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Old 09-21-2018, 10:00 PM   #15
rontammy0
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Quote:
Originally Posted by anth331 View Post
I’m thinking of either getting headers and the high flow cats or just getting the 3.91 gear swop I can only do one
Do gears and a stall....you will hurt feelings yet look completely stock.
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Old 09-22-2018, 06:35 AM   #16
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Quote:
Originally Posted by anth331 View Post
Do Hi Flow Cats really give you any more horsepower or, just make it louder?
I have a 13 SS L99 was thinking about buying some.
Yes high flow cats do add more power and add more volume to the sound. High flow cats with long tube headers will give you the best performance but will require a tune. If you don't want to tune the car and don't plan on putting headers on, or already have shorty headers, then high flow cats by themselves that bolt to the factory manifolds or shorty headers are a great upgrade.

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Originally Posted by HyperV117 View Post
I've heard that the stock cats actually flow pretty well. The only reason I have them is because the guy I bought my LTH's bundled them in. Otherwise I might have just gone with offroad pipes.
The stock cats are the biggest choke point in the 5th gen Camaro's exhaust. Once they're replaced or removed with an aftermarket high flow or off road piece the exhaust gets louder and the car makes noticeably more power.
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Old 09-22-2018, 08:52 AM   #17
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Bought these with long tubes, couldn't be happier.
Certainly increased the sound and power !
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Old 09-22-2018, 09:53 AM   #18
rontammy0
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Bought these with long tubes, couldn't be happier.
Certainly increased the sound and power !
How much were they if you dont mind me asking? It would be good to know if the cats that came with my longtubes ever puked.
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Old 09-22-2018, 11:46 AM   #19
christianchevell
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When I bought my stainless powers long ago they were about $200 for a pair of HFC and keep the car legal for having cats.

For the OP; Highflow cats in your case would mainly be used with various shortie headers not stock exhaust #1 by members on here over time I have read about, there are replacements out there the size of the stock two Cat set up but neither shorties or the cats fitting them are recommended as they are the set up mainly forced on those just squeezing by with SMOG inspections if lucky enough to do them in some areas. They would increase power slightly and the headers also even if shorties but not near as much as long tube headers. Either way with just highflow cats or shorties and HFC, or Longtubes and HFC your going to have to tune for the change.

On long tubes due to the difference in the distance the 02 sensors are the rear set gets disabled,( as it basically makes just mild adjustments from the readings between the two sensors );and readings of unspent fuel were done just fine by one set on many many prior engines before they invented two 02 systems for decades …. But the difference in distance calls also for the front o2s to not have a delayed response CEL code being activated eventually as its further down the pipe.....so to speak.

And the exhaust flow is better with longtubes and a merge spike is a nice feature on them and sizing along with stainless content which can vary things to check out. Changing the car to headers does lead to eventual starter heat soak issues where occasionally a person has to let it cool off if starting and restarting in hot weather like 90 degree stop and go and can lead to a dragging starter until its cooled off...just a fact of hot rodding life, and wrapping headers can help , a heat sock or shield for the starter....not so much it can also hold in heat..have one...and the stock heat shield is just a little curved piece of metal not effective.... Anyway just some thoughts on headers and HFC's I love mine help torch the gas for nice Decel popping on my dual mode and take out some rasp. On the other hand many if not most going FI do not do cats as they can fry them if things are not going well and that could lead to other problems, and then there is ….a 10k fine that could be levied against shops intentionally removing cats from cars equipped with them..rarely heard of but its out there and some shops absolutely refuse to remove and not replace cats.... Just FYI....have a nice day.

Headers HFC the way to go to avoid some gas smell and make power and sound and reduce some rasp with the HFC IMO and many others if you can go there...… other than that you could have to tune just for going high flows depending on which ones and the location of the sensors and if the stock ECU can handle the change in the info between the two O2s as they most likely are responding quicker and locations altered. There are of course threads about people going SOLO high flow cats or shorties in the site you can search over for more info.
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