I have developed a rattle in my cat. 89 F250 w/460. If I pull the cat and replace it with a 3" exhuast pipe, can I just disconnect and remove all the smog pump plumbing and leave the air pump hooked up at the serpentine belt. I just put new belts on and if can just run the pump without it pumping air to anything that might be the way to go. I do not have smog checks in my area and I know it might not be the green thing to do but my truck is in perfect tune and it is polluting a lot less than some of these cars spewing out a quart of oil every 500 miles. thanks.

 

What did I **** someone off LOL>

 

What, are you expecting an instant response? Removing the converter from your vehicle is dangerous. Even a perfectly tuned vehicle puts out lethal levels of carbon monoxide. While it is unlikely to ever get trapped anywhere long enough do anything, there are over 1000 deaths per year in the US from carbon monoxide poisoning, and over 5,000 cases of non-lethal poisoning per year. About 4 in 5 cases are directly related to vehicles that are missing their smog equipment.

Your 460 was built prior to the development of oxygen cycling which means that in order to reduce emissions, you vehicle is tuned to run slightly rich. This causes elevated levels of carbon monoxide and hydrocarbons in the exhaust, but very low NOX levels. Air is then injected into the catalyst to help the converter turn the HC and CO into harmless compounds. So while you may feel your 460 is cleaner that other vehicles, that is only because it has a cat and a functioning air pump system. Newer vehicles use the oxygen cycling method, which does not require vehicles to run rich and eliminates the need for smog pumps.

 

Thank you. That is what I was looking for. The trouble with postings is it is hard to tell what the intent of the post is ( I was trying to be humorous and bump it up at the same time). I just wanted to bump the thread back up that is why I put LOL in my post to make light of it hopefully it was not taken the wrong way.

By the way I did a search and your post is the first time that actaully explains the smog pump function, most just say rip it off and the cat. too, you know the posts I am talking about "yea my brother's cousin's uncle took his off and got 20mpg and 60 more hp" LOL.

 

Well, the factory cat doesn't rob that much power, but I would agree, the torpedo style cats are one of the more restrictive designs. The problem with a cat of that size is that the exhaust (being a gas) will try to expand to fill the entire thing. When a gas expands, it starts to cool down. The cooling causes the exhaust to slow down. This causes backpressure. The catalyst function does cause the exhaust to heat up but that is such a large catalyst that it probably doesn't offset the cooling effect fully. Also, the torpedo style cats are famous for clogging up. In fact, many of the people who "gained xxx amount of HP" noticed a difference from removing a partially plugged cat.

One approach I have used with quite a few customers is to use a high flow equivalent. The body is much smaller that the OE catalyst, but larger than most ordinary aftermarkets. I have had a few people tell me they were very happy with the sound and performance gains. In fact, with just the right sized catalyst, such as ours, you can gain a small amount of torque over a straight piece of pipe, and here is why.

When the exhaust burns inside the converter it heats up and expands. This causes the gases to start moving faster. So the exhaust coming out the back of the converter will be hotter and faster than the exhaust that entered. This functions a little bit like a jet engine that has no moving parts. It literally propels the exhaust through the pipe reducing backpressure and increasing torque at low RPM. I have even seen a converter shave almost .2 seconds off a track car. The car was a '88 Buick Grand National with a bored and stroked 4.0L engine. It was turbocharged and produced over 650 bhp. Without cats its best quarter mile was 10.44 seconds. With the cats on it, it did 10.28. The owner had the cats on it because he wanted the car to be street legal when he wasn't on the track.