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Discussion Starter · #1 ·
so sitting on heavy 20's with a WAI and basically straight piped exhaust im seeing 14-15 highway... now im going to do a tune up next week but it got me thinking, people around saying around 18-20- around town when tuned up right, but with an intake and larger rims, could it really be hurting my mileage that bad? the car had basically everything done at 80k on it now its got 128k

also, i know its got a few issues because i have to put the pedal past halfway just to get into traffic, so after a tune up should i still expect to see less than sasifying results?

and i would really miss my intake sound, so im wondering if i got an actually OPEN FILTER cai (i know the stock is fine blah blah) maybe with a heat shield and pipe into the fender would my gas mileage still suck? im really thinking about just going back to the stock airbox but dont want to lose the sound.
 

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Those mods cause the natural induction/scavenging effect to collapse, which hurts the engines total efficiency. Even my '96 Duratec, which isn't running 100% right (no codes, but I can tell its has a subtle issue) gets 19-21 around town and mid to upper 20s in the highway. It has gotten 34 mpg before. So if you Vulcan isn't getting over 20 mpg, somethings wrong, and those mods could well be part of it. That and if you drive in such a way as to get that sound you like, your gas mileage will suck.

Looking at your mods list, you have a K&N filter. Those will foul the MAF sensor, and could likely be a part of the poor economy. I quit using K&Ns years ago after I learned what total BS they are. I even just bought a CAI for my Turbocoupe that came with a K&N, I left the filter in the box and purchased an AFE ProDryS filter instead. I will sell the K&N on eBay. I've been burned before. Fool my once shame on you, fool me twice shame on me. Don't know why it took me three times to learn my lesson.

I have use AFE ProDryS filters on three cars all with excellent results.
 

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Big, heavy wheels are harder to turn, which puts more load on the engine and decreases fuel economy. That 18-21 mpg estimate is the EPA's number, but was tested for on OEM-sized wheels and tires. Calculate what the weight difference is that you're dealing with.

After so many years on car forums, this should honestly be pretty obvious to you Bobby. Go ask some guys who drive Donks what their fuel economy penalty is from running big-ass rolling stock on their cars...
 

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I agree that all those mods will hurt, not help MPG. Of course, the greatest effect on MPG is the driver. Put the pedal 1/2 way or more to the floor nearly every time you accelerate will send gas mileage down the toilet.
 

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The cause here may just be a faulty steering actuator.
 

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Discussion Starter · #8 ·
well i know ill get some mileage back after a good tune up (plugs, wires, coilpack, maf cleaning, maybe fuel filter and a few other things)

and i think im going to switch to a dry filter now.

and as far as my exhaust, the cat and the muffler are straight piped so i have the 2 precats and then a resonator nothing else.
 

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What exactly have you done to the exhaust and its O2 sensors vs the original factory setup? I don't know what year and engine you have.
 

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^
When was the last time that the front o2 sensors were changed?

If they have never been changed, it would greatly help your MPG...
I should really do mine :S
 

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1. open exhaust will hurt MPG badly, especially if the PCM is expecting back pressure.
2. WAI there's two MPG right there.
3. DUBs kill MPG, especially when your PCM is expecting 15 inch tires.

/snork
 
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