benefits to running a catalytic converter as opposed to just a straight pipe?

[GhostAccord]

Probably something that might be a bit loose inside your aftermarket cat. Your MPG loss is probably due to a heavier foot! I gained MPG when I did my exhaust swap....didn't want to piss off the neighbours.

An aftermarket header and cat don't really qualify for a discussion about OEM O2 sensor locations. My header had 2 bungs and my cat had one..... as well, none of them were in the stock locations. Except for the OBD2 O2 behind the cat.

[H.M.]

....Back pressure is unnecessary in the CB7. The O2 sensor that is BEFORE the cat corrects the A/F ratio, so why would you need any sort of back pressure?...

Anyone have comments on this comment?

Is backpressure unnecessary in the CB7 because the O2 sensor BEFORE the cat corrects the A/F ratio?

And if this is true, could you just cut off the exhaust pipe after the O2 sensor and have no performance issues (not discussing legal, noise, CARB or air quality issues here, just performance)

[GhostAccord]

I think people have to drop the term back pressure, back pressure in an exhaust is bad. Now keeping a certain exhaust diameter and length to maintain exhaust flow is a different story.

It's like using a gardening hose.... take the spray nozzle off and the water comes out and drops straight down. Vector or merge that same volume of water into a smaller nozzel and what happens? The engine itself doesn not need back pressure to maintain performance. However the exhaust has to maintain velocity. Ether with a merge collector made with scavenging design or a complete exhaust system.

[wed3k]

i want to say the o2 sensor won't know the difference...you'll need correct exhaust flow to maintain proper engine operation.

without proper engine operation, an o2 sensor will do its best and try and correct it.

[djcaz_aom]

Okay, let's get some clarification in this thread:

Thread Title: benefits to running a catalytic converter as opposed to just a straight pipe?

Answer: Although you MAY gain 1-3 HP by running a straight pipe, the cats on our cars are very high-flow in stock form. Also, you help keep the air clean by running a cat.

If you upgrade your exhaust to a larger size, just upgrade the cat to the same size.

sorry if there is a already a sticky i searched for exhaust but didn't come up with anything conclusive. I'm trying to figure out what kind of exhaust to get and wanted to get the best for the motor (h22a) to perform at it's best. I'm not concerned with it being super loud although i would rather it be on the quieter side lol.

Answer: Since no one answered your question based on the motor in your car, here goes. The H22A will breath best with a larger exhaust. 2.5" is acceptable, but running 3.0" is ideal. This remains true if you plan on doing upgrades to the engine internals, ie cams, valve-train, higher compression. The Apexi WS2 exhaust never disappoints and is very quiet.

If you plan on going 3.0", you can get the WS2 muffler alone and get the exhaust custom built. Just be sure to run the longest resonator you can fit under the car after the cat.

Need that back pressure man ,, and not having yoyr o2 sensors will mess up ur mixture which will make u run really rich having to buy a lot of gas ,, unless u are doing drags to loose a bit of weight , u dont anything gain in straight piping a street car but its up to you what u want to do

This statement is half true. (unless u are doing drags to loose a bit of weight , u dont anything gain in straight piping a street car)

Everything before this, EXCEPT the part about a rich mix equals more money at the pump, is just false.

1. From my understanding, CBs only have one O2 sensor.

2. The OP did not mention removing his O2 sensor, just running a straight pipe or catalytic converter and what exhaust would be best for his motor setup.

3. Back-pressure? Really?

Here is a good read: Destroying a myth.



Posted for those not wanting to follow the link:

Destroying a myth.


Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

- Adapted from Thomas V.

Although it's a BMW site, our ECU works the same way.

Here is a site dedicated to the topic: www.exhaustbackpressure.com

I hope this post helps and puts the thread back on topic.

If in any way, shape or form i am incorrect in my answers, please correct me with references as I have provided so that I may correct my post and learn from my mistake.

[Chronuss]

Probably something that might be a bit loose inside your aftermarket cat. Your MPG loss is probably due to a heavier foot!

Haven't change my driving style, just as spirited as ever. But the rasp and MPG loss made me think my cat has reached the end of its life cycle, as it probably has had between 75k and 100k placed on it, and the O2 sensor is older than that.

