I drive a 98 4cyl auto LE camry...new intake is my only mod. anyways, when i first got it i drove with the o/d on because thats how the i received it. at some point i took it off and found that i really liked the incresed engine braking and general control over the car. a few months later, the only times i put it on are when im merging on to highways or such. is there any decrese in fuel efficency or other negitive side effects that should cause me to keep it on?

Don't know about the exhaust and the effect o/d being on or off will have, but I do know that o/d is best suited for highway driving. The reason for o/d is to get your engine to run at lower RPM's while on the open road, thus burning less gas. In actuality, you should be turning it OFF when merging to keep it from going into that upper gear. If you want more response, then keep the o/d off and you will have more response on the gas pedal at higher speeds, but...you will burn gas more quickly.<br><br>I usually turn my o/d off when I'm driving in downtown traffic, merging into traffic on highway, or getting ready to pass someone. Also, when driving on mountain roads or up steep hills, it'd good to turn the o/d off so that the engine won't struggle to pull the car at such low RPM's. For that...you need a higher RPM.<br><br>Hope that helps you some. If you're unclear...call a dealership and have them explain the whole o/d thing.