I'm in the process of attempting to fabricate headers for a 3.8L Ford V-6. It's a special use engine that will be powering a homebuilt airplane using a prop speed reduction unit. This means that the engine will be running most of the time at around 3,900 to 4,000 rpm while in cruise.
The information I'm getting is that the exhaust header tubing diameter should be 1.5", not 1.75. Using 1.75 works fine for an all out competition engine, where it's run at maximum rpm all the time, like at the drags or at a circle track, but for my application, using 1.75" makes the engine peaky and tough to tune the carburator and causes uneven mixtures in the combustion chambers. Since the 3.8 already has a less than perfect manifold for this purpose, it's important to pay attention to information about proper header design.
The exhaust header flanges I have are cut for 1.75" tubes. That's the way most of the header flanges are manufactured, and custom header companies just install cones, or reducers to bring the tubing size down to the proper diameter to run the rest of the tubing.
So I'm trying to find a source for these reducers. Ideally, the reducer should have about half an inch of length at 1.75" before the reduction begins, then about another half an inch at the 1.5" diameter so as to facilitate mating to the rest of the 1.5" tubing.
Any ideas on a source?
Thanks, Corky Scott