Exhausting Development

Factory Double-Wall Exhaust Dilemma

It’s hard enough to make power when you know the playing field. Fresh engine, right rearend gears, perfect transmission setup – they all contribute. But when something as simple as an exhaust pipe that appears to be fine turns out to be a major performance deterrent, that’s a tough one.

For Mark Hoffman, his big-block ’68 Camaro had all the right stuff – and still seemed to perform in a lazy manner when he stepped on the throttle. After thorough research he still couldn’t find the problem, but it was clear further investigation was required.

Mark Hoffman’s beautiful ’68 big-block Camaro is original in many ways, including the exhaust system. It was this component that turned out to be the culprit in robbing him of performance.

A stop by the local exhaust shop for an upgrade to a Flowmaster netted a total change in Camaro personality. Not only did it improve the sound, but it woke up a sleeping giant. The change was remarkable and only set in motion a thought that something must have been wrong with the original factory exhaust. The original system did not appear damaged by the flat spot in the double wall tubing where it tucks under the frame. That was not the case.

Cutting through the double wall tubing revealed an interesting problem that from further research proved to be a common problem with these exhaust configurations. Over time, heat had caused the inner tubing to separate reducing the overall internal flow by as much as half. In effect, the tubing is reduced to less than a one-inch diameter total area.

For anyone with a vehicle with an original style exhaust system of this type, if your vehicle is experiencing any kind of reduced power over time, this might be a good place to check

This is what a double wall factory exhaust tubing looks like when it goes bad. This was not damaged by impact but simply through heat and time. It was extremely restrictive - as you might imagine.

The big block 396-cid engine features most of the original equipment but a few dress up items. The Flowmaster 3-inch exhaust was a logical and beneficial change.