The stupid exhaust question thread

[RHamill]

The o2's before the cats are used to maintain proper A/F (air to fuel) ratios, so those are important.

However, the ones after the cats, are used to detect problems with the cats, it's commonly told that removing the cats will burn valves and this or that, one guy says it will run rich, the other says it will run lean. There is plenty of guys who remove cats and are just fine, the engine light comes on, that's about it.

 

[MOBS]

Well that makes sense for the ones that have both types of O2 sensors, but the ones with single post-cat sensors(no pre-cat sensors) are still there to detect A/F mix. Without that signal, the computer will usually lean it out to idle roughly because it's receiving the lower resistance numbers a pre-cat O2 sensor would receive. Then ofcourse the IAC valve takes over and attempts to idle it back up.

For instance, on a ford, if you unplug the O2 sensor it'll default to open loop, which some people prefer because of the richer mix(especially when using cams with stock injection systems). I'm only speaking from past experience in tearing down these engines after running without cat/O2's. The later model engines get severely scorched in the top end(edges of the cast aluminum are rounded from extreme heat), ofcourse this also means they rarely have carbon buildup, lol. The earlier ones aren't nearly as bad, but I've seen scorched exhaust seats on a few and discolored valves on alot.

If you're able to run it and not be worried, then more power to ya, I just wish ya luck in the long run....I'll have to research these double O2 setups some more and see what changes occur when they're modified in certain ways. Oh I just LOVE having something to do

 

[RHamill]

What is the exact pipe difference from 88-95 trucks to 96-01 OBS trucks, I know all vortec trucks come with true duals from the factory up until the muffler, with 2 cats and 4 o2s.

How about the 88-95, whats the set up on those?

 

[dirtridinz71]

What is the exact pipe difference from 88-95 trucks to 96-01 OBS trucks, I know all vortec trucks come with true duals from the factory up until the muffler, with 2 cats and 4 o2s.

How about the 88-95, whats the set up on those?

My 92 stock exhaust was one O2 in driver side manifold, Y-pipe to single 3" pipe to 1 cat to SI/DO muffler with 2 1/2" or 2 1/4" tailpipes.

 

[ndians68]

A 1994 with the post-cat O2 sensor?! What state was this truck originally sold? Reason I ask is because of the post-cat O2, I didn't realize until recently that ANY of the 88-98's came with those late-model O2 setups. Makes sense that I found a few like that in CA, but they were all 96+ models, never knew of any pre-96's with that setup. But yeah, if you tuned out or used the resistor trick, I bet you'll noticed an increase in overall performance, unless ofcourse you just have leaky injectors and that's what's keeping it from running like crap.

not sure on that, i know the truck is from canada, when we first got it it threw codes, then changed the o2 and it quit but still smoked which was either vavle guides or because the oil return was cloged
and as far as we know it has not been tuned out... but will be when we get it tuned... unless we get rid of it

 

[Vigh_J]

Different Question

The dual pipes before the muffler are 2.25"??? Just inquiring as im looking at purchasing a DI/DO.

James

 

[MOBS]

RHamill, unless they were the custom model, most of the 88-95's were single O2 on driver's down pipe, then both pipes merged into a single large pipe with SI/SO cat, and that ran into a SI/SO muffler that dumped behind passenger rear wheel. The custom models(example: southern comfort, dixie customs, etc) did the exact same way up to the muffler, then it had SI/DO muffler with exhaust exiting on both sides of the spare tire.

Vigh_J, I honestly don't remember the size of the pre-muffler piping on the 96+ models, RHamill can prolly tell ya though. I do think it's in the 2.25" size tho.

 

[RHamill]

I'm interested in knowing the diameter of the pre muffler pipes on the 96+ also, if I had to guess it would be 2" or 2 1/8th inch.

 

[MOBS]

Yeah, it's definitely not 2.5" or 3".....it's somewhere in the 2-2.25" range. I was just looking at some earlier, didn't think to measure tho.

 

[Vigh_J]

Its 2.25... ordered a SUPER 50 series Flowy DI/DO

RECOMMENDATIONS for some shorty headers anyone???