Anyone run high-flow Cats to reduce hydrocarbon exhaust smell?

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jbc426

jbc426

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My cam has significant overlap, so the car smells rich at idle even running at 14.5 A/F. I started researching what guys are doing to combat the smell, and found a lot of guys run the high flow race catalytic converters with very good results. Anyone have any experience with this. I have a convertible, so it is an issue on cruises.

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14.5 is not the best mix for every situation. Might look into your tuning first: timing, carb tuning (not jets - power valve, air bleeds, etc).
Cats do lower the emissions but can also get overheated with too much fuel going into them. And, over-rich cats can smell a LOT worse...lol. Might want to possibly change cams if you can't get it better or tune it out.
For tuning help you could provide a lot more combo info.
 
Not discounting the use of cats but make sure everything else is optimized first as Moper says. He's right too, about over-rich cats smelling awful. Also, where & how are your exhaust pipes terminated?
This info is from slantsixDan
"These are very square-bodied cars that tend to create low-pressure areas behind them. With a straight-out-the-back tailpipe you're pulling exhaust along with you, which is (at best) unpleasant. With a down-discharge tailpipe, the exhaust hits the slipstream and doesn't get pulled along.

This is related to the reason why station wagons have side-(and down-)discharge tailpipes; the rear body shape of the wagon tends to create a BIG low-pressure area right behind it, so it really drags exhaust along, which is extra-dangerous because of the openable tailgate glass."
 
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No. I love the smell of hydrocarbons.
 
Timing! Please tell us the curve? Cam specs? My car would burn your eyes outta your head at 15 degree initial. I thought that was aggressive. I was coached and ended up at 26 initial. The car fires up with a flick of the keys. Idles nice and is crisper then a Doritos chip. I have a big cam and will always have overlap rich conditions but is far better then it was
 
jbc426 said:
My cam has significant overlap, so the car smells rich at idle even running at 14.5 A/F. I started researching what guys are doing to combat the smell, and found a lot of guys run the high flow race catalytic converters with very good results. Anyone have any experience with this. I have a convertible, so it is an issue on cruises.

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Are you injected,on an operating feedback loop?. Looks injected in your picture,what system firing injectors?
 
Why put emissions controls, which are a Band-Aid at best, on cars that don't require them? Some day the gov't will probably require it. Until that day comes, why would you want these costly and complex systems? Figure out what's wrong. Don't just put a Band-Aid on it!
 
While I would not run a cat unless leagally bound......

I did have to run cats on my Magnum many years ago when N.Y. State decided to up the anti and follow the standards set by California. Our cars were subject to a rolling dyno to prove it was good even at Hwy. speeds.

Even though my '79, 360 engine was stock except the Federal-Mogal 625 emmisions leagally carb, MSD6A, and dual exhaust off the exhaust manifolds, it was dual exhaust with an H pipe. Twin high flow cats were employed.

The whole exhaust system was custom bent and 2-1/4 inch stem to stern. I do forget where the cats were by. But the exhaust smell did clean up. Proper jetting and the car passed. Later, the MSD was added later and it really helped a lot. Dropping emissions even more while picking up mileage. Not so much in power.

How big is your cam and what is the engines compression?what carb are you running and its jetting? Step up springs/power valve?
 
Abodybomber said:
Are you injected,on an operating feedback loop?. Looks injected in your picture,what system firing injectors?
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Yes, it's injected and the feedback loop is operating as designed. The smell is only an issue at idle and/or very low speeds. The 3" TTI exhaust w/ H-pipe, turbo mufflers and oval megaphone tips exits at the rear.

The tune is custom, installed with a SCT Tuner using a factory OBDII JTEC computer. Performance, drivability and cold & warm start is impressive. The cranking compression is 195 to 200 psi. My cam is ground with a 108 degree lobe separation angle, 246 & 252 @ .050 with .560+ lift. I'm pretty confident overlap is the main source of the excess hydrocarbons in the exhaust at idle/ very low idle.

A lot of Chevy guys running similar cams and set-ups in their LS motors talk about the same issue.They write about using the pre-OBDII style metal substrate race cats to successfully eliminate the problem with no loss in power. Some of them even claim performance gains.

I understand that cats have a reputation as an smog related hindrance to performance that our older cars never came with, but design and performance advances have brought them a long way. Look at the Hellcat and super charged GM performance with cats.
 
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At first I thought you were using a carb and was thinking "Hah good luck" but since you have EFI... I'd say give it a shot if you're down with spending the money. No guarantee it will work and/or last a long time but I'd be interested to see what happens lol
 
I recently installed an aftermarket cam in my 06 SRT8 charger and ran it catless for 1 week. Smell at idle was pretty bad. Installed 3" Magnaflow spun metallic high flow cats and the smell is now gone with no loss in 1/4 mile performance.
 
