anyone running DUAL metalic cats?
04-04-06, 03:53 PM
#1
DRIVE THE ROTARY SPORTS
Thread Starter
iTrader: (5)
Join Date: May 2003
Location: CA (Bay Area)
Posts: 4,150
Likes: 0
Received 0 Likes
on
0 Posts
anyone running DUAL metalic cats?
Hey guys, i was wondering if anyone has done this yet and if so, if you could post a picture. i would like to run twin 3" inlet metalic substrate cats in parallel... the cores are about 4" in diameter, and from the measurements i took, it looks like i could fit two next to each other inside of the stock catalictic converters heat shield... which leads me to believe that this is doable. basically the plan as of now is to simply buy a midpipe, two 4" cats, and two Y's, and have them welded up... however im having a hard time finding Y pipes in 3" ID, that are compact enough to get the cats as close as they need to be. if anyone has any suggestions, ideas, or reasons why running two cats in parallel would be a rediculous idea please post.
thanks, heath friedland
thanks, heath friedland
04-04-06, 04:21 PM
#2
Senior Member
Join Date: Dec 2005
Location: Auburn, CA
Posts: 340
Likes: 0
Received 0 Likes
on
0 Posts
My question would be why do you intend to run two in parallel. I am running one 4" metallic at with a 300 cell per sq/inch core, and the back pressure is so insignificant that it caused me boost creep, just like an straight midpipe would. So, unless you are running a 4" exhaust the gain would be negligable.
The only reason I would see for parallel operation is for more effective smog control.
The only reason I would see for parallel operation is for more effective smog control.
04-04-06, 04:51 PM
#4
RX-7 Bad Ass
iTrader: (55)
BTW, trend in Japan is "midpipes" with highflow cats and a resonator - I guess you could call it a resonated high flow cat 
.
The metal cats are VERY compact. I think the only problem I could see with running them in parallel is you'd have a hot spot in the cats at the point where it's nearest the other.
With the FD, you can either have a quiet exhaust or a free-flowing exhaust, or somewhere in the middle. If you want quiet, there will be some compromise, be it power, weight, etc.
Dale
.The metal cats are VERY compact. I think the only problem I could see with running them in parallel is you'd have a hot spot in the cats at the point where it's nearest the other.
With the FD, you can either have a quiet exhaust or a free-flowing exhaust, or somewhere in the middle. If you want quiet, there will be some compromise, be it power, weight, etc.
Dale
04-04-06, 08:40 PM
#6
Rebreaking things
Join Date: Jun 2001
Location: 1 foot in Boston 1 in NJ
Posts: 2,586
Likes: 0
Received 0 Likes
on
0 Posts
Heath,
As you know I've been looking into this for over a year. I had a 4" metal substrate cat in my car that melted in less than 10,000 miles. My friend's core also distorted. I had a couple long conversations with an engineer at Random about this. They said the problem with rotaries is the rich AFR rather than the exhaust temp because the extra fuel drives up the temp through the exothermic reaction process. Initially Random offered a 4" core for the RX8 and ran into the same problem. They solved the problem by increasing the size of the RX8 core to 5"
Since the 20b is a lot bigger than an RX8 or FD motor I decided that 1 core (4" or 5") is not going to cut it. The first thought was to run 2 cores next to each other in the midpipe. You can create more room by staggering their placement. While this should fit, I'm not crazy about the idea of adding two Y pipes to the exhaust system. I think a better approach is to install two cats at the back of the car with 1 Y pipe and 2 outlets. The exhaust temp will be lower, but that will only effect how quickly the cat warms up to operating temp. There would still be room for two short mufflers before or after the cats. If they were mounted before the cats the glowing red cores would probably be visible from behind the car
Another idea I am considering is running a muffler system across the back of the car under the bumper like RE recently did. However, unlike their setup I would like to have 2 tail pipes come out of the bumper on either side -kind of like on the RUF Boxster body kit. The pas side pipe would have a block off valve that under most conditions would force all the air coming down the exhaust system around a bend, through a single 5" cat out the driver side. At high throttle openings the valve would open and divert most of the exhaust gas straight out the back of the car on the pas side. This would accomplish a couple things. First, you could use a restrictive exhaust system to keep noise in check when cruising, but have a more aggressive sound when you get on it. Second, you would get the benefit of having a cat at part throttle where the afrs are much leaner and the benefit of a midpipe when you're pushing it. You could also package this in a system that is similar to the dual cat catback setup described above by replacing one of the two cats with a midpipe and a block off valve.
