Bought the car with headers all the way back to a giant catback

[brucepick]

Well - jcfdillon's suggestion to find some workable way to help move the gas out of the system might have some merit, if the effort to move that gas is causing a reduction in the system's fuel economy.

I think the whole reason that this topic gets (some) attention is that in the performance world, getting rid of lots of exhaust is an issue. In my not-so-humble opinion, here in the fuel economy universe, it's not much of an issue. We're running our engines at about 1/4 to 1/3 of red line max rpms, and at maybe 1/4 to 1/3 throttle, when we actually are running our engines (see "Engine Off Coasting" = EOC).

When you also consider that the energy to run a fan or whatever would have to come from the same engine, I don't think there's much to be gained in worrying about what to do with a tiny bit of exhaust.

Unless you find a way to harness its energy efficiently. That's another discussion.

[some_other_dave]

My own personal guess is that if you are driving in an MPG-conscious manner, the difference between the stock exhaust and the one pictured would be minimal. With one exception:

The O2 sensor.

If you can have someone weld an O2 sensor bung onto the header some appropriate place (there are arguments for specific distances from the exhaust valve, or in the common collector, and probably arguments for elsewhere too!) and hook up a sensor correctly, you'll do better.

If you can't do that, or if it's too tough to figure out where "some appropriate place" is, then going back to the original manifold and hooking up the O2 sensor correctly will give you better economy than the current setup.

Regardless of either, a decent muffler will make your neighbors hate you a lot less...

-soD

[Ladogaboy]

Man, a whole lot of arguing over semantics, and (surprise, surprise) you guys are both right in your own ways. Especially in the realm of exhaust, an entire lexicon could be written, including a full thesaurus. But, at the end of the day, all this arguing does the OP no good.

First, I don't recall what car this exhaust came on, but the basic rule is: Naturally aspirated engines need *some* back pressure in order to function at optimal levels. The size of the piping will be determined by the amount of exhaust the engine can put out. Anything larger than a 1.5 - 2 inch exhaust on a small N/A will probably have a detrimental affect on performance (including mileage).

Turbocharged engines are a little different in that they already have built in back pressure from the turbocharger. Theoretically, the more you reduce back pressure after the turbocharger, the more efficient the turbocharger will be. That's why some small displacement turbocharged engines will have 3" or greater exhaust.

My recommendation is, continue driving with the car until you can find a cheap (probably used) OEM replacement for the exhaust. Leave the headers (it is not worth finding an OEM manifold), and the OEM exhaust should bolt directly up. If not, it might need a slight alteration, but that shouldn't be much. This way, you have the normal back pressure from the cat and muffler.

A couple of words of warning, though: Tubular headers can cause an increase in exhaust gas temperature (EGT), and if EGT gets too high, it can damage the cat. This is especially true in lean burning engines. Also, I wouldn't recommend putting an O2 bung/sensor in the header itself. Headers tend to take the brunt of the heat from exhaust, so any welding/modification could cause the headers to fail completely.

[TXwaterdog]

Meh, I can't see how the aftermarket exhaust system is really worth the trouble. If the noise is tolerable then maybe it's a reminder to not stomp on it. I say focus on other mods. the used system isn't really worth much. A stock system isn't worth the money and install for maybe .5mpgs. I'd say go for some LRR tires, some wheel covers, a belly pan.. etc...

[Ladogaboy]

Originally Posted by SimonSellsAustin

A stock system isn't worth the money and install for maybe .5mpgs.

The stock system might be worth more than .5 mpg if the back pressure is so little that the engine is dogging just to get up to speed. Also, putting a cat back into that thing will help emissions, smog, etc. I'm not sure how it is where the OP lives, but in California, the seller must ensure that the vehicle pass smog at time of sale.

[RandomFact314]

I don't even own this car anymore XD
I got a CRX, still has a cannon on the back, I plan on going back to stock though.
Thinking about headers but not sure quite yet... I heard the stock manifold is a "Choker"

[some_other_dave]

If the CRX has the stock exhaust manifold on it, leave it. Unless you are going to take the time and trouble to design and fab up a header yourself (and if you design it to work at low RPMs!) you won't be gaining measurable MPG by changing it out. The stock manifold is a "choker" really only at high gas flow levels--high RPMs and high throttle settings.

If your thought is to save money by getting better fuel economy, an aftermarket header will probably rust out or otherwise fail before it pays for itself, even if you find one that works for better MPG.
-soD

[RandomFact314]

Originally Posted by some_other_dave

If the CRX has the stock exhaust manifold on it, leave it. Unless you are going to take the time and trouble to design and fab up a header yourself (and if you design it to work at low RPMs!) you won't be gaining measurable MPG by changing it out. The stock manifold is a "choker" really only at high gas flow levels--high RPMs and high throttle settings.

If your thought is to save money by getting better fuel economy, an aftermarket header will probably rust out or otherwise fail before it pays for itself, even if you find one that works for better MPG.
-soD

Advise taken

[sc2dave]

Originally Posted by Ladogaboy

A couple of words of warning, though: Tubular headers can cause an increase in exhaust gas temperature (EGT), and if EGT gets too high, it can damage the cat.

WRONG!!!! Headers do not make it hot enough to damage cats. Cats get damaged by unburned gas that burns in the cat and eventually melts the insides,destroying the cat.

[Ladogaboy]

Originally Posted by sc2dave

WRONG!!!! Headers do not make it hot enough to damage cats. Cats get damaged by unburned gas that burns in the cat and eventually melts the insides,destroying the cat.

I'm sorry, but I'm going to have to default to what I have been told by professional mechanics and aftermarket tuners. The ceramic catalytic converters provided in OEM exhausts are designed to operate within specific temperature ranges, and if they are subjected to excessive heat, they will break down and fail. Typically, that increased EGT is the result of leaning out the AFR, but it can also result from changing the structure of the exhaust system. A typical exhaust manifold is cast out of iron, which means two things: One, it has more mass, meaning it can absorb more exhaust heat. Two, the stock exhaust manifold has a larger surface area, meaning it disperses the heat better. Headers have possibly 50% or less mass than the OEM manifold, and, while they do flow better, that only means that the hotter exhaust gets to the cat even faster.