Fast340cuda said:
I recently installed an aftermarket cam in my 06 SRT8 charger and ran it catless for 1 week. Smell at idle was pretty bad. Installed 3" Magnaflow spun metallic high flow cats and the smell is now gone with no loss in 1/4 mile performance.
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Good info! I've go a set on the way. They were just under $110 each, and slip fit to my collector flanges on one side and into the shortened pipe on the other.
 
magnummopar said:
Are you running an upstream and downstream O2 sensor or did you have the rear turned off with the flash?
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I have the upstream O2 installed just after the collector, and am running an O2 simulator for the non-existent down stream sensor.
 
magnummopar said:
I would install the downstream after you put cats on, it will run much better.
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It's turned on. The O2 simulator produces a nearly perfect wave pattern that mimic a perfectly tuned condition. Are you saying the computer is thereby tricked into further self-regulating the fuel trims etc? I wondered about that.
 
Second the vote for cats and running a downstream.

While they can and do function well with only the upstream, this is not reflective of the capabilities of the system as a whole.

The downstream sensor's primary function is to check the function of the catalyser but it also imparts data (at least in OE systems) to help with the modulation of air/fuel ratios.

It may be a good idea if you're thinking of this to either read the data sheet and tech manual for the injection setup, or contact the manufacturer directly. This will let you know if running a downstream sensor is beneficial and you can go from there.

- boingk
 
I plan to run cats too. Reason being is I don't want to smell like exhaust and I intend to enjoy my car with my family including my kids and I'd prefer to not destroy their brain cells with CO, CO2, NOX and HC gas emissions. I'm also not concerned with the 10 hp I'll loose at 6000 rpms from it.
 
Im old school and say "F" the cats!!!!!! but if you're using a computer and injectors, that will set the trim by reading the o2 on both side of the cat. Use the pre and post o2s as it will keep the cat tuned and will last A WHOLE LOT LONGER!
 
FWIW if I had EFI on my Duster I would seriously consider putting in some high-flow cats. The smell of pump gas fumes just gives me a headache nowadays; but race gas, that's another story of course lol!
 
MOPEkidD-3 said:
FWIW if I had EFI on my Duster I would seriously consider putting in some high-flow cats. The smell of pump gas fumes just gives me a headache nowadays; but race gas, that's another story of course lol!
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I agree about the fuel being burned as it relates to the fumes. I am running this car on 91 octane California pump gas, and the fumes are obnoxious. My 1970 E-Body burns 101 octane Street Blaze. Those fumes smell wonderful. I get compliments on those fumes all the time.
 
Yeah - it's the overlap. I think you'll be fine running them given the EFI. If you do get into a long period of idle situation you may get the cats hot and/or smell. I would include some basic shields on the cats and and interior insulation under the carpet as your floor will conduct a lot of that heat to the carpet. Modern cars use a ton of thermal shielding.
 
jbc426 said:
I agree about the fuel being burned as it relates to the fumes. I am running this car on 91 octane California pump gas, and the fumes are obnoxious. My 1970 E-Body burns 101 octane Street Blaze. Those fumes smell wonderful. I get compliments on those fumes all the time.
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dano said:
I plan to run cats too. Reason being is I don't want to smell like exhaust and I intend to enjoy my car with my family including my kids and I'd prefer to not destroy their brain cells with CO, CO2, NOX and HC gas emissions. I'm also not concerned with the 10 hp I'll loose at 6000 rpms from it.
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Plus you get the added benefit of your and my children having cleaner air to breathe...nothing worse than getting behind an old logging crummy at a red light with bad rings and crap jetted holley making the air unbreathable and your kids choke...being from PNW, I am sure you know what I am talking about:eek:

Cudafever said:
Im old school and say "F" the cats!!!!!! but if you're using a computer and injectors, that will set the trim by reading the o2 on both side of the cat. Use the pre and post o2s as it will keep the cat tuned and will last A WHOLE LOT LONGER!
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I missed something, the only way I know how to tune a cat is to take its guts out and string your guitar with them, otherwise, its just a metal can filled with ceramic honey comb and precious metals, no way to tune it.

jbc426 said:
I agree about the fuel being burned as it relates to the fumes. I am running this car on 91 octane California pump gas, and the fumes are obnoxious. My 1970 E-Body burns 101 octane Street Blaze. Those fumes smell wonderful. I get compliments on those fumes all the time.
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101 doesnt have any alcohol in it nor any fuel conditioning/cleaner in it thus the sweet smell of performance...
 
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