Big-block Mopar engines have been a popular choice for the street performance crowd for a long time, but until recently the aftermarket support was a little sparse. All of that started to change with the introduction of the Edelbrock RPM Performer cylinder heads and then the release of low-cost stroker kits. These days, it doesn't cost much more to build a 500-inch Mopar than it does to rebuild a 440. This 505ci engine was designed to showcase some serious street/strip muscle with an old-school dual-quad look. A combination of a stroker kit with a retro-fit hydraulic-roller cam, aluminum heads, and the CH-28 intake manifold fit the bill perfectly.
The 505 Mopar Wedge engine...
The 505 Mopar Wedge engine build started with a block from a '74 passenger car. The block was sonic checked and magnafluxed before starting the machine work.
This engine was destined for a street car, so the original 440 block was reused after passing a careful inspection and sonic check. Aftermarket engine blocks are available for the big Mopar, but they aren't really necessary at this power level. A wide selection of stroker pistons is available at a 4.375 bore size, but that would have required boring the block .055-over. Because we wanted to keep the cylinder walls as thick as possible for future rebuilds, we just went .030-over to a final bore size of 4.350.
The very first Mopar stroker motor that I built back in the '80s used a factory crankshaft with welded and reground rod journals. That old crank stayed together for a number of years, but today, high-quality forged stroker cranks are available right off the shelf. For this engine a 4.250 stroke crankshaft was purchased from 440Source. Other vendors, such as Callies, Eagle, SCAT and K1, also have Mopar stroker cranks in stock so there is a wide selection available these days.
Our connecting rods are SCAT...
Our connecting rods are SCAT big-block Chevy H-beam rods. These rods are 6.800 inches long, but the Mopar block is tall enough to accept rods as long as 7.100 inches.
We selected a crankshaft with 2.200-inch diameter rod journals so we could use Chevy big-block connecting rods. Using Chevy rods in a Mopar engine might seem odd, but there are a lot more Chevy rods on the market than Mopar rods, so they are a very cost-effective part to use. The Chevy rods are also available in a wide range of lengths, which gives the engine builder some additional choices to work with. Using a Chevy rod also lets an engine builder use the more common 2.200-inch rod bearings and the lighter 0.990 diameter piston pins.
We went with a set of 6.800-inch-long Chevy H-beam rods from Scat. These H-beam rods are priced very fairly, and they have an excellent reputation for motors in this power range. The 6.800 rods fit just fine in a Mopar block with the 4.250 stroke because of the tall 10.72-inch Mopar deck height. Even with the long Chevy rods, the Mopar block is tall enough that there is plenty of room for a full-length piston with a very conservative ring package.
Diamond Racing has shelf pistons...
Diamond Racing has shelf pistons for a 4.250-inch stroke Mopar big-block with 6.800-long Chevy rods. We ordered our pistons with a 5cc dome in order to raise the compression to 12.5:1.
With the closed-chamber Edelbrock heads, a flat-top piston in a 500-inch Mopar makes approximately 11:1 compression, which is near the limit that can be run with today's pump gas. For this particular motor we were willing to run race gas, so Diamond pistons with a small 5cc dome were custom ordered. The final compression ratio is right at 12.5:1 when the Edelbrock heads are installed with thick Fel-Pro head gaskets. The extra compression pumps up the power curve, but down the road we might regret this choice if high-octane gas becomes harder to find.
Mopar big-block engines all came from the factory with cast-iron cylinder heads. While a couple versions of the factory head are regarded as decent choices, we didn't want to spend time repairing 40-year-old castings when good alternatives exist. One of those alternatives is the very popular Edelbrock Performer RPM head. These Edelbrock heads are aluminum, which saves more than 40 pounds off the nose of the car, and they have a modern combustion chamber with good quench. The closed combustion chambers in the Edelbrock heads measure 84 cc, and they come with oversized 2.14-inch intake and 1.81-inch exhaust valves.