Camshaft selection has always been one of the hardest decisions we face when building an engine. Mopar's catalogs give suggestions for their line of camshafts based on the performance level you wish to achieve, and camshaft companies also give guidelines and approximate rpm ranges that their camshafts work within. And, if cam selection was difficult a few years ago, the choice is undoubtedly even harder today, when you consider the trend towards stroker crankshafts and aftermarket heads.
We decided to test a few of the Mopar Purple Shaft cams against some other cams from various manufacturers, to see how they compare in today's applications. Since our test engine is set up for use with a solid flat-tappet camshaft, we chose to stick with that platform throughout our testing. The test engine is a 421-inch small block based on a 360 block. We are using a Bloomer Performance Engineering 4.125-inch crankshaft, along with 6.300-inch H beam rods and custom 4.030-inch bore pistons to achieve a 13.0:l compression ratio when combined with our Edelbrock heads' 63cc chambers.
The Edelbrock Performer RPM heads were meticulously hand ported along with basic port matching of the Super Victor intake manifold by Vic Bloomer Cylinder Heads. We used a set of Crane Gold 1.6-ratio rocker arms and will list theoretical lift values with these in mind.
The engine was mounted to the Superflow dyno with a set of 1¾-inch Hooker Super Comp Headers, and topped off with a QuickFuel Q-950 Carburetor.
Horsepower comparison of Lunati 404A4, MP 590, and Hughes 6468 cams.
Torque comparison of Lunati 404A4, MP 590, Hughes' 6468 cams.
We ran all of our cams with a set of Schubeck Racing composite-faced lifters and set the valve spring load to meet their requirements. This allowed us to not need to break in several different camshaft and lifter combinations and the need to keep installing and removing the inner valve springs for proper break in.
To vary our camshafts, we decided to call a few cam companies and see what they recommended for this engine. Competition Cams offer their PN 20-249-4 as a nice street/strip cam that is comparable to the Mopar 557 cam. They also offered their popular TL300 Grind PN 20-632-4 as a performance improvement over the Mopar 620 grind.
We ran all of our cams with Schubeck composite-faced lifters and set the valve spring load
Howard's Cams showed some promising grinds in their catalog, but they recommended a custom grind that would combine a moderate duration with a relatively high lift as an improvement over the Mopar 557 cam.
Lunati Cams also got the call and recommended their 404A4 cam grind which is a comparison to the larger Mopar 590 cam in mind.
We also wanted to try a camshaft from Hughes Engines, who advertises a line of “Real Chrysler” cams. Dave Hughes recommended his HTL 6468AS Camshaft as a strong improvement over the Mopar 590 cam.
Horsepower comparison of Howards' Cam, MP 557, and Comp Cams 20-249-4.
Torque comparison of Howards' Cam, MP 557, and Comp Cams 20-249-4.
With all of these camshafts to be tested, that meant we would need to tear into our engine several times. So, we decided to try the new line of gaskets from Superformance. We ordered ours from Todd at Competition Wedge Engines. These gaskets held up great thru multiple teardowns.
For fair testing, we degreed each camshaft to the specifications shown on their respective cam card.
We started our test with the smallest Mopar Purple Shaft that we felt would work in our engine application, the 557 grind, PN 4120655. This cam has duration at .050 inch of 257 degrees on both intake and exhaust lobes, .594-inch lift, and a lobe separation of 110 degrees. This cam called for an installed centerline of 108 degrees. After a few pulls of the dyno to dial in the ignition timing, we got a peak horsepower of 557.9 at 6,500rpm, and a peak torque of 549.2 at 4,700 rpm.
The next cam selected was the Comp Cams grind PN 20-249-4. This camshaft had the same lobe separation, very similar lift numbers of .592 inch, and slightly longer duration of 262 degrees at .050 inch. Comp recommends it be installed at 106 degrees, compared to the MP 557's 108 installed centerline. The Comp grind really came on strong at low rpm, with a peak torque of 568.9 at 4,700 rpm and a horsepower peak of 540.5 at 5,700 rpm.
The next camshaft to be tested against the 557 was a custom grind from Howard's. This cam has a split duration at .050 inch of 260 degrees on the intake, and 264 degrees on the exhaust. Lift numbers were .656 inch on the intake and .662 inch on the exhaust, and a tighter 108-degree lobe separation. Howard's recommended it be installed at 104 degrees. This camshaft really helped our engine out on the top end, while still managing pretty respectable torque numbers down low with a peak torque of 565.8at 4,600 rpm, and a peak horsepower of 584.7at 6,800 rpm.