True dual exhaust

[Lifted94Blazer]

I have a blazer and it has a y-pipe into one cat then goes into one muffler and out one pipe. I want true dual exhaust, but the exhaust shop says it's against the law for them to modify the emmission control stuff. So, I was talking to a friend about this, and he said that if I don't have emmission control stuff on my truck when I go in there that there is no way they can modify it. He has done this on his trans am. He took the exhaust off and then had them put true duals on without cats. Has anyone else done this or heard about it? Also I thought about getting the exhaust off of a 96 or so 2-door tahoe because they have true duals all the way to the muffler.

[SIT N' LOW]

I dont know what the laws are in tx, but in calif. you cant add or remove cats from your vehicle. alot of your newer computer controlled trucks have O2 sensors right before the cat and some after. If you did add another cat, you would have to have 2 O2 sensors so the computer could adjust. 96 is when they started doing the duals which is good for x pipes :).

[Mark]

So would it be hard to add another O2 sensor if you add another cat? I've had a hard time finding someone to dual mine out as well. I believe the law is the same as faras adding or removing cats here in Texas. Unless you fall under the grandfather clause. If it didn't have it before, you don't need it now. But mine doesn't , I've also been told that it's really not worth getting true dual exhaust , becuase of the computer. Is this true?

[Lifted94Blazer]

couldn't you just stick the O2 sensor on the H-pipe(or x pipe) so that it reads from both sides. That shouldn't be hard.

[astroracer]

Just plugging an O2 sensor anywhere into the system won't work... On your '94 the sensor works off heat from the engine. On the '96's and later, the sensors are positioned in front of and behind the converters. The front ones use engine heat to calibrate the computer. The rears run off converter heat(much hotter then the engine).
If you just arbitrarily put in a sensor it will not get hot enough or will get too hot to function properly. This will not allow the computer to do it's job so your truck will not run right.
Along with this info... as was alluded to in a previous post "true duals" are not all they are cracked up to be. They can actually reduce your lowend torque and hurt performance... that is why you are reading alot about "X" pipes.
If all you really want is to get some "noise" out of your truck, leave the converter alone... it flows plenty of air for a stock 350. Go to a good muffler shop and have them take off the muffler. Have them run a 3" pipe out of the converter and split that into dual 2 1/4 aluminized pipes running out the back with some nice tips. I quarantee you will like the sound... the computer won't miss the muffler and you will not hurt engine performance.
I have the EXACT same set-up on my stock '95 and evrybody who hears it asks what I've done to the motor... It sounds REAL mean. Try it, it's fairly cheap and will get you the sound you are after. Mark

[Mark]

That's cool, but the only problem is we have to have a muffler in the state of Texas.

[astroracer]

That's to bad... Put on a Flowmaster two chamber, 3" single in and 2 1/2 dual out in place of the stock muffler. It will sound good...

[scrapin']

That's what I have on mine and it sounds pretty vicious. Only one problem, the resisnence inside the cab at certain RPM's is VERY loud, but my exhaust ends right after the muffler with a set of turn downs. When it went out the rear it was tolerable in the cab and still sounded good outside. You may want to invest in some dynamat in the rear wall of the cab and under the floor carpet to kill some noise. Later...

[astroracer]

But I LIKE the noise...:D

[1badgmc]

I'm running true duals on my '91. Dual 2.25" pipes. 2 cats. 2 Borla mufflers. They dump over the rear axle. It's as quiet as a stock truck at idle, but when you stick your foot in it it makes a nice throaty sound. At 80 mph on the highway it's quiet enough that you can talk to your buddy without yelling. I noticed a bit of a seat-of-the-pants gain and the computer hasn't acted up towards the whole deal. What all differences are there between a '91 and '94 electronics-wise?

[SIT N' LOW]

theres not much difference in the computer from the 91' to 94'. just because you may not be able to due true duals, doesn't meen you still cant good performance. I've experimented with my exhaust about 8 times. depending on the muffler you chose, you may want to run tail pipes on it. some run better with and some without. ya the noise might sound good when dumped, but you could also be loosing power. keep trying until it runs the best

[Lifted94Blazer]

Hey Jason, where'd you put your O2 sensor when you put true duals on your '91?

[1badgmc]

I didn't touch it. It's still in the same spot.

[Lifted94Blazer]

so it just gets info from one side of the engine now?

[1badgmc]

Yep. That's all it ever got before.