Someone had taken the cat off and this thing sounds like it has open headers which sounds terrible...I know it's illegal to take cats off but what I'm concerned with is if Ii go back with a pipe instead of a converter for cost sake will it hurt my low end torque? As far as I know it Does not have an o2 sensor after the converter ...my concern is losing low end grunt

 

Excuse my misspelling this auto correct on my phone is to blame!

 

The oem pcm's can adjust a/f up to 25% depending on the year.....removal of the cats, well, you just might be (under full throttle) at that max end of the ability to adjust scale, meaning....could cause minor issues..and of course, if the AF is off, well, it affects mpgs/perf as well.

 

What Would you recommend as far as an inexpensive converter?

 

4-stroke internal combustion engine requires no back-pressure to function correctly, removing obstructions from the exhaust system will only improve flow.
If you choose to use cat's you should use them in a dual-exhaust configuration for minimum back-pressure. Some cat's are better than others and there is such a thing as a high-flow catalytic converter, cat converters are categorized into 4 classes or cpsi (cells per square inch), catalyst cores are available in 400, 300, 200 and 100 cpsi versions, the lower the number the better the flow and for reference factory cat's are 400 cpsi and very restrictive.. cheers.
High Flow Catalytic Converters 100, 200, 300, 400 Cell

 

The problem you have with forums like this is that you get oodles of opinions and not a whole lot of facts.

Backpressure has little to do with torque. What produces torque is induction, which is a function of velocity in a naturally aspirated engine. Oversized pipes cause a severe drop in velocity, without the velocity, the scavenging effect that helps remove spent exhaust gases from the cylinders is defeated. So if your pipe sizing hasn't been changed from stock, you will get good scavenging.

However that being said, the stock cam profile is set up for use with cats. The cats do create some backpressure, so the stock cam is set up to accommodate that. When you run the vehicle without cats what you sometimes get is an over-scavenging effect. Basically what happens is that during the valve overlap period, the low pressure in the exhuast will draw too much of the unburned fuel-air mixture into the exhaust system, so it is not burned as part of normal combustion. This is not only a waste of fuel, but it messes with O2 sensor readings, which will cause a lean mixture to be detected. To computer will respond by adding more fuel. This results in a rich mixture that not only wastes more fuel, but actually reduces power output as well.

For reference, the factory cats are in fact 400 cpi, but that is not restrictive. A Nissan Titan 2004 and newer uses 600 cpi and is producing over 325 hp and gets pretty good fuel economy for the level of performance. Some cars are using as high as 800 cpi and are not suffering from performance degradation.

Unless you are running a turbo, supercharger, or an aggressive cam, a standard 400 cpi catalyst will provide more than adequate flow.

Disregard Gmans link, those are oriental made converters, which regardless of their claims, are NOT EPA certified, and for good reason, they do not meet minimum EPA guidelines. The cost of a converter is largely a function of the cost of the precious metals that make it work. If it costs less, it usually means that the manufacturer is using fewer precious metals, and that means it will neither work as effectively or last as long as one that has a proper loading.

 

Good stuff Khan but you failed to mention the 600 cpsi cat's on a titan are huge to allow that kind of flow, if you woyuld be so kind as to validate your info regarding catalyst substrate cpsi and it's relation to supported horsepower, i have been able to find very little genuine info.
After doing more research i am in agreement with you and did discover that 100 or even 200cpsi would have to pretty long to effectively scrub the exhaust and passing OBD II regulations would still be challenging, the motor woyuld have to be stone cold and cat's don't work when they are cold, i don't believe OBD 1 which is just a visual with hydrocarbon and carbon monoxide test may be feasible.
Also, you are kinda hard on both me and MBS.com in particular, do you have a beef with these people or have you personally experienced shoddy quality, since they are under the vehicle i am okay with some unsightly welds, what is the problem..

 

thankyou guys for your responses,the rebel that i am and the area that i live in i'd in all reality rather NOT have the convertor but with this being a 4.0 and no chance of it EVER having a nice v8 sound i dont mind going back with a convertor,i just dont want to break the bank doing so which means if my explorer will run just fine with no convertor and a nice quiet exhaust by all means thats the way ill go but if it wont run as efficient without as khan stated then ill definatly ill be putting one back on it...

