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Discussion Starter #1 (Edited)
working on my 1996 / 351w

alright so i'm preparing to do a handful of things simultaneously on my bronco. part of that includes new headers. at the same time, i'd like to replace my entire exhaust.

in the factory configuration, my bronco has two upstream o2 sensors, one catalytic converter, a downstream o2 sensor, and then a 2nd catalytic converter.

preferably i'd like to go with a single catalytic converter instead of two. i'm thinking i'd be ok if i dropped the second cat since that's after the 3rd sensor. that would make the order become two upstream o2 sensors, high flow cat, downstream o2 sensor.

that shouldn't create any CELs, would it? i don't know why, but ever since i bought my bronco i thought my initial research suggested i was pretty restricted on what i could do. but going back and revisiting with actual intent of doing something, i think my initial impressions were incorrect.


also...recommendations on exhaust size? 2.25? 2.5? 3.0?
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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That’s the exact config I have. Two upstream O2 sensors, y-pipe modified at the Y to go into a 2-1 cat, and then a 3” pipe, O2 sensor, Flowmaster muffler, then 3” pipe exiting behind the pass side wheel. It never threw any O2 codes. I have an EGR code but that shouldn’t have anything to do with the exhaust config I don’t think.
 

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Discussion Starter #3
That’s the exact config I have. Two upstream O2 sensors, y-pipe modified at the Y to go into a 2-1 cat, and then a 3” pipe, O2 sensor, Flowmaster muffler, then 3” pipe exiting behind the pass side wheel. It never threw any O2 codes. I have an EGR code but that shouldn’t have anything to do with the exhaust config I don’t think.
sweet, thanks!

now i have to settle on whether or not i keep my existing y-pipe or start from scratch, although i'm inclined to keep and modify as needed. it seems like just cutting the first cat and starting there makes the most sense.

i found some "direct fit" y-pipes with a cat included, but i have seen mixed results on fitment as well as the fact that i don't know about the quality of the converter itself.
 

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You shouldn't have any issues. And honestly - if you wanted to delete both cats (not saying you should) if you did throw a CEL, all you need to do is get a "CEL eliminator" which essentially threads into the after cat O2 sensor port and pushes the O2 sensor further away from the exhaust stream., thus eliminating the error code.
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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sweet, thanks!

now i have to settle on whether or not i keep my existing y-pipe or start from scratch, although i'm inclined to keep and modify as needed.
Yeah, my Y-pipe is the stock one, but it was just cut off before they merged and a some pipe added to go into a 2-1 cat. I may have a pic somewhere let me look.

Here's a pic that sort of shows the cat inlet side. You can see where the two pipes go into the cat - there is a small crossover pipe before the cat also that I forgot to mention.
 

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Addicted to Junk
85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Dropping the second cat is fine because there is nothing behind it to measure. Nowadays, the functions of those two cats are combined in "3 way" converters.

This is the Y-pipe i made for a obd1 96 351 (f350). Only one sensor. The flowmaster scavenger y-collector is the best flowing junction I've found. I have one on my 300 bronco too.


2.25" downpipes into single 3". I'm running a magnaflow spun metallicat on my bronco. It is high flow, and works well, but is very compact in size and muffles virtually no sound.

Here's the cat


See how small it is? This is the y-pipe on my 300 with long tubes.
 

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Premium Member
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Discussion Starter #7
You shouldn't have any issues. And honestly - if you wanted to delete both cats (not saying you should) if you did throw a CEL, all you need to do is get a "CEL eliminator" which essentially threads into the after cat O2 sensor port and pushes the O2 sensor further away from the exhaust stream., thus eliminating the error code.
That's a defouler, I believe. I'm familiar with those and that's my backup plan. Gonna run one cat, though.
 

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'92 Custom, '95 MAF 5.0
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Don't toss the old cats when you replace them. People are going crazy lately buying them up. Someone just contacted me about mine (I didn't have them advertised) and paid $60 for the 2-way and 1-way paperweights. I don't think I paid more than $100 for the new 3-way cat.
 

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Man of endless projects
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funny i have some old cats and scrap places wont take them without a VIN number or some BS liek that

on my old 96 302 i put the downstream in an upstream position and it never threw a code. so apparently its not a very sensitive to changes.

you can get a pre96 Y pipe if you weld o2 snesor bungs on them for the upstream and put a plug in the existing hole. thats where i put the downstream and was surprised it never threw a code
 

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Discussion Starter #10
Don't toss the old cats when you replace them. People are going crazy lately buying them up. Someone just contacted me about mine (I didn't have them advertised) and paid $60 for the 2-way and 1-way paperweights. I don't think I paid more than $100 for the new 3-way cat.
Oh for sure. If anything I'll bargain with the muffler shop for them to keep them and lower the price.

On my old Mazda, I bought a used catalytic converter for something like $100 from a local who replaced it with a race pipe. I took that and gutted it. Saved the guts. Pulled my cat and installed the gutted one. Sold the complete cat for something like $70 and a grocery sack of cat guts for $15.
 

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Discussion Starter #11
I will say...I feel much better about the whole exhaust thing. I feel kinda silly for having worried about it in the first place.
 

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Eric
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Just make sure the O2 sensors are replaced in their relative positions to the exhaust manifold collector. You don't want them too far upstream or downstream. Any remaining hydrocarbons in the exhaust stream need time to burn off before reaching the sensor, which is why it shouldn't be located too closely to the collector. Also, O2 sensors need to reach a given temperature before they send a signal to the EEC. The further downstream they are located, the longer it takes to reach that temperature and the vehicle will run rich until then.

