Can better Exhaust System give better MPG?

[sad-lumina-owner]

Obviously you can improve your HP by putting on a better exhaust system.

Can this translate into better MPG as well?

[KiwiBacon]

Generally no.

At the power levels that your engine works at for the majority of it's time (i.e. the range which mostly dictates your MPG) the exhaust flows are low and even a really tiny exhaust will produce little restriction.

There are always exceptions though. If anything in your current exhaust is plugged or crimped then you stand to gain something decent.

[curtis73]

It depends on a lot of factors. Improving exhaust flow CAN increase power and efficiency. The increase in power results from more airflow in and out of the engine. More airflow means more fuel requirement, so that part of the equation uses more fuel. If the stock exhaust was a restriction, then you will probably also increase efficiency.

The secret is, if your aftermarket exhaust increases efficiency more than it increases fuel, you'll end up using less "foot" for the same driving style and you might see increased fuel efficiency.

Most aftermarket exhausts advertise more MPG, but it depends on your driving style and engine configuration.

[Johnson16]

Online the same lines.............will a high end air filter increase mpg much? Any other mods that will help?

[MagicRat]

Originally Posted by Johnson16

Online the same lines.............will a high end air filter increase mpg much? Any other mods that will help?

Higher flow filters generally increase air flow at wide open throttle. However, because we do not drive at WOT much, they will not increase mileage appreciably, as compared to a clean, new stock filter.

As for other mods, there are some choices depending on the vehicle. Older vehicles which could be tuned (ie, adjusting ignition timing, carburetors, air management systems etc) could be improved over stock.

Modern cars, however, are generally optimized for mileage. Again, some vehicles might respond to certain changes, depending on the design and current condition.

One general thing does come to mind for higher compression cars - use premium fuel. Some cars can adjust their timing mixture etc to optimize the anti-knock capabilities of premium. Also, most premiums do not seem to have ethanol, (which has less BTU's (energy) per gallon than gasoline). So premium is, in theory a slightly more energy dense fuel.

My Cadillac DeVille (275 hp 32 valve V8 gets 15% better mileage on premium, because it can take advantage of the fuel's characteristics.
This more than compensates for the extra cost for premium around here.
But my '84 Supra is lower compression and less sophisticated and does not get better mileage on premium.