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Single to dual exhaust cats/sensor??

Rick W

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Oh wise ones....

On Rick’s Ranger Rig (97 4.0, 312,000), I want to change the single exhaust to true dual exhausts. The truck passes emissions now. With the other mods I’m doing, and mostly because I’m ancient, I can get an emissions inspection waiver. It’s only due for 2 more years in GA anyway. Two questions, and my only consideration is will the truck run properly, I’m not worried about the emissions laws, we’ll be exempt..

cat converters: right now, after the “y” pipe joins the two sides from the engine, it looks like there are two cats in a row, in series. I’ve never seen that before, is that right? If I swap to duals, will the truck run right without any cats?

O2 sensor: right now, the O2 sensor is downstream of the two cats. If I swap to true dual exhaust, where do I put the sensor and/or will it run right?

all help appreciated.
 


Dirtman

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A 97 4.0 should have 3 o2 sensors. One on each manifold, and one after the cats. The downstream sensor has no effect on how the engine operates it's only job is to monitor the efficiency of the cats.

As for the "two cats in a row" yes thats normal. Sometimes the second part is a resonator. And your truck may run without cats but its illegal to drive it without any in any state regardless of inspection requirements.
 

adsm08

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Point 1: Operation of an emissions controlled motor vehicle built for the 1975 model year or newer with the catalytic converter(s) removed, on a public road, even partially funded by federal funds is a federal felony. Local laws do not change this.

Point 2: A properly tuned system that includes properly sized cats will flow as well, or better, than a catless system. Local laws don't change this either.

Point 3 (1+2): Use cats in your dual setup. You can get good quality universal fit/weld-in ones for $50 a piece. It's only the direct fit OE-style ones that are stupid expensive.

Point 4: The discussion, open or implied, of the removal of cats is against forum policy as it potentially opens the forum, and Jim, up to liability should someone be caught running around without cats.

As for the disposition of your cat monitor sensor, so as to keep the check engine light off, place it in whichever side is closest to it's proper OE location, after the cat.


Your setup has "pre-cats" and "post-cats" (not, apparently, the same thing as a "post-malone" which I am not sure what that is, but I'm told it has nothing to do with Ted Danson's character from Cheers). This was a common setup in the late 90s to early 2000s. You still see it sometimes on newer cars, but it is not nearly as common these days.

Final point, not really related to the original question, make sure to read up on and understand the physics of scavenging and how pipe size to engine displacement works, and how your dual setup will effect the optimal pipe size. You are no longer building an exhaust for a 4.0L V6, you are building a pair of exhausts for a pair of 2.0L 3-cylinder engines.
 

gaz

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RickW,

For a good running 4.0L I recommend using the "Y pipe from a 86-88 2.9L which is a dual 2" I.D. setup, then continue with 2" all the way; your choice cat brand on each side with a crossflow muffler supporting dual 2" in/dual 2" out to the tail.

Headers would be nice with this
 

Rick W

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Oops!, Thanks for the heads up on the cat delete. Wasn’t thinking risk, and I always think risk! Senior moment...

& otherwise, this is exactly the info/feedback I was seeking. It’s definitely a budget project for fun, safety never an issue, but “right” is a requirement as well, hence the questions!

Another Q: Both of my “cats” have the 360 heat shields, not just on top, so I’m assuming they’re both cats. Any problem with splitting them one and one on the duals?
 

Rick W

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Final point, not really related to the original question, make sure to read up on and understand the physics of scavenging and how pipe size to engine displacement works, and how your dual setup will effect the optimal pipe size. You are no longer building an exhaust for a 4.0L V6, you are building a pair of exhausts for a pair of 2.0L 3-cylinder engines.
🤔 Point well taken, thanks, but it’s fluid dynamics, not physics. Physics is the billiard ball and driveshaft stuff, or the study of Alka seltzer I think. 😉
 

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Another Q: Both of my “cats” have the 360 heat shields, not just on top, so I’m assuming they’re both cats. Any problem with splitting them one and one on the duals?
Shouldn't be an issue to just have one HE cat on each side. A big driver of the pre and post cat setups was that the tech to meet tailpipe emissions standards with a single bed wasn't really there in the 90s, so they put a second bed down stream to help. Newer stuff works better and can do the job now.

