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.
Swapping your small-block...
Swapping your small-block heads for later Magnum heads is a great way to make power. There's a reason the top three finishers in this year's Engine Challenge used Magnum cylinder heads.
Magnum heads definitely make...
Magnum heads definitely make power, but require their own rockers, lifters, and pushrods due to their pedestal-mounted rocker arm system.
Factory big-block heads, such...
Factory big-block heads, such as the 906 and 452 castings (452 shown here), have big valves and good ports, but their combustion chambers lack quench area. However, the 452 castings have hardened exhaust valve seats, better for use with today's unleaded fuels.
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.
The 915 and 516 casting, "closed-chamber"...
The 915 and 516 casting, "closed-chamber" cylinder heads offer a combustion chamber with a great quench area, but the exhaust valves are somewhat small. We still prefer these heads over the 906 castings and simply have our machinist cut the exhaust valve seats for larger valves while performing the valve job.
Simply bolting on a set of...
Simply bolting on a set of factory closed-chamber heads can increase compression dramatically, thereby improving performance. Be careful, however, that you don't get the compression too high for the fuel you're using.
Aftermarket aluminum heads-such...
Aftermarket aluminum heads-such as the Indy heads shown here-are lighter than stock heads and also make great power, but you'll have to run additional oil lines from the rear of the block to oil the valvetrain.
Edelbrock Performer RPM cylinder...
Edelbrock Performer RPM cylinder heads are a great alternative to stock heads, incorporating the best features of factory heads with the reduced weight of aluminum.
Whatever heads you choose,...
Whatever heads you choose, treating the ports to a nice gasket-match and bowl-blend will certainly improve power.
Installing an aftermarket...
Installing an aftermarket cam is certainly a good way to increase the power output of your engine, but be careful. Too big a cam can be just as disappointing as a cam too small. We recommend calling a company such as Comp Cams and taking advantage of their experience to pick the right cam for your application.