Just bought a preowned SI (from an out of town dealership) and it has aftermarket parts.. how does this affect my cars performance?


Asked by Apr 24, 2013 at 04:44 PM about the 2008 Honda Civic Si

Question type: Car Customization

I recently bought a 2008 civic SI from an out of town dealer so I didnt do a test drive before buying it. The salesman I was dealing with said it was all stock.. the minute I drove it off the lot I knew it wasnt stock because ive already had a stock SI before buying this one. Well I pull off so my boyfriend(yes im a girl) can see whats under the hood. He tells me that theres an aftermarket exhaust, header, high flow cat, and a shifter stabilizer on it! I had no idea and glad the salesman didnt either or else I probably wouldnt have been able to make him come down on the car price as much as I did. But my question is I know what these parts are individually but all together performance wise what all is it doing? And just to note she does drive beautifully picks up quick and smooth. But I'd like to know exactly whats going on under my SI

5 Answers

Tom Demyan

So you want to know how the aftermarket parts that are on your car effect the performance from a stock SI? It will add some more HP, how much it would be hard to guess not knowing what parts are installed such as brand and what condition they are. If it runs fine, have fun with it. Only way to know any numbers is to test it on a Dyno.

CJ Michaels

the exhaust, headers, and high flow cat all have to do with air LEAVING your engine, so air will flow into the engine, out into the headers, through the high flow cat, and out the exhaust...the shifter stabilizer pretty much just strengthens up your shifter and makes shifting feel more solid, maybe feel a bit easier


Thanks for your input guys :) One more thing, do these parts hurt or help my gas mileage?

CJ Michaels

it will, but only barely, and depending on ur driving habits...studies show that u MIGHT see half a mpg better economy


I appreciate all the good advice. I guess for those of us who want the extra performance, we may be better off waiting for the RType to hit the US or keep our fingers crossed that the 2016 SI is worth the wait.

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