The third-generation Corvette is perhaps the most-overlooked model of all ‘Vette styles. Despite being saddled with carrying the Corvette nameplate through the smog years, some of the earlier models were factory-equipped with decent small- and big-block engine options. The focus of our article today is a 1969 Corvette stuffed with a Tri-Power 427 cubic-inch big-block engine that produced 435 horsepower upon delivery, and we’re going to release the sound and fury in the chambers by installing a set of Doug’s Headers sidemount headers and exhaust pipes – which offer good looks and easy installation to go along with the legendary Doug’s Headers performance and sound.
Big or Small, Doug’s Has them All
Doug’s offers these items to fit both the small- and big-block Corvette from 1963 to 1982, with appropriate variations in tubing size and dimension for the various engine styles. All of the part numbers feature 3/8-inch thick flanges to provide solid sealing characteristics, and all tubing is constructed from 16 gauge steel.
Thick 3/8-inch thick flanges help to keep the gaskets sealed up nice and tight, and provide a solid base at the cylinder head.
The Doug’s Headers product is designed to be at the premium end of the spectrum – these aren’t your garden-variety headers welded up by a guy working out of his home garage. “Our difference comes down to quality – we use a 3/8-inch thick flange, the gaskets are a premium HTX material, and we even buy the tubing direct from the mills. In addition, after we bend each tube, each tube is hand-polished to remove any stress risers or grip marks that might exist because of the bending process before it is coated or chromed. All of these things help the product to look better and last longer,” says Doug’s Exhaust R&D Manager Don Lindfors.
The small-block headers come with a standard metallic ceramic thermal barrier finish [PN D380], but are also offered in black hi-heat finish [PN D380-B] and chrome [PN D380-C]. Small block headers feature 1 7/8-inch primary tubes and fit all of the 265 to 400 cubic inch engines. The chrome big-block headers that we used in our installation [PN D381-C] have much larger 2 1/8-inch primaries and fit all big-block engines from 396 to 502 cubic inches in the C3 bodystyle. The big-block headers are also available in metallic ceramic [PN D381] and hi-heat black [PN D381-B] finishes.
Left - Tubing is bent from premium 16-gauge mild steel and polished before coating or chroming. The company feels that this extra step helps to provide a top-quality product. Right - These heat-resistant isolators keep the sidepipes firmly attached.
Practical and Cool
“The tube-routing design of these headers was actually done way back in the early ’70’s, and they were made for a road-race team to be able to get a good-sized exhaust on the car since the Corvette’s stock tunnel doesn’t really provide room for exhaust to run under the car,” Lindfors explained. “It wasn’t a cosmetic decision at the time; it was really designed to be able to get a big free-flowing system on a lowered, road-race car.”
The three muffler options – from left, the reverse-flow muffler, the standard glasspack, and the high-flow glasspack.
The 4-inch diameter side tubes are also offered in all three finish styles [PN’s D930, D930-B, D930-C], and bolt to the existing holes in the Corvette’s rocker panel. They are a clamp-fit to either the small- or big-block headers, and three different muffler inserts are available. The standard glasspack insert [PN D950] offers a throaty sound but quiets down the engine’s output level to keep the folks in your HOA happy, while the high-flow glasspack [PN D952] offers – yep, you guessed it! – higher flow, and an accompanying sound increase to go along with it. For the hardcore, the reverse-flow muffler option [PN D951] serves up the best performance, but the most noise.
The sidepipes are a clamp-fit to the header collector.
Although they look like a tight fit, this project could be accomplished easily on a Saturday with plenty of time left to hang out in the pool.
Easier Than You’d Think
We headed down to the Doug’s Headers R&D facility in Irwindale, California, to follow along with the installation of the complete system on Greg Raymond’s gorgeous red ’69 Convertible C3. Installation of the complete system is fairly simple – almost before we had the camera out, the guys were just about done with installing the headers, and then it was on to the sidepipes, which didn’t take much longer. “This system is much simpler to install than you’d ever believe by just looking at the header. Removal of the manifolds on both small-and big-block engines in this Corvette generation is pretty simple, and because of the way these headers slip up from the bottom, it slides in there real easy,” explained Lindfors.
Since there is plenty of room to work with in the chassis for the headers, which pop into place from underneath the car, the biggest struggle (which actually wasn’t much of one) was getting the exhaust manifold gaskets lined up and in place. Greg selected the standard glasspack mufflers, which clamp to the collectors and take a few minutes to wiggle into place. A couple of heat-resistant isolators are used to attach the sidepipes to the existing holes in the Corvette’s rocker panels, and that’s about it. A couple of hours over an afternoon, and new life has been breathed into this C3.
Development work is a tedious process, but the Doug’s Headers team keeps a couple of goals in mind when producing a new set of headers for a specific application. “Whenever we design a header, we bring the car in, and it will generally tell you where it wants the tubes to be because you’re working with limited space,” says Lindfors. “What we do from there is figure out how to use the lengths and diameters that we need and try to optimize all of those lengths so that they are as close to equal as possible in each application. Of course, it’s important to remember that every time you put a bend in the tube, it changes the effective length of the tube because it slows down the flow. Airflow is laminar – it wants to go straight, and as soon as you start bending it, it wants to slow down. We have to look at all of those things to make sure we achieve the goals we are looking for.”
These fit nice and tight to the body, but with any side-mount exhaust care must be taken when exiting the car unless you want some new tattoos – of the crispy-skin kind.
The End Result
The whole install could be done in three or four hours – Don Lindfors, Doug’s Headers
How’s the sound quality, you ask? Great – it’s a rich, throaty growl that perfectly matches the character of this big-block classic, without any annoying drone or harmonics. And although we didn’t dyno on this particular car (as the car is actually owned by an employee), Lindfors says that a typical installation will see anywhere from a 10-15 percent horsepower gain depending on the health of the car.
We got a chance to borrow the car after it had yet another swap, and was wearing the matte black version of the side pipes with the D952 Maximum Flow inserts – the least-restrictive (and loudest) of the three silencer choices. Here’s what it sounds like:
Owner Greg Raymond couldn’t be happier with the way these side pipes sound and perform, and we think they make an already gorgeous car even better looking with that glorious splash of chrome setting off the deep red color of the Corvette.