Action-Packed Big-Block Test In these days of all-aluminum, injected small-blocks, is it hard to get excited about something as simple as a carbureted big-block Chevy? Not if you're a loyal reader of Super Chevy it isn't, as the mere mention of the phrase "big-block" should get those old juices flowing.
Why such a fuss over old technology? While a cast-iron, carbureted motor that weighs more than a metric ton is hardly a technological marvel, there is no denying the results of replacement/displacement principle. When it comes to making power, bigger really can be better. The greater the displacement, the easier it is to reach a given power goal. Obviously you are not going to make big power with displacement alone, but with something as simple as a set of heads and cam, serious power is just an afternoon away.
Perhaps the best thing about owing a big-block Chevy is in addition to the serious horsepower potential, big motors also offer big torque. No amount of technology is going to artificially create thunderous torque at lower engine speeds unless that technology includes some sort of boost pressure. Having a Rat that makes 500 hp is one thing, but that 500 hp feels more like 600 when you combine it with over 500 lb-ft of torque low in the rev range. It is all that wondrous torque that pins you back in your seat and puts a smile on your face.
Having extolled the virtues of big-block ownership, let's take a look at making a good thing even better. In this case, our good thing started out life as a simple 454 offered by Demon Engines. This Demon 454 was created to cater to cost-conscious BBC enthusiasts and as such featured nothing more exotic than a cast crank, forged rods and a set of forged pistons.
The forged aluminum pistons featured 18cc domes to help improve the static compression ratio over your typical flat-top or even more performance-sucking dished factory BBC slugs. When combined with the typical 119cc combustion chamber, the 18cc domes produced a static compression ratio of roughly 9.5:1 depending on exact deck clearance and head gasket volume. Think of the Demon 454 short-block as a sensible upgrade to a high-mileage factory motor.
The Demon 454 short-block also featured a four-bolt (Gen IV or V) block. Some may question the cast crank, but we have exceeded 1,000 hp using factory cast cranks so you are unlikely to ever damage one under power. Crank failures are usually the result of oil starvation or detonation, all of which can be traced back to neglect by the owner. Demon also offers the 454 short-blocks with 4340 forged cranks, but feels the money for the crank upgrade is better spent on displacement or airflow.
The cost-conscious 454 from Demon was sporting a set of reconditioned peanut-port heads. The factory iron heads were given the once-over, including a fresh valve job, surface and new springs and retainers courtesy of Comp Cams. This particular Demon 454 (it offers a number of different BBC combinations, ranging from this near stock rebuild to 1,500-plus-hp supercharged stroker assemblies) was configured for towing and/or mild street performance. Use of the stock peanut-port heads naturally restricted the peak power output, but the combination was designed to offer plenty of low-speed torque at an affordable price point.
Applications for the 400hp Demon 454 included performance street, marine and even truck and/or RV usage to replace the typical tired (and sluggish) high-mileage, big-block. Continuing the torque theme was a mild hydraulic flat tappet cam and dual-plane intake manifold. The mild XE256H Xtreme Energy cam used in the 400hp 454 offered a 0.480/0.485 lift split, a torque-producing and idle-friendly 212/218 duration split and a 110-degree lobe separation angle.