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I'm planning on a custom manifold and dual exhaust for my JD as well, and down the road, perhaps a supercharger too. I know for a fact these mods are not allowed in any classes in our area (not even unlimited), but this is just going to be my toy and not a competition rig. Although, it would be nice to pull once in a while, just to take on the sled and see how it'd do. The problem with most of the 2-cyl JD's is the one-piece intake+exhaust manifold. I saw a custom one made from a plate of 1/2" cold-rolled steel with some plumbing fittings welded on to form the intake runner and exhaust elbows. On this particular tractor, the manifold was the product of necessity. The engine was running very high compression and would turn the stock manifold red, then overheat within a couple minutes of starting. His custom manifold allowed the engine to breathe and run at normal temperature. I wouldn't call it beautiful, but it was nicely constructed. I have an idea for how I'd like to make a manifold for my JD: The intake runner should be close the location of the stock manifold's, so the throttle linkage doesn't have to be tweaked, bent and redesigned a whole lot. It'll also prevent running into clearance issues with the carb and fan shaft. I'd like a connection between the two exhaust locations, running along the top of the manifold. Not a full-size tube, like the 2-in-1 design of the stock manifold, just enough to allow some cross-flow. The exhaust runners should have flanges to bolt on the exhaust stacks (with gaskets). That way, the manifold can be compact and easier to install/remove (as compared to having a long exhaust tube sticking up on each side). Basically, I plan to start by taking measurements from the gasket and stock manifold. That'll allow me to locate where the ports will be, where the carburetor flange should be, fastener hole locations, and how much room I have to work with for the exhaust routing. Should be a fun and challenging project. Good luck! I'm working on the same dream. I do have some safety concerns, and am working out where I want the pipes to end up and where I may want to add heat shields to protect other engine parts and people moving around the tractor.
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