Change Cam–Gain 77 HP!

Shell out $219; pick up 77 hp. Swapping out that stock cam for a healthy aftermarket high-performance hydraulic flat-tappet cam, lifters, and valvesprings is one of the most cost-effective changes you can make—provided the rest of the engine is up to the job of feeding, sparking, and exhausting the hungry camshaft.

In tests conducted on an 8.6:1 355ci small-block Chevy at Westech Performance, a wimpy stock replacement bumpstick used on millions of carbureted Chevy small-blocks was compared to Erson’s hot TQ40H hydraulic cam installed with matching lifters and valvesprings. The stock cam held the engine’s potential back like a cork stuffed in a bottle. Despite the potential of a good intake, heads, and exhaust system, the engine made only 336.4 hp at 4,700 rpm before lurching into valve float by 5,500 rpm. Still, the stocker was designed to make torque in grandma’s grocery-getter, and its 398.8 lb-ft torque output at 3,700 rpm made the engine suitable for weekly go-to-market sojourns.

It was time to wake this baby up with a cam transplant. We swapped springs too, replacing the tired stockers with new Erson chrome-silicon springs that let the engine rev higher to take advantage of the new cam’s improved breathing potential. Reacting like Popeye swallowing a can of spinach, the engine’s peak power output jumped to 403.3 hp at 5,600 rpm—nearly a 24 percent improvement. Torque output at the peak improved to 418.7 lb-ft at 4,400 rpm.

But there’s no free lunch: As is typical with a larger cam, the gains came at the expense of the bottom-end. To increase engine output, you have to raise the motor’s rpm potential, shifting the power and torque curves higher. Below 2,800 rpm, the engine’s horsepower and torque production was slightly lower than the baseline numbers. The cam didn’t come into its own until the engine climbed above 3,200 rpm—but above that point, it left “grandma’s cam” in the dust.

The bottom-end torque production on low-compression engines like this one is more sensitive to cam selection than would be the case on a higher-compression mill. A higher ratio would get back some of the lost bottom-end—or just wind the engine quicker into its power-band with a high-stall converter and low rearend gears.

All in all, swapping-in a hydraulic cam with 0.050 duration in the 220-230–degree range was the best bang for the buck in terms of power and torque production we tested for this section. At 76.9 hp for $219.14 (including gaskets), it works out to about 35 cents per horsepower!

By Marlan Davis

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