Project Plymouth Valiant Effort Engine Upgrade

The rotating assembly we're using consists of Mopar Performance's 4.00-inch stroke crankshaft and Eagle's 6.123-inch connecting rods (PNs P5007252 and CRS6123C3D respectively). For pistons, and a lot of the ancillary items we needed, we contacted Summit Racing and ordered a set of Keith Black forged pistons (PN UEM-KB744-060) and Total Seal rings (PN TSR-T3690-65). For those of you keeping track, these pistons are a flat-top design with two valve reliefs. Although we said that we would not be using any tricks to refine the parts we're using, we did balance the assembly. There's no reason to not have these parts balanced.

This brings us to the heart of this endeavor, and that's the camshaft. According to believed instructions, a roller cam is not supposed to fit in this new-or any small-block Mopar-without some serious modifications. Since we wanted a camshaft with lobes that look like they had no ramps (read: big), a roller was really the only logical choice for us, but what about this roller-cam stigma? We wanted to find out what cam would best suit our needs, and the best way to do that is to contact a cam manufacturer. We called the tech line at Comp Cams, gave them our specs, and then asked them to make two recommendations-one for a flat tappet design and one for a roller design. Lucky for us, the guys at Comp also let us know that they have just released (as of this writing) a new solid roller-lifter that they said would fit into a small-block Mopar (PN 8043-16). Since they told us they had the lifter issue covered, we had them tell us what camshaft we should use, and waited to hear their numbers.

What they suggested was a custom grind cam with .619 and .615-inch lift, and .247 and .280 degrees of duration at .050-inch lift. This cam was ground on a tight 106-degree LSA. Before you guys cry foul and say it's not streetable, we'll let you know when we get it put in the Valiant. Besides, that's what makes this one cool, remember? One last thing to remember when running a roller camshaft is that the factory cast-iron distributor/oil pump drive must be changed to a bronze unit (PN P3690874). Again, we got ours from Summit Racing.

Top O' This Heap
To seal the cylinder bores, a set of Mopar Performance aluminum cylinder heads (PN P5153849) were used. These heads have a 63cc combustion chamber, 2.02/1.60-inch valves, and valvesprings rated for camshafts up to .575-inch lift. We would need to change the springs for our engine. Replacing the factory springs are a set of Comp's (PN 999-16) valvesprings, which also required some spring pocket-machining, and new retainers. The new springs are a larger 1.55-inch diameter. The retainers are PN 732-16 and use 10-degree valve locks (PN 613-16). For rocker gear, a set of Comp's Pro Magnum rocker arms (PN 1322-16) finish the heads. Since we decided that the engine's parts would simply be bolted on, we did not do any porting on these heads-not even a gasket match. We're sure that power will be down slightly because of this. Our combination of rotating-assembly parts in the block resulted in the pistons sticking .025-inch out of the cylinders, so we knew that an off-the-shelf gasket wasn't going to cut it. The main reason we surmised that reasoning was that if the average head gasket has a compressed thickness of .040-inch, and the pistons stick up .025-inch, that only leaves a margin of .015-inch of room between the cylinder-head face and the piston. We like to have a quench area in the cylinder of about .040-inch so we contacted Cometic Gaskets and ordered up a set of their MLS head gaskets with a compressed thickness of .070-inch (PN H1765070S). This gave us .045-inch of area, and we felt safe with this margin. The rest of the gaskets are also from Cometic (PN PRO1000T). The math showed us a final compression ratio of 11.94:1.

Now, at the beginning of this reliving-of-our-youth engine build, we mentioned over-carburetion, and nothing screams of over-carburetion like a tunnel ram with dual carburetors. In today's day and age, there really is no logical reason to run a tunnel ram on the street. We're not logical, and we're going to. Anyway, the setup we chose to run is Weiand's Hi-Ram intake (PN 1995), and two Holley 465-cfm vacuum secondary carburetors (PN 0-1848-1). Theoretically, that equals 930 cfm. Not overly overkill, but it'll do. We followed that up with the appropriate linkage and air cleaner assembly (PNs 4023 and 7221 respectively). We're quite certain that we can get more power with a good single-plane intake and single carburetor, but remember, this is an old school build.

Well, now it's assembled and ready to run-hopefully run. As of this writing, we're getting ready to load it up and hook it to the proverbial lie detector. Tune in later to see if we struck gold with our build, or crapped out.