In general, the word "Chevy" is usually involved when "headers" are mentioned. That has seemed to be where many people's experience or knowledge of "headers" comes from. Reason? Chevies NEED help in the area of exhaust manifolds. They did have some '60s Corvette cast iron Rams Horn manifolds with 2.50" outlets, but the normal version was more like 1 7/8" to 2.0" in diameter. NOT to mention their smaller pipe diameters. So, for power and efficiency, they need headers for best results.
Chrysler products, usually had better under-car systems (as to pipe diameters and muffler restrictions). As normal as the factory Chrysler exhaust manifolds might look, they were better than what GM used, from the looks of them, to me. TTI does have larger pipe diameters, front to rear and can make the lead pipes to fit the manifolds you are using.
By observation, ANY header with the collector under the floorpan WILL hang too low to not scrape things like speed bumps and such. Even some sharper entry aprons for businesses. Such things might seem minor things to put up with, BUT when you have to slow down to do those approaches and such, THAT means everybody behind you is having to alter their speed so they don't collide with your vehicle with headers. The "shorty" block-huggers that do not have collectors are better in that respect.
The shorter block-hugging headers are not much better than normal cast iron manifolds, as to the pipe length to the flange. Basically just getting the exhaust gasses to the flange and the head pipe with no tuning effect from individual pipe length. They will flow a bit better due to the smoothness of the inner pipe areas, but an Extrude Honed stock manifold would be very similar WITHOUT all of the hassles of headers. Header gaskets are also critical to get the reinforced, high-heat versions rather than the soft ones that used to come with the cheap headers of prior times. If the header bolts ever got loose, the gasket would blow out . . . more maintenance issues, so better to use the better ones to start with.
Years ago, somebody put a pressure/vacuum gauge on their exhaust system. They discovered that "back pressure" was nil until rpm got over about 3000rpm or so. Normal driving? Not enough to worry about. Under WOT power over 2500rpm or so (think 4bbl secondary opening in "passing gear"), then back pressure happened. Under normal highway cruise situations, not much real advantage in efficiency to headers.
The reason so many OEMs started using tubular exh manifolds was that the tubes were not the heat sink the cast iron manifolds were. More exh gas heat got to the cat converters quicker to get them fired-off for better cold start emissions performance. In a time when OEMs did not want to spend the money on heated oxy sensors. Maybe a few more horsepower, too, but by the time those few horsepower get to the rear wheels, (multiply the flywheel horsepower by .85 to approximate what gets to the rear wheels on a TorqueFlite equipped Chrysler product, from my figurings years ago). Can an additional 3 horsepower at the rear wheels really be felt and validated anywhere else than on a drag race track? Without knowing it's there?
So . . . chase down some Chrysler B/RB HP exh manifolds and get them extrude honed or just leave them normal internally. THEN save up for the TTI pipes and mufflers of your choice. The HP manifolds will look neat as the TTI pipes support them being there.
The EFI oxy sensor bungs need to be near the lead pipe flanges. Maybe 4" to 6" back, or whatever Holley recommends. It has been documented that self-learning EFI (fully learned) can add up to 2mpg on the highway, due to better fuel atomization, but NO additional horsepower at WOT. Also, no "4bbl feel" as 90% of the possible air flow capacity happens near 75% of total throttle opening. At least fo rthe 2bbl EFIs. Hard to justify the expense of the full-meal kit on fuel savings alone, to me. Other benefits do exist, though, in cold start performance and drivability.
Just some thoughts and observations. YMMV
CBODY67
