02 Sensor locations (4.3/5.0 vs 5.7)

[sync]

Been digging looking at exhaust stuff.

JBA makes a really nice stainless Y-pipe but, it's setup for a TBI motor. Which means 02 sensor ports would need added for a Vortec motor.

What I'm seeing is, the 5.7 comes with 2 cats, with four 02 sensors, 2 pre-cat and 2 post cat and a "dual out" exhaust. Goal is a "single" 3" from the Y-pipe all the way out the back.

But looking at the 4.3/5.0 Y-pipes (such as the magnaflow 23457), its setup for a pre-cat and post-cat sensor as well as the two off the manifolds.

So if you were to convert to a "single" setup, would BOTH post-cat sensors need to be moved behind the single cat, or could one be in front and one behind? I'm assuming, just plug the TBI port location, and put them both behind the cat.

Are the 5.7 computers tuned differently in this regard?

Also, related. Is there a corolation between size (cubic inches) of a motor and the size (length) of the material in a catalytic converter?

 

[alpinecrick]

I've had the same questions myself. Pretty sure the computer would have to be tuned and/or a delete for one of the post cat o2 sensors.

Once again donning my flameproof suit and P95 mask............the info I have been told is the "dual" 1 7/8" exhaust on the the 5.7's actually flows pretty well, with the biggest obstacle being the muffler, and can support 300 or so hp. This comes from a gent who worked in a 4wd shop in the 90's that had a wheel dyno, and had the Vortec trucks on the dyno with various modifications. He also mentioned the intake side will do the same.

 

[sync]

I've had the same questions myself. Pretty sure the computer would have to be tuned and/or a delete for one of the post cat o2 sensors.

I did run across an old thread on here on a guys 96. He had his exhaust redone in the "single" setup with both post-cat sensors behind the single cat. Said it worked fine with no codes thrown.

I'm inclined to believe it'll work fine, since both of the those sensors are checking to make sure the cats (or cat) are simply working. The ones off the manifolds help control air/fuel ratios.

 

[alpinecrick]

I did run across an old thread on here on a guys 96. He had his exhaust redone in the "single" setup with both post-cat sensors behind the single cat. Said it worked fine with no codes thrown.

I'm inclined to believe it'll work fine, since both of the those sensors are checking to make sure the cats (or cat) are simply working. The ones off the manifolds help control air/fuel ratios.

Good point. It should be less expensive with a single cat setup to replace the exhaust, and the bends could possibly be smoother where the current two pipe setup begins to parallel each other on the passenger side.

 

[Jesse_Wenting]

Recently came across this situation after swapping out my 350 for a 305 in my 98 K1500 after she threw a rod. Currently still running the 350 ECU and not really sure what my plan is moving forward. Want to use the proper ECU, but the 305 is a temporary fix so I don't really want to invest in an entire exhaust system that's only going to need replacing later down the line (Exhaust system needs gutting as is, so I can't just save the 350 components for later)

Gonna post any progress and keep an eye on this thread though. Nice to see one that's not dead finally lol

 

[Bombader]

Recently came across this situation after swapping out my 350 for a 305 in my 98 K1500 after she threw a rod. Currently still running the 350 ECU and not really sure what my plan is moving forward. Want to use the proper ECU, but the 305 is a temporary fix so I don't really want to invest in an entire exhaust system that's only going to need replacing later down the line (Exhaust system needs gutting as is, so I can't just save the 350 components for later)

Gonna post any progress and keep an eye on this thread though. Nice to see one that's not dead finally lol

Lol I did the opposite 305 popped replaced with 350 still running 305 ECU and exhaust, seems like it runs fine and it passed two Commiefornia SMOG checks before the existing break in the catalytic screen got bad enough for the post cat O2 to throw a code. But back to the actual subject, you guys should be just fine running the 305 exhaust and moving the third "blended" O2 sensor from before the cat to after the cat or maybe you could just run one 02 sensor after the single cat with both sets of wires tied together.