Isn't the backpressure of current autos calculated into the fuel injector mapping? And by reducing backpressure, some of the air/fuel that's pulled into the cylinder escapes out of the exhaust valves (because there wasn't sufficient backpressure to keep it there) so when the cylinder is compressed for combustion, it won't be as packed with air/fuel as it should have been?

I don't know much about this subject. This info was something I recall reading in a racing book/magazine a few years back. The article was about matching exhast systems to engines and then tuning them in correctly.

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