Cats (Catalytic Converters) with Higher Flow - Team Integra Forums - Team Integra
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Cats (Catalytic Converters) with Higher Flow

Posted 02-14-2002 at 12:00 AM by MichaelDelaney

A. Where to Get Them:

Carsound website:

This is the cat core without the needed extension tubing, flanges, and O2 sensor bungs. You will need to have a local exhaust/muffler shop weld these on for you or weld them on yourself.

B. How A Cat Works

from all-catalytic-conve

The purpose of a catalytic converter is to convert harmful hydrocarbons, carbon monoxide, and nitrogen oxides into harmless compounds. The catalysts inside the catalytic converter convert carbon monoxide and hydrocarbons into carbon dioxide and water, and nitrogen oxides back into nitrogen and oxygen.

The catalysts inside of the catalytic converter are precious metals such as platinum, palladium, and rhodium coated on a ceramic honeycomb structure or pellets. When exhaust contacts the catalysts a chemical reaction takes place converting the harmful exhaust gases into harmless compounds. Most modern converters contain two distinct catalysts, the reduction catalyst and the oxidation catalyst.

The first stage, or reduction catalyst, consists of a ceramic honeycomb coated with platinum and rhodium. In this section of the converter, Nox emissions are converted to oxygen and nitrogen. The exhaust then flows to the second stage, or oxidation catalyst. It is here where unburned hydrocarbons and carbon monoxide are burned or oxidized by passing them over a platinum and palladium honeycomb. The oxygen from the first stage further aids this oxidizing.

The third stage of controlling emissions utilizes an engine management system. Although every automotive manufacturer employs different methods and components, most utilize an oxygen sensor mounted upstream of the converter which transmits a voltage to an onboard computer. This voltage reading varies with the amount of oxygen present in the exhaust gas. The ideal air fuel ratio for gasoline is 14.7 to 1. If the ratio of air is less than 14.7, then there will be fuel present in the exhaust after combustion therefore creating a rich condition. A lean condition occurs when the ratio of air to fuel exceeds 14.7 to 1. The engine management system uses the voltage reading from the oxygen sensor to make adjustments to the air to fuel ratio, which in turn will either increase or decrease the amount of oxygen present in the exhaust gas therefore controlling the chemical reactions in the catalytic converter.

C. Comparative Flow Specs for Different Manufacturers and Stock Cats and Dimensions of Carsound Cats:

Originally Posted by Dave Stadulis of SMS Products

The larger cat is the 2-1/2" 94006 built to fit a JDM header and a stock B pipe flange location. The smaller cat is the 2-1/2" 54006 built to fit the early GSRs with a JDM header and stock B pipe location. In the link you'll also see the difference between the 2-1/2" ID cat outlet and the stock ITR B pipe inlet of 1-3/4" ID.

As for differences, I use a slightly different style floating flange than some of the others but this doesn't make a difference in fit or performance. I do tack weld the heat shield in multiple locations down each side now. Some of the Carsound spot welds had broken in the past causing a rattle. I don't know of any rattles since I started doing these extra welds back in the early summer (2001).


I just wanted to post a little info for all to review on the Car Sound Cats. There always seems to be a debate on which hi flow cat is the best, just like the great header debate. Below are flow numbers for various cats and test pipes. This test was supposed to have been performed by Comptech at 28" of vacuum. (Test info was pulled from the net, so I can only assume it is correct).

Stock NSX 242.1 cfm
Stock Type R 223.6 cfm
Stock Integra 218.3 cfm

Catco (metal core) 2.25" 223.8 cfm
Catco (metal core) 2.5" 271.9 cfm

Random Tech 2.25" 297.1 cfm

Catco (std. core) 2.25" 338.2 cfm
Catco (std. core) 2.5" 388.0 cfm

Car Sound 2.25" 342.7 cfm

Test Pipe 2.25" 407.1 cfm

cfm = flow capacity in cubic feet per minute

Unfortunately, the 2.5" Car Sound Cat and 2.5" test pipe was not measured. I've read that folks have had some problems with the Random Tech Cat. I sell the Car Sound Cat, frankly because Larry Widmer of Endyn runs it on his beast (3" version), he has had no problems with it over 3 years and has recommended to me.

There are some shops/guys that sell bolt on Car Sound Cats. All Car Sound 2-1/2" Cats are not the same. For the universal set up here are the following to choose from, I've also listed the EPA Engine Limit and CARB Engine Limit for each one.

