Quote:
Originally Posted by niky
You never want backpressure.
Basically this. Restricting the end of an over-large exhaust does nothing but cause problems. Those of us who've used exhaust silencers on large mufflers could tell you this. It just adds lag and saps power without any benefits in fuel economy.
Even the best stock manifolds of that era are nothing compared to a properly designed mild mandrel-bent aftermarket header set-up. They're cast iron with poor interior flow and surfacing and often the galleries are too restrictive.
Best thing to do: take a picture of your manifold and compare it to whatever you can find on Honda forums. If it's a cheap knock-off with crush-bends, it's hurting power and losing you MPG. Try to find a secondhand performance header that will fit your engine instead, if you can't get a stock manifold.
A well-designed set of breathing modifications will often increase fuel economy, unless it interferes with MAP function on your Civic (and they usually don't... not as with MAFs) or O2 sensor function. I had a full set-up on my car that didn't affect fuel economy one bit. And it got even better after we tuned the ECU.
That car being a Honda, instead of chasing theoretical lost MPG that you're not sure is lost, it might be better to add something that can gain you MPG, for sure. Lots of cheap tuning solutions for Hondas, from ECU-swaps to chips to Hondata (pricey though) systems... just check for legality in your particular state...
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no, it doesn't have crush-bends in it. I don't think modifications will help much in my case. It is already a VX. It is basically factory modified for high MPG. Those exterior aerodynamic mods will just make it look like ass. I'd be happy if it got the 40+ mpg it is supposed to get. Right now I'm prepping it for paint.