as flat-tops because the dome prevents even distribution of the burning mixture, again hurting power somewhat.
Building an efficient and powerful engine is one thing, feeding it with enough fuel and air to work properly is another proposition. By increasing cubic inches and compression, and adding a bigger cam, we'll usually need to increase the induction volume as well by adding a larger carburetor and a more efficient intake manifold. Again, proper selection of these parts depends greatly on the size and performance level of the engine you're building. Generally, a warmed-over street small-block will require at least a 750-cfm carburetor, and big-blocks can require an 850 cfm or larger carb to achieve their potential. Factory multiple carb induction is a viable option if you can find it, but we tend to prefer the simplicity and drivability of a single four-barrel setup. Remember to match the rpm range of the intake manifold to the rpm range of the camshaft you selected, and also remember that you need to expel the additional gasses you're putting through the engine. Factory manifolds and exhaust should be replaced by quality headers and free-flowing duals for your new engine to operate properly.
