Pit Stop: Are Exhaust Headers a Waste of Money on the Street?

QUESTION

Lately, on several of the Corvette forums, the “experts” have been saying that tube headers on an engine are a waste of money. They say they only make the engine louder. I always read that headers are good for at least a 10-percent increase in horsepower.

I’m the original owner of a 1968 Corvette with a 327 L79 engine with Hedman headers. Have I been wasting my money keeping headers on the car?

Michael Raymond
Santa Clara, California

ANSWER

Full-length, long-tube headers nearly always improve torque and power over stock, cast-iron exhaust manifolds. But you can’t necessarily put a specific hard number or a percentage on it. The more radical the engine in terms of its cylinder-head flow and camshaft, the greater the amount of power increase you’ll see with headers. With headers, expect to see measurable torque and power improvements above 2,000 rpm (most dynos can’t test below that level), with the greatest improvements occurring upstairs. This assumes you don’t go overboard and install headers that are too big for the rest of the combination or the engine isn’t so feeble its exhaust ports get saturated upstream of the headers: Think of wheezers like those old front-wheel-drive GM 173ci (2.8L), V6, 60-degree motors back in the 1980s. In other words, it’s not just headers alone, but the exhaust-port efficiency taken as a whole.

My colleague, Richard Holdener, once did a header-versus-stock exhaust manifold smackdown on a grocery-getter Chevy 350. The 9.7:1 motor had late-1970s No. 882, 76cc chamber, cast-iron “smog” heads; a stock flat-tappet hydraulic cam (about 0.190 degrees duration at 0.050); and (ugh!) a Rochester 2G two-barrel carb. On a Chevy, you can’t get much milder than that! GM “Ram’s Horn” cast-iron exhaust manifolds (similar, if not identical to those typically used on Corvettes) were compared to long-tube street headers with 1⅝-inch primary tubes and 3-inch collectors. Both the stock manifolds and the headers were hooked up to a full Hooker Headers 2.5-inch exhaust system with mufflers that were designed to fit 1970-and-later Camaros.

Even at this level, as tested on Westech Performance’s SuperFlow engine dyno, the headers raised both power and torque throughout the motor’s 2,200- to 5,100-rpm test range. At the peaks, headers gained 6.6 lb-ft of torque at 3,000 rpm, with a 6.7hp increase at 4,500 rpm. Throughout the entire sweep, on average, headers were worth 6.3 lb-ft and 4.4 hp. Gains tended to be the highest over 4,000 rpm, with an improvement of more than 9 numbers occurring at 5,200 rpm after the power began falling off. The engine was too mild to run safely above that point, but with a larger-cam, this trend indicates 5,500-plus-rpm improvements would likely be greater.

Your L79 327 was factory-rated at 350 hp, using GM flat-tappet hydraulic cam PN 3863151 (0.447/0.447-inch lift, 0.221/0.221-inch duration at 0.050, 114-degree lobe-separation angle). Its static compression was claimed to be 11:1, the cast-iron “fuelie” heads with 2.02/1.60-inch valves were decent for that era, and its Rochester Quadrajet carburetor flows more than 700 cfm. With 1⅝x3-inch headers, 2.5-inch dual full-length exhaust pipes, and modern performance mufflers, I’d expect about a 10- to 20hp gain over stock cast-iron manifolds.
In the Corvette’s case specifically, don’t run headers through a restrictive post-collector S-turn into any funky side pipes. In that case, the S-turn and side pipes would become the cork in the bottle.

Contacts

Hedman Hedders; Whittier, CA; 562.921.0404; Hedman.com
Hooker Headers (A Holley Performance Brand); Bowling Green, KY; 866.464.6553; Holley.com/brands/hooker/
Westech Performance Group; Mira Loma; CA; 951.685.4767; WestechPerformance.com

Ask Marlan A Tech Question: pitstop@HotRod.com

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