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Discussion Starter · #1 ·
So a few months ago I had my SLP Loudmouth II exhaust installed. My question is this. If I install high flow cats, will I get a better sound and performance, or just better flow? I've also heard that MPG will increase with this mod. Comments, suggestions?
 

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High flow cats will yield higher flow which gives you higher HP. But the higher flow will most likely also give you a check engine light with a code that the emissions checkers love to bust your balls over. That's my understanding at least.
 

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depends on what hi flow cat you use. the jba's and mopar's are supposed to work without throwing codes. while Kooks, slp, etc somtimes do but not always.
 

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Discussion Starter · #4 ·
I think I'll just go with long tube headers. Long tube vs. High flow cats? I'm just guessing that the headers would give better performance right?
 

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high flow cats are at the end of the long tube headers

the difference between longtube high flows and shorty high flows is that shortys high flows are considered "catted mid pipes" because you need pipes on both sides of the cat to reach your xpipe and your shorty's collector.

long tubes collector bolts straight onto your cats, which has a shot tube that bolts straight up to your xpipe.

thusly long tubes are so much longer they dont need catted mid PIPES. they just have cats on teh end of the tubes.

if you go with long tubes. u get high flow cats.
if u get shorties u get high flow catted midpipes.
the difference is the header length, not the type of cat you have
(ok maybe slight difference from brand to brand, but not really)
 

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Discussion Starter · #6 · (Edited)
high flow cats are at the end of the long tube headers

the difference between longtube high flows and shorty high flows is that shortys high flows are considered "catted mid pipes" because you need pipes on both sides of the cat to reach your xpipe and your shorty's collector.

long tubes collector bolts straight onto your cats, which has a shot tube that bolts straight up to your xpipe.

thusly long tubes are so much longer they dont need catted mid PIPES. they just have cats on teh end of the tubes.

if you go with long tubes. u get high flow cats.
if u get shorties u get high flow catted midpipes.
the difference is the header length, not the type of cat you have
(ok maybe slight difference from brand to brand, but not really)
I see now. I was under the impression that the with the long tubes you didn't need high flow cats at all and that was the reason that it threw codes and was tough to pass Smog. I figured that for the short tubes I would need catted mids. Thanks 4 the clarification & info.
 

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theres a lot of different ways to do it. i mean you can keep the stock "headers" and just replace the cats, it would be a lot cheaper and easier install, but you wouldnt get the same gains. all longtubes except for the mopars have thrown codes. i'd love to tell you exactly why but i think its just a combination of things (increased flow, different exhaust temperatures, the high flow cats, i dk). but like dudeiwin said, if you get LT's or shorties then you should definitely replace the cats. on long tubes u'll have to
 

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btw in reference to my above post... the collector is the area in which the 4 tubes from your exhaust ports come together and the exhaust collects and comes into 1 pipe


all long tube sets come come with high flow cats( i think). i know the mopars do, its included in their price of 1100. best bang imo. less you wanna spend more time at the track. then you may wanna look into the bigger ones.

the reason they dont pass smog is because they relocate the position of your cats.

in cali, if your cats move from any position that is not the way they came from the factory, you can fail. even if you pass the 02 inspection.

its possible to use some of the higher output long tubes (kooks, SLP, dynatech/dynomaxx) and not get codes, but it takes proper placement of teh sensors, and sometimes a bit of tuning. theres also something.. oh what are they... something you can insert in your headers by drilling holes, i think upstream of the sensors that help to reduce the chance of your codes bein thrown.

called like 02 Foulers or something i cant remember.

even then, even if you get a longtube setup that throws no codes. in cali a lot of times you will still have so much exhaust flow that the tail sniffer they put up your exhaust pipe will still get angry and you could fail.

a lot of cali guys on here just find a uh... how do you say.... friendly neighborhood inspection dude? that or keep the stockers to throw on when u gotta inspect. apparantly in cali you dont have to get a new car inspected until 5 yrs after you bought it.

here in TX< you gotta do it once a year. but we dont have nearly as strict of tests :p w00t w00t texas wins!
 

