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

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↑I wrote
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!

Magnummopar wrote
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 honeycomb and precious metals, no way to tune it.

If there is not enough gas to "light", the cat, the cat will plug. If there is too much gas the ceramic Honeycomb will Melt......then plug.(and your carpet as well, without a heat shield of some sort.
 
Cudafever said:
If there is not enough gas to "light", the cat, the cat will plug.
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you have any science behind that statement ? You are saying if the engine is lean the cat will plug? On Dodge MPFI systems, the rear O2 has nothing to do with fuel trim, it is to monitor cat efficiency, however, if the pcm senses an issue in the cat it will set a code which will make the engine run worse but it doesnt affect fuel trim. Just like removing the cat will set a code because it has same voltage reading on both sensors rather than a higher reading on the rear due to more heat generating more voltage in sensor.
 
magnummopar said:
you have any science behind that statement ? You are saying if the engine is lean the cat will plug? On Dodge MPFI systems, the rear O2 has nothing to do with fuel trim, it is to monitor cat efficiency, however, if the pcm senses an issue in the cat it will set a code which will make the engine run worse but it doesnt affect fuel trim. Just like removing the cat will set a code because it has same voltage reading on both sensors rather than a higher reading on the rear due to more heat generating more voltage in sensor.
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Truth,here...
 
magnummopar said:
you have any science behind that statement ? You are saying if the engine is lean the cat will plug? On Dodge MPFI systems, the rear O2 has nothing to do with fuel trim, it is to monitor cat efficiency, however, if the pcm senses an issue in the cat it will set a code which will make the engine run worse but it doesnt affect fuel trim. Just like removing the cat will set a code because it has same voltage reading on both sensors rather than a higher reading on the rear due to more heat generating more voltage in sensor.
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This would seem to support the concept of leaving my O2 simulator in place of the post-cat O2 sensor. If there is no fuel trim associated with it, there would be no point for using a post-cat O2 sensor, other than letting my know when the cat has failed. Correct?
 
OK, they're in. I followed the break in procedure recommended by the manufacturers, warm up the car at idle for 4 minutes and then hold it at 2500 rpm for 3 minutes.

They turned a nice wheat color just like the head pipes on my street bike, so they definitely fired up. The hydrocarbon smell is gone, but I will have to drive it for a few days to give a better review of the install including any performance difference. There is no noticeable change in exhaust note, but I've only had it in the driveway. I'm going to take it out for a spin and see what's up.

Cats.JPG
 
jbc426 said:
OK, they're in. I followed the break in procedure recommended by the manufacturers, warm up the car at idle for 4 minutes and then hold it at 2500 rpm for 3 minutes.

They turned a nice wheat color just like the head pipes on my street bike, so they definitely fired up. The hydrocarbon smell is gone, but I will have to drive it for a few days to give a better review of the install including any performance difference. There is no noticeable change in exhaust note, but I've only had it in the driveway. I'm going to take it out for a spin and see what's up.

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Hope you tuned them too:eek: . I am not a fan of O2 simulators, I prefer to have them turned off with a flash or install it and let it do its job....
 
magnummopar said:
Hope you tuned them too:eek: . I am not a fan of O2 simulators, I prefer to have them turned off with a flash or install it and let it do its job....
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I disconnected the battery while welding them in, so it self tuned to that . There is a subtle change in the exhaust sound. It sounds smoother and is ever so slightly quieter. I think it might have lost a touch of top end, but it might not have. It's too hard to tell without time slips. It did add a little on the bottom end and the car runs ever so slightly better/smoother off idle. I think it likes the back pressure.

They absolutely cleaned up all the hydrocarbon smell though, and with such limited effect on performance, I recommend this change to others who are looking to clean up the noxious odors of hydrocarbons on their street rides.

My air cleaner is still too restrictive, and I am trying to figure out what will fit on there and feed cold air to it throu the cowl. I will probably gain more from that than I might have lost from adding cats.
 
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We had to run high flow cats on our rally cars in SCCA for a year or 2. No power-robbing effect was noticed on our 250-275 HP boosted 2.6L engine.

But here is what is mystifying me in this whole situation. Why run 14.5 AFR at idle? It is absolutely normal to run higher (leaner) AFR's under idle and light loading conditions. Is a fixed AFR a limitation the computer or carb begin used here? I guess am missing some info here.....
 
I apologize for not being more concise. The number 14..5 is rough average from memory. My portable wideband fluctuates from roughly 14.2 to 15.1 at idle. The voltage on my pre-cat O2 varies between .25 & .37 volts if memory serves.

I really need to hook my wideband back up to get a precise A/F ratio number.
 
OK. The need for running the 14.5 stochiometric AFR at idle and light load is not there for engine protection.... but maybe so for idle smoothness with a cam. 'Lean burn' was up around 18:1 IIRC; maybe not what you want for a performance engine but 15 and even 16 don't bother me at light cruise, and is what I am looking for for fuel mileage on the street.