Just my $0.02.
 

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Discussion Starter #13
ok...small update...

i went to my usual exhaust guy yesterday and then two others.

the take-away
1) the usual exhaust guy (who i have remembered told me before that cutting out one cat wouldn't throw a CEL) said he'd charge me about $220 to cut out both cats and weld in a new cat that i would bring. but that's reusing the y-pipe and the muffler to exit.
2) my 3rd o2 sensor is actually behind the 2nd cat
3) another shop said roughly $300 to do the same thing but they would use their cat. however, they did NOT even look at it. the guy told me he'd have to put it up on the lift to get an exact price. but, he's at lunch so he couldn't do it right now. lol... yea not using those guys
4) the 3rd shop said it wouldn't work b/c it would throw a CEL

after some serious internet digging and a couple calls to magnaflow, i can get an OEM replacement forward cat for about $150 + tax. the cats for the 96 are heavier (more metal) and more expensive than the ones for 95 & earlier. the 92-95 cat is the same shape and size but only ~$100 since it, apparently, has less ceramic material.

i did find a full replacement from magnaflow for about $300 for a 91 bronco. that has the y-pipe, a collector, and then into a single cat. now, i would have to weld in the appropriate o2 sensor bungs but otherwise, are they the same shape from the brick and aeronose years? it's listed for a 91 / 351w / E4OD. i think it should but thought i'd get a second opinion.

i am wavering on the full exhaust replacement for cost concerns. but i would still like replace both cats with one new cat in the cheapest way possible.
 

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'92 Custom, '95 MAF 5.0
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When I did mine, I opted for the clamp sleeves for the cat instead of getting it welded on. I don't see any good reason for a permanent install, unless you've got a show vehicle and you want people admiring the beautiful welds underneath... Being able to unbolt stuff is a good thing, IMO. It also gives you some leeway in exact measurements. So, you could go that route and save some $$$ on the installation cost.

I later went to my exhaust guy to get an upstream leak fixed. The Magnaflow y-pipe was somehow a bit too narrow and not seating properly with the headers' collectors. He did a cut and re-weld to get it spaced properly. While working in there, he never objected to my using sleeves on the cat.

BTW, Eastern Universal 70318 is the cat I used. It looks like they're only ~$60. I was thinking I paid around that when I said it wasn't over $100, but figured I must have been associating the price I got for my stock cats... That's some crazy symmetry, in hind sight.
 

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What kind of headers are you installing? Reason I ask - I've got JBA shorties going on the '95. You can buy a stock replacement y-pipe (that doesn't have a cat) from Jegs for like $200. You could add a Universal cat to that for $100 (if that). And go from there.




Flowmaster also sells a ton of different size / style universal cats that I've had good experience with and they aren't pricey.
 

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Discussion Starter #16
i'm planning to use bbk shorties.

this is the cat. it's the forward replacement.


i wasn't sure if the y-pipe was the same shape outside of the variations in o2 bungs. it looks like they are. i really like that jegs y-pipe.

the preferred cat i would use would be a spun metallic one, but if i used one, i'd have to also buy a y-collector for the y-pipe, which is why i was asking about fitment. that y-pipe from jegs looks like exactly what i'd want...EXCEPT that it's for a 302 instead of the 351. so i'm thinking it wouldn't work w/o modification...

now i've got to go back to the lab and keep researching...
 

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95 5.8L XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Electric, Manual, KYB Quads, 31x10.5x15's, 299K
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You can look into Magnaflow for a Y-Pipe, P/N 23661, then look for it online... 2.5" Exhaust Pipes mandrel bent all Stainless Steel, 2 O2 sensors 1 in each exhaust Pipe but probably have to weld in a bung for the 3rd O2 sensor. It comes with 2 Cats, 1 is part of the Y-Pipe the other attaches to the exit of the 1st one. You can use the 2 or just the forward one as I did. You can sell the 2nd Cat and recoup some of the cost or hang on to it!!!
Magnaflow 23661 | FORD BRONCO | 5.8L | Front/Rear | Catalytic Converter-Direct Fit | Standard Grade EPA
$527.49

SKU: 23661 UPC:841380061898Weight:0.00 LBSShipping:Free shipping to the US & Canada

Magnaflow 23661 | FORD BRONCO | 5.8L | Front/Rear | Catalytic Converter-Direct Fit | Standard Grade EPA

Bronco catalytic
 

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Discussion Starter #18
this is what i found prompting me to ask if the 91 would fit the 96.


or this one


notice the pictures are identical. so maybe the bosal is a rebadged magnaflow


if the 91 will bolt up (outside of the o2 bungs and that tube sticking out of the cat - which i'll just close off - then i might get one of those i posted above. .
 

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95 5.8L XLT, Hedman Shorties/MF SS Y & Muff, E4OD, Electric, Manual, KYB Quads, 31x10.5x15's, 299K
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The MF you posted is SS with no extra shipping fee and the Bosal is Aluminized Steel with a $20 extra shipping fee.
 

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Addicted to Junk
85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Now you see why I just custom built mine! So many choices and none of them really sparked my interest. The flowmaster scavenger y-collector flows better than all of em, and has a unique sound, do to it being an actual collector, and not just a Y shaped pipe.

I too use the band clamps to hook the muffler to the tail pipe and y-pipe.
 
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