bighoss77

picked up a '99 Hx with the cvt auto trans... as most know this is supposed to be the civic that gets 40mpg hwy. question is, would adding an intake and exhaust system decrease mpg by using more air/fuel? or would this help my mpg by making the engine more efficient? reason i ask this is, i bought the car halfway taken apart (bad trans), it was missing half the exhaust, and missing the stock intake. parts stores and ebay want between $60-$120 for the missing exhaust piece, but i can find used header and exhaust systems local for around that price, and local people want $30-$50 for the stock intake system, but i can get a cheapy intake tube/filter for that price off ebay... it does not have the lightweight hx wheels on it anymore, i plan on running si wheels (this is going to be an Si clone for looks, but stay hx for economy) so that will more than likely kill a mpg or two... just looking for input.

Solster

you May see better MPG with the intake but as for the exhaust i have seen a lot of power from adding a Header to my cars but never a MPG as the O2 sensors are never in a Good spot and you still have to have Cat or the ECU will throw a Cel. if your just talking about the airbox and intake tube to the throttle body you wont see alot of change in MPG but might make up for the Si wheels

bighoss77

well i was also reading up on a different site and a few people have been doing a warm air intake for better mpg, i know this site is mainly about performance, but since this is an hx model i might as well make better at what it does.

HeXtacY5

An air intake tube will do nothing on any car unless you have significant engine work. Stick to the stock airbox & get a K&N drop-in filter.

Secondly, if you want to maintain high fuel efficiency, stick to the cat/header set-up. If anything get a higher flow cat or the Magnaflow header/cat combo thats 1 piece. Its more money but its better quality and higher flow. As for the piping, i dont think it'll be worth going to a bigger diameter than stock. Maybe 2" with a better muffler. The Magnaflow shouldnt impede your MPG either.

Lastly, I believe the 15" SI rims are a bit heavier than 13"-14" HX rims so the added weight will impede some MPG a bit but nothing significant.

94preludeguy

Leave it exactly how it is.