that must be correct because that is exactly what i have 4 sensors and three cats. well thanks for the help guys

 

cali emission trucks '01+ have 4 sensors... two precats, monitored upwind and downwind, and then the Y pipe leading to an UNMONITORED bigfatnasty cat.... the big fat nasty cat can disappear and the engine/pcm has no clue...

cali trucks are actually much easier to run true dual or H/X pipe duals on for this reason, which I highly recommend because that Y pipe is the issue.

 

So the only reason to keep the last big cat is for the visual inspection for smog correct? but if i removed it would it enhance performance?

 

er...uh... maybe...

those big cats breathe pretty good... and.. they run hotter than the actual exhaust that passes through them, creating an area of low pressure that drafts exhaust pulses out of the collector- exhaust is ALL about scavenging the pulses instead of letting them cool too quickly and creating barriers the pulse behind it has to bust through (creating back pressure.... back pressure is BAD.. scavenging is GOOD)...

the REAL obstacle in OE exhaust is the Y pipe... get rid of that thing... the cat behind the Y actually helps clear the exhaust from the collectors and Y.. if you really want it to breathe right, keep the kitty (or replace it with a high flow) and get the eff rid of that Y pipe.

 

So i have been thinking about this for a while now and i have an idea and would like an opinion. so if the y pipe is the enemy here, but i need to keep my two pre cats and one post cat, is a good option to get aftermarket headers and then have separate piping and have them both collect into a dual muffler? so the join together to one at a muffler instead of a y pipe basically and i would keep all cats. Thoughts?

 

it isn't so much as having the y-pipe that was the problem, it was the crappy design on the 99 and older trucks. (two down pipes into cat, major restriction, there was a pic around here at one point) The 2000 and up trucks redesigned the exhaust, so the pipes actually come together first, and then its a single inlet cat. Flows a lot better.

Do you have california emissions on your truck??

 

yes i do, each side after headers have a cat then it collects into the y pipe then another bigger cat then muffler. 4 o2 sensors post cat pre cat on each side

 

Well, it makes doing true dual easier.

 

true duals like totally separate and two mufflers?

 

Not all 2500 had 4 o2 sensors. Standard had 2 the heavy duty's had two per side(duel cats). Cali seems it had them on everything. That's good because most people that run duel exhaust only monitor one side. My plan is to run long tubes into two cats X pipe into twin mufflers out the back.