Exhaust Want to add cats

JD1964

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I’m looking to add cats to the aftermarket exhaust on my 92.

1. The car has dyno runs with 400hp at the wheels and I don’t want to restrict that. Can this be accomplished?

2. I would like to retain my existing exhaust components and splice the cats in. I currently have shorty headers, x pipe and flow master mufflers and tailpipes. Can this be done with available aftermarket cats?

3. Is there room for cats near the back of the x and just before the mufflers?

Thanks
 
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Mustang5L5

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1.) I've been lurking on a number of cat threads around the internet/fb groups. From what i'm seeing with dyno sheets, folks are adding newer aftermarket cats to their modified cars and seeing a slight bump in torque, and losing maybe 3-5HP.

2.) most of the cat setups are pretty short and can be welded in.

3.) there might be, but ideally you want them as close to the engine as possible to keep them hot. The hotter they are the more efficient, and that also prevents them from fouling up due to clogging if the mixture is a tad rich. Keeping them hot helps burn off all that "junk"
 
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manicmechanic007

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Free or cheap is what you want
There used to be a recall on Tempo cats and we had hundreds? at the dealer
Look into 1994 Tempo cats
Buy 2 and weld them in (or bolt them) in right behind the headers
Use no mufflers
I did this years ago on a 289 swap I did in a 1980 4 pop
 

manicmechanic007

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If you are flush with cash
Have a good muffler shop install the best cats they can find
The aftermarket cats have very little radioactive elements and some wear out quick (P0420 or 430 follows)
That is not a issue on your 92 John but I would still try to find factory cats (good used is okay too)
They used to say at the junkyard that they did not sell cats (epa regulation) not sure if still true
No mufflers and you will possibly gain a few horse power not loose a few
 

manicmechanic007

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You might find some free or cheap ones at a auto shop
I have 3 out back now that I replaced because of 1996 and newer code P0420 will not pass I/M on paper
The cats work fine if you were to tailpipe check the emissions (pass 1.2 CO @ 220 HC)
That is what you want anyway if you are tired of the stink of raw fuel out the pipes
 

JD1964

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I wonder how two big truck cats would work in place of the foxbody mufflers? Would they work ok back there? Right now I have Flowmaster 40 series so they're pretty loud. Would big cats instead of the 40's be even louder?

Thanks for the advice
 

JD1964

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...and yes, I would like it to be cleaner. I have a wideband on it now and it cruises in the mid to high 14's in AF ratio. So that's not overly rich.

The blower belt is off right now and I'm back to NA for the time being. I had a bad injector on one cylinder and it was lifting the head and blowing compression into the water jacked, then puking the coolant out the overflow bottle. I now have new 42lb injectors and calibrated maf in the NA configuration. In NA is not blowing any coolant. I'm hoping it was just that bad injector and my plans are to put the belt back on and tune fuel and timing again. I have Moates Quarterhorse and all the software on hand. Just need to go through a learning curve. Good thing is when I ordered the maf calibrated for 42's I also got the data sheet with it. I understand I can plug those values into the program and it will streamline my tuning efforts.

The combo was running fantastic before that one injector went bad. I was just about to put some sticky tires on it to really cash in on the fun, and thats when it started puking coolant. I have decked block, decked heads, Cometic gaskets, ARP head studs...... it shouldn't be puking!!
 

General karthief

wonder how much it would cost to ship you a pair
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Here is what I think, look for truck cats that match your existing pipe diameter, install them as close to the headers as you can, you can keep the mufflers, it will be a little less noisey.
JMO
 
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manicmechanic007

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John,
I am not sure if it would be louder
Not familiar with flowmaster 40 sound
Mentioned Tempo because the cats are long and skinny
I have a ton of room under this louse I am building so that is why I plan on big truck cats
I am going to get that 429 spinning so I want more flow capability than I will have flow
Your built motor will need some big ones too
Don't throw the flowmasters out until you see how loud it is
 
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7991LXnSHO

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I wonder how two big truck cats would work in place of the foxbody mufflers? Would they work ok back there? Right now I have Flowmaster 40 series so they're pretty loud. Would big cats instead of the 40's be even louder?

