Hello all, hoping someone can help me out with a issue I'm having.

I have a 2011 MCS with ~52000 miles. This summer I've started adding some mods. NM Cold Air intake, Alta boost tube, intercooler, Manic Stage 1 tune and most recently an Invidia Q300 DP-back exhaust.

I've always averaged 31-32 MPG with my take mileage indicator giving me a reading of ~380 miles to a tank. I always use 93 octane. My fuel economy figures haven't really changed with any mods, even the tune. But this past week with the Invidia installed my MPG average has dropped to 25-26 and I get 320 miles to a tank indicated at best. Has anyone else seen this? If this is normal I suppose I could live with it (considering my OEM exhaust has been disposed of.... *head-desk*).

I'll admit when I installed it that it didn't mate up to the OE downpipe the best, and I do want to try to get it a little more flush, but it doesn't sound or look like it's leaking at that or any joints. I also didn't use any sealer which I want to change as well.

 

My guess is that you're just pushing down on the loud-pedal more to hear the cool new sounds. That'll tank your mileage pretty well.

 

Has it been a little bit cooler over there since? Usually a change in temperature can make your MPG fluctuate as well as driving habits like Felines stated. Some good info here.

 

When I went with a free flowing intake (AEM Scoop Intake system, expensive!) I notice I had to push the pedal down more just to get up to speed, there was less low-end torque do to the freer flowing intake that really give you more HP and took away low-end torque when my foot is lighter on the throttle. I'm not saying the open air type intakes reduce torque altogether, they do have torque but only when WOT.

My AEM intake has crazy torque at WOT, but at moderate to low throttle is was a bit sluggish and less responsive. Now you add a high flowing exhaust and now your MPG is lower, that low-end torque helps keep your MPG up, but you didn't upgrade your intake and exhaust for gas mileage. There are always compromises when adding intakes and free flowing exhausts. Some find a larger turbo is a better match for larger diameter exhausts with a high flow intake, port your head enough and you change port velocity requiring a larger turbo.

What's your exhaust diameter?

 

It is probably a couple of factors:

1) more enthusiastic driving.
2) Winter blend of fuel has been out for about a month.
3) Your engine is an air pump. You have allowed more air in and reduced the restriction on getting the air out. A more efficient inter-cooler for denser air (more in) and a tune to allow the injectors to properly mix all the extra air with fuel; more air = more fuel.

Systemlord has a valid point. Any performance mods should work together. Achieving the proper balance with mismatched performance parts usually result in a less than stellar overall performance. You can have dead spots in your torque curve or a late start on the curve.

Many speed shops offer packages that have been designed to work together. I have not performed any performance upgrades to my Mini but I have another vehicle that has the "total package" system and it turned out better than any system that I could have designed.

 

This! After I got my DP installed my MPG went from an average of 27+ city to 19-21. It's been about 2 weeks and at this point the sound is no longer as loud and aggressive. Now that it's broken in I'm back to driving at a normal pace and MPG have gone up.

 

I figured it out. Overall my driving habits didn't change. It was really a matter of me not being on the highway as much in the past week, not getting my highway mileage in there, and having reset the average MPG dial. I'm back up to 31 mpg after two commutes to school.

 

When I had my MAF replaced, the mechanic mentioned the ECU needs a few "drive cycles" to adjust to large temperature changes. I've always wondered what constitutes a drive cycle as I have a short commute similar to bombardier and have noticed fluctuations in MPG and power. Does the engine need to reach operating temperature for a certain amount of time or miles for the ECU to adjust the mixture?