Q: Catless up / down pipes

I have read a number of posts on this forum where people have made references to catless up / down pipes. From the context of these messages I got the impression each pipe had some form of catalyst contained within and the replacement with catless versions increased performance / fuel economy and eliminated the possibility of the catalys breaking up and damaging the turbo (in the case of the uppipe).

 

On another car forum I participate on it has been implied references to catless downpipes are references to the removal of the catalytic converters (which is connected to the downpipe). This seems odd to me as I've never heard of anyone referring to a catalytic converter as a catless downpipe nor do I get the impression so many people on this forum would remove the catalytic converter from their vehicles.

 

Can anyone clear this up for me? Do the downpipes for our cars have a catalyst in the pipe itself? Or are references to a catless downpipe really references to an exhaust system where the catalytic converters have been removed?

 

Thanks.

If your car is a stock 2005 model, there are a total of three catalytic converters.

 

One in the uppipe.

One in the downpipe.

One in the midpipe.

 

If you have not already, you should really replace the catted uppipe with a non-catted version from a later model Subaru or aftermarket ASAP. The catted uppipe can damage your turbo if it begins to shed fragments. You can search for more info.

 

Aftermarket downpipes come in catted and catless versions. The catted versions are supposed to be "high flow". Depending on your state, these may or may not be strictly legal.

 

Many people who have done exhaust mods have retained the midpipe cat, though some have gone completely catless.

 

Why so many cats? Mainly to do with startup emissions when the engine and exhaust system are cold. Once warmed up, the cars generally run clean enough to pass sniffer tests with one or two cats.

 

Note: a point of potential confusion. The stock exhaust has a shorty downpipe and separate midpipe. Aftermarket downpipes usually contain combined downpipe and midpipe section.

 

Hope that helps.

Thanks Miles. I'm still unclear as to what is meant by downpipe and / or catalytic converter. Are these two separate items? Or is the downpipe a component of the catalytic converter? It has been my understanding the catalytic converter is an entity in and of itself and that the downpipe attaches to it. Thus they are two different things. However, based on the other forum discussion, it may be they are one and the same.

For this piece, they are integrated, see pic of Cobb catted downpipe. Cat is in welded section at rear.

Think of your entire exhaust system as sections:

 

Exhaust Manifold/Header - refers to the same section - from the engine heads to the point where the exhaust gases coalesce to flow through usually a single pipe.

 

Up pipe - For us, the short section of pipe between the exhaust manifold and turbo.

 

Down pipe - The section of pipe from the turbo that mates up with a later section (mid pipe) to take the exhaust gases directly to the rear of the car

 

Mid pipe - section from the down pipe to usually around the rear axle. Often times there are few bends. Just a straight shot back.

 

Axle back - Usually the various plumbing to meet the mid pipe and take exhaust around the axle, and includes the mufflers for most cars.

 

In the 2005 Legacy, the up pipe, down pipe, and mid pipe all have a catalytic converter inside.

 

Catless up pipe is preferred for everyone. Catless down pipe is preferred for spending less money on a down pipe. Usually 200ish compared to 500ish, catless to catted.

 

There are a few systems on the market that replace everything from down pipe to the exhaust tips under the bumper. They're usually catless.

 

A picture is worth a thousand words. Thanks, madrig.

Thanks guys. It appears my knowledge of this is dated. Much appreciated.

There is a lot of good information in here but it can still be read very confusing. Referring to the second half of the OEM downpipe as a midpipe can and will probably confuse a lot of people. The midpipe is typically the first piece in a catback exhaust system. seanyb505 broke it down quite well. However in typical nomenclature the midpipe for our cars only has a resonator.

 

In factory form our exhaust consists of a header, no cat, to the uppipe, has a cat 2005-06 models, to the downpipe, contains 2 cats 05-09 models, to the midpipe, resonator, to the axle backs, each individual muffler.

 

Many people, myself included have removed all of their catalyst from their exhausts.

...Referring to the second half of the OEM downpipe as a midpipe can and will probably confuse a lot of people...

 

Subaru has their own terminology. Subaru in their own technical information refers to front, center and rear exhaust pipes.

 

The front+center sections together are what some people call a "downpipe". What Subaru calls the rear exhaust pipe is what carries exhaust from those sections to the mufflers.

What subaru uses for terminology and what the community uses may differ. So when shopping for aftermarket parts the terminology is not what subaru uses in their manuals.

Not another argument over this crap. Whatever you say.

Not trying to argue with you, I'm just stating that how the community refers to parts differ from how the Subaru manual does. I never said that how you defined the parts was wrong, it just differs from how the community refers to parts.

 

Its the same thing as Kleenix and tissue. They are the same thing but do you ask someone for a tissue or a Kleenix?

Let's just make sure the OP gets his questions answered, that's what we're here for, OK? This forum has helped me a lot, so I like to return the favor when I can.

