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Old 02-28-2006, 12:21 AM   #21
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For the SE NA guys.....on my '95, I have 1 O2 sensor on the exhaust manifold so I can use the plain 2 way. My OD on the downpipe is < 2.5, so I'm 2.25.

Car-sound recommends the 91006. That'* a different pipe size (2.5). And the entire length of the small oval is shorter (13 in), than just the body of my stock cat (14 in).

The standard 94000 oval would be a much better fit. But it looks like car-sound is purposely steering away from that. And recommending the slightly wider pipe flow.

My guess it has to do with internal resistance of the small vs standard oval on a 3.8 L...

Or car-sound has a team of monkeys working on their "application finder".



edit; Just read the previous recent posts. I'm doing the 94005. and car-sound must have a team of monkeys working on the "application finder".
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Old 02-28-2006, 12:36 AM   #22
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I'm not sure I would be confident running a 91000 converter that comes so close to the test weight and engine displacement of my car. I wonder if it would be wise to have some 'headroom' in these categories, especially when doing extensive modding?

I still find it interesting that the Magnaflow tech recommended a 94806, while the website suggests a 91006.
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Old 02-28-2006, 12:52 AM   #23
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I was going to get the 91000 series because that is what the site recommended and Bill was adamant about it in our other thread. The 94000 makes more sense fit wise. If you have 2 O2 sensors, the 94806 would make some sense.

I'm still concerned about the pipe size, but that i can ask of the exhaust shop I'm having do it. Before I order the cat.
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Old 02-28-2006, 07:11 PM   #24
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So it seems like the 94000 series might be the best fit? What else can we find out about the 91000? Will it actually overheat, or will it cause the rear O2 to throw a Catalyst Inefficiency code? Anybody currently using the 91000?
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Old 02-28-2006, 09:59 PM   #25
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It will only overheat if you have a very rich mixture and a lot of un-burned gasoline gets to the cat; other than that, it should work with no problems. Both part numbers are more than sufficient for any of our applications with the exception of cars that need the version with the O2 bung. The weight rating is for EPA purposes only. EPA has calculated what they feel is the ideal cat size, based on the size (weight) of the vehicle, and engine size. They assumed that the heavier and bigger the vehicle, the larger the engine, which in today'* technology, is not true. The higher rating can make the design of the cat more restrictive.
Be careful because Magnaflow also sells OEM replacement cats that are not high performance. Cats were designed as a Band-Aid for people that are too lazy to take care and tune their cars. In the past, I have tuned carburated cars, with all the emissions equipment and cat removed, and they still passed emissions with flying colors.
My nephew has a Mitsubishi Montero, 4-Cyl., with a header, emissions equipment removed and a Weber DGV aftermarket carburetor and still passes emissions with flying colors. Yes, I did rejet and retuned the carb and he keeps the engine in great condition. He is a College student and could not afford the $1,200.00 for a new carburetor from the dealership, or $550.00 for a rebuilt one. So, we went the Weber DGV route that cost $194.00 with installation kit.
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Old 02-28-2006, 10:06 PM   #26
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A little bit of research someone did for me is located here:

Direct replacement
http://www.car-sound.com/catalog/dir...spx?PartID=186

Little more expensive though. $100 vs $60
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Old 02-28-2006, 10:09 PM   #27
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The direct replacement is built to OEM specs and is not a high flow unit.
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Old 03-01-2006, 02:14 AM   #28
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Quote:
Originally Posted by ssei1995
The higher rating can make the design of the cat more restrictive.
This is exactly the kind of information that needs to be in this thread. Thanks for the great post, ssei1995. Do you have any numbers or findings that can substantiate this statement? I only ask because the Magnaflow tech claimed the flow difference between the 91000 and 94000 series is negligible. It would be great to have some hard facts that point one way or the other.

Also, do you know anything about the flow differences between 2-way and 3-way converters?
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Old 03-01-2006, 10:55 AM   #29
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A friend who races in SCCA is required to have the cats on his car. While the engine was in the dyno, different cats were attached to the exhaust. I will say there is more restriction on the 3-way cat than a 2-way. Also, the smaller size cat, with the same pipe size showed more power than the larger sized cat.
Take a look at the link from Random Technologies and see the size of the high flow cat they sell for the GTP'* and the performance gain from the OEM cat.
http://www.randomtechnology.com/new_products_gp.html
Also take a look of the chart for the results of their testing.
Also look at their universal fit cats and see their size.
http://www.randomtechnology.com/products.html
I was tempted on using a cat from Random, however the price kept me away from them. They are the cats my friend eneded using on his SCCA Camaro.
Here is more tech info from Random:
http://www.randomtechnology.com/technical.html
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Old 03-01-2006, 11:44 AM   #30
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Wow.... great links. Anybody who needs a thorough explanation on the workings of a 2-way or 3-way converter and the reasoning behind converter size selection, visit the Random Technology Technical Page.

Here are a few excerpts from that page:
Quote:
Originally Posted by Random Technology Technical Page
Most converters produced in recent years contain two monolith "bricks" spaced several inches apart from each other... With its honeycomb construction, a monolith substrate consists of a number of relatively small “tubes” or cells through which exhaust gasses pass. The size of the cells and their length determines the amount of restriction and to some degree, the extent of catalyzing action.

...Obviously, the bricks within a converter create the major resistance to exhaust flow. Over the years, various brick densities have been used, with the most common now being 400 cells per square inch. Converters with bricks having 200 cells per square inch were once common, and might appear to offer high exhaust flow potential. However, the walls in 400 cell bricks are thinner, so flow capacity isn’t much different, given the same face area. And face area is a major player in determining the flow efficiency of a catalytic converter... But another factor, and one that’* often overlooked, is brick length - longer bricks offer higher flow resistance. On the other hand, if a brick is too short, it won’t offer sufficient area to effectively control exhaust pollutants. Converter manufacturers use different precious metal loadings of washcoats and vary them according to brick length and density. Since all catalytic converters must meet standards established by the Environmental Protection Agency, (EPA) their efficiency in controlling exhaust pollutants is a given - provided a particular converter is installed on the type of vehicle for which it was designed.
Long story short, it seems Random Technology reflects the sentiment that you should use the smallest converter that still meets your engine displacement requirements. It would appear that the Magnaflow 91000 series is appropriate for the L27 and L36, just as some members here have been suggesting. I'm not sure whether this changes for an L67, because effective displacement is increased due to the supercharger (as willwren stated earlier).

But at what point do you modify your engine so much that the CID recommendations no longer apply? I'm not suggesting I'm anywhere near that point, but I imagine that a high output motor would defy the recommended displacement ranges. If I had an L36 that could make 300hp at the wheels, would the limitations of the 91000 series be restrictive? Perhaps a better example would be a normally aspirated V8 from a Nextel Cup car. I'm sure these engines produce far more output than most other engines of similar displacement (and yes, I know they don't run catalytic converters ). So when have you modded enough to require a larger converter than other cars with the same CID?
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