Our buddy’s ’68 Valiant track car had the need for some more speed so we decided to step him up with a 427-inch small-block. Our goal was a 500/500 engine, that is 500 lb-ft of torque and 500 horsepower. We went with a lot of cubic inches because we’re looking for a big fat torque curve, which will work on the street as well as at the track. The short-block construction was covered in detail in the October 2010 issue of Mopar Muscle. This month we finish up the top of the motor and get it installed.

The Short-block

Our Mopar Performance P5007552AB engine block was bored to 4.060 inches by Gray’s Automotive and then filled with a 4.125-inch stroke crankshaft from K1 Technologies. The connecting rods, also from K1, are 6.200 inches long, with a small-journal2.00 inches. The pistons are forged units from JE with deep dishes to keep the compression down to a pump-gas friendly 10.5:1. The bob-weight for this rotating assembly was only 1,780 grams, so we figured the engine was going to spin the needle on the tach just fine. The October issue went into detail on a number of little problems that we encountered, so keep that article on hand if you’re planning to build one of these engines.

Cylinder Heads

With 427 inches to feed, and a goal of 500 horsepower, we knew that we needed a set of cylinder heads with good airflow. We wanted aluminum heads in order to save 50 pounds of weight up front, but our budget ruled out the more exotic W-series cylinder heads. In the end, we picked a set of closed-chamber Performer RPM cylinder heads from Edelbrock. The Edelbrock heads are a replacement type cylinder head with stock port locations. These heads use standard 59-degree valvetrain components to keep the cost down. The use of standard valvetrain parts does limit the size of valvespring that fits, but we didn’t anticipate a lot of valve lift for our application so that was OK.

In order to meet our power goals we did need to have the heads fully ported. After some research into the subject, we decided to go with the Stage III porting from Hughes Engines. The Stage III option is a full CNC porting package, which also includes new 2.080-inch intake valves. The guys at Hughes went through our heads completely, machining the ports and combustion chambers and then surfacing the heads. They also performed a high-quality valve job and pressure tested the heads after the CNC machine work was complete. Peak flow numbers for the Stage III package are right at 300 cfm on the intake and 200 cfm on the exhaust. Numbers like that are more than enough flow capacity to achieve our power goal of 500/500 so we felt confident of our target. We didn’t flow these heads ourselves after porting, but flow sheets for the Stage III porting service are available on the Hughes Engines website.


As discussed in the October article, our original plan was to go with a hydraulic roller camshaft. We wanted to go this way to reduce the maintenance level and to keep things nice and quiet on the street. However, we could not find a set of hydraulic roller lifters that would fit the R3 engine block so we had to switch to solid roller lifters. We decided to keep our hydraulic roller camshaft after the engineers at Comp Cams told us that we could run solid roller lifters on it if the lash was set really tight. The camshaft that Comp specified for us is a custom grind using their new XFI lobes. The grind number is CRS 3017B/3037B HR113. Duration at .050-inch is 236 on both the intake and exhaust, while lobe lift is .363 intake and .358 exhaust. The camshaft is mild for 427 inches, but once again, we were looking for a Viper type power curve with the torque peak around 4,000 rpm.