CAT Question
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Joined: Apr 2007
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CAT Question
I have a 1990 F350 460 Crew Cab. About a week ago I detected a slight wistling sound when I got on it. It was very minor and I kind of srugged it off and would deal with it at another time. I also detected a slight increase in fuel consumption and a slight decrease in power. The other day I was pulling a trailer and I came to a very steep hill. The power I usually had was not there. I stomped on it and the whistling sound increased. Then all of a sudden I heard a kind of quick sucking sound and then the truck went ape s&*t. Tack jumped and power was back. It hit me. The cat had just blown through. Now, heres my question. If i hollow the cat out or put a staight pipe in its place will it mess the engine up? Will the mixture be off. A very knowledgable friend says if I get rid of the cat without remaping the mapsensor it will run too lean. Is this true? Do they make a high flow cat? I am hightly against cat's. The ones in trucks that is. The truck exceeds the weight requirement for emmissions so it is exempt. Can I get away without a cat? What do you reccommend? I want to get this fixed. I just got a camper and I want to be set.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
The cat has no control over the engine fuel mixture at all, the engine computer contols that on the fly with feedback from it's sensors. The best thing you could so for this truck is replace the complete exhaust system, the factory system is painfully restrictive, that motor should have a single 4" at least. If that's not in the books at this time, just do whatever you need to make it run, but consider replacing the cat wih an aftermarket high flow unit. You may not have emission regulations in your area, but there no reason you should knowingly contribute more than necesary to our very real air polution problem.
Posting Guru
Joined: Mar 2007
Posts: 1,757
Likes: 2
From: Florida
Getting involved with emissions is just another jolt of who is right and who is wrong.Paul is right...the stock exhaust is VERY restrictive especially for that big boy...upgrade your exhaust to your own specs because everyone has their opinions on the use (or lack thereof) of cats,so only you can be the judge....either way...ditch that old one it's killin ya.And either wa you'll get more power, better response and better mileage.....Conanski....when are u gonna make a gallery?I wanna see ur ride....
Former ******
Joined: Nov 2004
Posts: 4,901
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From: Salt Lake City, Utah
The factory cat is not as restrictive as some people think, however, they tend to break apart and clog themselves. This is likely what has happened in your case. I recommend using 2 high flow cats in parallel. Since you are exempt on a weight basis, I think you would be fine running without. However, cats are not the major exhaust restriction in most systems. However, it is your truck, you be the judge. If you decide to go catless, use a piece of pipe, a hollow shell acts as an exhaust restriction. A 4" in my opinion is too large, go with dual 2.25 exhaust with a crossover or h-pipe.
Posting Guru
Joined: Mar 2007
Posts: 1,757
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From: Florida
2.25 duals in a 460?I'd say at least 3 inch duals with an x pipe or a single 4 inch out that back....the 2.25 will give it way to much backpressure and probably choke it......if you are basing your decision solely on cost...look at the prices for the high flow cats......then u should decide......4 inc pipe willprobly be too big so I'd go with 3 inch....
Former ******
Joined: Nov 2004
Posts: 4,901
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From: Salt Lake City, Utah
The factory pipe size for a 460 is usually 2.5" or 3" single exhaust from the factory. If you overly enlarge the exhaust size, you loose the exhaust velocity, and until your exhaust velocity reaches a certain point, your engine will not scavenge efficiently. If your engine does not scavenge efficiently, you will have little torque. Dual 2.25" is larger than 3", so you would be larger than factory. It will not choke the engine down, it will breath better than stock. If you doubt my claim that 2.25" duals are larger than 3", check this out.
3x3x3.14 = 28.26
2.25x2.25x3.14 x 2 = 31.7925
3x3x3.14 = 28.26
2.25x2.25x3.14 x 2 = 31.7925
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