stock exhaust - it's unbelievably quiet! Why?

Geoff-AU

HKS Hi-Power

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There is a post on here by a fussy bastard who's almost as particular as me and he said the HKS Hi-Power has zero drone at any load or RPM point. He's right. HKS have done some brilliant engineering on this one.

This exhaust is perfect for me - I want something quiet when just cruising (and at light throttle below 3000 RPM it sounds almost as quiet as stock) but if you stomp on it then it gets a really nice sound (which is also what I want). A friend drove mine on the weekend and said he was "changing gears just for the sake of it" so he could listen to the exhaust.

JARblue

And this is why everyone gets worse gas mileage after a new exhaust install despite the fact that a freer flowing exhaust should get better gas mileage all other variables being equal.

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dave11

Isn't that the truth!

Geoff-AU

Only true at light throttle / load.

At full throttle you have more airflow, which means more fuel gets injected, and your economy will be worse. Often, because you're flowing more air than a stock car, you hit new map cells that are tuned very conservatively because the stock engine doesn't normally go there. Those cells are usually richer and more retarded than normal, which also hurt economy.

Unlikely to happen in an NA car where bolt-ons are only worth a few percent but turning up the boost in a 90's turbo Nissan absolutely does this "Rich & Retard" effect on the stock ECU.

JARblue

No one cares about gas mileage at full throttle though

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