Since the motor had been previously broken in and run, we elected to replace the conventio
The Profiler heads were unique in that the 290cc intake ports featured neither a traditional rectangular nor an oval-port shape, but a combination best described as "roval." The intake ports were essentially the size of a performance-oriented rectangular port with the corners rounded to improve flow. For a given area, a round port flows better than a square (or rectangular) one. The port shape required replacing the dual-plane intake from Procomp with an Edelbrock RPM Air-Gap. The Air-Gap was similar in design but featured ports designed for rectangular-port, big-block heads. These offered the best match for the ports in the Profiler heads. Ideally, the heads and intake can be port-matched, but we decided to run them as is to illustrate the combination used by most enthusiasts.
The HEI distributor and plug wires from Procomp were retained. With the right curve, we se
The new heads, cam, and intake were run with a Holley 950 HP carburetor, which flows more air than the 750 HP run on the original low-buck 454. Despite the moniker, the 950 HP is actually a 750 body with an 850 baseplate. The combination actually flowed less than a standard 850 but works well on a variety of different (milder or smaller) engine combinations that might not work well with the larger 850 carburetor. The two final changes included upgrading pushrods and stamped-steel rockers originally supplied on the engine. The pushrods were not actually a necessity, as the 3/8-inch pushrods shared the 8.250/9.250 lengths with the 5/16-inch pushrods, but make sure to specify the proper guideplates when ordering the heads.
Run with a set of 2.25-inch dyno headers and a Meziere electric water pump, the modified 4
It is obviously possible to install a wild solid roller cam and even mill the heads to up the static compression ratio if you desire more power, but with this engine we were looking for a combination of daily driver and weekend warrior-something that could easily pull double duty without costing a fortune in fuel and still post some respectable e.t. and trap speeds in a suitable Camaro or Chevelle. The combination of aluminum heads and 9.4:1 compression meant the motor was plenty happy on 91-octane pump gas and could even be run on 87-octane with the right timing curve.
Run with Lucas 5W-30 synthetic oil, a set of 2.25-inch headers, and a Meziere electric water pump, the modified 454 produced 564 hp at 6,100 rpm and 542 lb-ft at 4,500 rpm. This represented a gain of 119 hp over the previous combination. Note that the peak torque value was unchanged, but it was moved higher in the rev range. Idle vacuum changed by 1.7 inches, and this combination might like a converter with a slightly higher stall for optimum performance. But the upgrade does illustrate that the Demon engine is a solid foundation for a performance buildup. Check back with us next month to see how well the cast crank and stock rods stand up to even more power as we add a homemade, low-buck turbo kit.
Dyno Results
Replacing the heads, cam and intake on the Demon low-buck 454 resulted in some serious power. Where the original low-buck combination offered peak numbers of 445 hp and 542 lb-ft, adding the aluminum Profiler heads, XE284H cam, and Edelbrock intake upped the peak numbers to 564 hp and 542 lb-ft. Even more power is available with wilder cam timing and/or more compression, but the increased cam duration would sacrifice low-speed power, mileage, and throttle response. The big-block offered more than 500 lb-ft of torque from 3,500 rpm to 5,800 rpm. Had we loaded the modified combination lower than 3,500 rpm, the torque production would have exceeded 500 lb-ft well below that engine speed, possibly as low as 2,800 rpm. That, my friends, is one impressively broad torque curve. Is it any wonder enthusiasts choose big-blocks?