Are you running an HEI ignition by any chance to help the completeness of combustion? I ask because my son and I successfully tuned out the smell and richness at idle with a Crane Z-268 cam. (Not sure at this time how that cam's overlap compares with yours.) Adding HEI for a better initial flame was a part of getting better, more complete combustion.

The other probable factor for you with a lot of overlap is that the O2 sensor based AFR will give a false lean reading if there is excess UNBURNED fuel in the exhaust, which it sounds like there is. So your true AFR is very likely lower (richer) than the sensor is telling you. The O2 sensor just measures free oxygen in the exhaust, not unburned fuel. If combustion is not complete, then actual free O2 content of the exhaust will be higher and the O2 based AFR will interpret that as leaner than the AFR really is. So your 14.5 average AFR will be falsely high with incomplete combustion.
 
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I appreciate the comments and information. Yes, I'm running an aftermarket coil on the factory JTEC ignition. I looked up the cam you referenced, and it has significantly less duration at .050. Even more significantly is that it is ground with a 112 degree lobe separation angle versus the 108 LSA I am using.

My spark plugs are a near perfect vey light tan with the color change right in the middle of the ground strap and 3 threads down on the threads. This leads me to believe the O2 sensor is pretty close, even with my overlap.
 
Well, I am finding out that with the new ethanol fuels, the plug color readings are a very different animal than in the old days. My son's 340 plugs are so clean that I can't see any color in the traditional sense. So I would not count on that.

If you are smelling fuel in the exhaust (unburned fuel) , then it is truly a guarantee that the O2 sensor based AFR will be off. I am not just arguing to argue or prove I am right; it just is the way they work. An accurate conversion from the free O2 measured in the exhaust to an AFR number REQUIRES the assumption that there is 100% combustion of the fuel. If there is not 100% combustion, then the AFR conversion is guaranteed to be in error. This can all be looked up if you don't believe it.

With cold engines and a lot of overlap at idle for a carbed engine (and even smaller overlaps for EFI'd engines), O2 based AFR meters will have errors.
 
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Having the mixture as close to stoich' as possible at part-throttle as opposed to lean allows the cats to work most efficiently in the chemical reaction aspect. The balance of different gases is such that the cats are able to convert the max amount of it to less harmful stuff as it flows through, and not burn up at the same time. They're pretty sensitive devices, if you're burning oil/running rich/leaded gas etc. over time the element inside gets coated with crap basically and stops working.
 
jbc426 said:
I disconnected the battery while welding them in, so it self tuned to that . There is a subtle change in the exhaust sound. It sounds smoother and is ever so slightly quieter. I think it might have lost a touch of top end, but it might not have. It's too hard to tell without time slips. It did add a little on the bottom end and the car runs ever so slightly better/smoother off idle. I think it likes the back pressure.

They absolutely cleaned up all the hydrocarbon smell though, and with such limited effect on performance, I recommend this change to others who are looking to clean up the noxious odors of hydrocarbons on their street rides.

My air cleaner is still too restrictive, and I am trying to figure out what will fit on there and feed cold air to it throu the cowl. I will probably gain more from that than I might have lost from adding cats.
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A bazillion years ago, Car. Craft tested a 11 second 455 Pontiac Firebird with and without those cats..They lost less than a tenth ,on the quarter...
 
jbc426 said:
Nope, I smell no unburned fuel in my exhaust anymore.
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Then the cats are somehow removing the excess fuel, but unfortunately that does not mean your AFR reading is correct as explained.

I would be concerned that these are not going to last. That is the common outcome of fuel rich exhaust into a cat. They are not intended to remove excess fuel but to convert excess CO to CO2.
This has all been said before in this thread.
 
nm9stheham said:
Then the cats are somehow removing the excess fuel, but unfortunately that does not mean your AFR reading is correct as explained.

I would be concerned that these are not going to last. That is the common outcome of fuel rich exhaust into a cat. They are not intended to remove excess fuel but to convert excess CO to CO2.
This has all been said before in this thread.
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I understand and appreciate what you are saying, but by your own statements, it's pretty clear that you are unfamiliar with the Mopar ECM I am using. Each and every mis-fire the engine may have is recorded for each specific cylinder. This information is downloadable on a scanner. In over 2000 miles, there were less than a dozen mis-fires total. Also, Mopar doesn't use HEI. Their ignition is integrated into the ECM. HEI is actually a misleading term as it is the name of GM's electronic ignition. The motor is not mis-firing, and despite your beliefs to the contrary, the A/F ratios are very close to being spot on according to my plugs.

Speaking of reading plugs from engines running on modern gas, it is not hard to do if you know how. There is more to it than just looking for color after a few miles. I check mine after several hundred miles and they look as one would expect on a well tuned motor.

My other car has a six pack on it. I used the same wide band on it to jet the carbs. You got me thinking about what you had mentioned regarding O2 readings when there is excessive oxygen in the exhaust. That motor has even more duration and overlap than this one, and the O2 readings reflect exactly what you said. At idle, they go off the scale beyond 22-1 A/f ratio and beyond until the gauge blanks.out of range. Just off idle, it clears up and goes back to reading accurately. The plugs on that motor are ideal looking as well.

