Why Aren't Headers Standard Equipment?

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On my vehicles, the cast manifolds are works of art. So intricate and beautiful that they crack at the fourth exhaust port. Given the age, replacement isnt an option. I run long tube headers. They sound better, little else can be said for them.
 
I fly a 4cyl 200HP Cessna Cardinal RG. It originally came with one muffler per side, with a single tailpipe. Not exactly a tuned exhaust.

I recently purchased a "powerflow" exhaust, which is simply a tuned 4-into-1 header, with very long primary tubes, tuned for the LOW RPM of aircraft engines.

The difference in performance has been significant. I have no way to measure HP, but I can measure rate of climb and service ceiling. I gained about 300 feet per min rate of climb. Also gained about 1500 feet service ceiling.

It also increased my fuel consumption. More HP requires more fuel.

Contrary to claims about increased economy, I do not see any practical flight conditions where I can achieve better fuel economy. Put another way, a given amount of HP requires a given amount of fuel. The restrictive stock exhaust simply limited the maximum output of the engine, but when the throttle is reduced, to a given output, fuel flow matches the work required.
 
Airplane engines are a little different, though. They are a wonderful example of an ICE turning something and adjusting output based solely on throttle and mixture (yes, Cujet, I know about variable pitch props, I'm just simplifying). No transmissions, gearing, or computer controlled injection.
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Most of the textbook stuff one reads on ICE theory fits much more closely to the airplane engine than what we see in a car these days. Most of us certainly have seen improvements in various vehicles thanks to exhaust.
 
Why? Because it is not a good use of the R&D and production money. You can get much more out of the same cost if your car is designed with better engine (i.e. variable valve timing or variable intake opening) than different tubing length / width.

Also a much bigger header only increase top end HP at the expense of bottom / mid range, so why bother?

Mazda use it for their skyactiv motor because of their piston and injector design that can benefit more from it. It is not as useful for the more common / old school engine design.
 
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