..........................................Body.... ...........
.........EPA.....CARB....Body....Length..Overall Length


54006....5.0L....5.0L....4"............9".....13". .




For the oval units the flange width is included in the above body dimensions, so actual body width is somewhat less.

I use the 94006 unit, from pictures I've seen some others may be using the 54006. The 54006 is easier to work with since the body is smaller but it is also rated for a smaller engine and therefore can't flow as much as the 94006. Now the 93006 and 95006 should flow more than the 94006 but they are both wider and one is much longer, so space becomes a problem. Why is the 94006 better than the 54006? The 94006 is an oval and therefore has a larger area of catalyst and with that you get more holes for the exhaust gases to travel through and less losses.

While I don't know who you'll buy your weld-in or bolt-in cat from, please make sure you know which cat you are getting, what comes with the cat (gasket/doughnut), is it the proper length, do the bolt holes line up on the flanges and on OBD II cats where does the 2nd O2 sensor mount?....

Flow through a cat is based on how many cells there are. You determine this by multiplying the brick area by cells per square inch.

The cells per square inch is the same for all CarSound catalyst material (bricks), so the only way to get more flow is by increasing the cross sectional area of the cat. CarSound offers one other larger cat (overall 4" x 7") versus the 4" x 6.5" of the 94006. Now these dimensions are of the outside of the cat so the % changes aren't extremely accurate. But if you compare those sizes the larger cat should have an area of about 7% more than the 94006. However, this cat (93006) is a little more than twice (the price of) the 94006.

D. What Are The Carsound Models Used? :

Originally posted by SMSP on Sept. 14/2004

I use Carsound but there are some models within the Carsound line that I wouldn't use. The only 94*** cats I use are the 94106 and 94166 for OBDI and II GSRs 99 and older. The 9400* had some brick failure problems especially, if you were running on the rich side.

For 90% of my sales I use the 93505 (2.25 in.) and 93506(2.5 in.) . I've had one failure in the last 2 years with these and I build alot of these things for my customers and for alot of other shops. If you need the 3 in. OD cat go with a 93509 and mod your tubing to make it fit.

Also, the heat shields can break spot welds so I add 12 more spot welds per side.
The good thing for most people is that the 93500 series cats are now OBD2 EPA compliant.

For California however, the only California compliant Carsound cats are the 43000 Series.

E. SMSP Spun Bodied 300 cell Aftermarket Cats :


I asked Jim Justice of Justice Racing Engines to flow test 4 cats for me. The first was the Carsound/Magnaflow 93506 with a 400 cell catalyst, which I use for most 2-1/2" applications, the second cat is what is now known as the "Challenger" cat ( MD's Note: that's not the brandname btw and I didn't show it in this thread because he's not selling it) with a 300 cell catalyst, the third was of a spun bodied 300 cell metal catalyst and fourth was the same spun bodied cat but with the standard 400 cell catalyst.

Jim had to make an adapter to run these on his flow bench and all tests were performed as an intake test, flow being pulled through the cat. Jim told me he switched the flow direction and the numbers were within 1%. He did a baseline run at 28" with just the adapter to get a reference point.

Test conditions were Temp. 62.2-62.5F, Humidity 31.6-32.0%, Bar. 29.74

Cat ... Flow (CFM) @28" % Increase/Decrease in Flow wrt the 93506

Adapter-Baseline : 506 cfm +53.8%

Carsound 93506 : 329 cfm -------

Challenger : 353 cfm +7.3%

Spun Body 400 Cell: 336 cfm +2.1%

Spun Body 300 Cell* : 365 cfm +10.9%
* = Metal Substrate Cat

My thoughts:

Since the "Challenger" cat uses a catalyst (300 cell) with larger holes than the 400 cell Carsound, I expected it to do better. Don Flores at DFE Enterprises also tested these 2 manufacturers but in the 2-1/4" size and also found that the Challenger performed better. Thanks to Don again for those tests.

I was somewhat surprised that the spun bodied cat with the 400 cell catalyst (same as the Carsound) did better, although only 2.1% since the brick size is smaller and therefore has less holes for the exhaust to go through. My conclusion is that it must be due to the spun bodied design. This makes for a nice smooth internal transition, where as the Carsound and the Challenger are the standard stamped steel bodies with 2-1/2" ID nipples inserted in either end and this provides a slight flow obstruction on the outlet side.