As you know I've been looking into this for over a year. I had a 4" metal substrate cat in my car that melted in less than 10,000 miles. My friend's core also distorted. I had a couple long conversations with an engineer at Random about this. They said the problem with rotaries is the rich AFR rather than the exhaust temp because the extra fuel drives up the temp through the exothermic reaction process. Initially Random offered a 4" core for the RX8 and ran into the same problem. They solved the problem by increasing the size of the RX8 core to 5"
Since the 20b is a lot bigger than an RX8 or FD motor I decided that 1 core (4" or 5") is not going to cut it. The first thought was to run 2 cores next to each other in the midpipe. You can create more room by staggering their placement. While this should fit, I'm not crazy about the idea of adding two Y pipes to the exhaust system. I think a better approach is to install two cats at the back of the car with 1 Y pipe and 2 outlets. The exhaust temp will be lower, but that will only effect how quickly the cat warms up to operating temp. There would still be room for two short mufflers before or after the cats. If they were mounted before the cats the glowing red cores would probably be visible from behind the car
Another idea I am considering is running a muffler system across the back of the car under the bumper like RE recently did. However, unlike their setup I would like to have 2 tail pipes come out of the bumper on either side -kind of like on the RUF Boxster body kit. The pas side pipe would have a block off valve that under most conditions would force all the air coming down the exhaust system around a bend, through a single 5" cat out the driver side. At high throttle openings the valve would open and divert most of the exhaust gas straight out the back of the car on the pas side. This would accomplish a couple things. First, you could use a restrictive exhaust system to keep noise in check when cruising, but have a more aggressive sound when you get on it. Second, you would get the benefit of having a cat at part throttle where the afrs are much leaner and the benefit of a midpipe when you're pushing it. You could also package this in a system that is similar to the dual cat catback setup described above by replacing one of the two cats with a midpipe and a block off valve.
Last edited by CCarlisi; 04-04-06 at 08:42 PM.
04-04-06, 09:22 PM
#7
DRIVE THE ROTARY SPORTS
Thread Starter
iTrader: (5)
Join Date: May 2003
Location: CA (Bay Area)
Posts: 4,150
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by axr6
My question would be why do you intend to run two in parallel. I am running one 4" metallic at with a 300 cell per sq/inch core, and the back pressure is so insignificant that it caused me boost creep, just like an straight midpipe would. So, unless you are running a 4" exhaust the gain would be negligable.
The only reason I would see for parallel operation is for more effective smog control.
The only reason I would see for parallel operation is for more effective smog control.
so a single cat wouldnt last long.
Trending Topics
04-04-06, 09:30 PM
#8
DRIVE THE ROTARY SPORTS
Thread Starter
iTrader: (5)
Join Date: May 2003
Location: CA (Bay Area)
Posts: 4,150
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by CCarlisi
Heath,
As you know I've been looking into this for over a year. I had a 4" metal substrate cat in my car that melted in less than 10,000 miles. My friend's core also distorted. I had a couple long conversations with an engineer at Random about this. They said the problem with rotaries is the rich AFR rather than the exhaust temp because the extra fuel drives up the temp through the exothermic reaction process. Initially Random offered a 4" core for the RX8 and ran into the same problem. They solved the problem by increasing the size of the RX8 core to 5"
Since the 20b is a lot bigger than an RX8 or FD motor I decided that 1 core (4" or 5") is not going to cut it. The first thought was to run 2 cores next to each other in the midpipe. You can create more room by staggering their placement. While this should fit, I'm not crazy about the idea of adding two Y pipes to the exhaust system. I think a better approach is to install two cats at the back of the car with 1 Y pipe and 2 outlets. The exhaust temp will be lower, but that will only effect how quickly the cat warms up to operating temp. There would still be room for two short mufflers before or after the cats. If they were mounted before the cats the glowing red cores would probably be visible from behind the car
Another idea I am considering is running a muffler system across the back of the car under the bumper like RE recently did. However, unlike their setup I would like to have 2 tail pipes come out of the bumper on either side -kind of like on the RUF Boxster body kit. The pas side pipe would have a block off valve that under most conditions would force all the air coming down the exhaust system around a bend, through a single 5" cat out the driver side. At high throttle openings the valve would open and divert most of the exhaust gas straight out the back of the car on the pas side. This would accomplish a couple things. First, you could use a restrictive exhaust system to keep noise in check when cruising, but have a more aggressive sound when you get on it. Second, you would get the benefit of having a cat at part throttle where the afrs are much leaner and the benefit of a midpipe when you're pushing it. You could also package this in a system that is similar to the dual cat catback setup described above by replacing one of the two cats with a midpipe and a block off valve.
