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#4: 10-11-2012, 11:32 AM
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Title: OTM Dir. of Engineering
Location: Automecca
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Originally Posted by 1055 View Post
Im sick of the flex pipe in my one piece manifold/up pipe combo leaking. Aside fromthe minor heat expansion and slightly better fitment, does it serve a purpose? Whats to stop me from removing it and putting in a piece of pipe that doesnt leak?
1) There aren't ANY one-piece tubular header systems that don't leak. It's a "when", not an "if", with very few exceptions.

2) Does the flex serve a purpose? Absolutely. There isn't a "minor" amount of heat expansion, it's actually pretty substantial at high EGT's.

If you cut out the flex and weld in a piece of straight pipe, you will almost certainly crack your header. When the pipe hits 1500F, it going to expand radially and linearly. This is only exacerbated in thin-wall tubular headers. That growth must be mitigated somewhere. Slip joints in lower headers (and the flex in the OE cross pipe) handle this well (though like I said, slip joints are designed to leak unless extremely hot), and a flex in an uppipe help handle this. Eliminate those, and at best you'll get gasket leaks at flanges where they warp. At worst, you'll crack welds. Our headers are on the bottom of the car, in exactly the worst place for environmental exposure, so rapid temperature transitions are par for the course.

Your best option? Go back to a stock header/uppipe combo if the car isn't one run on the bleeding edge more often than not. If it IS a race car, or you think you HAVE to have headers, then replace your leaky flex with one of extremely high quality.

Be warned, though, that unless welded correctly, anything you do will very likely crack at the weld.