The clear winner of the test was the spun bodied 300 cell metal catalyst cat. With almost an 11% improvement over the Cat that I've been selling for over 2 years.

The old 94006 and 94066 cats did show some problems with the matting breaking up and the catalyst coming loose and then breaking up. The 93506 cat has proven to be a great improvement over those 94*** cats. To date I know of only one of my 93506 cats failing and that was on Willard's car which sees it's share of the track.

So it looks like we have 2 more hi flow cats to choose from. But pricing will dictate the path forward.

None are CARB OBDII compliant. Carsound has just started to make one to fit that build but it runs about $80 more than the 93506. I've only sold a couple of those but I sell a bunch of the 93506 to the CA guys. So I can only assume it gets them through the sniff test.

Thanks again to Jim Justice for doing the test for me and the Honda community.

Spun Bodied Cat 300 Cell Internal Honeycomb



Carsound 93505 2.25 in. 400 Cell Internal Honeycomb


Spun Bodied 2.5 in. Cat

Renault 2.5 in. Diesel Cat Used for Gasoline Sport Compacts used by Hytech


F. Aftermarket High Flow Cats Versus Testpipes On A Daily Driver:

Comparing a 2.5 in. testpipe (RED) to a 2.5 in. Carsound cat (BLUE) in the same ITR ( 1.8L B18C5 ) with a CAI, Toda B cams, an SMSP 4-2-1 long hybrid header (2.5 in. OD collector), and SMSP 2.5 in. OD exhaust, Apex Power FC fuel tuning:


There is virtually no difference. So there is no CEL code 45 to worry about and you don't have to worry about performance or passing emissions or polluting the about a win-win situation!! Thanks goes to Chris for doing the dyno test.

G. How Do I Know If My Stock Cat Is Defective And Why Did It Fail?



Fig. Top is a NORMAL CAT, Middle is a Failing Cat, Bottom is a Defective cat:

Catalytic converters are defective when they become clogged or poisoned. You may sometimes be able to feel when a converter is partially clogged, or defective, when you do not go any faster when you step on the throttle. This may also be accompanied with a noticeable drop in gas mileage. A clogged converter will cause increased backpressure in the exhaust system. This increased backpressure prevents the engine from breathing properly which in turn may cause the engine to quit after a few minutes of driving or feel like an e governor limiting the RPM's the engine can achieve. You may actually hear a whistling or choking sound when applying the throttle.

A catalyst that has broken apart internally and is loose in the system or has worked its way back to the muffler can also cause rattling noises. This rattling may be prevalent at idle but go away as speed is increased. Sometimes you may tap on the converter with a rubber mallet and hear the core rattling. If you discover any of the above your converter needs to be replaced.

Since there is no inspection port for you to see if you have an actual clog in a converter there a couple things you may try to help diagnose a defective converter. Many mechanics will remove the oxygen sensor and look for a change in the vehicles performance. If a performance change is noted, your converter needs to be replaced. You must be extremely careful if you run the engine with the oxygen sensor removed since there is a risk of fire and asphyxiation caused by escaping engine exhaust and exhaust gases.

A vacuum gauge that also has a fuel pressure gauge, or a pressure gauge that has a 1 to 10 pound scale, may also assist you in diagnosing a clogged exhaust.

If you connect the gauge upstream of the converter, either in an emission test port or by fashioning an adapter in the oxygen sensor hole, you can measure the exhaust backpressure. A general rule of thumb is no more than 1.5 pounds of backpressure. Another test, using a vacuum gauge, is to measure the engine vacuum at curb idle and at 1600 RPM. If engine vacuum is 21 inches at curb idle and 15 inches at 1600 RPM then there is a good possibility your catalytic converter needs to be replaced.

You may also take the converter off the vehicle and check it for damage or clogging. Shining a flashlight into the core of a honeycomb style converter will reveal whether the honeycomb is partially clogged, damaged, or loose from the edges.

Finally, a converter can be defective because it has become poisoned. When a catalytic converter becomes poisoned it loses its ability to effectively control emissions. Some common causes for poisoning and converter degradation are using leaded fuel, fuel additives containing lead, an out of tune engine, engine management system failure, faulty engine sensors, just to name a few.