On thing to remember about 90s vehicles, particularly when dealing with EFI and cats. We started using catalytic converters in 1975. We started doing EFI in 1986 (give or take). Your 97 was deisgned closer to the advent of both technologies than it was to today. The tech on both systems has advanced significantly in the last 20 years.



🤔 Point well taken, thanks, but it’s fluid dynamics, not physics. Physics is the billiard ball and driveshaft stuff, or the study of Alka seltzer I think. 😉
Fluid dynamics is a subset of physics. Physics is the discipline of science that deals with all physical interaction.
 

Rick W

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Fluid dynamics is a subset of physics. Physics is the discipline of science that deals with all physical interaction.
Hmmmm, perhaps...

Physics is the theory. It is the concept, it indicates parameters that should be considered. While physics is never changing, our understanding of physics is incomplete, and our understanding is still evolving.

B31D1638-2E42-41E6-9E59-8A50660CA71F.jpeg


Fluid dynamics is primarily chemical engineering, it is the applied science of how the gases (fluids) work in the chambers through the valves out the exhaust, etc., how they expand on combustion, and how they contract while cooling and flowing down the exhaust pipe. To your point about the evolution of the systems from 86 through 97, they are a result of developments in the applied sciences of fluid dynamics, thermodynamics, coupled with advances in materials science (better materials, better steel, better alloys). The jumps in light years in all these things in the last 50 years or so has been based primarily on two things: the development of computers, and instant Global communications and access to data and research.

Physics is the platform, the concept, the playing field. It is the basis of “how” and “why”. Fluid dynamics is the tool, the wrench that turns the nut, the applied science a.k.a. engineering techniques to design the pipe, the mufflers, the cats, etc. We can design the system because we have fluid dynamics. The system design is possible because we understand physics, but it is done with fluid dynamics. So we’re both right, but with only physics, we’d be sitting on the side of the road imagining how the car would go, and with fluid dynamics, we’d be gone!

Two very very important points in reflecting upon this: I got my degree about 100 years ago, and mostly, I wrote all this before my morning coffee.

And I’ve always said, my education working at a hardware store and trying to keep my $135 3WD Chevy pickup running when I was a kid, was an equal or greater education than the four years of engineering!!!
 

97RangerXLT

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@Rick W on Cartalk Tom and Ray have always said (and I paraphrase): Reality often astounds theory.

so true. I have a two year degree in engineering and a four year degree in IT/ computers... that quote fits both professions.

AJ
 

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Unless you'll sleep better with 2 tailpipes, save yourself some money and buy one 2 1/2" high flow cat and run a single 2 1/2" system. It'll flow more than enough for a 4.0, cost a lot less than a dual system, fit better and be apt to rattle a lot less. If the exhaust pipes are too big it slows down the flow of exhaust and hurts scavenging at lower RPMs. If you've heard that some engines need backpressure, it's not true, they need flow velocity.
 

Dirtman

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Unless you'll sleep better with 2 tailpipes, save yourself some money and buy one 2 1/2" high flow cat and run a single 2 1/2" system. It'll flow more than enough for a 4.0, cost a lot less than a dual system, fit better and be apt to rattle a lot less. If the exhaust pipes are too big it slows down the flow of exhaust and hurts scavenging at lower RPMs. If you've heard that some engines need backpressure, it's not true, they need flow velocity.
Your points are all valid BUT that doesn't change the fact that dual exhaust is just plain cooler... :ROFLMAO:

Alot of the crap we all do to our toys serves no valid purpose beyond being "cool". :icon_rofl:

But you could also do single cat & muffler split into dual tailpipes to get the "look" but save some money.
 

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Dual tailpipes on a single exhaust is the equivalent of taping a sausage to your leg under your polyester pants before going to the disco.
 

Dirtman

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Dual tailpipes on a single exhaust is the equivalent of taping a sausage to your leg under your polyester pants before going to the disco.
I prefer to use a pickle...
 

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Well you can tell by the way I use my walk, I'm a woman's man, no time for talk.....

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Stayin' alive.........
 

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I thought you were Polish, you could use a Kielbasa.
 

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