Catted DP vs Catless DP + (aftermarket) cat in midpipe

(05 LegacyGT 5MT)

So I've pretty much decided that Stage 2 is where I'd like to be. I want to pass emissions and stay "road-legal" (don't wanna be towed for lacking cat), so I will need one cat.

I have decided on the CNT Catless Uppipe, but I'm deciding between the CNT Catted or catless Downpipe.

Catted would make things simpler; I'd just run a custom 3" exhaust (from downpipe) with a resonator and muffler(s).

But would it be worthwhile to go with a Catless DP and put a custom 3" cat "downstream" instead? Would this route confuse sensors? Is this beneficial in any way?

I'd be getting an infamous tune, would that eliminate any CELs?

Thanks!

no sniffer. obd only.

Visual fail though...

Thats what I'm expecting when they look at mine, I'm sure they do a cat check like they do here in CT.

If you are planning on putting a cat in the DP or even further down stream then you might as well just get the catted DP. For the sake of the sensors the catted DP will save you some O2 issues. It will be easier than trying to add one in and a tune for a stage 2 set up should eliminate any CELs. In NJ all we have is the OBD scan but a cop can still ticket you if they check under the car and find nothing. Not sure how Canada does it.

-Jake

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I've yet to go to a station that does a visual of the whole exhaust system.

2nd...

(knocks on wood)

Agreed, catted doesn't cut down on your performance on a street driven car. On a track only car, catless is the way to go.

-mike

If you are planning on putting a cat in the DP or even further down stream then you might as well just get the catted DP. For the sake of the sensors the catted DP will save you some O2 issues. It will be easier than trying to add one in and a tune for a stage 2 set up should eliminate any CELs. In NJ all we have is the OBD scan but a cop can still ticket you if they check under the car and find nothing. Not sure how Canada does it.

 

-Jake

 

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Thank you! Just what I wanted to hear! You can't pass an eTest here with a CEL, and they do a sniffer + visual. A buddy's buddy got his car towed since he was catless. Do _NOT_ want that trouble!

Agreed, catted doesn't cut down on your performance on a street driven car. On a track only car, catless is the way to go.

 

-mike

For a track car, sure. But for a road car I agree, definitely get it catted. Last thing you want to do is be in front of a cop car at a light and have him sniff your cars stinky butt. Emissions violations are not cheap.

Get a cat for about $150 more. Its well worth it down the road, your car wont smell awful when at a stop light and you will be saving the environment as well. the cat is an amazing invention and it would be terrible for us not to use it. Non cat systems are for Race applications. for normal street driving and a Conservative OTS Stage 2 Tune, Catted is just fine. Go Catted.

I was always planning to run a cat. Just where is what I was wonderin about.

I was always planning to run a cat. Just where is what I was wondering about.

Cat's require a certain temp to be effective. Temperature and pressures in the exhaust are higher before the cat. If you put the cat further downstream, you may not have enough heat to get it working, and you will have an extra hot, long run of pipe before the cat, throwing lots of heat. If you were to say, put a cat where the stock resonator is, I would recommend heat wrapping the section before it to keep heat in and temps up.

What are you thinking for a "custom" exhaust? Anything crush bent is a waste of time, trust me. Your local shop (probably) does not have a mandrel bender. It is going to be labor intensive to build out of mandrel sections, but it can be done.

I had recently considered taking a cheap catless downpipe, a 300 cell cat, some v-band clamps, and making up a swappable setup where the cat can be easily removed for "offroad" use. Just a thought.

with catted, you don't gain as much power as the uncatted but you also run into fewer problems.

That's a bit simplistic. Cats come in many chemistries, sizes and cell counts. While the factory ceramic items are very restrictive, the cats used in WRC cars are shown to cause no loss of power whatsoever. A good aftermarket metal substrate cat should show little to no losses over a catless downpipe. Perhaps a slight hit in spool.

Cats work when they are hot. Putting it downstream simply reduces its effectiveness.

Street cars should have cats. Simple.

That's a bit simplistic. Cats come in many chemistries, sizes and cell counts. While the factory ceramic items are very restrictive, the cats used in WRC cars are shown to cause no loss of power whatsoever. A good aftermarket metal substrate cat should show little to no losses over a catless downpipe. Perhaps a slight hit in spool.

All of this is correct.

I had recently considered taking a cheap catless downpipe, a 300 cell cat, some v-band clamps, and making up a swappable setup where the cat can be easily removed for "offroad" use. Just a thought.

Thats what I do on my Beretta...

One pipe has a Cat the other pipe has a shell of a cat and a 3" cutout... The cat shell is there to simply give the exhaust gases somewhere to expand and quite it down a bit Since I'll install that part and drive it that way to the strip... With just the 3" cutout the exhaust was ridiculously loud. I mad the cutout/cat piece removable since it hangs a bit low for driving it on the street.

I'm going to be welding in a small Magnaflow Ceramic cat in the legacy soon since I'm a bit tired of the stink, and with how much I drive it, it simiply just should have a cat.

Also for guys who plan to swap out an offroad catless when they get to the track, make sure you have a tune ready to load onto the ecu when you do that. The tune will be different for cat v. catless (it may not yield different hp/torque but the tune itself is going to be a little different)

-mike

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