Agreed. Your answer was right but it wasn't the most clear at the same time. You're right this forum is very helpful and that is partially due to the clarity of knowledge. If you go to shop for a midpipe you aren't going to get the second half of the downpipe your going to get the part with the resonator and y-pipe. All it is is nomenclature

I'm an engineer by training, and work with engineers. I've found one of the occupational hazards of being an engineer is one is trained to feel there is always a "right" answer and it is your duty to always have it.

Huh maybe that's why we can't agree. I'm an engineer as well

Let's just make sure the OP gets his questions answered, that's what we're here for, OK? This forum has helped me a lot, so I like to return the favor when I can.

I did receive the information I was seeking. Thanks to all who contributed.

If your car is a stock 2005 model, there are a total of three catalytic converters.

 

One in the uppipe.

One in the downpipe.

One in the midpipe.

 

2 cats in the stock DP and no cat in what is commonly and rightfully referred to as the mid-pipe. perhaps you meant ; one cat in the front pipe. The Subaru diagram doesn't have anything labelled downpipe. This is confusing.

 

There is a lot of good information in here but it can still be read very confusing. Referring to the second half of the OEM downpipe as a midpipe can and will probably confuse a lot of people. The midpipe is typically the first piece in a catback exhaust system. seanyb505 broke it down quite well. However in typical nomenclature the midpipe for our cars only has a resonator.

Ah, I have something to add that has not been addressed: should you have any cats or not.

 

Technically, it is federally illegal to modify an emissions control system in any way. However, there is no system in place for anybody to check up on that. States differ significantly on what you are allowed to do and this matters a whole lot more because many states actually check to see what you've done (safety/emissions inspection). Therefore it depends on what your state cares about and what they check.

 

For example, in Massachusetts, there is no sniffer check and there is no visual check. They hook up to your OBDII port and if the car reads ready, it passes. In California, there's no way you're going to get away with that. So regardless of what you do, you need to figure out some way to make sure that you pass your states inspection. No inspection? All set. Nobody will come find you for running catless exhausts.

 

Now, that's your obligation and it's requirements for passing state inspection, as they apply to each of us in our home states. Which means, there is a large portion of us in the U.S. that can get away with no catalytic converters in our cars at all and there is no appreciable penalty.

 

So ... if you can get away with it, you absolutely should not have a cat in the uppipe. It's there because it improves cold startup emissions, which is why Subaru included it. But it is indeed a threat to the turbo and conventional wisdom on this site says that we care more about our turbos not blowing up than the the difference in cold-start emissions. Obviously, Subaru the company has slightly different priorities on that point than we do. You can do what Subaru thinks is right or you can do what we think is right. Up to you.

 

As far as the downpipe goes, it's a little different story. There is nothing after the downpipe which can be damaged by a failing and shedding cat. And any cat in the downpipe is significantly further away from the hottest point of exhaust gases at the head. In other words, it cools off enough by the time it gets there that it's not really a danger.

 

So why not have any cats in the downpipe? It is slightly more efficient because there is no restriction at all. However, aftermarket downpipes which have what is known as high-flow racing cats have incredibly well-flowing catalytic converters. In addition, you have gone from 3 cats in the stock configuration to one high-flow cat. Your already 80% of the way there and you are still getting some catalyzing benefit. In the end, the difference between aftermarket single catted and catless is on the order of about 5hp. It's going from three stock cats to one high-flow that makes the most power difference. And it's the bellmouth design on the aftermarket downpipes that matters more than anything else in terms of power gain. Without the cat, you get smelly exhaust gases in the cabin and you are less environmentally friendly.

 

If you get a catted downpipe, you are greener and pollute less, but cats are made up of precious metals like platinum and palladium and thus are very expensive (on the order of about $500 for a cat, hence the price difference between catted and uncatted downpipe.

 

In terms of environmental friendliness, keep in mind that it's what we all do in aggregate that matters way more than what any one individual does. You will note that all kinds of small engines have no emissions control of any kind. Boat motors usually have no emissions requirements either. What about diggers and other heavy machinery? Race cars and NASCAR and Formula 1 and all those run catless engines. But there are way (way) more daily driven street cars and long-haul diesel big rigs on the road than all those other types of motors combined. So cats on street cars makes the most difference to the environment.

 

Now let's look at the number of enthusiasts that modify their exhausts. Again, an infinitesimal number compared to the number of daily driver muggles out there. One guy running a catless exhaust doesn't make any difference at all. 20,000 people running catless street cars doesn't matter much either. But if all 350 million Americans drove catless cars, that would be big enough to matter to the environment.

 

Personally, I bought a high-flow racing cat and I'll leave the 5hp on the table and I'll be more environmentally friendly (to an extremely small degree) and it cost me more money and Massachusetts doesn't care enough to check.

