Aftermarket exhaust and gas mileage

I have a 2008 scion tc and i want to get aftermarket exhaust will i get better gas mileage or will it decrease? i would like some second opinions on this.

Getting an aftermarket exhaust for a brand-new car would seem to imply that you are looking for a “performance” exhaust system. One of these systems will reduce backpressure slightly, and as a result, top-end engine power will be slightly increased.

In theory, it might also yield slightly better gas mileage. However, since the biggest single factor in a car’s fuel economy is actually the driver’s behavior, one of these exhaust systems may have the opposite effect on gas mileage. Once you have installed this accessory on your car, it is very likely that you will be driving the car so as to exploit the effect of that new (loud) exhaust system, at which point your gas mileage will decrease very badly.

And then there is the question of what other effects this aftermarket system might have on your engine. If the backpressure is thrown off from the factory’s original specifications, it is possible to wind up with burned exhaust valves, and that would not be covered by the factory warranty. In fact, this exhaust system could be a very convenient excuse for the dealership to void the warranty in the event of any engine-related problems.

If Toyota offers a “performance” exhaust system for this car, then you might want to consider that one. Installing any aftermarket equipment on a new car makes you susceptible to voiding of your warranty, but this can be avoided by using the vehicle manufacturer’s own performance
equipment.

If you are looking for improved mileage, don’t bother. Any change is likely to be minor and may be higher or lower. Like VDC I would have to guess you are looking at some sort of “performance” system. A standard system is very unlikely to result in any measurable change in mileage.

By far, the biggest restriction to air flow through the engine will still be the throttle butterfly valve. The only way to reduce the drop in pressure across the throttle is to open it more which causes the engine to make more power and use more gas, or to upshift at lower rpms, possibly even regearing the car so the engine isn’t spinning so fast at cruising speeds. At lower rpm, the engine doesn’t need to have the intake restricted so much to make a given amount of power. Another way to reduce throttle valve airflow restriction is the old hypermiler’s trick of intermittent engine runs, aka “pulse and glide” where you go down the road with the engine at nearly full throttle for a few seconds and then coast for a long ways with the engine off and then restarting the engine to repeat the cycle.

Sometimes a loud exhaust will improve your gas mileage mostly because you find yourself driving real slow in order to not get a noise ticket.

As per the above posts, don’t waste your money. The manufacturer has tuned the exhaust for best overall performance and economy!! They need every mpg as much as you do! You really don’t want to second gues the world’s most sucessful car company.

If you want to save gas, fine tune your driving style, and you will be amzed at the results.