Stock turbo, 3" cat/exhaust w/muffler

want to upgrade to 4" exhaust, back of cat
(not getting rid of cat and definitely not upsizing while its working!)

how hard is it to go from 3" turbo to 4" exhaust
and would I still get much benefit from the 4"?
just looking to keep my egts down while tuning the truck a little bit

 

The CAT for was choking a good 100°F on the pyro and 2 psi boost back when I was just running the stock fuel plate. That was 200+hp ago. FWIW..

 

You will only be losing the cost of the exhaust. There will be absolutely no gain in performance or drop in EGT's unless you do a full exhaust from the turbo back.

 

if you cant do the cat removal for emission reasons you can get a 3 to a 4 adaptor from napa.it still wont improve anything unless you take the cat out.

 

thanks, thats what I needed to know
spend my money somewhere else while I have that cat on...

 

After this much time, the cat is not going to get any better. Especially with all the new power you are putting through it. Is there any reason to keep this thing on? Any more goodies for the engine are lost with this orifice in the exhaust pipe..

 

If it's old, the guts are probably starting to fall out. If I were you, I'd ram a steel rod or sturdy broom handle into the cat to make sure it's not falling apart.

Probably best to remove the cat and then ram it 20-30 times with swift hits to make sure the inside components are still intact. Then I'd shake the cat a little to make sure nothing is loose inside and then reinstall it in the stock location.

Clearing the cat of loose debris by following the steps above will help decrease emissions, increase engine life, increase fuel economy, and possibly increase horsepower a little bit.

 

Does your truck have a cat because it is a California truck or are you talking about the resonator ahead of the muffler.

 

truck 215pump, not originally from CA
orig owner moved here, then truck went to Oklahoma
I brought it back to CA. It had a straight back from turbo
silly me, I worried I'd have problems returning to ca so he had the stock pipe with/cat/muffler and put it back on for me, he had tossed it in the barn
I can't remember how many miles it had when the guy in OK bought it and removed the cat.
btw CA DMV never even looked...
a cat is not required if there wasn't one when you brought it to CA
had it dyno'd on a mustang, they didn't think my cat was faulty
(just restrictive)
I do not want any noise thats not necessary
my shop will re-dyno after the plate, clutch, gsk and timing,
so I'll see how things look and go from there
I thought about gutting the cat once, but they are EXPENSIVE and
I'd rather lose it than damage it...

 

I see now you have a 12v and not a 24v. The 12v guy's would know better but I seriously doubt you have a cat, it must be a resonator to help reduce exhaust drone/noise. The 24v engines don't have cat's just a resonator which is straight through design and causes no back pressure.

 

The 12V engines came with Cats since 1994 up to 1998. As they age the become plugged and restrictive. Also the more flow (power) you put through them the pressure drop goes up. So it only gets worse with more mods. Like I said before, I gained 2 psi boost and dropped 100°F by just dropping the cat on the stock exhaust. The 4" probably gave another 50°F drop at the same power level. (about 280-300 hp) The problem is finding a shop that can do a 3"-4" adapter and pipe to go into the stock muffler.

The resonator came in with the 24V engine in 98.5 models.

 

Thanks Lil Dog, that clears things up for me. I Didn't know the 12v trucks had Cats.

 

BIG BLUE 24:
Loved your subtle humor in the steps you used for evaluating the catalytic converter''s inner integrity! A Bosch roto-hammer equipped with a 10" long x 3/4" bit in the hands of determined user also works well for testing the density of a cat's inner ceramic material...or so I've heard.