Back on the dyno, the pulls yielded 652 hp at 6,100 rpm and 623 lb-ft at 4,700 rpm with over 600 lb-ft of torque being maintained between 4,100 and 5,600 rpm. That is one flat torque curve. The minimal porting job gained 34 hp and 26 lb-ft of torque-well worth the effort.
We were so excited with how the RPM heads performed, we called a friend in Edelbrock's engineering department to share the good news. He told us the engine would be a perfect testbed for the new Victor 440 heads Edelbrock was about to release and asked if we would like to try a set. Are you kidding? We couldn't get to Edelbrock's Torrance, California, facility fast enough.
The combustion chamber of...
The combustion chamber of the new Victor head (right) is a more modern, heart-shaped design. The increased quench area promotes more turbulence in the chamber, making it much harder for detonation to get started, and it also makes for a more efficient burn. The Performer RPM head (left) is a highly refined, aluminum rendition of the much sought after closed-chambered Chrysler 915 head. Exhaust-valve size for the Victor stays the same at 1.81 inches, but the intake-valve size was increased to 2.20 from 2.14 inches. If you plan to swap in the new Victor head on an existing engine, make sure to take into account the chamber size and how it will affect the compression ratio. At 75 cc, it's down 9 cc from the Performer RPM head at 84.
The new Victor 440 heads have raised intake and exhaust ports. The exhaust ports have been moved up 0.250 inch while the intake ports have been raised a whopping 0.650 inch. The intake-valve sizes have also been increased to 2.20 inches compared with the RPM heads at 2.14 inches. The heart-shaped combustion chambers are new and measure 75 cc. Edelbrock has also cast enough material into the heads that you can take the ports all the way out to Max Wedge size. What can only be described as cast-in spacers on the intake sides of the heads allow you to use your existing Victor 440 manifold when you make the swap. They come with valves and seals, but because most will be destined for racing applications, valvesprings are left up to the racer.
At the time we got the new set of heads, no one was making application-specific rocker arms for the Victor 440. Comp Cams and T&D Machine Products got together and fixed that problem and now offer rockers designed just for these heads. The exhaust rocker configuration didn't change much, but the larger-sized intake ports required that the intake rocker be offset for pushrod clearance.
Back on the dyno at JMS, the engine made 692 hp at 6,400 rpm and 637 lb-ft at 4,900. That's a 74hp and 40-lb-ft increase with a change of cylinder heads only. Yes, the compression ratio went from 10.5:1 to 11.0:1 because of the chamber-size reduction, and that may have contributed some power, but not overly so.
Studying the dyno sheets, we noticed the engine was pulling 2.1 inches of mercury at peak rpm. It was obvious that the new high-flow Victor 440 heads were straining our poor old 850 carb, and it couldn't keep up. With a little more air, we thought there might be some more power left, so we bolted on a Holley 1,000-cfm HP carb for the test and did another pull. With the larger carb, the engine made 711 hp at 6,400 rpm and 641 lb-ft at 5,100 rpm.
With a cylinder-head change and a carburetor upgrade, we gained 93 hp from our baseline pull without any porting. The torque curve looked more like a table top than a curve. Over 600 lb-ft of torque was available from 4,100 rpm to 6,100 rpm; that's a 2,000-rpm sweep.