 

Make your own choices. Enjoy.

 

Here's an example of what I'm talking about. Which one do you think flows better? What about compared to an empty pipe? The one on the right is actually closer to an empty pipe than it is to the one on the left.

http://www.awe-tuning.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/s/t/stock_vs_hjs200cell_mp412c_1280_1.jpg

One more point regarding the nomenclature. For historical reasons, the uppipe is commonly called the uppipe. In the 4th gen LGTs, you can see why. These are pretty classic setups where there is a high mount turbo and exhaust gases often flow out the bottom of the motor or at least the side and pointing down on V-motors. Therefore, the piping has to travel "up" from the head to the turbo and once exiting the high mount turbo, has to travel back "down" under the car.

 

More recent turbo Subaru designs have turbos mounted down low and you will often hear some other terminology like j pipe or x pipe, etc for other parts of the exhaust. Just as often, you will hear people say uppipe and downpipe when referring to these designs even though they don't travel up and down any more. The old nomenclature tends to stick around.

 

That said, remember it like this: The manifold is many pipes into 1 (or 2), the uppipe is upstream from the turbo. The downpipe is downstream from the turbo. The catback is downstream of where a cat would normally be and usually the mufflers can be found somewhere aft of a cat (or where one would normally be if you had one). Everything else is matter of degrees and specificity and there's occasionally some room for confusion since not all exhaust systems are broken up into exactly the same size and number and names of pipes. Enjoy!

To be perfectly clear on nomenclature - in sequence

 

1. Manifold - The two cast-iron pieces that mount to the bottom of each cylinder head. The passengers-side manifold also has a connector flange to Joint Pipe Assembly, Exhaust, Rear (see below)
   
2. Joint Pipe Assembly, Exhaust, Front - the metal pipe that connects the two cast-iron manifolds. This pipe has a flex-joint incorporated into it.
   
3. Joint Pipe Assembly, Exhaust, Rear - the pipe that connects the manifold assembly to the inlet (bottom) side of the turbo. On 2005-2006 LGT/OBXT models this "pipe" included a catalytic converter element. The OEM pipe always contains a flex joint and a bung (2005-2006) for an Exhaust Temp Prob.
   
4. Exhaust Pipe Assembly-Center - The pipe that connects the outlet (back) side of the turbo to the rear exhaust components. This "pipe" contains a catalytic converter element.
   
   
5. Exhaust Pipe Assembly-Center, Front - The pipe that follows the Exhaust Pipe Assembly-Center, and contains the after-catalytic element. There is a bung in this pipe, after the catalytic converter where the after O2 Sensor connects. This pipe is specific to manual and automatic transmissions.
   
   
6. Exhaust Pipe Assembly-Center, Rear - The pipe that connects the "front" exhaust pipe assemblies to the mufflers. This pipe has a built-in resonator and a hard "Y" at the end which has connector flanges where the mufflers attach.
   
7. Muffler Assembly - Connects to the Exhaust Pipe Assembly-Center, Rear. The last element in the exhaust setup.
   
   

#1 and #2, collectively, are known as the "manifold". The Joint-Pipe Assembly-Front is also called, individually, the "Cross-over Pipe" (CP) which is available as an Aftermarket (AM) replacement for the stock version and it will also contain a flex-joint. The complete assembly (Manifolds and CP) can, and often is, replaced by a complete aftermarket (AM) "header" assembly either in a stock-type Unequal Length (UEL) or an Equal Length (EL) header style.

#3 is known as the "UpPipe" (UP). In AM versions, this can be solid, or contain a flex joint similar to the flex joint in OEM pipe.

#4 and #5, collectively, are known as the "Downpipe" (DP). This can be purchased (AM), with a catalytic converter, or without. Those with catalytic converters, always have a bung for the OEM O2 Sensor, and possibly an additional stub for an aftermarket A/F sensor. Most AM non-catalyst DPs do not have an O2 sensor bung and are essentially a straight pipe (often referred to as a "track" pipe). Connectors flanges can be either OEM "donut" (DF) or "flat" (FF) type connectors. DF type connects directly to the stock mid-pipe FF requires an adapter. Like OEM the DP is specific to automatic and manual transmissions.

#6 is known as the "MidPipe" (MP). In AM versions, this may contain a resonator, though it typically does not. It also, typically has a separate "Y-Pipe" and is flanged on both ends to connect to the MP and the mufflers. See #7 below.

#7 AM Mufflers can be OEM-Y-Pipe connector flange style, or specifc to the AM MP/Y-P connectors.

The 05-06 OEM uppipe has a flex joint in it? I really thought that was a solid pipe, but I admit I never removed the heat shield from mine to inspect it when I took it out. Huh? Learn something new everyday on LGT.com.

Learning is good.