Can anyone tell me if adding the RRM Piggyback ECU will hurt my gas milage alot if at all?

 

Don't know what it'll do to your gas milage, but it will force you to start using 91+ octane fuel, so that will cost more.

 

Won't hurt your mpg at all. You should actually be getting better gas mileage when stomping on it as it isn't as rich as before. For the most part if your just cruising around you should get the same mpg as stock.

 

I think the mpg will stay roughly the same but your monthly gas money will increase due to pas prices (raising and droping all the time) and your now using 91 octane instead of that 85 octane before... But better performance, who cares bout that little money huh?

 

I always use 91 octane anyway. I can drive further on a tank of gas and fill up less often and that saves me money in the long run.

 

It makes little to no sense to run 91 octane fuel in an engine that only needs 87 octane. You're just throwing money away. Higher octane fuels have higher flashpoints, so they're necessary in higher compression engines, and engines tuned for significantly greater than stock performance, but is completely unneeded in the stock engine.

If running higher octane actually gave you better gas milage, as you think it does, then all manufacturers would say their car requires it so they could put the slightly better MPG number on the sticker.

 

run your car both ways for a couple weeks and check your mileage and see. thats what I did and it works.

 

Otter, we are talking about changing the ECU of the Lancer from the stock to RRM Piggyback ECU. That ECU changed all the fuel/air ratio and all that and so it requires higher octane of fuel. Higher octane just means higher combustion rate, not necessary for higher compression. I can have RRM Piggyback which runs in 91octane and with a turbo and use low compression engine. You are partly right because you are talking about a brand new never-been-touch car.

We are talking about changing the ECU of the Ralliart to make it better performance. But you are correct again about the mileage vs. gas. You won't change the mileage vs. gas if you change the octane. They set it to 91 because they programmed it to have higher combustion rates, you need better gas. Using higher/lower octane than the manufacturer recommendation will only cause harm to your engine. So if you run stock engine with stock ECU, use 87. For cars with RRM Piggyback ECU, use 91.

 

They did not change any combustion rates. Combustion rate of fuel is a property of the components of that fuel. They most likely advanced the timing and thus would need higher octane to prevent pre-ignition (knock). And otter is completely correct, the higher the octane the higher the flash point, which means you can compress the vapor to much higher pressures without having it heat up enough to ignite from the increased pressure, as opposed to igniting off of the ignition source (spark).