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Discussion Starter · #1 ·
I have the BluePrint 347 with Holley EFI (~400HP) and stock FFR 302 headers and side pipes. A bit too loud for my liking. I understand catalytic converters will help reduce the noise. It sounds like some swap out the cats for J pipes when taking the car to the track. Do the cats reduce noise much? Looks like the FFR 302 headers come off and are replaced with shorty headers and cats which connect right up to the side pipes, yes? What suppler (part numbers) do you recommend for shorty headers and cats?

I’m also looking at Car Chemistry’s Silencer Insert for the side pipes. I understand they might cut 7-10dB. Any recommendations appreciated.
 

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I had the cats and shorty headers and yes they do cut down the noise. Mind you I have a 410W EFI. The wife hated it and had me go to headers dump the cats. She likes the sound now.
 
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IMO the CATs do reduce the noise somewhat. I also used the Gas-N side pipes which are quieter than those sourced from Factory Five. For me, combination was awesome. It was quiet enough so that you could talk to your passenger during a normal cruise. When you jumped on it, a nice throaty growl that was loud enough for me. My engine was a 4.6L DOHC engine, said to be inherently quieter than a SBF, so maybe engine was part of the equation. I also found that the Gas-N side pipes did not run a hot as other builds using headers and FF sidepipes. I liked the combo a lot, but don't know how much HP was given up. The second owner had the car dynoed, 298 HP at the rear wheels which was spot on for the engine.
 

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I also installed the CATs to slightly drop the noise. Since I try to drive my Cobra as much as possible, I also like not smelling fuel. The car is still loud, just not bleeding ears loud.
 

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I was trying to find out similar info a few months ago

 

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Discussion Starter · #6 ·
IMO the CATs do reduce the noise somewhat. I also used the Gas-N side pipes which are quieter than those sourced from Factory Five. For me, combination was awesome. It was quiet enough so that you could talk to your passenger during a normal cruise. When you jumped on it, a nice throaty growl that was loud enough for me. My engine was a 4.6L DOHC engine, said to be inherently quieter than a SBF, so maybe engine was part of the equation. I also found that the Gas-N side pipes did not run a hot as other builds using headers and FF sidepipes. I liked the combo a lot, but don't know how much HP was given up. The second owner had the car dynoed, 298 HP at the rear wheels which was spot on for the engine.
Where did you source your shorty heads and cats?
 

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Where did you source your shorty heads and cats?
If you are interested in getting cats. I can send you mine as they are just collecting dust. They are old old and only have a 200 miles on them.

Try BBK for mustang shorty headers. I have 351 headers.
 

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I have the BluePrint 347 with Holley EFI (~400HP) and stock FFR 302 headers and side pipes. A bit too loud for my liking. I understand catalytic converters will help reduce the noise. It sounds like some swap out the cats for J pipes when taking the car to the track. Do the cats reduce noise much? Looks like the FFR 302 headers come off and are replaced with shorty headers and cats which connect right up to the side pipes, yes? What suppler (part numbers) do you recommend for shorty headers and cats?

I’m also looking at Car Chemistry’s Silencer Insert for the side pipes. I understand they might cut 7-10dB. Any recommendations appreciated.
I'm running Car Chemistry interests (Summit Racing) in the J pipes with shorty Pypes Headers and FFR exhaust on a 306 carbed. The noise level is significantly less than before the inserts.
 

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You find the headers and for a 100 bucks and shipping I'll send my cats. Hell I'm surprised no one has come and stolen them from my garage yet
 
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Discussion Starter · #11 ·
I also have a BluePrint 347 with Holley EFI. I run BBK 1515 headers and GasN touring side-pipes. After installing the side-pipes, I added Cats to comply with my state's DMV requirements -- GESI G-Sport 300 CPSI EPA Approved 2.5in Inlet/Outlet x 4in Dia Body x 7in OAL Catalytic Converter I had the cats welded into the J-Pipes at a muffler shop. The cats definitely reduce the noise.
Is there a reason you did not use the FFR #14265 - 1996-2004 Catalytic Converters cats? Did you use the FFR j pipes?
 

