by samandkimberly » Sat Aug 11, 2012 9:29 pm
I've been looking closely at the stock headers. The their ID is about 30mm which is the same as the exhaust ports, not ideal, but not horrible either. But there are 3 obstructions in the stock header: first, there is a big chunk of weld in the ID of the header right at the exhaust port from welding the flanges on. Nothing that can't be solved by running a 1 3/16 end mill in there and filing a little, or just going at it with a die grinder. Second is a similar buildup of weld, and a generally crappy transition in the collector where the two head pipes join. I solved this by cutting the collector off with a hacksaw, cleaning up with a die grinder, and rewelding. Lastly, the collector/header is about 39mm ID, which translates to a slightly smaller area than the two head pipes. I'm leaving this alone for now, but I'm sure a new collector going to the muffler, maybe 1.75 tube would bring benefits and not be too hard to do for anyone with basic welding skills.
Of course a race header will be better for max horsepower. But the stock system has a lot of potential for improvement with only a couple of hours of work and may be better for a hot street setup.
Sam