Exhaust Manifold: Built for Boost

Posted by Rob 0 comments
I’ve found eBay turbo manifold zen, with a little support.

The odds of finding an off-the-shelf FE3 turbo manifold are pretty slim. The odds of finding an off-the-shelf BP turbo manifold are quite good. This is good news since the exhaust port spacing on the FE3 and the BP are similar. They’re close enough that a tubular BP manifold (turbo or not) can be used for an FE3 with some modifying. How it’s used depends on the cylinder head flange. If the flange is tightly contoured to fit the BP head, then it will most likely need to be replaced with an FE3 specific flange due to the lack of space for drilling new holes, and/or elongating existing. If it’s a rectangular, then it can probably be modified to fit the FE with some grinding, drilling and hole elongating. Such was the case with my manifold.

New holes were drilled, other existing holes elongated and the top inside of the flange was angled to avoid interference with the head. Then the number 1 and 4 exhaust ports were widened to better match the FE3. Not ideal, but adequate for a budget build.

Once mounted, the eBay manifold fit nicely without any interference. The biggest issue with these headers is tearing at of the tubes at the head flange. This surely comes from the questionable metal quality, thin wall tubing and the weight of the assembly (header, turbo, downpipe…) cantilevered off the head flange while being subjected to vibration/shock.

I decided to address this using a support arm. This is a fairly typical approach with long tube headers and turbochargers when attempting to ease and stabilize load. Rather than attaching the arm to the manifold, I attached it to the downpipe (which is bolted to the turbine housing) and then mounted the bottom to the motor mount adapter plate. I originally used a thin wall square tube which tore shortly after installation. I repaired the torn tube by adding a solid rod inside the tube to which rod was then welded to the bottom mounting tab. The rod appears to have added the strength needed to support and control the load, as it has lasted since installation. I’m not the only one that has seen success with this armature approach. Another Miata owner running this same manifold with a support arm on a BP has several years of daily driving, autocrossing and track events without failure.

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