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When I was looking for a solution, I contacted FFR and was told:
"we don’t have a catalytic converter solution for a small block Ford, you will have to take the standard J-pipes to a custom exhaust shop and have them install cats into the J-pipes. Yes, if you’re going to run the J-pipes you will need Fox body Mustang unequal length shorty headers such as BBK #1515."
The impression I got is that FFR #14365 is for a 351 engine, but I am not sure. I was disappointed that I would not be able to just swap out the j-pipes for the FFR cat assembly. One reason I selected the GESI S SPort cats is that they are short enough that the Oxygen sensor bungs would not have to be moved. The muffler shop charged for 3 hours of labor (it wanted the car with the exhaust system installed so it could properly splice in the cats). If I recall, the GESI S SPort I have are EPA compliant, I think that there are other models that are non-EPA compliant that are less expensive. Finally, I added heat-shield from Heatshiled Products from Summit.
Vehicle Hood Light Automotive tire Automotive lighting
Automotive exhaust Automotive lighting Bumper Gas Muffler
 

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Discussion Starter · #14 ·
When I was looking for a solution, I contacted FFR and was told:
"we don’t have a catalytic converter solution for a small block Ford, you will have to take the standard J-pipes to a custom exhaust shop and have them install cats into the J-pipes. Yes, if you’re going to run the J-pipes you will need Fox body Mustang unequal length shorty headers such as BBK #1515."
The impression I got is that FFR #14365 is for a 351 engine, but I am not sure. I was disappointed that I would not be able to just swap out the j-pipes for the FFR cat assembly. One reason I selected the GESI S SPort cats is that they are short enough that the Oxygen sensor bungs would not have to be moved. The muffler shop charged for 3 hours of labor (it wanted the car with the exhaust system installed so it could properly splice in the cats). If I recall, the GESI S SPort I have are EPA compliant, I think that there are other models that are non-EPA compliant that are less expensive. Finally, I added heat-shield from Heatshiled Products from Summit.
View attachment 365197 View attachment 365198
They look great, much nicer than the FFR cats. So, if I understand correctly the FFR J pipes with BBK 1515 shorty headers won’t fit by default with the 302 engine and stock FFR side pipes? Although it’s close enough that with some minor modification to the J pipes they can be made to fit. If I ever wanted to swap the cats out for a track run I’d need a ’second’ set of custom J pipes. I assume the GasN side pipe fitment is identical to the stock FFR side pipes.
 

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the BBK 1515 shorty headers with the 302 J pipes fit fine w/o any modification. that's the set up I have on my SBF. I'd try to call FFR to see if their cats fit like the 87-95 J pipes (#13861) or the 96-04 J pipes (#13891). The description of the cats on the website makes it sound like it should work with shorty headers and a SBF but the dates (96-04) suggest that it's for a 4.6L modular engine.

edit: after a bit more research, looks like the FF Cats are for the 4.6L modular engine. so yes, you'll need to fabricate your own cats like Rockman and have a spare set of 302 J pipes for the track.
 
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Where did you source your shorty heads and cats?
The J-pipes and CATs were from Factory Five. The Ford sourced shorty headers that were known to fit were no longer available when I did my build. I did, as the manual suggested, was to simply turn the stock manifolds around and install pointed forward. I did take the manifolds and have them ceramic coated prior to installation. Clearance from the steering shaft to the DS manifold was so tight, I filed a relief channel into the manifold for clearance. Otherwise, install was per the book. I did take the CAT/J-pipes and had them ceramic coated too.
I tried JBA shorty headers, but the flanges to connect to the exhaust were not in the same place as the manifolds. Trashed a set of headers trying to make them fit.
 

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I put cone inserts in the end of my side pipes and it dropped 8db,
I tried car chemistry inserts plus cones and it dropped even more, I’ll have to find my notes to se exactly how much but it was a lot quieter.
 
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Discussion Starter · #18 ·
I put cone inserts in the end of my side pipes and it dropped 8db,
I tried car chemistry inserts plus cones and it dropped even more, I’ll have to find my notes to se exactly how much but it was a lot quieter.
Where did you get the cone inserts?
 
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