high flow cats
#2454842
02/20/18 11:28 PM
02/20/18 11:28 PM
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Joined: Jan 2003
Posts: 28,069 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
Joined: Jan 2003
Posts: 28,069
Irving, TX
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Have any of you played with high flow cats on your late model cars? I'm looking at swapping the cats on my pint size Benz. They're known to be a choke point and I'd like to open it up a bit. My concern is making sure the car doesn't get stanky exhaust like old cars and the cat-delete modified AMG cars we get in the shop.
The cats on this thing are really short and fat (bodies 4" long and 6" in diameter) and I'd like to try keeping them in the same space if possible.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: high flow cats
[Re: feets]
#2454949
02/21/18 04:13 AM
02/21/18 04:13 AM
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Joined: Aug 2005
Posts: 6,017 Salem
Grizzly
Moparts Proctologist
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Moparts Proctologist
Joined: Aug 2005
Posts: 6,017
Salem
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Feets, I only get that smell when my truck is cold. A few minutes and the rotten egg smell goes away. Thinking you are experiencing the same thing when a Customers' car gets fired up out in the lot and gets rolled into your shop. If I had to pin point when the smell goes away, I'd say it's when the O2 sensor has enough exhaust heat in it to go open loop. Also trying to say: throw those convertors in the garbage, live with the smell, and enjoy your 20hp and +2mpg you'll be getting.
Mo' Farts
Moderated by "tbagger".
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Re: high flow cats
[Re: feets]
#2454991
02/21/18 09:56 AM
02/21/18 09:56 AM
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Joined: Apr 2005
Posts: 4,923 new berlin wisconsin
Mr T2U
master
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master
Joined: Apr 2005
Posts: 4,923
new berlin wisconsin
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i had kooks high flow cats on my 08 bullitt mustang. car is heavily modified with gt500 supercharger and other mods, makes 650 rwhp.
the cats worked just fine as far as flow and no stink. the problem was they flowed to well. the computer didn't read enough temp differential between the front and rear o2 sensors, or whatever the computer checks with the rear o2's, and thought the cats were defective. it gave me a check engine light. the newer "green" cats from kooks are supposed to correct that problem.
perception is 90% of reality
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Re: high flow cats
[Re: feets]
#2455037
02/21/18 12:38 PM
02/21/18 12:38 PM
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Joined: Jan 2003
Posts: 28,069 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
Joined: Jan 2003
Posts: 28,069
Irving, TX
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The smell I'm talking about is unburned fuel. The owner-straight-piped AMG cars we get in the shop stink like an old carburetored car running rich. I don't want to get that stink in my daily driver.
As for the downstream O2 sensors, they've been disabled already.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: high flow cats
[Re: feets]
#2455095
02/21/18 02:42 PM
02/21/18 02:42 PM
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Joined: Mar 2007
Posts: 3,287 West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,287
West Coast, USA
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The smell I'm talking about is unburned fuel. The owner-straight-piped AMG cars we get in the shop stink like an old carburetored car running rich. I don't want to get that stink in my daily driver.
As for the downstream O2 sensors, they've been disabled already. I had the same overly rich fuel stench from my EFI'd 408 Magnum at idle. That was the only time I noticed it anyway. It was bad enough that anyone near the car would get all offended and try to fan them away while I cruised through. I have a full TTI 3" exhaust, and welded in a pair of relatively short (7 " by 3" inlet & outlet with about a 4" thick body) metal matrix, high-flow cats just after the collectors. The metal matrix honeycombed structure is coated with the same rare metals as the ceramic matrix cats, but they flow 30 to 40% more. It made a huge difference in cleaning up the smell. It's gone now, except when you first start the car. It takes a few minutes for the cats to get hot enough to "light off". It very slightly smoothed out the exhaust note, but there was absolutely no difference in power output. The little 408 spins out 630 ft lbs of torque with no power adder. I may install them on my 500" RB if I can't get the idle to clean up more with some fine tuning. I think most of my problem is from the overlap I'm running on the cams, as the A/F ratios are nearly perfect.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: high flow cats
[Re: feets]
#2455272
02/21/18 08:50 PM
02/21/18 08:50 PM
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Joined: Jan 2003
Posts: 25,951 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,951
Rio Linda, CA
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Put Hi-Flow cats on my Viper, no stink and it passed California Smog Check with numbers close to stock. Was louder though.
The INTERNET, the MISinformation superhighway
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Re: high flow cats
[Re: John_Kunkel]
#2455291
02/21/18 09:39 PM
02/21/18 09:39 PM
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Joined: Jan 2003
Posts: 28,069 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
Joined: Jan 2003
Posts: 28,069
Irving, TX
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Put Hi-Flow cats on my Viper, no stink and it passed California Smog Check with numbers close to stock. Was louder though. You'd notice the stink with side exit exhaust. Do you remember if they were 100 or 200 cell cats?
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: high flow cats
[Re: feets]
#2455676
02/22/18 04:08 PM
02/22/18 04:08 PM
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Joined: Jul 2011
Posts: 960 Chicago
PurpleBeeper
super stock
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super stock
Joined: Jul 2011
Posts: 960
Chicago
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I don't recommend high-flow cats IF you live in an area that runs emission test. My high flows threw a P0420 code immediately.
If no emission tests in your area, then I recommend the shortest-nothing-inside-them cats you can find OR just cut open your cats, gut them & weld them back up (hollow)....my 2-cents.
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"
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Re: high flow cats
[Re: feets]
#2455683
02/22/18 04:20 PM
02/22/18 04:20 PM
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Joined: Jan 2003
Posts: 8,403 Highland, MI.
Sunroofcuda
master
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master
Joined: Jan 2003
Posts: 8,403
Highland, MI.
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OE cats typically have 400-600 cells per square inch, plus as prev. mentioned, aftermarket cats do not have nearly as much washcoat (precious metals) applied to the bricks, thus the much lower price vs. OE. Also, much shorter lifespan & durability than OE. Also, the only aftermarket cats I'm aware of that are 50-state legal are Magnaflow - they ponied-up the $$ to gain CARB approval.
No Man With A Good Car Needs To Be Justified
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Re: high flow cats
[Re: Skeptic]
#2455952
02/23/18 01:43 AM
02/23/18 01:43 AM
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Joined: Jan 2003
Posts: 28,069 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
Joined: Jan 2003
Posts: 28,069
Irving, TX
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Smell from Catalytic Converters is from 1-sulphur in the fuel and 2-overly rich A/F-i.e. poor tuning. Cats are purely reactive, they don't add anything. The Cats that trip the P0420 codes are just crap, you might as well just straight pipe 'em. The reason they trip the lights is that they scrimp on the expensive Platinum and Palladium. Thank you for the remedial class in catalytic converters. Again, I'm not concerned with the sulfur smell. That isn't happening. I simply want a cat that will be moderately effective and not smell like straight piped exhaust. As for passing emissions, yeah, I can do that.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: high flow cats
[Re: feets]
#2456070
02/23/18 12:31 PM
02/23/18 12:31 PM
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Joined: Jan 2005
Posts: 4,450 Michigan
MarkZ
Worthy
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Worthy
Joined: Jan 2005
Posts: 4,450
Michigan
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If the quality of aftermarket cats are that bad I wonder if you could find an OEM set that were pulled from a car with a similarly rated power level.
1987 Fifth Avenue - 512/518/D60
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