from the editors of:
GM High Tech Performance
LOG IN / SIGN UP
GET THE MAGAZINE
tech & how to
engines & drivetrain
Chassis & Suspension
paint & body
Best of the Best
GM High Tech Performance
Engines & Drivetrain
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
View Full Article »
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.
Vortec Cylinder Heads
Super Chevy tech article on Vortec cylinder heads
Do-It-Yourself Small-Block Cylinder Head Porting - Tech Article - Chevy High Performance Magazine
Read the tech article on Do-It-Yourself Small-Block Cylinder Head Porting, brought to you by the experts at Chevy High Performance Magazine.
Tech: Port It Yourself - Cylinder Heads - GM High-Tech Performance Magazine
Porting cylinder heads has long been a right of passage for serious hot rodders looking to add power on a modest budget. Check out this Tech: Port It Yourself article - GM High-Tech Performance Magazine
Vortec Cylinder Heads - Super Chevy Magazine
The voting booths are closed and the decision has been made, next up on our engine test is GM's Vortec with its great head design from Super Chevy Magazine.
recent how to articles
How To Install Emissions-Legal Headers on a 2002 Corvette - Fresh Lungs
How To Choose the Right Tire for Your Classic Corvette - Tire Talk
Chevy Performance Tech Q&A - December 2014
How To Build a 1,200 HP LSX Engine - Pump Gas Powerhouse
Chevy Resto Tech - November 2014
subscribe to the magazine
Subscribe and Save 74% off the Cover Price!