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Discussion Starter · #9 · (Edited)
theres a lot of different ways to do it. i mean you can keep the stock "headers" and just replace the cats, it would be a lot cheaper and easier install, but you wouldnt get the same gains. all longtubes except for the mopars have thrown codes. i'd love to tell you exactly why but i think its just a combination of things (increased flow, different exhaust temperatures, the high flow cats, i dk). but like dudeiwin said, if you get LT's or shorties then you should definitely replace the cats. on long tubes u'll have to
So if I do just the long tubes with stock cats I'll see a good gain, but if I do Long tubes with high flows then It'll be even better right? So how much more HP will the high flows give you on top of the long tubes?
 

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Discussion Starter · #10 ·
all long tube sets come come with high flow cats( i think). i know the mopars do, its included in their price of 1100. best bang imo. less you wanna spend more time at the track. then you may wanna look into the bigger ones.

the reason they dont pass smog is because they relocate the position of your cats.

in cali, if your cats move from any position that is not the way they came from the factory, you can fail. even if you pass the 02 inspection.

its possible to use some of the higher output long tubes (kooks, SLP, dynatech/dynomaxx) and not get codes, but it takes proper placement of teh sensors, and sometimes a bit of tuning. theres also something.. oh what are they... something you can insert in your headers by drilling holes, i think upstream of the sensors that help to reduce the chance of your codes bein thrown.

called like 02 Foulers or something i cant remember.

even then, even if you get a longtube setup that throws no codes. in cali a lot of times you will still have so much exhaust flow that the tail sniffer they put up your exhaust pipe will still get angry and you could fail.

a lot of cali guys on here just find a uh... how do you say.... friendly neighborhood inspection dude? that or keep the stockers to throw on when u gotta inspect. apparantly in cali you dont have to get a new car inspected until 5 yrs after you bought it.

here in TX< you gotta do it once a year. but we dont have nearly as strict of tests :p w00t w00t texas wins!
:lol: ... and yes luckily I do have a "friendly" neighborhood ,certified smog check mechanic, which let me know that if I ever needed some "help" with my Smog check, that he's the man for the job.

I wasn't aware that the Mopar Long tubes came with high flow cats. It's a good thing that they were my first choice!:)
 

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yessir they do. technically they are considered more of mid length headers which is why they never give CELs.

they were my first choice as well. but the JBA was a very clsoe second and i chose them instead and got the total package (including mids/catback) and so far im really pleased, without even having the cats on yet(damn backorder! i get em this week hopefully)

go for them mopars!

oh and the mopar "hp increase" or wahtever they tell you, is with those high flow cats.

hope ive been helpful, post up if u got more question, ive become pretty well versed on the bolt ons since ive spent WAY too much time researching for myself :)
 

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yep I have the mopar LT's and ive noticed some good pickup as the car has adjusted to them. im seeing MR squiggles much more often now. you will like it.
 

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Discussion Starter · #13 ·
I think I got all of the info I needed out of you guys. Thanks a lot for the tips!
 

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Has anyone done any dyno's that rate the LT's available?
 

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yes lots have. An RT with CAI, lt's, highflows, cat back and tune usually sees about 315-335 rwhp (stock runs about 280)
 

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I've got high flow cats and LT headers from Dynatech. I love the sound and performance and will dyno it pretty soon. My only concern is (at least with these cats) that 1) they sit a bit lower than stock so be careful when you go over the bumps, I've already scratch the bottom of my cats a bit :( 2) They cause a CEL (code P2096). There are these lower O2 sensor spacers (called O2 Simulator) that are supposed to take care of the P2096 CELs. I installed them but the same CEL came back on again. So now I'm working with my service guy to come up with a solution to "fool" the computer to turn off the CEL. My car is 2007 so still have a few years before needing to do Emission testing. Hopefully by then I'll find a solution. And finally I'd also go with a set of cylinder heads, it costs some $$ but it is all worth it! The car really goes and pulls hard :D
 
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