cats with true duals on obs

**nined4bowtie** · 07-03-2006, 02:00 PM

in a few weeks i plan on having a true dual exhaust made and use 2 cats on my 94. Tryin to figure out if i can run a single 02 senosr on a true dual exhaust setup. since i only have one 02 sensor can i get away with just using the single o2 sensor on the passenger side and not have to put one on the drivers side?? i've searched the forums but only get info on the vortec setups.

**airdeano** · 07-03-2006, 09:10 PM

youll have to run the single O2 as there is no place in the
computer to plumb a second.
the O2 located on a stock TBI is in the driver side exhaust.
you can use an O2 extention, but id be easier to use the
driver side as the wiring is pretty much there.
what camshaft are you running to need dual exhaust?

airdeano

**bigolblackie** · 07-04-2006, 05:17 AM

I run longheaders,cats,with a true dual exhaust. I didnt know what to do with the o2 either. The pros put my exhuast together,they put the o2 in the pipe driver side only,in the pipe,just after the end of the header,but before the cat.:fsc:

**nined4bowtie** · 07-04-2006, 08:04 PM

i have a stock cam. planning on doing a tbi/vortec swap after i rebuild the block. i have a set of shorty headers no cat with a si/do flow 40 and its not enough rumble for my taste. would like to do 2 1/4 inch to the mufflers then 2.5 the rest of the way. my other option is to buy an aftermarket y pipe but then i have to get it chopped up to fit right because of my lift kit. think this is to much exhaust for my motor?? trying to plan ahead

**airdeano** · 07-04-2006, 08:59 PM

Originally Posted by nined4bowtie

think this is to much exhaust for my motor??

yes, yes it is.

airdeano

**Nickleahy23** · 07-07-2006, 12:13 AM

i have shorty headers and true 2 1/4 duals with a super 40 on each pipe and i really like how it sounds. It might not be the loudest but when you step on it, its destinctive and sounds great. Doesnt sound the same as every other truck out there. More of an old muscle car sound.

**TigerEyz3** · 07-07-2006, 08:20 AM

Originally Posted by nined4bowtie

in a few weeks i plan on having a true dual exhaust made and use 2 cats on my 94.

You do know that this is technically a violation of federal law, right?

Originally Posted by airdeano

Originally Posted by nined4bowtie

i have a stock cam. planning on doing a tbi/vortec swap after i rebuild the block. i have a set of shorty headers no cat with a si/do flow 40 and its not enough rumble for my taste. would like to do 2 1/4 inch to the mufflers then 2.5 the rest of the way. my other option is to buy an aftermarket y pipe but then i have to get it chopped up to fit right because of my lift kit. think this is to much exhaust for my motor?? trying to plan ahead

yes, yes it is.

The stock TBI doesn't need that much exhaust space. And what you have described may even reduce your current performance due to reduced exhaust velocity/scavenging. Factory setup was a single 3", which IMO was more than the motor needed. My factory 255HP vortec came with dual 2" pipes to the muffler, then a single 3" tailpipe. Today's higher output vortec motors (5.3L) are running a single 3" pipe post-cat.

As far as getting more rumble to suit your tastes and keeping your performance up a bit, maybe a different cam and/or muffler is in your future.

Below are a couple of alternatives that you can do while thinking over the cam/head/block situation:

run dumps/turndowns under your truck bed - that'll boost the volume you hear in-cabin
run a Dynomax Bullet muffler (can be done with the turndowns, too) - supposed to be one of the loudest mufflers available

**Pauly** · 07-07-2006, 11:41 AM

The 6.0 and 8.1L vans and trucks are running dual 3" exhaust. In the 6.0L, there is a 3-4" long piece of 2 1/2" pipe that comes out of the exhaust manifold, then it steps up to dual 3" all teh way to the dual in single out muffler.
T^hat exhaust is beautiful.

In case you doubt the dual 3" info, I have personally measured at least 4 vehicles, both vans and trucks with the 6.0L.

My 1997 Vortec 350 came with dual 1 7/8" pipes that ran from the manifolds to the cats(called headpipes). These stock headpipes in some of the stock bends, crimped down quite a bit smaller than 1 7/8".
Now I run dual 2.5" headpipes from the headers to the dual 2 1/2" cats.
The 3/4 ton trucks Vortec 350's used dual 2 1/4" headpipes. I wish GM installed the 3/4 ton exhaust on ALL the 1/2 ton vehicles, the stock cats on the 3/4 ton trucks are even larger. I thought it was weird that GM installed 2 different diameter exhaust on its truck, esp. since both the 1/2 ton and 3/4 ton both used the same Vortec 350. Perhaps it is because the Vortec 454 was available in teh OBS 3/4 ton trucks???

I personally think dual 2 1/4" would be OK on a TBI esp. if the pipe bender uses a crimp style, non mandrel pipe bending machine. The 2 1/4" pipe would probably squish down a bit smaller. The exhaust will flow only as much as its smallest diameter part will allow.

I ran dual 2 1/4" on my old 1984 GMC 1/2 ton with a 1989 F-body 305 roller cam engine. It ran fine.

Just my opinion though.

peace
Pauly