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Hey folks. I am the proud new owner of an 04 Si. I drive 160 miles a day for work, and am looking to increase fuel mileage.

I am looking at either AEM or DC short ram intake (carb legal)
and looking @ DC 4-2-1 header (again carb), and either DC cat back or Ractive cat back (I had ractive cat back on my CRX & EF hatch & loved it)

I cant seem to find much info on mileage increases, so help me sell my wife on dropping a grand, and what I can expect to get outta the upgrades...or point me in a good direction.

BTW I was running an EF Hatch with dohc ZC, aem short ram, dc 4-2-1 and ractive cat back & was getting wayyyyyy better mileage...till the zc spun a rod bearing but would like to get the same kinda mileage outta the Si

 
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Wouldn't adding items that increase horsepower lower MPG?

If it did raise mpg why wouldn't Honda make it that way?

 
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All the parts I listed have the downside of more noise, which most consumers don't like. More HP does NOT mean less mpg. There are many folks who have boosted D series and gained sizeable increase in mpg, as long as they kept their foot outta it, but with boost comes less longevity. All about trade offs. For me I need more mpg, not really the hp gain side of it.

 
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True, you can't have it all! I would give up a quiet engine for some mpg. That's the nice thing about engine management, you can have a daily fuel/boost map and a more hp oriented map.

Fuel economy tires would also help.

 
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not sure about the Si, it's the K-series, right? since you talking about carb, i am supposing you are not talking about canadian Si (equivalent to EX in US)

 
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Have u thought about an economical tune?

 
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If you bolt on a new intake, just make sure you clean out your throttle body with some TB spray and wipe down the plate. The Weapon-R Secret Weapon is a pretty quiet intake IMHO.

 
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I have experienced a slighly better MPG gain with the AEM CAI, DC header and full CB exhaust. But the gains are minimal.

 
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doesn't make any sense to drop a grand to improve mileage .
how much gas can you buy for 1000$ ,,in my area that would buy you 278 gallons !!
at 35 miles a gallon that will let you travel 9730 miles so if you improve your mileage ...lets be generous here..3 miles per gallon to 38 then you will travel 10564 miles ..or in other word saving 22 gallons in the 9780 miles that you traveled at 38 MPG ,,,for a savings of .....79 $$ ...congratulations on being the worst investor on Wall Street ..invest 1000 earn back 79 !!!!!

 
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I get better mpg with my aem cai. Added megan headers and cb to the mix. You will get better mpg as long as u dont hear that intake, lol. happy modding.