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Complete Chevy Big Block Build & Testing - Action-Packed Big-Block Test

We Pick Up 116 HP With A Simple Swap To RHS Pro Action Heads, Edelbrock Intake And A Lumpier Comp Cam.

By Richard Holdener, Photography by Richard Holdener

The dual-plane intake manifold from Pro Comp offered a near-ideal combination of torque and power production for use with the factory (peanut) oval-port heads. The intake was fed by a 750hp Holley carb, while exhaust chores were handled by a set of 2.125-inch Hooker Super Comp headers. In addition to the intake manifold, Pro Comp also supplied the billet distributor and plug wires, while the spark plugs came from EG. Equipped as described, the Demon 454 produced 401 hp at 4,700 rpm and 508 lb-ft of torque at 3,400 rpm. Hardly a high-rpm screamer, the combination offered plenty of torque right in the most usable portion of the rev range.

Torquey big-blocks are always popular, especially when they are affordably priced, but what if we are looking for something a little more action-packed? Not a full-on race motor, but something that can show taillights to the modern competition without breaking the bank? In reality, our 454 was just begging for the opportunity to strut its stuff. With over 500 lb-ft, torque production from the mild 454 was already impressive. Now all we had to do was improve the upper portion of the rev range by allowing the motor to breathe.

With an excellent short-block at our disposal, we took a long, hard look at the power producers, namely the heads, cam and intake. The dual-plane intake was already perfect for our application, but unfortunately the Pro Comp manifold was designed for the oval-port heads and would not fit the rectangular-port heads we had in mind for our big block. The Pro Comp dual-plane intake was replaced by an Edelbrock Performer RPM Air Gap. Similar in design to the Pro Comp piece, the dual-plane intake offered a balanced combination of mid-range torque and peak horsepower production. For street use, a dual-plane is almost always preferred over the peakier, single-plane manifold.

Obviously, the stock peanut-port heads had to go. With a combination of small intake and exhaust ports as well as small-block-sized intake and exhaust valves, the stock iron heads could hardly be considered performance oriented. That they flowed just 235 cfm on the intake and 172 cfm on the exhaust meant they were better suited for a small-block application than a healthy big-block. Sealing the replacement deal was the fact hat they were constructed of heavy cast-iron. Just the mere thought of lifting them during the head swap strained a muscle or two. For any motor, but particularly for a Rat, aluminum heads should be considered a must.

For our stump puller, we turned to Racing Head Service (RHS). Though it offers both aluminum and cast-iron performance heads for the big-block (as well as a wide range of small-block heads), we stuck with the lightweight aluminum castings. This narrowed our selection down to the 320cc Pro Action and 360cc Pro Elite heads. Since our relatively mild 454 was not in need of CNC-ported cylinder heads that offered 400 cfm, we chose a set of 320cc as-cast, Pro Action aluminum heads.

The RHS Pro Action heads offered patented Clean-Cast technology, which is designed to optimize port-to-port transitions and airflow efficiency. The 320cc heads offered impressive airflow numbers, especially compared to the stock peanut-port heads. Where the stock heads topped out at 235 cfm, the RHS Pro Action heads offered 375 cfm (at 0.700 lift). Closer to lift values we planned to run, the RHS heads still outflowed the stock heads by as much as 100 cfm.

The impressive intake and exhaust flow can be partially attributed to the increase in valve size from the 2.06/1.72 combination on the stock heads to 2.25/1.88 combo on the RHS heads. The stainless steel valves were combined with a multi-angle valve job, hardened seats and premium valve guides to make for serious out-of-the-box performance. Just for good measures, RHS tossed in a refined water jacket to improve thermal conductivity and a thick deck surface for superior sealing.

By Richard Holdener
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