Secondary cat delete / add downpipe - Hyundai Genesis Forum
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post #1 of 4 Old 06-12-2019 Thread Starter
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Secondary cat delete / add downpipe

Any gains deleting my secondary cat and adding a downpipe?
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post #2 of 4 Old 06-15-2019
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Removing any cat will free up your exhaust flow and give some gains. I always run with the primary cat in and delete the secondary with a Megan Racing test pipe, this particular one is resonated so it helps tone the exhaust a bit lower. I noticed a definite difference just from this alone but of course nothing super amazing.

Most of the downpipes out there are 3 inch and going from 2.5 -> 3 -> 2.5 inch pipes will work. But in my experience the gasket that came with mine were barely a good fit I had trouble with exhaust leaks. Had to hunt down a 2.75" gasket to use instead.

If you decide to get rid of both cats then I hope you do not mind smelling fuel out of your exhaust all day, to me it becomes obnoxious and overwhelming -- not what I would want for a daily driven car. Plus the CEL light.
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post #3 of 4 Old 06-16-2019
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Any gains you said? Not really to be honest with you, in my opinion it's a waste of time and money deleting the secondary cat and adding a Dp unless you plan to go full Tbe 3".

I mean think about it your removing the secondary cat that's one thing, but then your buying an aftermarket Dp which is 2.25-2.50" same as the stock,
So your spending money on a shiny SS 2.25-2.50" Dp that will give you zero gains. Only difference here is aftermarket is shiny and SS unlike stock.

If you really want to feel some gains I suggest you remove the main cat "O2 Housing" and do it right the first time and go 3" from the turbo all the way back. I am currently running and highly recommend the Turbo XS stealth back system which removes the stock o2 housing and secondary cat it's a beautiful Tig welded, SS system which retains the stock mufflers. You get the benefit of a full Tbe system without all the excess noise. Now please keep in mind this system is considered a bottleneck because you're going from 3" in from the turbo back and you're still retaining the stock mufflers which is 2.25-2.50".

This setup works great for me because I get the full benefits of a full turbo back exhaust without all the noise by retaing the stock mufflers. In the future im debating whether I'm going to get a Cat-Back exhaust to complete the 3" in exhaust system. The stealth back system is $350 and very well worth it I couldn't be more happier running this setup it's awesome!

Also the previous post mentioned smelling gas once you remove both cats. I honestly don't have that problem what so ever. I read previous threads of some forum members saying once they installed a full Tbe they smelled gas, but that only lasted for a day or two after that no more gas smell.

Also he mentioned a cell which is true once you remove the stock O2 housing, however once you get a tune that will eliminate the cell. I highly recommend you get a tune on your car as well as this is what makes the most power on this platform not the bolt on's, the bolt on's compliment the tune. I'm currently running a Prw stage 1 tune highly recommended if your a Bk1 manual tranny.

Last edited by BigBallah; 06-16-2019 at 08:30 AM.
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post #4 of 4 Old 06-16-2019
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Yes that's true, I should've clarified that getting a downpipe itself isn't going to do you any good. I also said most are 3 inch not 2.5 inch but that doesn't really matter, it won't be something you'll notice and not worth it. Deleting the secondary cat with a cheap test pipe does make a difference. I know because I've done it, and swap it out for smog checks, it's noticeable.

Not everyone wants to run with both cats deleted for one reason or another. You will smell the exhaust fumes/fuel from your car more without any cat. In the past I have heard of some people claiming it wasn't the case with their car (not a turbo genesis), but very few and far between. You'll be running rich with a turbo when you are not just cruising and you will be outputting a fuel smell. At idle it still would be noticeable in my experience. I've ran my car with and without cats and I do notice it the smell is obvious... I'm not talking about just the genesis but also 3 of my previous cars . It makes sense, the cat is there to scrub your exhaust for emissions and without it then you're exhaust fumes will smell (more than normal).

Last edited by ChiefStarBlank8; 06-16-2019 at 11:15 AM.
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