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The Iron Alternative
GM Performance's New Vortec Heads Promise Big Flow Numbers For A Modest Investment
Nov 10, 2005
Chevrolet Performance Parts
Detroit, MI 48232
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The Iron Alternative
GM Performance Parts' new Vortec Bow-Tie iron cylinder heads are available in small- and large-port configurations, and available either bare or fully assembled. Assembled small-port versions carry PN# 25534421 and large-port assemblies carry PN# 25534431. Bare heads are also available.
Similar in outward appearance to familiar 23-degree heads, the new Vortec Bow-Tie promises to deliver the performance equivalent of a comparable aluminum cylinder head.
Designed for a variety of applications--including street and racing--the new Vortec Bow-Tie head accepts both early-style, six-bolt raised-runner intake manifolds and later-style Vortec manifolds.
One of the design details that will immediately identify the head is this cast-in Bow-Tie symbol on the outside of the casting.
The key to the new head's performance capability is taller, narrower intake runners, which help increase velocity while maintaining volume. The small-port head has 185cc intake runners, while the large-port version boasts a tunnel-like 215cc runners.
Another clever design detail is the "GM" logo cast on the base of each intake runner.
The deck surface thickness of the Vortec Bow-Tie head is 0.450-inch.
Valve cover mounting provisions on the heads includes both early-style perimeter covers and the later-style center-bolt covers.
The heads come with screw-in rocker studs (not seen here). Note the Vortec insignia, too--an identifier of the new heads.
The combustion chamber design is not unlike the aluminum Fast Burn head, including a kidney bean-shaped chamber that promotes a quick, complete light-off of the air/fuel charge. The chambers displace 65cc.
When ordered as an assembled head, the Vortec Bow-Tie comes with the same 1.32-inch-diameter, 332-pound springs that were part of the LT4 engine. With them, the camshaft can't exceed 0.530-inch lift.
Big, stainless valves are used in the Vortec Bow-Tie. The intakes measure 2.00 inches in diameter, while the exhausts are 1.55 inches across.
McLaren Performance performed 108 dyno pulls during 515 hours of development, comparing the Vortec Bow-Tie against other GM heads on a ZZ4 crate engine. There were 23 combinations tried, including a variety of intake manifolds, camshafts, rocker arms, and carb spacers.
As per GMPP's recommendations for the ZZ4 crate engine, a 650-cfm four-barrel carburetor was used for all the dyno test sessions.
When the dust settled, the new iron head from GM Performance Parts outperformed the stock--though admittedly smaller-volume--aluminum cylinder heads of the ZZ4, as well as the aluminum Fast Burn head. With the small-port Vortec Bow-Tie, the Hot cam, 1.6 rockers, a single-plane intake, and a 2-inch spacer, the ZZ4 generated a best average of 391 hp. A similarly configured setup with the large-port heads made 386 hp, on average. Both figures are a staggering jump over the stock ZZ4's 328.5hp average.
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