While we're on a similar subject we should point out the 1964 and earlier intake manifolds use six bolts per side, 1965 and newer use five. For those planning to use an original Tri-power intake the manifold and heads must be compatible.
New Tricks for an Old Goat
The goal for Willis' engine was to produce horsepower and torque numbers similar to those of a 383 Chevrolet, however we had to face facts—lots of things have changed since the 389 was in production and it could benefit greatly from some new technology.
One of the updates was a hydraulic roller cam from COMP Cams. There are good reasons for abandoning flat tappets—the reduction in friction and the longevity of components with today's oils with reduced zinc are among them. According to the experts at COMP, rollers allow higher tappet velocity, more lift, and reduced valvetrain friction (often resulting in a 15-plus horsepower gain). COMP tells us that in nearly all circumstances, a roller camshaft design will outperform its flat-tappet counterpart. Basically that's due to a roller cam behaving like a "bigger" or more aggressive flat-tappet cam. Continuing the quest to reduce friction we opted for COMP Cams' full roller rockers.
The roller cam we chose was from COMP's Thumpr series. These sticks are unique in that they have a mean, lumpy idle with no sacrifice in low-end power. COMP says this comes from a combination of an early intake valve opening, long exhaust duration, and a generous amount of intake and exhaust overlap. We just know they have that muscle car sound and pull from idle on up the rpm scale.
Another area where most vintage engines can stand some improvement is ignition, but one of the goals was to keep the engine's vintage look. To satisfy both requirements the points in the original distributor were swapped for a PerTronix Ignitor. This stealth approach to electronic ignitions is ultra reliable, doubles the voltage to the plugs and makes dwell adjustments a thing of the past. To complete the new/old theme a black 40,000V Flame-Thrower coil and PerTronix "stock-look" spark plug wires were added. The wires use the same core as their 8mm wire but have a 7mm flat black silicone jacket that provides state-of-the-art performance with an OEM appearance. Topping off the engine is a Quick Fuel Technology carburetor on the aftermarket dual-plane manifold that was on the engine.
Other than the cam and valvetrain components, the internal parts necessary to refresh this engine came from Summit. One phone call got everything we needed so we headed to VHRD/Pro machine and shortly after our Poncho was on the dyno.
There's no arguing that modern engines with all their technology make huge horsepower and torque numbers easy to come by, but building any vintage engine isn't about what is, it's about what was. On the dyno the engine posted solid numbers, 352 hp at 5,100 rpm. But, more importantly, by 2,500 rpm it was making 369 lb-ft of torque, a max of 416 at 3,300 rpm, and it averaged 390.43 between 2,500 to 5,500 rpm. The goal was to build an engine with vintage appeal that made lots of torque, was reliable, and didn't cost a bundle. That's what we wanted and that's what we got.