As you know I've been looking into this for over a year. I had a 4" metal substrate cat in my car that melted in less than 10,000 miles. My friend's core also distorted. I had a couple long conversations with an engineer at Random about this. They said the problem with rotaries is the rich AFR rather than the exhaust temp because the extra fuel drives up the temp through the exothermic reaction process. Initially Random offered a 4" core for the RX8 and ran into the same problem. They solved the problem by increasing the size of the RX8 core to 5"
Since the 20b is a lot bigger than an RX8 or FD motor I decided that 1 core (4" or 5") is not going to cut it. The first thought was to run 2 cores next to each other in the midpipe. You can create more room by staggering their placement. While this should fit, I'm not crazy about the idea of adding two Y pipes to the exhaust system. I think a better approach is to install two cats at the back of the car with 1 Y pipe and 2 outlets. The exhaust temp will be lower, but that will only effect how quickly the cat warms up to operating temp. There would still be room for two short mufflers before or after the cats. If they were mounted before the cats the glowing red cores would probably be visible from behind the car
Another idea I am considering is running a muffler system across the back of the car under the bumper like RE recently did. However, unlike their setup I would like to have 2 tail pipes come out of the bumper on either side -kind of like on the RUF Boxster body kit. The pas side pipe would have a block off valve that under most conditions would force all the air coming down the exhaust system around a bend, through a single 5" cat out the driver side. At high throttle openings the valve would open and divert most of the exhaust gas straight out the back of the car on the pas side. This would accomplish a couple things. First, you could use a restrictive exhaust system to keep noise in check when cruising, but have a more aggressive sound when you get on it. Second, you would get the benefit of having a cat at part throttle where the afrs are much leaner and the benefit of a midpipe when you're pushing it. You could also package this in a system that is similar to the dual cat catback setup described above by replacing one of the two cats with a midpipe and a block off valve.
04-04-06, 09:33 PM
#9
Wouldnt the airpump solve all these catalytic problems? Succinctly Im under the distinct impression that if you want a cat on a rotary you need an airpump.
Ive been considering running 2 in series for improved emissions, noise supression, and exhaust restriction. The loss of flow and gain in weight dont bother me. But, I'm going to be running the stock airpump into the cats.
Dave
Ive been considering running 2 in series for improved emissions, noise supression, and exhaust restriction. The loss of flow and gain in weight dont bother me. But, I'm going to be running the stock airpump into the cats.
Dave
Last edited by Narfle; 04-04-06 at 09:34 PM. Reason: mind expansion
04-04-06, 11:11 PM
#10
DRIVE THE ROTARY SPORTS
Thread Starter
iTrader: (5)
Join Date: May 2003
Location: CA (Bay Area)
Posts: 4,150
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Barban
Wouldnt the airpump solve all these catalytic problems? Succinctly Im under the distinct impression that if you want a cat on a rotary you need an airpump.
Ive been considering running 2 in series for improved emissions, noise supression, and exhaust restriction. The loss of flow and gain in weight dont bother me. But, I'm going to be running the stock airpump into the cats.
Dave
Ive been considering running 2 in series for improved emissions, noise supression, and exhaust restriction. The loss of flow and gain in weight dont bother me. But, I'm going to be running the stock airpump into the cats.
Dave
04-04-06, 11:38 PM
#11
Originally Posted by RotorMotor
nope. injecting air will RAISE the temp of the cats
The heat produced by the action of catalyzing the unburned crap is lower than that of the exhaust gases. Catalyzers dont burn up because theyre "working too good". Catalyzers burn up because the EGT's are through the roof on our cars. Pumping ambient air into the mix will only lower net EGT's thus negating any effects of the increased catalytic efficiency and a big bag of chips. But, yes a good tune is irreplaceable.
Last edited by Narfle; 04-04-06 at 11:42 PM. Reason: the voices told me to
04-05-06, 12:27 AM
#12
I believe there was a thread where an engineer basically said you NEED the airpump since the AFR are so rich into the cat, that the additional air is needed to assist in catalytic process.
As such, I still run an airpump into my highflow 3-inch metallic-cat.
Note, last time I looked at the INLET side of the cat, the core was intact, however it was orange in color and had a spider-web like substance on the front of the core.
:-) neil
As such, I still run an airpump into my highflow 3-inch metallic-cat.
