I feel the power gains at all rpms, but especially low end and when pulling away. I cut my old muffler in half do I could see the inside. It was shot, looked like someone had hit it with a blow torch. It really made a huge different.

 

So, anyone give thought to leaving the cats and ditching the muffler(s)?

Another thought is to use one of the Flowmaster super 10 mufflers. Yeah, not much muffling at all but you can say you have a muffler.

Just sayin' . . .

 

Haha good one. I still have stock exhaust on my truck, it's not loud. I'm just saying that it doesn't matter what we run for exhaust here cuz we don't get checked. I will eventually do something with mine.

 

The guy who put my muffler on decided he doesn't want to mess about removing the cats and putting in a piece of pipe. He said he thought about it but he would be liable if anything ever came about so I guess I'm gonna stick with it.

 

Or you could do what I did and unbolt the exhaust from the rear of the cat....take a tire-iron or if you have a long enough drill bit used for cutting into cement/brick....just drill or bust out the "honey-comb" inside...remove all of it you can....the rest you can't get to....just fire the truck up for a few secs and it'll blow out.....re-connect your exhaust.......bingo...freer flowing and louder.....takes less then 30 mins to do.

 

I'll throw out two scenarios when I ditched the cats. Neither may apply to you. BTW, I live in middle Tennessee. No smog check in my town, but some bigger near-by places have a sniffer check and possibly a visual.

1) 86 Mazda RX7. About three cats in a row, Y out to two big can mufflers. Not the Rice mufflers, just stock big can stuff. I got into some situation when working on the car where I needed to get those rusty bolts off. The car was running pretty bad anyway and I've long heard that bad cats can cause all kinds of havoc, so off they went. Straight pipe went in. The car was so rice sounding and loud that I couldn't stand it. I was back the next week having the straight section replaced with a Full Boar brand steel wool packed "glasspack". Quietened it down a bit. My power didn't seem to change through any of this.

2) 85 F150 5.0L. Codes galore and a wimpy stock muffler due for replacement. I decide to get rid of the 'power robbing' cats and go for a HD muffler to get all the power possiblt from my new Blazer RV cam. It was one that the shop made. Similar to a Flowmaster, possibly a MelloTone. It's 1/8" plate and they never rust out. Cut out one Cat, opened up the other and busted out the honeycomb. I left the O2 sensor. Still had the codes, and I seemed to lose ALL power. Ran like a dead dog. Gas consumption dropped from 17mpg to 10 mpg. The shop said they had never seen anything like that and they hadn't done anything that should have caused it. I had them stick a Cherry Bomb Glasspack in the place of the old cat. It was a little smaller diameter that the rest of the exhaust. The trucks pipe 'tone' improved and my driveability issues vanished. Power went way up and the 17MPG came back. My "theory" is that I had eliminated backpressure with the free flow exhaust and my O2 sensor just didn't have time to "read". Adding a little restriction back to the system was what the doctor ordered.

BTW, my trusty muffler shop refuse to cut off the cat the last time I asked, citing "liability issues'. I went back home and got out the sawzall. They got me back in the next hour to replace the damaged section of "pipe".

 

Yup, a certain amount of back pressure is necessary for proper performance of a vehicle that has electronic monitoring. It's not like the old days when you could just open up the carb and let the juice and air flow in.

 

That works real well IF you don't have inspections. OP has inspections--visual and pipe--every two years.

 

Hey all,
I've got a 96 F150 XL with the 300 i6 and am currently thinking of replacing its muffler and removing one of the cats (the rear one)

My main question is what effects will this have on the truck all together, I'm going from a stock muffler to a "Flow Pro" (thats all I really know about the muffler) and I'm looking to remove the rear cat while leaving the O2 sensor in still.

Will my truck start throwing a code if I do this or should everything be fine so long as I leave that O2 sensor in? I'd still have the 1 cat with the sensor behind it and where ever the one before it is. So going from a 2 cat system to 1 with a better muffler.

 

I have a 1990 with a 5.0, 2 cats and single flowmaster and I can barely hear the exhaust. I dont want Loud just a low rumble like some of you guys are wanting. If I remove the second cat, will it throw a code or not? Will it mess with the drive-ability? Has anyone done this with success?

 

You've got OBD2 so indeed you need to be mindful of not removing the cat that is forward of the rear O2 sensor or you'll surely set a code. Sounds like you're aware of that. I think you should be fine, but can't say I have specific experience in this regard.

FWIW, on my '91 I6 the only "muffler" is the two stock cats. After that, it's just all pipe.

 

just went through the whole smog thing in Cali with my 93.Moved from Nevada.
There is a number on your cat(s) that has to be entered into the computer(the smog techs) and it has to match the application or it will fail.
I got a replacment cat from magnaflow and had no problems with it passing.
Plus the old cat on my truck had two ports on the top that were blocked off.The truck ,before replacement of new cat had some drivability issues which i could never trace down,while replacing the old cat i noticed two tubes coming down from the back of the engine which in turn i found out should be connected to the cat which in turn go to the egr system. Once i reconnected the cat to the two tubes my issues went away.

 

i put a magnaflow cat back 2.5 system on my 93 with a 5.8 which has the big torpedo cat. nice low rumble at idle but when i get on it it sounds really throaty!