Quote:
Originally Posted by JBurer
Carlos gave me some insight on how he determined length via trial-and-error... something to do with being able to see a change in the metal color and that telling him when the fuel had expended most of it's energy. He'd cut the pipe there and weld up the rest of the exhaust.
When I dynoed my car, I did have a higher peak horsepower with the new manifold, but noticeably slower spool time. This was the old Dynamic Turbo RX-7 from Miami in the late 90's.
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It is no black magic, it is common knowledge of 4stroke engine and turbochargers.
Since spinning the turbine is all about energy, the less energy you waste before it reaches turbine, the best spool and power you get as it is not the speed of the gases that turns the turbine, it is the heat energy of the exhaust. The faster you get the gas onto turbine blades, the less energy is wasted by cooling (=heating the exhaust manifold). This is the reason for opting for smaller headers.
The reason behind the most power with long headers was because the turbine was single inlet type and the primaries were just separated longer thus not letting the pulses to work against each other. Twin turbo (one bank of cylinders feeding each turbo) or twin-scroll turbine housing do the same with very short headers.
And when searching for the point where most energy is expanded (though I cannot see any reason why one needs to find it) can be found easier: using EGT sensor and moving it in the exhaust.