By 
Unscrupulous Swap Meet Hawks Are Peddling (for More Money) 2.00-inch Ramʼs Horn Manifolds for the Bigger 2.50-Inch Design.
The Lighter and More Efficient ’04 Z06 Manifolds Make a Great Alternative.
Over the decades, Chevy Ram’s Horn V-8 exhaust manifolds have been relatively acceptable for general operation and high-rpm use. They do not compare favorably to four-tube or tri-Y headers, but we’ve never talked to a user who did not find them acceptable. This year the factory released its latest LS2/ZO6 cast-iron, four-tube manifolds and they look to be the best-flowing factory manifolds ever produced.
Ram’s Horn Exhaust Manifolds and Fakes
Anyone who has been around for a time knows that the ’62-’70 327 and 350 Corvette cast-iron manifolds with the large 2.50-inch inner outlet diameter are the best-flowing factory cast-iron manifolds of their era. Similar-looking manifolds with smaller-diameter exhaust pipe outlets for the 283hp and 250hp 327 engines were also produced. These had 2-inch inner-diameter exhaust outlets, not 2.50 inches.
We have heard lately that swap meet hawks are trying to sell these smaller-diameter exhaust outlet manifolds as the real deal, and they fool you by measuring the outer diameter of the wall, not the inner diameter of the outlet. So do not be taken.
We include in this story a few different Ram’s Horn exhaust manifolds for you to be wary of, plus two donut gaskets, one 2.5-inch and one 2-inch. If the Ram’s Horn manifolds you see do not accept a 2.50-inch-diameter donut gasket, they are not the real deal. The 2-inch manifolds are everywhere. As you can guess, they have little resale value, which is why there’s a hoax.
New ’04 Z06 Exhaust Manifolds
If you need high-flow, close-fit, cast-iron exhaust manifolds, check out these new ZO6 Corvette units. The manifold casting number on the right side is 12561256. The left side is 12561255. Shown here are factory originals without the heat shield, as well as a pair sent by Greg Thurmond at GTS Customs to JET-HOT Coating for wall smoothing and inner/outer coating.
These four-tube manifolds look to be the slickest Chevrolet has ever produced for a production engine. They definitely required further review. According to GM Powertrain’s Randy Fox, these new LS2/ZO6 exhaust manifolds flow 4 percent better than the current and past LS1/LS6 exhaust manifolds. Fox also let TheAutoBuilder know that the real story on these manifolds is their lightness. They are said to be 33-1/3-percent lighter than the manifolds they replace. They have a state-of-the-art 3mm wall thickness, while the LS1/LS6 exhaust manifolds have a 4mm-wall thickness.
