Quote:
Originally Posted by sugarwood
SSIs and an M&K muffler reminds me of something I've always wanted to ask, so I am very glad this thread was started.
Does the act of simply replacing a stock exhaust with a less restrictive header exhaust automatically increase horsepower? Or does the engine need to be re-tuned or rechipped to take advantage of the new exhaust? I would think the latter since the engine timing and cam is the same as it always was, right? Is it like having a larger diameter garden hose but not turning the faucet any higher? To take advantage you need to turn up the faucet?
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it depends on many things.
This is a great primer.
Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine
The tuning part is a bit beyond my understanding, but in short if you put on an optimized header, that reduces back pressure at the exhaust valve. Thus exhaust gasses exit more easily at peak torque. This lessens exhaust gas contamination in the combustion chamber. The denser air/fuel then burns faster. This allows a reduction of timing, and thus lessens your combustion fighting against the piston as it travels up to tdc. This improves efficiency of the engine, giving moe power. Thus tuning to the new exhaust is needed for ideal power.