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high flow cats #2454842
02/20/18 11:28 PM
02/20/18 11:28 PM
Joined: Jan 2003
Posts: 28,063
Irving, TX
feets Offline OP
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Irving, TX
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
Re: high flow cats [Re: feets] #2454944
02/21/18 03:55 AM
02/21/18 03:55 AM
Joined: Jan 2003
Posts: 20,644
So Near, Yet So Far
topside Offline
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So Near, Yet So Far
There's one on my GMC Dually - which is just like your MBZ, right? - and it picked up some grunt, has no odor, and sounds pretty husky with a Dynaflow muffler and otherwise stock full exhaust.
Probably not much help except the bump.

Re: high flow cats [Re: feets] #2454949
02/21/18 04:13 AM
02/21/18 04:13 AM
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Posts: 5,994
Salem
Grizzly Offline
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Salem
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. shruggy

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. twocents

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".
Re: high flow cats [Re: feets] #2454991
02/21/18 09:56 AM
02/21/18 09:56 AM
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Posts: 4,910
new berlin wisconsin
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Mr T2U Offline
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new berlin wisconsin
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
Re: high flow cats [Re: feets] #2455037
02/21/18 12:38 PM
02/21/18 12:38 PM
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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
Re: high flow cats [Re: feets] #2455095
02/21/18 02:42 PM
02/21/18 02:42 PM
Joined: Mar 2007
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West Coast, USA
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Originally Posted By feets
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)
Re: high flow cats [Re: feets] #2455272
02/21/18 08:50 PM
02/21/18 08:50 PM
Joined: Jan 2003
Posts: 25,618
Rio Linda, CA
John_Kunkel Offline
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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
Re: high flow cats [Re: John_Kunkel] #2455291
02/21/18 09:39 PM
02/21/18 09:39 PM
Joined: Jan 2003
Posts: 28,063
Irving, TX
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Irving, TX
Originally Posted By John_Kunkel
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
Re: high flow cats [Re: feets] #2455365
02/21/18 11:55 PM
02/21/18 11:55 PM
Joined: Jan 2003
Posts: 4,394
The Pale Blue Dot
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The Pale Blue Dot
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.

Re: high flow cats [Re: feets] #2455676
02/22/18 04:08 PM
02/22/18 04:08 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline
super stock
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Chicago
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"
Re: high flow cats [Re: feets] #2455683
02/22/18 04:20 PM
02/22/18 04:20 PM
Joined: Jan 2003
Posts: 8,390
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
Re: high flow cats [Re: Skeptic] #2455952
02/23/18 01:43 AM
02/23/18 01:43 AM
Joined: Jan 2003
Posts: 28,063
Irving, TX
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Originally Posted By Skeptic
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. biggrin


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
Re: high flow cats [Re: feets] #2456070
02/23/18 12:31 PM
02/23/18 12:31 PM
Joined: Jan 2005
Posts: 4,366
Michigan
MarkZ Offline
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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
Re: high flow cats [Re: feets] #2456100
02/23/18 01:32 PM
02/23/18 01:32 PM
Joined: Sep 2003
Posts: 19,239
north of coder
moparx Offline
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north of coder
Originally Posted By feets

As for passing emissions, yeah, I can do that. biggrin


cheater, cheater, chicken dinner ! tsk or however that goes...... biggrin
beer







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