 

MBS is an importer of Chinese goods, and they have broken EPA laws repeatedly. It is currently illegal to import any catalytic converters that are not made in North America. This is because the EPA must be able to randomly drop in an inspect the manufacturer to make sure they are meeting the necessary quality standards. This is difficult to do when the manufacturer is overseas.

With platinum being valued at between $1300 - $1700 per ounce, new aftermarket converters that cost less than $100 will not function correctly on a vehicle, its just not possible to contain enough material at that point to be effective. So yes, their quality is extremely shoddy. The Chinese do make sure their product looks good, but physical appearance is meaningless.

The Titans cats are not huge, where is your information to suggest they are? They are 5" diameter round body units, which is not huge. Plus there are 4 of them arranged in two inline banks. There are lots of 400 cpi units on domestic applications that are producing less power that are larger in cross section.

As far as information to tell how much power a cat will support? Thats a function of flow. The information about how much a cat will flow is not only spotty, much of it is downright bogus. This is in part because the flowbenches that are used are often not calibrated correctly, most are mean to flow cylinder heads, not exhaust components. And they way they measure flow is not the same way that actual exhaust flows.

Also for a cat, how much flow or HP it can support varies. If a cat could in theory flow enough to support 300 hp, but it could not possibly meet the emissions standards at that power level, it will be given a rating more in line with what it is emissions certified to handle.

400 cpi catalysts with fairly standard sized bricks are often rated by the old OBD-I (pre-1996) standards which is displacement (Liters/CID) and GVWR. On OBD-II applications these ratings are mostly meaningless. A typical 3x5" oval substrate 4" of internal length with a proper loading is usually rated up to a 5.9L and 6,000 lbs GVRW. This means that converter can mean the flow and emissions requirements of a vehicle with up to those specs. In reality they can actually handle the flow of even larger applications though the heat of larger applications can cause them to fail prematurely, so you get no manufacturer warranty once you exceed those ratings.

Once you actually get into the world of high flow catalysts, the lower active surface area hurt their ratings because they have less opportunity to reduce emissions, and the cat cannot have a rating higher than its ability to keep the emissions standards in check.

I worked in the industry for over 9 years, so experience has taught me what a properly made cat can and cannot handle. We used the Eastern Tru-Performance brand (only brand we found to work effectively) on 8.0L plus GM 3/4 and 1 ton trucks without issues, we routinely used them on modified 300+ hp Subaru WRX and STIs, Mitsubishi Evolutions, Neon SRT-4s, Corvettes, Mustangs, etc. including my own personal highly modified Ford Thunderbird Turbocoupe. They not only meet the flow requirements just fine, but they could handle the emissions requirements too.

Have these cats been flowbench tested? I am not aware of any. But in my opinion, the flowbench test produces such inaccurate results when measuring the flow of catalytic converters as to be meaningless. This is evidenced by the fact that some people are quoting that a 200 cpi Magnaflow bench tests at 280 cfm, while another group rates one at less over 600 cfm. Neither are accurate values. Flowbenches are designed to flow a cylinder head which has been ported. An individual port on a cylinder head will not flow nearly as much air as a catalytic converter will unless if a a massive race only type head. In order to accurately measure the flow of major exhaust components, a much larger motor and blower is needed to maintain an accurate and stable reading. The system much free air calibrate before hand and then run multiple tests on the same unit so the values can be averaged out. The unit must then be recalibrated and another unit from the same manufacturer must be tested. The test would need to be done on three separate samples from the same series from the same manufacturer in order to pretend to be meaningful.

The test would still not be very meaningful because firstly, exhaust does not move as a continuous laminar flow they way a flowbench does. It occurs in high energy pulses, once pulse occurring each time an exhaust valve opens and the hot high energy gases begin flowing and dynamically expanding into the exhaust system. The way a flowbench tests is very different flow this.

As far as I'm concerned, real world results are more meaningful, and I've run into many vehicles that were running 3" single converters and pushing over 300 hp through them. The most powerful one I have run into that was dyno confirmed was a highly modified 2005 Corvette that was pushing out 1100 hp. It had a huge blower on it. We ran 3" cats, on on each bank, so it was pushing over 500 hp through each cat. The owner of this car actually intended to use it on the street, which is why he wanted cats. The car was clearly built for the drag strip however. The car passed emissions just fine.

Unless you have a high output supercharged or turbocharged engine, a standard 400 cpi converter will probably be all you would ever hope to need.

 

Just weld in a pipe and finish off the exhaust with a nice muffler. The cat not being there wont hurt a darn thing.