Any engine builder will inform you how vital cylinder heads are to power and performance, so enthusiasts trying to spruce up their budget Chevy 305 small-block (SBC), or the larger and more popular 350, should find GM’s Vortec heads a worthwhile investment.
People within the know often claim that these cast-iron Vortec heads from the ’90s are the best-flowing SBC head design from the factory. The argument is backed by actual flow numbers, with this Hemmings comparison showing Vortec heads improving intake flow by as much as 30 CFM (cubic feet per minute) during maximum lift.
Unsurprisingly, the improved flow characteristics allow the engine to breathe higher and unlock more power, evidenced by MotorTrend gaining an additional 50 horsepower from a ZZ4 small-block after bolting on a pair of stock Vortec heads. Other advantages, when put next to a regular small-block head, include improved engine efficiency, because of the Vortec heads’ ability to run the next compression ratio.
Many post-Sixties small-blocks featuring flat-top pistons and 76-cc combustion chambers are sometimes clocked at running 8.5:1 compression, which, when swapped with Vortec heads that use 64-cc chambers, see their compression ratio jump to 9.8:1, leading to higher efficiency and a 5% bolt-on increase in horsepower.
Vortec heads should not without flaws
It’s value mentioning that Chevy’s Vortec heads have performance DNA, featuring 170-cc intake ports borrowed from the Gen-2 LT4 small-block’s aluminum head design. Nonetheless, the valves were less aggressive and far smaller than the perfect of Chevy’s Double Hump small-block heads, measuring at 1.94 inches for the intake and 1.50 inches for the exhaust. Factory Vortec heads got here in two castings: 10239906 (#906) and 12558062 (#062), identified by the sawtooth mark on them. While each 906 and 062 heads were virtually similar, the 906s initially had two versions: one with a single-angle valve grind and the opposite with a three-angle valve grind. These Vortec heads fit all SBC engines (from 1955-2002), excluding LT1, LT4, and LS-style engines.
Before you select on these budget Vortecs, there are just a few things to take note, starting with the intake manifold. GM decided to vary the Vortec’s bolt pattern from the standard small-block’s six-bolt pattern to 4 per side, meaning the intake manifold is now an eight-bolt arrangement. The bolt size and layout are also different. Something else to notice is that running Vortec heads would require using center-bolt-style valve covers and Vortec-specific gaskets, which, depending on who you ask, may or might not be annoying.
Cracks are also not unusual with these, especially since they’re from the late ’90s, a time when Chevy had just a few unique pickup trucks in its lineup. You possibly can, in fact, buy these heads refurbished or brand-new, because the aftermarket support is pretty comprehensive. In today’s sea of performance aluminum heads, these modest cast-iron Vortecs seem underappreciated and arguably deserve a better look.
This Article First Appeared At www.jalopnik.com
