Alright, you all may think this concept is stupid and kind of defeats the purpose but here it goes. I just dropped in an ls with a gsr tranny, and plan on making some more power down the line whether I go built ls or ls/vtec, I want to just get the exhaust done since I dont like mine and I have a really bad leak, so why not just go ahead and get it out of the way? I am looking into what header I want to mate to my custom exhaust I want to get, yes custom I dont want a brand name catback, so please dont tell me to get one. I have a old DC 4-1 header I was going to use, but one of my friends has a hytech replica on his b16 and loves it. He got it off ebay for $160 and hasnt had any problems, and loves the power it makes, so im thinking what a deal!! Now I was intending to get custom 2.5 in piping to begin with and I already bought a flat black 2.5 in vibrant streetpower muffler (which ive heard great things about). Now comes the problem, I would like to run my stock cat for emissions purposes as well as keeping my exhaust from getting too loud/raspy cause I wasnt planning on using a resonator. I know the hytech replicas have a 2.5 in collector that is probably not going to work with a stock cat. My question is what should I do? Im debating getting a magnaflow 2.5 in cat, are there cats good quality? Will it keep the raspyness down? Is there an easier route to go and still keep my cat? I need to make a decision in the next week, so please somebody help me!!

 

As long as the flanges bolt up, you shouldn't have a problem. Temporarily I ran a mismatched exhaust going from a 2.5" collector to a 2.5" high flow cat to a 2.25" exhaust. I had to modify the length of the cat and swap it to a 3 bolt flange on the exhaust side, but it worked fine and was very quiet. When I later deleted the cat and changed to a full 2.5" exhaust, it turned buzzy/raspy and sounded like hell. I'm thinking the high flow cat made the difference in sound. If it's your street car, I'd keep the cat.

 

Thanks for the info!! What do you all think about a resonator? yay or ne?

 

BTW ive decided on a magnaflow 2.5 in high flow cat part # 93506, any thoughts?

 

they're good and it'll keep your noise down for DD.

 

what are your experiences with power losses though? (with the cats, high flow cats and resonators?)
When I swapped my motor from my rex to my hatch, the car dynoed (without changing anything other than cars/injectors [obd0-obd1]) with like 35 less hp... found out it was cause the resonator, cut it off, welded straight pipe on and got back up to what it showed when the motor was built...
Now I'm finally getting a new exhaust cause I hate what came on my hatch (3 in exhaust with buddy club axle back... it has a cat, but judging by sound its been hollowed) so I'm wanting to know cause i have a fully built dd ls/vtec n/a that i'm waiting on the 2.5 in piping to come in for a custom exhaust w/ fl. black vibrant muffler. I also want to cut down on raspiness, but also don't want to choke my motor! I know this is impossible but I want to find a good median and keep as much power as possible while making the exhaust quieter than it is now. also, i have a dc 4-2-1 one piece header that is probably killing me, just haven't got around to upgrading!

anyway, i've debated high-flow cats for quieting the sound, but how is it any less choking than a stock cat? Or actually, does anybody have any experience/actual numbers of difference between cat and high flow cat without changing anything else?

sorry, not trying to thread-jack, but figured you and i have such similar questions, we could both benefit from people answering either/both of our questions!

Good luck!

 

This is from a very knowledgeable member here smsp a little older post but here is part 1 of a cat test https://honda-tech.com/forums/all-motor-naturally-aspirated-44/flow-testing-results-4-catalytic-converters-1128725/ and part 2 https://honda-tech.com/forums/showth...ight=flow+cats

Going from a test pipe to a 2.5 smsp cat quieted the car down a bit the raspiness I had at 2.7k-3.2k had been silenced

 

Good info did the tone change at all with the high flow cat over the test pipe? Im concerned without a resonator its going to be really high pitched, did you notice the tone being a little deeper, or did the tone stay the same just less raspy?

 

If I get my exhaust done in the next 2 weeks like I intend to, ill let you know how it sounds.

 

Awesome man!! Thanks...

 

I would go with a resonator. The tone did change to a deeper. With the testpipe there was a raspiness around 3k that soudned hollow terrible sound I tell you LOL.