Originally Posted by mahout

Was your manifold installation done well" Were the ports matched? Gaskets trimmed and flushed? Was the manifold polished? These things have a monster effect on the air flow. The amount of air and fuel are established by the cylinders sucking in on the intake stroke. The amount of air/fuel that actually gets in is set by the resistance of flow into the cylinders, primarily the intake valves but also the manifold flow resistance. If your manifold is not matched, flowed and ported the engine may have to work harder to produce the needed power, whatever that may be. And thats poorer mpg. You say increased performance. the more power the less mpg. And...
And of course there's always injector problemstoo.
Out of curiosity did the manifold supplier claim more power and nothing of economy? Many manifolds designed for increased power with better flow at max rpm actually don't flow as well at lesser rpm; manifold design is a very tricky excercise. Your mpg easily can be the result of all of these.
Seems I remember some SS racer manifolds that we flowed didn't get as good street mileage. Wish I had documented that but then it didn't matter.
Last, but not least, you should go back to the high test gas for a fair assessment.

Good luck.

Originally Posted by jvm051

Octane boost is a complete waste, and not only that, it can do damage to your car. My previous car was a 2006 Mustang GT. I had just installed a custom Tune from a mail order speed shop on my car, and had detonation. So I decided to put in some 104+, and I got a CEL. I brought the car to a local dyno, and after a single run he noticed that the spark was going out at higher RPM's (misfire) He pulled the plugs, and found a residue that was the same color as the octane boost. Popped new plugs in, and the misfire was gone. My O2 sensors were also taking longer to go into closed loop as well, which may also have been from the octane boost gumming them up. Do a google search on Octane Boost, it is junk. Most of them don't even raise the octane a single point. As far as using Higher octane than what is needed, all this does is waste money. Higher the octane the slower the burn, so unburnt fuel is being wasted through the tailpipe.

Originally Posted by TrickyPantz

Does anyone else actually have this installed? I'm looking at buying one and I want to have more than one person's opinion about how it effect mileage. I looked around in the mods section, but they're only interested in power and sound. which btw they claim it is very good at.

Originally Posted by TekXoID

So I've been back to premium for the last 3-4 fillups since my 26MPG blues, and I've gotten:

I don't believe it's the higher octane rating, but lower grade just gets consistently worse mileage for me, so I don't know what to think, I'm just going to continue using it.

Originally Posted by Fa1

I don't see how higher octane is going to give you more miles per gallon. The ecu was tuned to run on 87. Octane is just a measure of resistance to detonation and higher octane ratings means it just burns slower then a lower octane rating. If you put a higher octane that 87 in your fit, the ecu will automatically retard the timing to match the slower burning, higher octane fuel.

Originally Posted by TekXoID

So I got a T1R B-Max Intake, sounds great, definite performance gain, love it!
I did the Idle relearn after installing it, but after being on for half an hour the fan didn't come on at all so I hope that's not part of my problem, it does seem to be running fine.

What I don't love is the drop to an AWFUL 25MPG from my average 35.5MPG so far (I have a Sport AT with 1500 Miles).

I have been driving the same, minus 3-4 times flooring it to test out the new intake.
The only difference that could have caused this MPG change that I can think of, other than the intake, is that right before I installed it I filled up on 87.

I know everyone is going to argue about this, but I usually use 94+Octane booster which costs me around $1.00/gal. because my dad works for sunoco and our whole family gets a flat discount, so I don't care about the extra cost involved with the higher octane.

A few of my friends with stick shift Fits use high octane too, and compared to any other gas, they consistently get 3-6MPG more with it, findings made on very consistent calculated and scangauged testing.
So, I am wondering if it's the low octane that I started using all of the sudden, or the new intake, or both.

My understanding with the intake is that more air, more gas = better performance and less fuel economy, right?

I didn't think it would be this drastic, is there any other factors I should take into account that could have caused this change in fuel economy?

My Fit is pretty standard other than the intake and dead pedal, but I'll take some pictures today anyway.

Thanks for your input guys.