Parts Department
The first change our pal had in mind was making a move to a more modern camshaft profile. he had heard good things about the Comp XE HL series of hydraulics, which are some very fast-acting and aggressive .904-inch lifter profiles. There are basically three XE HL camshafts available for the Mopar small block, ranging in duration from 275 to 285 to 295-degrees. Mistake one occured when our friend chose to go with the XE 295 HL, the biggest of the series, with a whopping 251/257 duration at .050-inch lift and .564-inch lift. The engine can't have less lope than it started with, right? This cam is rated to 6,800 rpm, well past the intended rpm range of this 360, but the decision was made to over-cam the engine for the wild sound and big lope. To control the cam action, a set of Comp's latest beehive springs (PN 26915) designed for the LS1 were picked. That was mistake number two. The Comp Cams LS1Beehive springs are an excellent spring when used as intended, but with only 105 pounds on the seat and 280 pounds over the nose, these springs would have to work miracles to control the intense action of the XE HL profile. A good choice was made when our friend decided to use a set of mildly ported Edelbrock heads, a nice upgrade from the production iron 587's.
Buttoning It Up
The engine was cleaned and detailed as planned, and the new cam installed, along with a new double roller timing chain and Mopar's timing chain tensioner kit. With the aluminum heads in place, the engine certainly did look like a much more serious piece than the older version of the engine. It was put up on the dyno to determine if the added punch would match its looks. Back to Westech, and the engine was once again fitted with the 1 5/8-inch headers and the identical induction system used in the previous baseline testing. No additional parts were brought to the party, so the entire day was devoted to tuning. In the end, the engine showed 439.8 lb-ft of torque and 456 hp-a gain of 23 lb-ft of torque and 40 hp.
Critical Analysis
While the power gains were nothing to scoff at, and 450-plus horsepower from a 360 small-block is pretty stout output, we had to believe there was more in the combo. These power levels could likely have been achieved with the smallest of the HL series cams-the 275-with better power production through the midrange. With the relatively small header and moderate compression ratio, the camshaft was much bigger than optimal. Frankly, in the correct combination, to make use of a cam that large, the engine speed at peak power should have been closer to 6,800-7,000 rpm instead of 6,300. Conspiring to hold the rpm range down was the spring choice. The 26915 spring is designed for a very specific application known for an exceptionally light valvetrain with very low inertia. In this application, the cam/spring combo was simply not appropriate to maintain control of the radical action of the HL cam and relatively heavy valvetrain. The (PN 26120) beehive-spring is designed for big-block Chevy applications, but easily adaptable to the small Mopar, and likely would have fared better. This theory was borne out when the engine was later installed back into the car, and valve float became more readily apparent, particularly under the faster engine acceleration rates experienced through first gear.
The detail that raised our hackles more than any other-there was no effort to machine the block for a zero deck height. With the closed chamber Edelbrock heads, a zero deck would have provided the advantage of an optimal .040-inch quench clearance. As it was, the pistons remained .020-inch in the hole, opening the quench number up to .060-inch, far from ideal and a definite disadvantage in detonation tolerance and engine output. There may well have been another 10-15 lb-ft tossed out because of the .020-inch of extra clearance. The increase of a couple of tenths of a point in compression ratio resulting from decking the block would also have been welcome with the aluminum heads.
A great deal of effort went...
A great deal of effort went into adapting these springs to the Edelbrock heads, as witnessed by the custom-made seat locators beneath the springs.
An appropriately spec'd dual-spring...
An appropriately spec'd dual-spring assembly (as was used on the original 360 combo) would be a better choice. Comp recommends their 978 springs with the XE 295 HL camshaft, which would provide 126-pound seat load and 348 pounds over the nose installed at 1.850-inches. If in doubt, go with the recommended pieces.
A timing chain tensioner from...
A timing chain tensioner from Mopar Performance can easily be retrofitted to earlier blocks. This will help in true-timing abilities.