The X Factor
Though technically compromised, split headers offer a construction option that a single-collector header can't: we can run an X-Pipe.
An X-Pipe combines both headers' downpipes into a collector of sorts and then splits them back into two exhaust pipes. The collector's smaller diameter briefly increases the velocity of each exhaust charge, which reduces the dynamic pressure at that point. That, like the header collector, gives each exhaust charge a lower-pressure/higher-velocity place to go. From there the exhaust gases that would ordinarily travel along one pipe get the option of going through both exhaust pipes. The design gives the engine its best chance to build power across a broad speed range, something that made NASCAR builders adopt it. And that really benefits smaller engines that can't afford to spare any power.
As appealing as the power gain is it's almost secondary to another reason: smaller exhaust pipes. The engine doesn't care what the exhaust looks like downstream of the X so long as it maintains the right combination of volume and velocity. The 2 1/4-inch inside diameter of the pipe we calculated has 4 square inches of internal area. A pair of 1 5/8-inch inside-diameter pipes (16-gauge 1 3/4-inch OD pipes) has 4.15 square inches of area, which is close enough for our purposes. Yes, that means the pipes neck down after the X but remember that the X gives each exhaust event the option of going through both pipes rather than just one.
Most suppliers, Patriot included, carry bends in all of these sizes. And because the two pipes are small they'll prevent this Stovebolt from droning like a heartsick calf. For good or ill the X will also diminish the crackle that Stovebolts are prone to make when split into two smallish pipes.
Unfortunately, X-Pipes for smaller, lower-performance engines like this don't exist due to a lack of demand. That means we had to build ours. It really isn't tricky in the least, though. In fact building your own X gives an exhaust the potential to fit a car like a glove.
It took some thinking but we achieved our goals without sacrificing power or sound, though we don't have the opportunity of demonstrating the sound here! So you'll have to take our word for it: mandrel-bent exhaust systems and X-Pipes offer benefits beyond bragging rights.
11. Woolery built the X by first marking two 2-inch U-bends perpendicular to their radius. He brought the lines back to the tube's centerline.
12. He then plotted more lines on each side of the area at the 45-degree mark. Then he cut along those lines.
13. Rotating those cut ends 180 degrees transforms a U-bend into a straight with a jog in it.
14. It wasn't necessary at this point but Woolery welded up one leg of each jogged section prior to cutting along the line perpendicular to the tube's centerline.
15. The modified U-bends meet at their cut sides like so. At this point he welded the halves together to form the core of the X-Pipe.
16. After Woolery welded the second set of legs to the other side of the X-Pipe he jacked up the finished assembly and welded it to the downpipes. Until now all photos show the front of the car to the right but this shows it to the left.
17. We wanted a traditional sound so we chose traditional mufflers: Patriot's Smithys. We built the X from 2-inch pipe to suit the Smithy inlets and necked down the outlets to fit the smaller 1 3/4-inch pipes. We designed the system around the longer 26-inch cases so we can go shorter if need be.
18. The outlet pipes are pleasantly simple. Woolery cut one U-bend apart at the middle to create the rise and return. He cut the legs off another U-bend to make the arch. He welded that pipe together straight.
19. The pipe closest to the car's centerline clears everything perfectly, hence the straight shot. The one on the outside would've hit the damper body so Woolery offset it a touch.
20. The offset was simple: Woolery just kicked it over enough to clear. That put the tailpipes closer together, a look that a lot of six-cylinder enthusiasts embraced in the past to distinguish their cars from the V-8–powered machines. The foreground is the muffler side.
21. Woolery then jacked up and aligned the tailpipes. He set the gap between the pipes the same way as he used in the front: by clamping them together with 3/4-inch plywood between them. He welded tabs between the pipes to maintain their alignment.