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Z/28 302 Engine Build and Dyno Test - She's A Spinner

Super Chevy Builds A High-RPM 302.

By Richard Holdener, Photography by Richard Holdener

Except under extreme circumstances, you don't usually find 150 hp by bolting on a single component like a new carburetor or even a wilder cam profile. This is especially the case if you are starting with a motor that is already producing nearly 1.2 hp per cubic inch. To reach our goal of 500 hp, the little 302 would need to exceed 1.65 hp per cubic inch, a serious number in anyone's book. Reaching that specific output meant replacing not one but all of the major power producing components, starting with the Duntov 30-30 cam. The factory solid flat-tappet cam was both outdated and insufficient in terms of lift and duration to meet our needs. Though a modern equivalent to the Duntov cam would be worth an easy 20-25 hp over the original, our lofty power goal required swapping out the flat-tappet design for a serious roller profile. Comp Cams supplied the custom roller cam that offered a 0.640/0.621 lift split, a 256/260-degree duration split (at 0.050) and a tight 107-degree lobe separation angle. The custom roller offered super aggressive ramp rates to maximize not only peak power but power production throughout the useable rev range. Comp Cams also supplied the matching roller lifters, hardened pushrods and 1.52 ratio roller rockers.

With our cam needs met, we turned our attention to some deep breathing exercises. Back in the day, the fuelie heads were the hot set up for a 302, but time and technology marched on. Given the relatively small displacement (most heads are designed for 350 or more cubic inches), we'd normally look for port volumes on the small end of the scale. But this high-rpm build up was anything but normal, so we stepped right up to a set of heads offering 210cc intake port volumes.

With peak power scheduled to occur somewhere near 7,500 rpm, our buzzy little small-block could take full advantage of the airflow offered by the sizable port volume. Airflow Research supplied a set of its 210cc Eliminator heads. Since we wanted to maximize peak power numbers, we opted for the "competition" version that featured additional port work to increase the intake/exhaust flow rates from 299/222 cfm to 311/237 cfm.

In addition to the 210cc intake ports, the AFR Eliminator heads also featured a lightweight (8mm) 2.08/1.60 valve package, full CNC combustion chambers and 80cc raised exhaust ports. Additional features included 3/4-inch head deck surfaces and dual valve cover bolt patterns. These heads represented a huge step up the performance ladder compared to the original fuelie heads.

With the head flow taken care of, we turned our attention to the intake manifold and carburetor. Given our head and cam choice, peak power was going to be well past 7,000 rpm, so we chose an intake manifold accordingly. The natural choice was a single-plane manifold, which was designed to optimize power production higher in the rpm range. Since most of the intake manifolds are designed with 350 ci in mind, the intake would allow our 302 to effectively rev even higher. All things being equal, an increase in displacement will mean a drop in where the motor makes peak power. If a 350 produces peak power at 7,000 rpm with a given combination of heads, cam and intake, employing the same components on a smaller 302 will result in peak power somewhere north of 7,000 rpm. We saw this when we ran our Legendary Small-Block series, as the 327 and 302 were equipped with the same heads, cam and intake and the 302 produced peak power 500-600 rpm higher. We chose a ProComp single-plane, high-rise intake and Holley 750 HP series carburetor to top our 302. The combination offered plenty of airflow and the proper resonance tuning to optimize top-end power production. It would have been fun to try a dual-carb tunnel ram on this high-rpm screamer, but we couldn't get our hands on one in time for testing. A huge thanks goes out to Westech's Steve Brule for building this motor and curing a few minor issues we had during testing.

By Richard Holdener
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