??????????

 

yes, i think gutting cats does increase your power and gas mileage, especially if you have 130,000 miles plus on the clock, ive done it to a 302 and my 300, made the 302 run a heck of a lot better, both these trucks had 200k + on them with STOCK converters, what i dont understand, how can the original owners not notice the decrease in fuel economy and power??????

 

Easily. It happens VERY slowly and over a long period of time
so the change is very incremental. Same thing with shocks.
They seem not too bad until you swap them out for a new set
and then it is "Wow! It sure rides nice now".

Ed

 

Also, keep in mind that modern catalysts don't really rob any power like the older ones do, unless they get clogged up, usually caused by prolonged neglect of a drivability problem or lack of maintenance. Also, even when everything goes right with them, like anything else, they evenually wear out and fail. When the catalyzing elements inside the cat deplete, then carbon builds up on the matrix, and clogs up. This causes a chain reaction. The engine runs worse, and that results in more carbon. More carbon causes more clogging, and he viscious cycle continues.

 

Good point Argo. So would your vote be to keep the cat until failure?

 

Yes, unless I was building an off road only truck. I also would remove it (temporarily) if I planned on doing alot of mud bogging or water fording, since the sudden change in temperature can cause thermal shock and break up the guts and clog the output.

 

no, I didn't knock the insides out. I just ran without them. When the day comes that I need to smog the Beast I can put them back on without buying new ones.

 

homenf, "Did it serve any performance gain?!?!" LOL

 

I have an EFI, and I want to run a 2 1/2 in. single eshaust through a glasspack. If I remove the cats, will my mileage decrease??? I've read mixed reviews in this thread. Or, shouhd I just gut them???? I'm looking for a bit better fuel economy. I've done a complete tune-up, including fuel filter, plugs, wires, cap, rotor, K&N filter. She runs excellent, but only get 15 mpg at best driving 55. She's got a 3.08 rear with a 5 speed. Is 15 all I should expect?????? Please help with any suggestions for economy improvements. I also need to check my O2 sensor......

Duche400

 

I think that 3.08 with overdrive at 55 mph is lugging the engine. I think that in the 29-31 inch tire range, 3.08 without overdrive is the sweet spot with a 300 at 50-65 mph. FYI a 235-75R15 tire is 29 inches. What are your RPM? I turn 1,838 RPM at 55 mph without overdrive (verified with a scan tool) and get 21 MPG. When I had 3.55:1 gears and a 5 speed, I could only get 18 MPG, and that was in 4th gear at 2,100 RPM. In 5th gear it would drop to only 14 mpg at 1,690 rpm. By my calculations, you're only turning about 1,470 RPM in overdrive with 3.08 gears. That works in a car, but with all the aerodynamic drag these things have, it's probably struggling a bit. You might actually get better mileage at 70,when your RPM would be about 1,880 rpm. However, checking the O2 sensors isn't exactly a bad idea either, especially if you have alot of miles on it.

 

I'll give it a try. Wow, so I shouldn't use overdrive, hey?? Where I drive it, I never take her above 65. I'm a 55-58 driver. Hey Argo, another quick question...the truck has cruise, but it quit working about 5 years ago. I never had it fixed, but do you have any suggestions on what it could be??

Another thing...I see you have a traction-loc. Is it aftermarket?? I'm considering installing one...any thoughts?? I mean I really don't need 4 wheel drive, but it does get pretty slippery on these Upper Michigan roads!! I had a '76 F100 with a 300 and three-on-the-tree. It had a 3:50 posi and she gripped like no tomorrow!!! I'd like that for the '92. I've read that they're not too difficult to install (good, because I'm no mechanic).

Thanks,
duche400

 

1)Test it for fuel economy for a week with 4th and a week with 5th and see what works better for you. If the efficiency goes up, then your gears are too tall, and you might want to upgrade to 3.73s if you do a differential swap, so that your overdrive will be useful. That would put you at about 1,800 rpm at 55.

2)Your truck may be in danger of bursting into flames. No BS, the cruise modules on these trucks will go up, there was a big recall campaign for it. Unplug your cruise control for now, and ground the horn wire separate of the speed control. As for fixing the cruise, I'd go with an aftermarket one (Motorola has a nice one that will work off of the VSS).

3)I got an axle from the junkyard and had the Trans and Drive class at school build it with 3.08 gears and a trac-lok. I got the used trac-lok off of Ebay. I was able to keep driving the truck while the other rear got built, then I swapped the rears in a day over thanksgiving weekend. Don't try and do it yourself, it's very easy to make very expensive mistakes. It's not hard if you have the know how and the tools to do it.

 

Thanks for the technical support. I'll try a week in both gears, then I'll let you know.

 

I'll agree that the sweet spot for a 300 involves 3.5 gears, 31ish inch tires, a 1:1 gear (or equivalent to the afore mentioned) and cruising 60-65. I consistently get 18-20 out of my truck without an overdrive.

As for exhaust sound, my favorite was a high flow cat with pipe back to just before the rear axle. It reverberates off of the bed and gives a nice low tone to it. I liked running just the cat more than running just the muffler, FWIW.

But right now i'm running a single flowmaster 40 (blew the cat) and it isn't too bad, it just gets to droning on the interstate.

Justin

 

I have an 86 f-150 and i just gutted out the cat and cut everything off about 3 feet behind it and slapped on a glass pack. It dont snap or cackle but it has a deep tone that will shake the doors and windows in my house. It sounds great even above 3000rpm's. It sounds like an old cummins