Civic VX: Headers vs stock exhaust
 

Bought a partially molested/riced out Civic VX. One of several things I have to undo are the headers that were put on it. How bad is my fuel economy going to suffer with header assuming all other factors are the same?

Also, where can I buy the stock manifold and CAT?

Before you know for sure what your actual FE numbers are with the exhaust manifold and header, I wonder if you want to invest in stock items. The race mods might work well with proper driving, maybe better than stock if they are good items. A tuned exhaust manifold and muffler has the support of some on this forum as a good FE move. Any chance you could run them for a while, track FE carefully, and get a baseline on the car in current form? Or have you done that already?

The only "performance" mods it has are K&N intake and headers. The rest of the mods were really tacky exterior mods. How do you tune the custom exhaust? Is there an adjustment somewhere? It also has one of those retarded fart pipe mufflers. The O2 sensor port is on cylinder 1 exhaust instead of where they all come together on the OEM manifold.

There are a number of on line calculators that will tell you what the ideal size is for exhaust and headers so you can get an idea how over sized they are.
I would place an ad on craigslist and contact people who are selling VX parts asking if they have these stock parts, you could get them for scrap value.

A 'tuned' exhaust manifold is made that way. you can't 'tune' it.
With thAT said, you need to look at or tell us, the od of the pipe that is leaveing the maifold. If it is too big, your screwed.
There was a thread on here last month on this exact issue..
Basicly what you probably have is a pos, noise making ricer setup.
I doubt that any real intelgent thought went into whAat was bolted on.

"we' have said this before, and 'others' have belittled it(they are wrong) but there is an optimal size in od exhaust pipe for every size of engine. If you are not at that size then you are not going to optimize the engine's ability. PERIOD.

And if your here, you are not going to be running your engine at 4000 rpms more than 5% of the time. Or 3000rpm.

here:
How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

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.

Exhaust Size Calculator

this one is VERY simple.
NOTE: MAX horsepower......something none of us should see more than one on a car.

your right.
POTENTIALLY, the pipe could be small enough to allow for enough pb.......but until YOU measure it......why are we having this discussion?

I'm guessing the 1.5" pipe diameter the calculator is referring to is the final exhaust not the pipe diameter coming out of each exhaust port. lets say, for example, the pipe diameter I have is too large, then what?