If your vehicle is burning an excessive amount of fuel or misfiring, due to some of the reasons above, it is just a matter of time before converter failure. A constant rotten egg smell emitting from the tailpipe is a sure sign of the impending failure of your converter.

If you do determine that your catalytic converter is defective, it is extremely important that you determine the reason for its demise. Always have your emissions checked on an exhaust gas analyzer after the new converter is installed to ensure your engine and engine management systems are operating at their peak efficiency. Failure to find and repair any fault will result in a premature failure of your new converter.


1. Out Of Tune Engine

Anytime an engine is running out of tune due to improper air/fuel mixture, misfiring cylinders, faulty engine sensors, incorrect ignition timing, etc., damage to the catalytic converter will be incurred. Proper and regular servicing per the auto manufacturers recommendations are necessary to prevent premature catalytic converter failure.

2. Excess Fuel Overheating The Catalytic Converter

An engine that is performing at peak efficiency will burn all the fuel in the combustion chamber during the combustion process. An engine that is not performing properly, that is not burning all the fuel, will allow unburned or excess fuel to enter the exhaust system. When this excess or unburned fuel contacts the hot core of the converter it will ignite. This constant infusion of unburned fuel will cause temperatures to continuously rise above the designed operating temperature until the core of the catalytic converter will actually melt. Possible causes for the excess fuel entering the exhaust system are an incorrect fuel mixture, incorrect timing, corroded spark plugs, worn and cracked ignition wires, improper fuel pressure, a faulty oxygen sensor, sticking float, faulty fuel injector or a malfunctioning check valve.

3. Oil or Antifreeze Entering Exhaust

When oil or antifreeze enters the exhaust system and contacts the hot core of the converter the oil and antifreeze will burn off leaving carbon deposits. The carbon deposits will coat the core of the converter thus reducing the catalytic converter's ability to convert from harmful emissions into harmless compounds. As the carbon deposits continue to accumulate, the pores in the ceramic catalyst will become restricted and block exhaust flow through the exhaust system. The resulting increased backpressure will result is a loss of power and overheated engine components. Possible causes are worn piston rings, faulty valve seals or valve guides, blown head gasket or intake gaskets, or warped engine components.

4. Malfunctioning Oxygen Sensor

The oxygen sensor measures the amount of oxygen present in the exhaust gas. Depending on the voltage generated by the oxygen sensor, the engine management system will change the air/fuel ratio to obtain the desired oxygen level present in the exhaust gas. A malfunctioning oxygen sensor sending an erroneous reading to the engine control system can cause a too rich or too lean condition. A rich condition will cause the converter to overheat and melt down from the unburned fuel being ignited while a lean condition can result in a misfire that can lead to the same result. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits.

5. Broken Exhaust Hangers Or Misaligned Exhaust

An exhaust system that is misaligned or allowed to rattle will cause the fragile ceramic catalyst inside the converter to break apart. When the core breaks or becomes loose in the converter the brittle ceramic catalyst will continue to break up into smaller pieces that will eventually block the flow of the exhaust. This increased backpressure will lead to loss of power and heat build up

Originally posted by SMSP in Jun/2002

re: Cat Failure

This post is meant to be a general statement regarding Carsound cats. The following is the response I got from a Magnaflow employee concerning some question I had about the mat that surrounds the catalyst/brick. Magnaflow is a company that is part of the Car Sound Exhaust System company.

"With regard to the mat-it is designed to cushion the ceramic substrate, and is completely functional in that respect. The mat is not required to come to the edge of the substrate in order to cushion the substrate. Of possible cause for substrate failure in which the mat deteriorates is what we refer to as Thermal Failure. At excessively high temperatures, caused by rich fuel mixtures which are not completely burned in the combustion chamber and ignite in the catalytic converter, the stainless steel case expands to the point where the mat is separated from the the case. As exhaust always follows the path of least resistance, the exhaust begins to flow between the mat and the case instead of through the substrate itself. At this point the mat is exposed to exhaust flow and begins to deteriorate. After a period of time, the mat disintegrates and the substrate, which is a brittle ceramic, comes in contact with the steel case and breaks up. So in some cases, the mat disappears because of an excessive heat factor instigated by unburned fuel due to a rich fuel mixture."
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  1. Old Comment
    so what size i cat would a stock LS take? a 2 inch inlet/outlet? or 2.25? ALL stock exhaust
    Posted 03-23-2012 at 05:31 PM by Mineis4Door Mineis4Door is offline
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