Chevy Header And Exhaust Tech - CHP Insider

Dan Lemons Of Lemons Headers Breaks Down Header Design And Exhaust Science

Stephen Kim Aug 1, 2008 0 Comment(s)
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We're all for getting freaky. Whether it's a 632 in a Chevy II drag stud, an SB2.2-headed street machine, or an LS1 in a Rustang, freaks add a dash of zest to a hobby prone to vapid parity. The big question is where freaks get their headers. That's where Dan Lemons of Lemons Headers comes in. If you have a combination for which off-the-shelf headers simply don't exist, Lemons will build you a set in any conceivable configuration. A former employee of a major header manufacturer, he founded his own company in 1997. His first crack at building custom pipes was a set of massive 2.5-inch headers for a customer's big-block '68 Camaro. Lemons somehow got them to fit-and almost overnight he had 10 more orders for his now-famous creation. Today the company specializes in hard-core race headers, where surviving inclement wheelstands is as important as making maximum power. Here's what Lemons has to say regarding header design, exhaust theory, installation tips, and how custom headers are built.

Stepped Primaries
With stepped header designs increasing in popularity, what are their benefits over a nonstepped design? According to Lemons, a stepped header scavenges better than a straight-tube header and broadens the torque curve. Furthermore, Lemons' race collectors utilize a transition cone, which also assists with scavenging. Making sure the flange opening is larger than the head-port opening improves flow as well. "When we are determining the proper tube size for an application, we will sometimes use a stepped header as an in-between size," he says. "For instance, if a 21/4-inch tube is too small for a certain application but a 23/8-inch tube is too large, then we'll build a header that's stepped from 21/4 to 23/8 inches."

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Primary Diameter
"I don't think there is an easy rule of thumb or formula for determining proper primary diameter, and it more often comes down to what works in the real world," says Lemons. "Engine builders and experienced header builders are usually a good source for input. When sizing a header, there are obvious things to take into consideration such as displacement, compression ratio, and horsepower. However, we must also consider the weight of the car. Heavy cars need more torque, as do cars with big tires. On a car with small tires, we may use a bigger tube to kill some of the torque and help manage the shock to the tires at launch, especially if there is nitrous or a blower. If a car utilizes a full exhaust system, we may lean toward a larger tube or collector size, since even a straight-through muffler will still add some backpressure. Converters with lower stall speeds will require more torque than a high-stall converter-hence smaller tubes-while nitrous and blower motors like bigger tube sizes. To illustrate our point, let's suppose you have a 540ci big-block with 14.0:1 compression making 900 to 1,100 hp on motor plus another 300 to 500 hp on nitrous. In a 3,100-pound car with 10.5-inch tires, a 5,500-stall converter, and mufflers, the motor would typically need a stepped 21/4- to 23/8-inch header with 4- to 41/2-inch collectors."