Note, last time I looked at the INLET side of the cat, the core was intact, however it was orange in color and had a spider-web like substance on the front of the core.
:-) neil
04-05-06, 12:40 PM
#13
DRIVE THE ROTARY SPORTS
Thread Starter
iTrader: (5)
Join Date: May 2003
Location: CA (Bay Area)
Posts: 4,150
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by M104-AMG
I believe there was a thread where an engineer basically said you NEED the airpump since the AFR are so rich into the cat, that the additional air is needed to assist in catalytic process.
As such, I still run an airpump into my highflow 3-inch metallic-cat.
Note, last time I looked at the INLET side of the cat, the core was intact, however it was orange in color and had a spider-web like substance on the front of the core.
:-) neil
As such, I still run an airpump into my highflow 3-inch metallic-cat.
Note, last time I looked at the INLET side of the cat, the core was intact, however it was orange in color and had a spider-web like substance on the front of the core.
:-) neil
04-05-06, 12:40 PM
#14
DRIVE THE ROTARY SPORTS
Thread Starter
iTrader: (5)
Join Date: May 2003
Location: CA (Bay Area)
Posts: 4,150
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by M104-AMG
I believe there was a thread where an engineer basically said you NEED the airpump since the AFR are so rich into the cat, that the additional air is needed to assist in catalytic process.
As such, I still run an airpump into my highflow 3-inch metallic-cat.
Note, last time I looked at the INLET side of the cat, the core was intact, however it was orange in color and had a spider-web like substance on the front of the core.
:-) neil
As such, I still run an airpump into my highflow 3-inch metallic-cat.
Note, last time I looked at the INLET side of the cat, the core was intact, however it was orange in color and had a spider-web like substance on the front of the core.
:-) neil
04-05-06, 02:01 PM
#16
Originally Posted by M104-AMG
I believe someone used an electric airpump either from a Corvette or Mercedes.
:-) neil
:-) neil
-s-
Last edited by scotty305; 04-05-06 at 02:03 PM.
04-05-06, 02:20 PM
#17
Lives on the Forum
Originally Posted by scotty305
I was reading a Bosch engine electronics book, and it said that the air pump is not necessary if the engine is tuned lean enough.
04-05-06, 08:38 PM
#19
Old School
Join Date: Mar 2001
Location: Baldwin City, KS
Posts: 473
Likes: 0
Received 0 Likes
on
0 Posts
The nice thing about the metal cats is they can be made almost any length and diameter. I would think you would want a large diameter low cpi (less heat buildup and chance of clogging) catalyst thats very long (still cleans a lot of air). I remember a website that talked about having many different sizes and lengths of catalyst. I think they even made custom sizes and had racing applications but I don't seem to have it bookmarked and I don't think it came up in a search engine either. I think I got the link from a thread on this forum though. Not all metal cats are equal either. The Random one seems to melt. I used this one...
http://www.davesport.com/cgi-bin/davesport/DCAT325.html
It sais this...
"These cats hold up to extended anti-lag on race cars, so they'll hold up to anything!"
They haven't met the heat generation of a 20b I bet either. They are a little small for emissions use but you could put several in series. You might call them and find out if they can get a longer one too and who their supplyer is. Your going to want to put any cat on a 20b way downstream in any case. I just don't like the idea of the split catalyst system. Too big and expensive and too much heat in one area.
http://www.davesport.com/cgi-bin/davesport/DCAT325.html
It sais this...
"These cats hold up to extended anti-lag on race cars, so they'll hold up to anything!"
They haven't met the heat generation of a 20b I bet either. They are a little small for emissions use but you could put several in series. You might call them and find out if they can get a longer one too and who their supplyer is. Your going to want to put any cat on a 20b way downstream in any case. I just don't like the idea of the split catalyst system. Too big and expensive and too much heat in one area.
04-06-06, 12:01 AM
#20
Originally Posted by Matt Hey
<SNIP> I used this one...
http://www.davesport.com/cgi-bin/davesport/DCAT325.html
It sais this...
"These cats hold up to extended anti-lag on race cars, so they'll hold up to anything!"
<SNIP>
http://www.davesport.com/cgi-bin/davesport/DCAT325.html
It sais this...
"These cats hold up to extended anti-lag on race cars, so they'll hold up to anything!"
<SNIP>
I love it.
:-) neil
Thread
Thread Starter
Forum
Replies
Last Post
KAL797
Test Area 51
0
08-11-15 03:47 PM