Thanks for the advice
That’s too far back. They have to get hot to work as catalysts. Up front where they belong is where you will want to squeeze any convertors in.

Here are two truck cats to help,
A1EDF4D3-5880-4F87-8D82-58124CA3A40A.png
 
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manicmechanic007

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John,
Happy to hear about a blower
Your blower is just trying to force some Crap (reversion) up into the fuel injectors
Rail clean the injectors once in a while using the Motorcraft (pressurized cans) or Ford stuff (liquid in bottle)
DRI was just a term they made up when they put a plastic cap over the pintle valve ports
Deposit resistant not deposit proof
 

JD1964

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No, I’m sure it was a bad injector.

The old ones were 30lb and I had them out on the bench. At the time I removed them from the Mustang I did not know one of them was bad.

I was putting together an LT1 from a 94 z28 for swap into a 79 Malibu wagon and wanted to use the 30’s. Before putting them on the LT1 I did a resistance test and it showed that one of them had excessive resistance.

That’s when I finally realized what was likely causing the problem in the Mustang. Lean condition in that cylinder causing excessive pressure under boost. So much pressure the head would lift slightly and loose the cylinder pressure into the water jacket. You know, the SBF thing with only 4 head bolts per cylinder weakness.
 

manicmechanic007

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To you chosen few guys that play seriously
You should just get a test rail from any donor car
I have 2 in my garage I use to test spray patterns and drizzle
Only test one every few years but having the extra rail allows me to do it
I plugged all the other injector fuel feeds and just test one injector at a time
I test using the Ford injector cleaner (the old ford carb cleaner in cans was the same stuff)
 

manicmechanic007

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Funny story about the superchargers and the 4 head bolts
Had a husband and wife drag racing team at Bonneville Raceway Park back when it was still open
Both had GT Mustangs both had Paxtons on them
Guy came in every Monday for about a year complaining of a coolant leak
His wifes car never did it. Our motor guys drove it all over around and around pressure test and dye (the works)
Finally I got chimed in and took it for a drive.
The boys just had not been running it as hard as the owner was when drag racing
I laid into that sob and scared the chit out of our best motor man
Came back to the shop and he was ready to park it and return to customer so I parked it in a stall
We walked away and I noticed a few spots of what looked like alien blood
Come to find out the beast blew all the coolant out the radiator cap (every time he got on it hard)
I told him to cut a few or every other fin off the waterpump or otherwise slow it down
Never heard back from him. His car was new at the time and the head gaskets were good (supposedly)
I do not remember if the dye changed color or not indicating HC's in the coolant
 

Mustang5L5

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Reaching back into my way back maxhine, I had a buddy with a fox who did stupid things with exhaust.


He ran a stock 5.0 with only the stock 4-cat H-pipe and that thing was LOUD! It also sounded like crap. He eventually did an off-road H-pipe and Dynomax mufflers (rememver those) and it sounded better and quieted the car down a tad.

He didn’t like it, so he drilled holes into the exhaust. I’m talking a dozen or so 1/2” drill bit into the mufflers.

Still wasn’t great so he took the mufflers off and ran off-road h-pipe only.

This was a stock 89GT. Car sounded like the world was coming to an end but barely ran 15.1. My stock AOD car used to walk away from him from a stop.
 

2000xp8

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If you put them where the mufflers go they won't do anything. Without heat they are useless. Between distance from the engine and airflow under the car, in the back they won't be very hot.
I too had friends with stock h pipes and no mufflers, it is crazy loud and in a not good way.

If this were me? I'd just buy a catted x pipe and swap it on.
It will eliminate experiments, headaches and failures.
Surely it's the most expensive route, but it's low risk.