We've all heard the talk. It seems to run the gamut from, "Dude-headers are worth 100 hp," to the naysayers who snivel "Headers? They aren't worth the trouble." The truth is actually somewhere in the middle. Because results can vary so wildly, we decided to take a look at some past testing just to see what works and what doesn't.
If you're new to performance engines, and all headers tend to look alike to you, you might want to start with Jim McFarland's treatise on header design on page 62. This will give you the basics on why headers are designed the way they are, and why they don't all look the same. For this story, we're going to perform several header comparisons to shed some light on that age-old question of how much power headers are really worth.
All the dyno tests in this section were performed on different small-block Chevys, but when it comes to headers and exhaust tuning, this same information is completely relevant to any engine-only the header sizes change to match the displacements. This is a relatively busy subject with plenty of variables, but once you get to know all the important characters in this horsepower and torque stage play, the ending is always fairly predictable. Most of all, have fun with this. This is one session involving lots of hot air that's actually helpful.
Headers vs. Cast-Iron ExhaustWe'll start with a very mild Goodwrench 350ci small-block test with stock cam timing. The idea here is to compare the power output of a stock small-block 350 with cast-iron exhaust manifolds and headers. Because this is a mild engine, the peak power difference occurred relatively early in the power curve, with a maximum 34 hp and 53 lb-ft of torque gain at 3,400 rpm. That's an excellent 19 percent improvement in torque. Had the engine been fitted with a decent camshaft to allow the engine to make more power around 5,000 rpm, the improvement would have been even greater. However, this test does point out that even a stock engine will respond to a decent set of headers. As power potential increases with a good set of heads and a camshaft, headers and a free-flowing exhaust system become absolutely essential components.
Test 1: Stock GM Goodwrench 350 with Q-jet and aluminum intake, stock iron exhaust manifolds, a stock camshaft, and a 211/42-inch exhaust system with turbo-style mufflers.
Test 2: The only addition is a set of 151/48-inch Hooker street headers with the same exhaust system.