Quote:
Originally Posted by Joe1234
I thought the problem was back pressure. The stock setup has the correct back pressure while aftermarket headers with no cat will not have enough back pressure.
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You
never want backpressure.
Quote:
Originally Posted by Ryland
The idea behind a tuned exhaust is not adding resistance to get the "right" back pressure, because a small exhaust should have very little if any back pressure, so why would a larger exhaust have back pressure when a smaller does not? because the exhaust is moving in pulses and it takes time for each pulse to travel down the exhaust pipe, if you have a larger pipe then it will take longer for that pulse to travel to the end, to large and it will bounce around enough that it will start traveling backwards, causing back pressure, so no, closing up the hole at the end of to large of an exhaust pipe will not help.
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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...