Hey guys, I am fairly happy with my 351 just had to have my e4od done but no biggie. When it was out I had forgotten about my exhaust issue it comes off the manifolds 2.5" all the way through the 2nd cat then it reduces down to 1 7/8" . I was debating on running just one cat a flowmaster Y pipe run it down 2 1/2" into a single magna flow 9100series cat( this is a obdII 351 mind you) then into a aeroturbine muffler then behind the right rear.
Will just one cat be sufficent for the monitor O2? 2 1/2" or 3"? either way it will flow nicely. What do you guys think? My cats are fine just the aftermarket ones flow better and I can get $180 to scrap mine.

Thanks
Curtis

 

go for it........and if you are getting the trans rebuilt have them install a shift kit, it will be the last time you rebuild it.

 

Tranny is done I exploded my one planatary(aluminum one) replaced with a 6 pin diesel one, shift kit, superior pressure riser and a Derale 18000gvw cooler with a 650cfm fan and 3qt extra pan E4OD is in good shape now.

Curtis

 

Thats the way to do it.......

 

A highflow 2.5" is fine for a stock motor, bigger will help upper HP but will hurt low rpm TQ some.

 

since this i obd II you must keep all 3 o2 sensors and keep the cat configuration thats there otherwise the computer will have issues. but that doesnt mean you cant still run a better setup. I would get some BBK 5.8 shorty headers, have a custom y pipe made at 2.5" you will need to run a hi flow cat and the 3rd o2 will follow then 3" from cat out stock location

 

I am alittle confused, I know the o2s right off the manifolds are required I thought the 3rd one was a monitor for temps. I woulden't mind keeping both of them but this thing is really quiet, when I put my old borla cat back on it I started it up with just cats and no louder than with the borla on it. For it to be that quiet it has to be restricting it I hear all of these newer trucks with just cats and they are really loud. I don't want annoying loud but I like the sound of a 351 I hear more sucking from the intake than out the back.

Thanks
Curtis

 

You can run an aftermarket cat no problem, and I guarantee it'll be louder. The 3rd O2 sensor can be replaced with a dummy load as it doesn't affect engine operation, but it will throw a code if you just unplug it. You could just mount a fitting in the pipe behind the new cat if you like and plug it in too. That's what you are up against though, if you want to loose the stock cats, you will need to replace the whole factory Y-pipe most likely. You could also hollow out the original cats, cut off the secondary and attach an aftermarket cat too, same result.

 

Thats what I was looking at doing putting the bung in the pipe and running the 3rd o2. I was going to cut the 1st cat out at the Y and use either a flowmaster Ypipe or have my exhaust guy make one up and run it all 2 1/2" with a aeroturbine muffler. If it by chance throws me a light where can i get a o2 simulator?

Thanks again
Curtis