It's inevitable. As soon as we start to make respectable power with our General Motors Performance Parts 350 H.O. crate engine, all reason goes out the window and we are seduced by the lure of bigger horsepower numbers. The little power devil who sits on our shoulder is the one whispering in our ear, "Go ahead, do it! Plug in that bad-boy roller cam. Go ahead-you'll love it!" Through last month, we had managed to stay on the conservative side of things and we left you with the results of testing a GM Performance Parts Hot hydraulic roller cam with 1.6 roller rockers. That mild hydraulic roller and rocker system made a respectable 401 hp and 428 lb-ft of torque. Keep in mind, this is with a bone-stock set of iron Vortec heads. But we wanted more.
Cam It UpWe started by rooting through the hydraulic roller side of the cam catalogs, but decided that if we were serious about power, the only choice was a mechanical street roller. We talked to the guys at Comp Cams, and for the same price as a standard off-the-shelf cam, they created a cam that spec'd out at 280/288 with 0.538-inch lift with 1.6 rockers, or slightly more lift than the previous GM Hot cam. Unfortunately, even this cam exceeded the capability of the beehive springs, and we ended up using larger dual valvesprings
Converting to a mechanical roller cam also requires a pile of new parts. While all of Comp's Street Rollers now come with an iron gear for the distributor drive, you will still need new lifters, pushrods, roller rockers (if you don't already have them), some type of cam button, a new timing set, and a specific roller cam fuel pump pushrod. We've outlined all the parts necessary for this conversion in the Parts List chart, but some details are worth mentioning.
Perhaps the most important point for any roller cam is ensuring that you limit the cam's fore-aft movement. This requires a cam button placed on the snout of the cam that limits movement through contact with the timing chain cover. We're using one of Comp's cast-aluminum two-piece cam covers, but a reinforced stock cover will also work. We like the rollerized cam button since it is not subject to wear and is also adjustable to accurately set the camshaft endplay.
Using a more aggressive camshaft also meant that we needed a stronger valvespring. We decided to use the Comp 977 spring, which is a larger 1.430-inch diameter dual spring that specs out with 155 pounds of load on the seat at 1.850-inch installed height and 419 pounds at 1.250 (or 0.600-inch lift). This is a good dual spring, designed for lots of rpm yet not so big that it would pull the pressed-in studs out of the heads. This obviously meant that we also had to remove the heads and machine the spring pads from the stock 1.250-inch diameter to the larger 1.430-inch diameter. The best plan would have been to install ARP screw-in studs at the same time we cut the springs pads, but we were in a hurry and didn't make that change-shame on us.
The TestAfter our dyno flogger Ed Taylor completed the cam swap into our GM Performance Parts 350 H.O. engine and as soon as the engine warmed up, he cranked the throttle wide open. Because we added 22 degrees of duration to the intake side, we expected to lose some low-speed torque, which did occur between 2,600 and 3,600 rpm. Comparing the torque to last month's best run using the much shorter-duration GM Performance Parts Hot hydraulic roller cam, the torque loss did occur. But by 4,000 rpm, we were gaining power with a 420 peak horsepower number compared to last month's 401. With the larger cam, we didn't expect peak torque to increase by much, and it didn't. But what was surprising was that the larger cam's peak torque occurred at 4,400 rpm while the much smaller Hot cam's peak torque chimed in at 4,200. We expected the peak torque to be at a slightly higher rpm, but for a street car this is still very manageable.