[GhostAccord]

That's the crappy thing about OBD1 cars, no plug in diagnostic to make it easy to check the cat. On an OBD2 car you watch the two O2 sensors. If the upstream PO2S voltage is moving up and down and at the same time the down stream SO2S voltage stays steady. The cat is good or the SO2S is bad.....lol

[darkgreenaccord]

OKAY! In conjunction with the op's original question.... Honestly there isn't a HUGE difference either way. If you remove it, put a resonator or glasspack in its place or you'll get a fast and furious sounding Honda.lol it will smell a little different but as long as you aren't puffing you exhaust fumes it shouldn't bother you. with it, you'll be legal, without it youll have a bit more noticeable exhaust note.

[danf20bcb7]

And a honda with out some sort of resonator or cat sounds really raspy sounding.

yeah my f20b has no cat nor resonator, 2.5" all the way back into a magnaflow. totally regret pulling the cat off, i hate and i mean hate the noisy honda sound. tho i do like hearing a honda at the track bouncing off rev limiter. but thats diff not driving normally everyday with an effing headache lol.

[deevergote]

Just to clarify... again...

There is no o2 sensor in the cat. Not on US models, anyway.
The CB has only ONE o2 sensor. The locations vary: F22A1 has it in the upper portion, easily visible from above with the hood open. The F22A4 and F22A6 have the o2 sensor lower on the manifold, on the "downpipe", if you will. It is closer to the cat, but it is not ON the cat. The o2 sensor's existence and its location are completely unrelated to the car's need to have a catalytic converter.
Generic header designs will often have an o2 bung in both locations, for easy installation in any 90-93 Accord. The existence of 2 o2 bungs does not suggest the need for 2 o2 sensors... it merely exists to make the part cheaper to mass-produce, and have it be usable in any F22Ax equipped Accord.

[CB7 Sleeper]

1. Damn its hard to understand anything you write, need an English tutor?

2. All CB7s have one, yes (1) O2 sensor, being that they are OBD-1. 90-91's have one in the manifold, 92-93's have them in the downpipe BEFORE the catalytic converter.

3. Back pressure is unnecessary in the CB7. The O2 sensor that is BEFORE the cat corrects the A/F ratio, so why would you need any sort of back pressure?

Obviously, you are NOT entitled to your .02 cents, you aren't entitled to anything when you're spreading false information and blowing smoke out of your own exhaust pipe. You think you know what you're talking about, you don't, and how dare you question the veterans who have been on this site for years giving great information and helping out those in need of the CORRECT information. It's insulting.

Congratulations, you have successfully made yourself into just another asshat noob member whom nobody has any respect for, and now the next time a new member searches for an answer for a similar question to the OP's, they'll have to read through your bullshit babbling, then end up completely confused over the topic, and post a thread of their own where all the veteran members will have to answer the same question AGAIN, and possibly deal with this sort of stupidity again as well. Thanks for keeping the cycle going. ....

Ignore this post, my brothers genius mind at play.

I do have a question though, is back pressure necessary in these cars? O2 sensors correct the A/F ratio but only within a certain range, right? I thought back pressure was more important to older carb engines and stuff. Please correct me if I'm wrong, I don't necessarily understand back pressure.

[deevergote]

Back pressure is NOT necessary (as everyone but that one dumbshit has said over and over again... see what happens when a dumbass opens his mouth?)

Older cars, yes... cars that do not have electronically regulated fueling can benefit from having some back pressure to help ensure proper cylinder filling (probably at the expense of some reversion.)

In our electronically regulated / computer controlled fuel injected vehicles, backpressire is nothing more than a restriction.



Backpressure will exist at some point regardless. At low RPM, a low-velocity exhaust flow can become turbulent, and that turbulence will create backpressure. This can increase when you widen the header/exhaust piping, requiring more exhaust gas and heat to maintain a high velocity. On the other end of the spectrum, once you've reached the exhaust's maximum flow ability, back pressure becomes a restriction once again. Ideally, you want the least amount of back pressure possible within the engine's most usable range. More specifically, you want the highest exhaust flow velocity possible throughout the engine's most usable range.

[BurtonRiderT6]

Deev we need the beating the dead horse smiley. It appears no one is reading the entire thread prior to posting.

[deevergote]

Sometimes I think beating the dead horse is the only exercise I get these days!