Cam Pro Plus has the ability...
Cam Pro Plus has the ability to read every aspect of a cam lobe and chart the data. Cam-lobe design features-jerk rate and lift per degree of rotation, along with a complete examination of the ramp-are some of the points. This can't be accomplished with a degree wheel. Both cams were well within published specs.
The Plan
HPP's protocol for this story is simple: Test the engine with a stock-style TPI and aftermarket EFI cam profile, and then switch the manifold/induction system. In total, four different induction systems are analyzed, however, the camshaft that works well with the stock-length TPI manifold isn't optimized for the other intake manifolds with a much shorter runner. The manifold runner length varies from approximately 5 to 8 inches in total. This value is independent of the runner in the cylinder head. A Vortec cylinder-head runner is approximately 6 inches long. The total intake track length of the different manifolds varies from approximately 11.75 to 14 inches in comparison to the stock TPI's 24 inches.
For an engine to make the most power, the intake valve timing needs to be matched to the tuning (resonant) characteristics of the intake manifold. The runner length is the dominant effect in the equation, while the cross-section does play a much less important role. Due to this, all of the intake manifolds were tested with the camshaft used with the long runner TPI, and then retested with a more applicable grind that takes advantage of the shorter induction path. Since the second cam won't work well with the stock-style TPI, that system wasn't tested with it.
The Cams
For our exercise, the TPI or long-runner cam is identified as Cam No. 1. It's from Comp Cams, PN 08-304-8. The duration is stated as 210/220 degrees at 0.050-inch lift, intake and exhaust, respectively. Cam-lobe lift is 0.332-inch intake and 0.342-inch on the exhaust, and the lobe centerline is 114 degrees. The cam was installed at an intake lobe center of 110.5 degrees.
The short runner Cam No. 2 was custom-ground by Bullet Cams to Bob Wise's own specifications. RaceKrafters has extensive engine-building experience and often employs its own cam profiles. This bumpstick has 226/234 degrees of duration at 0.050-inch lift. Cam-lobe lift is 0.353/0.355-inch, the centerline is 112 degrees, and the cam was installed at 108 degrees.
The contrast in throttle-body...
The contrast in throttle-body design is best represented by the 75mm Ram Jet single butterfly in comparison to the Holley four-barrel style. Though not shown, the Holley Stealth Ram throttle body uses two butterflies, one per each bore.
Harland-Sharp full roller rockers were fitted with a 1.6:1 ratio on the intake valves and 1.5:1 on the exhaust valves. This produced a net lift of 0.531/0.513 on Cam No. 1 and 0.564/0.532 on Cam No. 2. The cylinder heads were upgraded to 2.02/1.60-inch valves over the stock 1.94/1.50 design.
The Manifolds
Stock-length TPI: Due to the high flow capacity of the Vortec cylinder heads, a stock GM TPI isn't used. Instead, ACCEL large-tube runners and a High-Flo Edelbrock Vortec manifold base is employed with an ACCEL twin 58mm throttle body (stock is 48mm). The plenum is a stock GM piece ported by RaceKrafters. This induction system is the same length as the stock GM design but has larger passages to promote better airflow. (This is the only setup with EGR provisions, so it will be the only one capable of passing smog inspections in smog-test states.)
Holley single-plane: Similar to a single-plane carburetor manifold, this design allows the use of a 750-cfm four-barrel air door, which is basically a carburetor throttle body. This manifold is the closest in operating characteristics to a carburetor system than any of the others. The end runners are 8 inches long, while the center path is 7.5 inches.
Holley Stealth Ram: This one has an upright plenum and is similar to the system GM used on the factory LT1 EFI engine, but the Holley has a 7-inch long-runner, while the LT1 is nearer 4 inches. A Holley twin 58mm throttle body is used.
GM Ram Jet: The GM Performance Parts manifold is a short-runner design with a more direct flow path to the cylinder head than the TPI. It's known for good flow characteristics and the ability to support higher engine speeds than the stock TPI. This manifold features a 5.75-inch long-runner. The throttle body is an LS1-style with a single 75mm butterfly.
The ACCEL high-flow, large-tube...
The ACCEL high-flow, large-tube runners were mated to an Edelbrock Vortec High-Flo base. The Vortec cylinder head has a unique bolt pattern and port entry, and can't use a standard TPI manifold.
The Holley single-plane manifold...
The Holley single-plane manifold does little to hide its carburetor DNA.
Fully dressed, the single-plane...
Fully dressed, the single-plane still may be confused for a carburetor at first glance. The nice feature of this system is the ability to use a large carburetor-style air filter when installed in the car.