Last month, we introduced you to the GM Performance Parts 350 H.O. crate engine. We began testing using the Deluxe model that comes completely outfitted with a water pump, HEI distributor, spark plugs, and a 600-cfm vacuum secondary carburetor. In search of more power, we added Hedman headers, an Edelbrock Performer RPM Air Gap dual-plane intake, and a 750-cfm Holley double-pumper carburetor.
Those simple bolt-on changes pumped the 350 up from its stock power rating of 330 hp and 380 lb-ft of torque to a stout 377 hp and 415 lb-ft of torque. While we were impressed with the small-block's significant gains, we felt that a cam change would be worth even more. That's what we're going to dive into this month.
Mild HydraulicThe 350 H.O. engine comes with a mild yet even-balanced dual-pattern flat-tappet hydraulic camshaft. Based on the lift and duration numbers, we expected that even a slightly larger performance hydraulic would make much bigger numbers. The first cam we tried was a Comp Cams Xtreme Energy 262 cam. Our goal with this selection was to see how much power we could make while maintaining near-stock idle quality. Ed Taylor installed the Comp Cams hydraulic and soon had the 350 up and running. While power did improve, the gains were so minimal that we have not listed them in the dyno chart numbers. Instead, we decided to jump right into the next larger cam in the Xtreme Energy stable-the 268.
Again, Ed swapped sticks with the help of a Comp Cams two-piece timing chain cover he installed just for this purpose. If you intend on doing multiple cam swaps, this heavy aluminum unit is an outstanding time-saver. With a couple of hours of labor behind him, Taylor was again making noise, this time with the more aggressive Comp XE268 cam. After a quick 20-minute break-in session and a few pulls to establish the proper timing and recheck the proper air-fuel ratio, Taylor made a series of full-throttle runs to collect the numbers. Even with the much longer duration, the 268 cam made more torque down low than the stock 350 H.O. cam, but not as much as we had hoped. Peak horsepower also picked up 7 more hp than the original cam.
At this point, the little 350 H.O. is making 377 hp and an amazing 415 lb-ft of torque with a relatively mild cam. The larger 268 didn't make dramatic increases in power, which points out just how good the original 350 H.O. cam really is, since these minor increases in power would be difficult to see in the quarter-mile. A longer-duration flat-tappet hydraulic cam would obviously make more peak power but would also sacrifice low-speed torque to accomplish this, so we decided to go a different route and jump up to a hydraulic roller cam instead.
Roll OnListed in the GM Performance Parts catalog is a relatively obscure hydraulic roller cam package originally designed for off-road LT4 fuel-injected engines that offers a mild intake lobe using stock roller lifters tag-teamed with a set of GM Performance Parts 1.6:1 aluminum roller rockers. We've had previous experience with this cam and decided it was a perfect match for the 350 H.O. engine package and the Vortec heads. The beauty of this system is that you can purchase a complete cam, lifter, pushrod, and rocker arm set from GM Performance Parts that will bolt right into the 350 H.O. because it's a one-piece rear main seal engine fully machined to accept a hydraulic roller cam package. GM Performance Parts chose to originally equip the H.O. with a flat-tappet cam to keep the engine affordable. But we wanted more power, so the swap was a natural.