We decided to test two different...
We decided to test two different cams, both LPE grinds. The milder of the two will work in an emissions application yet still bumps the stock lift by 0.115 while the larger of the two cams kicks the lift up to a stout 0.631 inch.
Cam It Up
Some may suggest at this point that we add a performance-style intake. According to the guys at LPE, their testing has shown that despite the truck manifold's pedestrian image, it's a great manifold, so we instead decided to bolt in a camshaft. The first cam is what LPE calls its GT2-3 cam, which is mild enough to generate a stock idle (20.7 inches of vacuum at 800 rpm) yet pumps the lift and duration up substantially (see the Cam Specs chart) by adding 0.115 inch of lift on the intake side alone! This is still using the stock 1.7:1 Gen III shaft rocker arms. Since we were adding a more aggressive camshaft to the mix, Dyno Bob also swapped the stock beehive springs for a set of Comp Cams performance LS1 beehive springs just to handle the additional lift and rpm.
One of the great things about the Gen III small-block is how easy it is to swap cams. Dyno Bob removed the rocker shaft and pushrods, pulled the accessory drive and balancer off, and then yanked the timing cover and cam gear. If you spin the engine over two revolutions with the rockers and pushrods off before removing the cam drive, the lifters will sit up out of the way so the cam can be removed without pulling the intake! The biggest hassle is properly positioning the timing cover and tightening the stock torque-to-yield balancer bolt.
Since all Gen III engines come with hydraulic roller cams, we even reused the stock hydraulic roller tappets, making a cam swap even more affordable. LPE decided to also add a Cloyes adjustable timing set to the engine in case we wanted to move the cam around, but for this test, we left it dialed in straight up. Looking at the dyno numbers, this first camshaft gave up a little torque below 2,600 rpm, but added an astounding 76 hp at 5,800 rpm! This combination pushed the peaks up to 378 hp at 6,000 and 366 lb-ft of torque at 4,800 rpm. If you compared the horsepower peaks, this little cam was worth 65 hp over the stocker while also adding 21 lb-ft at peak torque. Keep in mind that all we've done is bolted in a conservative camshaft, a set of Comp valvesprings, and a set of 131/44-inch headers.
The first and simplest modification...
The first and simplest modification involved merely bolting on a set of 131/44-inch headers. Ideally, this engine might have made even more torque and similar horsepower with a set of 151/48-inch headers, but the larger pipes were all we had.
Now it was time for the big camshaft. This time, LPE pulled out a much more aggressive mix of lobes that most certainly will qualify it as "fairgrounds lumpy." This is LPE's GT1-1 cam that bumps the duration at 0.050 up to 229/242 degrees of duration while the valve lift skyrockets to 0.631 inch for both intake and exhaust. That's 0.175 inch more lift than the stock cam! While this is a big cam for a little 325ci engine, it also promised some healthy horsepower numbers. Dyno Bob again went through the drill of swapping cams, which he accomplished in less than an hour. After he brought the engine back up to temperature, the cam's more aggressive nature showed up with 10 inches of manifold vacuum at its 900-rpm idle speed.
After several power pulls, it was obvious that we had traded low-speed torque for horsepower since the big cam created quite a torque dip between 2,000 and 3,500 rpm where the motor lost as much as 50 lb-ft at 2,400 rpm. This is typical of a big cam with lots of overlap. The power almost overlapped the original stock engine's level between 3,000 and 4,200-then the big cam began to make some serious noise. From 4,400 to 6,800, this little small-block rocked! Peak horsepower jumped to 413 at 6,600 while torque peak settled in at 369 lb-ft at 4,800 rpm. This also created an 1,800-rpm power spread between peak torque and peak horsepower. Remember, this is still with the stock truck intake, throttle-body, and stock heads!