In our last installment, we visited RaceKrafters Automotive Machine in Lancaster, PA to test the Edelbrock RPM Air-Gap LT1 Intake Manifold on a nearly stock 355cid LT1. Using a much smaller plenum volume, longer runners, and a larger runner cross section, the Edelbrock intake seemed a shoe-in for increased performance. However, when tested with the stock heads, it failed to increase power output nearly as well as we'd hoped. When Bob Wise of RaceKrafters and myself scratched our heads, it seemed there were only a few possible explanations. The first, and most logical, was that the larger cross section of the runners created a greater mismatch with the stock heads' intake ports, causing air turbulence and an obvious restriction in flow. The second was that the intake really wanted a 58mm throttle body and not the 52mm unit we were using, though with merely a 355-cube motor this seemed unlikely. And third, there could be some other factor we weren't taking into account such as plenum shape, or perhaps even an excess of casting flash inside the intake.
To test the first of these theories, we gave Edelbrock a call to obtain the Performer LT1 cylinder heads (part No. 61909) and hydraulic roller cam (part No. 2108). With a modest 170cc intake runner, higher flowing design, and 1.94/1.55 valves, these heads are capable of an easy 24 horsepower according to Edelbrock. The Performer LT1s are a stopgap between the stock aluminum heads (for an F-body or Vette) and either the factory LT4 heads or Edelbrock's LT4 casting. The small runners make the Performer LT1s ideal for more modest stock-cube builds. Edelbrock's LT1 cam follows suit with 218 degrees of duration at .050 and .525-inch lift on both the intake and exhaust, designed for naturally aspirated motors with either stock or aftermarket self-adjusting rockers. Though RaceKrafters had previously installed a Comp Cams roller, the extra intake duration and lift would take better advantage of our new heads. Pairing the Edelbrock intake and 52mm throttle body with this head and cam package seemed a sure winner, but there was only one way to find out. Follow along to see how this stock-cube combo performed.
The Edelbrock heads and cam produced both a stronger top end and a much flatter torque curve. With Edelbrock's complete top-end package, a good cold-air intake, and a high-flowing exhaust system, your LT1 should have no problem keeping up with even a bolt-on LS1. Yet the cam is mild enough that I wouldn't expect any idling or vacuum issues; heck it might even pass emissions in Cali! We are still not finished with our evaluation of Edelbrock's intake, so stay tuned for another installment when we continue to tune-up our little 355.