The bottom line is that high duration, high overlap cams are designed to keep both valves open at the same time. This allows unburied fuel and air into the exhaust. No amount of tuning is going to change that. High flow cats are an inexpensive solution to having to live with the odor that results from running high overlap cams. Why don't I just put a smaller cam with a wider LSA? Because I like performance. This little 408" motor pulled my 3700lbs car to a win in front of a Hellcat in the quarter mile. It will probably do it again this year at Track Day for Spring Fling, but will smell a lot better on the road between then and now.
 
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I ran a straight through cat on a newer 450hp turbo car before and really liked it. I tried with a straight pipe and fumes were knocking me out in traffic (figuratively of course) and worried about the fuzz since it was so smelly.

I found a "race cat" for offroad use for around $200 and it cut the fumes down by probably 75%. Not as much as a normal cat but also didnt affect HP much if at all. The cat was special made by a retailer though I got it second hand. when you looked through, it looked like a glass pack muffler with the holes around it. Id recommend that in a heart beat.

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hitempresonator-side.JPG
 
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snailpower said:
I ran a straight through cat on a newer 450hp turbo car before and really liked it. I tried with a straight pipe and fumes were knocking me out in traffic (figuratively of course) and worried about the fuzz since it was so smelly.

I found a "race cat" for offroad use for around $200 and it cut the fumes down by probably 75%. Not as much as a normal cat but also didnt affect HP much if at all. The cat was special made by a retailer though I got it second hand. when you looked through, it looked like a glass pack muffler with the holes around it. Id recommend that in a heart beat.

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That's a good converter.....
 
jbc426 Wrote:
The bottom line is that high duration, high overlap cams are designed to keep both valves open at the same time. This allows unburied fuel and air into the exhaust. No amount of tuning is going to change that. High flow cats are an inexpensive solution to having to live with the odor that results from running high overlap cams. Why don't I just put a smaller cam with a wider LSA? Because I like performance. This little 408" motor pulled my 3700lbs car to a win in front of a Hellcat in the quarter mile. It will probably do it again this year at Track Day for Spring Fling, but will smell a lot better on the road between then and now.
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Usually the opposite, when at idle. At higher rpm is when it could/can pull some unburnt fuel from the intake valve to the exhaust during overlap.
At idle it Let's burned exhaust gas back, into the intake charge at idle. Intake charge pressure around 0 exh above.
There are some who have/can fix this problem with carb modification of the "air bleeds" I'm not that smart, I drill holes in butterflies.
Everyone says that it's the high duration cam that mess with the o2 sensor, that show more oxygen(and fuel that it can not read)into the exhaust) I just can't see it getting there from intake to exhaust at idle!?
 
Thinking about what you said about your ECM, the only "misfire" it can sense is if a spark plug or injector fails to fire, right? If that's the case you could easily still have cylinders misfiring from the heavily diluted charge in the cylinder; when the exhaust gets pulled back in during overlap at idle, it creates pockets of already-burned gas within the cylinder; like EGR but not controlled. When this happens it can't ignite from the spark so on the next stroke the piston just pushes it all out; inevitably there will be unburned fuel in there because the cylinder didn't actually "fire" when it was supposed to. And all this time the injector is firing each intake stroke regardless of how much oxygen is available in the cylinder when the valves close.

I don't really get the lean readings at idle for high-overlap cams though I'm kinda stumped on that lol.
 
MOPEkidD-3 said:
Thinking about what you said about your ECM, the only "misfire" it can sense is if a spark plug or injector fails to fire, right? If that's the case you could easily still have cylinders misfiring from the heavily diluted charge in the cylinder; when the exhaust gets pulled back in during overlap at idle, it creates pockets of already-burned gas within the cylinder; like EGR but not controlled. When this happens it can't ignite from the spark so on the next stroke the piston just pushes it all out; inevitably there will be unburned fuel in there because the cylinder didn't actually "fire" when it was supposed to. And all this time the injector is firing each intake stroke regardless of how much oxygen is available in the cylinder when the valves close.

I don't really get the lean readings at idle for high-overlap cams though I'm kinda stumped on that lol.
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I believe what you are suggesting is possible, but you sure are sure stuck on the misfire thing. It's a brand new motor almost perfectly even 200 psi cranking compression, running an "closed (corrected term)" loop EFI, brand new wires, plugs, cap and rotor and perfectly colored plugs. It runs as smooth as silk. It's not misfiring. Well, aside from 9 times in 2000+ miles. You can hear and feel a misfiring motor.
 
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Now that makes sense, if its misfiring, then you would get the extra oxygen to the o2 and the extra fuel for your cat............. (or nose without it.) Your misfire counter is only counting how many time your spark plug did not fire. Not how many time you're cyl didn't make a BANG. SPARK! NO BANG, extra oxygen in the exhaust.
 
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