I have a 2010 Fit Sport Auto. Does anyone know if gas mileage will go up or reduce if installing an aftermarket Greddy exhaust? I tend to keep the car in best gas mileage as possible, but upgrading the exhaust will gain more air flow at back-end does that give the car better gas mileage?

 

As I have it understood. No.

Here it is Fit's and newer cars in general have smarter ECU's which can adjust fuel delivery, modify timing, and pulse length (time injectors are open) according to what the sensors are reading. Our car adjusts fuel via the mass flow sensor in the throttle body, O2 sensor in exhaust, throttle position sensor and other sensors. Now if you open the exhaust up via aftermarket exhaust you will decrease the back pressure, reducing your available torque (which the Fits have little of). In doing so the motor will have to work harder to move its weight, hence use more fuel and lower mpg.
BUT on the flip side if you open the intake side (via intake or freer flowing elements) you can get more air into the motor during the suction stroke. More air equals more oxygen to burn with your fuel. Now the car might read the increase in air flow and ask more of the injectors to compensate. This could reduce mpg. BUT since you have gained more air flow on just about every part of the rev range, your car will move its weight easier with less input of your right foot, which could reduce fuel consumption and increase mpg. Also the injector can only provide as much fuel as the fuel pump, and injector flow rates physically allow. Although you might be thinking that your air to fuel ratio might run lean due to more air with same-ish fuel, but it won’t since the air flow change is only slight and the stock injector have some wiggle room plus the engine will pick up on this and adjust timing. I mean don’t expect huge gains but some can really be seen (if your driving is a constant).

Now you think why not do both simple, when you do both the ecu will adjust itself to these new parameters more air in, quicker exhaust out, more fuel to compensate. Those looking for more power get their largest gains in this scenario. But fuel consumption and mpg suffer (a bit). Also when u have an exhaust u want to hear it more often


I look forward to intelligent feedback. But let’s keep the ripping to a minimum, it’s only an idea.

 

I think the simple way to say is if we want to get good mpg, then don't mod the car.

 

Nah.. Simply put.. Get a quality intake and some iridium spark plugs... and #1 watch your foot... also increase tire pressure

 

I think is much cheaper to mod on our Fit than a Si, since the exhaust itself is cost less half than the Si

 

I would say I/H/E to get a better mpg and easy driving.

 

I would also like to put some of my thoughts in as well about mileage. They can also add to the efficiency of your car. This means that some of the performance parts can actually improve your gas mileage, if you can keep your foot off the gas! A more efficiently operating vehicle will also last longer if you keep it well maintained.