A free flow muffler can improve mileage but by not by much. It would take a long time to recoup the cost of a new muffler.
Diesel.
No. A car will get better mileage with the correct tire pressure.
The gasoline that is recommended by the manufacturer is the best fuel to use.
Anything that allows the car to breath better will free up POWER :D
Gas mileage in any car depends on many things. Some are: How hard you accelerate. How well maintained the car is. Long or short journeys (short give worse mileage). How heavily loaded the car is. Whether you have a roof rack (without gives better mileage).
Yes, higher octane gas does give higher gas mileage for your car. However, the increase in gas mileage may not as great as the increase in the price of the higher octane gas.
for any car to get better gas mileage get a better flowing intake and/or exhaust or get it tuned
New spark plugs with the proper gap will give your car the best possible gas milage.
it will only if your car requires 89. If your car is designed for 87, then 89 will provide no benefit.
get a better car
better gas mileage
The muffler makes your car run quiet