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I have Flowmaster 40s, they sound great, like an actual muscle car. I hate the glug-glug-glug water sound that I hear from many newer Mustangs with aftermarket cat-back systems.

But mufflers are only half the battle. The first thing I did in terms of exhaust was switch to JBA shorty headers (California compliance, not a lot of choice there). The sound was night and day after the switch, even though the rest of the exhaust was the garbage stock stuff. I've read that some on here switch to full-length headers and/or no cats/X-pipe or whatever, which is fine if your home state doesn't care. I'm just saying that the sound can change a lot with even shorty headers and stock mufflers/Y-pipe.

My view is if your plans include headers, do those first, then figure out how much more "sound" you want out of aftermarket mufflers because settling on mufflers first and thinking you nailed the sound might not last once you swap out the exhaust manifolds for headers.
You're in LA, right? I'm about 2hrs east of you.

Anyway, my plan (later down the line) is to just get a set of OEM exhaust manifolds and have them ported instead of getting a set of shorties. My understanding from reading various threads here is that ported OEM manifolds give you better HP than shorty headers. Being in California and all, I'd like my engine to be as "sleeper" as possible. Having ported out OEM manifolds will achieve that objective while also gaining more HP ;).

As for me, I replaced my two primary CATs a few years ago after one of them went bad with Magnaflow High Flow units (CA legal, of course). Even with that little repair / upgrade / mod and the rest of the exhaust system being OEM, it gave it a little bit of "glug glug glug" tone at lower RPMs. I can't wait for the day that I get a full catback system in place. Oh, and I'll be doing an X-Pipe with a set of secondary CATs immediately behind the CAT as my smog guy said that's perfectly CA legal if replacing the stock Y-CAT-pipe.
 

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You're in LA, right? I'm about 2hrs east of you.
Ya, Los Angeles. People may ***** and moan about smog laws but I grew up here when there were smog alerts and days (not many, but there were some) where we kids were told to either not go to school at all or not have recess. Do you understand? So damn smoggy that running around for 10 minutes could screw up your whole day (that irritating cough that won't stop for hours as much as you try to hold it in). There were days when I could go outside and convince myself I lived in Kansas because I couldn't see any of the local mountains (I live in the San Fernando Valley so there are mountains viewable in every direction) through the haze. I will take the regulations over that garbage any day. And today, with smog regs, we have stock pony cars putting out 500, 600, 700+ HP. I'm not going to cry about a few cats on my exhaust. This is one of those instances where "the greater good" is actually true.

Sorry, I'm a gearhead and HATE Ralph Nader for what he did to muscle cars (blame the car, not the untrained driver, ruin performance and raise insurance) but I'm in agreement with you can generate power while polluting less. I've lived it, it works.

Anyway, my plan (later down the line) is to just get a set of OEM exhaust manifolds and have them ported instead of getting a set of shorties. My understanding from reading various threads here is that ported OEM manifolds give you better HP than shorty headers. Being in California and all, I'd like my engine to be as "sleeper" as possible. Having ported out OEM manifolds will achieve that objective while also gaining more HP ;).
That may be true and I agree that stock manifolds will be more "sleeper" than any headers with the resulting change in sound, but there's no way that those stock log manifolds flow as good or better than even shorty headers that are designed to minimize blowback into the other cylinders. Now I can believe that the improvement can be so slight that who cares, why pay $$ for basically nothing beyond a more aggressive exhaust note, but log manifolds are the worst. Of course I can also believe that only shorty headers might be worse without improvements in the rest of the exhaust system but my car is aftermarket from the heads back. And for the record I have no annoying drone from the Flowmaster 40s out back (turndowns just past the lip of the bumper bottom).

As for me, I replaced my two primary CATs a few years ago after one of them went bad with Magnaflow High Flow units (CA legal, of course). Even with that little repair / upgrade / mod and the rest of the exhaust system being OEM, it gave it a little bit of "glug glug glug" tone at lower RPMs. I can't wait for the day that I get a full catback system in place. Oh, and I'll be doing an X-Pipe with a set of secondary CATs immediately behind the CAT as my smog guy said that's perfectly CA legal if replacing the stock Y-CAT-pipe.
That's interesting because I've been told that in California (and some other states) you can't change anything in terms of the cats, not only must you keep the same number of them but there are CARB approved cats with specific part numbers that must be there, so even getting 3 cats in the right places but using the "wrong" ones (flow better) is verboten. You can get CARB approved headers, you can get aftermarket CARB approved cats or cat systems (like the 441111 Magnaflow system I bought with much better tube bends for much better flow). After the cats, nobody cares.

I would actually be on board with wiping out that third cat, replacing it with an X-pipe and then adding 2 more cats after that if it's legal. For-real true dual exhaust. But it's my understanding that I can't. Now that is something that bothers me in this anti-pollution world, that the specific parts are more important than results. I think that if you buy approved cats you should be able to mount them however and wherever so long as the car blows below the max on the various poisonous gasses. But apparently they don't care about that, only about what parts they've been paid off to accept. Nothing's perfect.
 

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Having ported out OEM manifolds will achieve that objective while also gaining more HP ;).
Although every HP counts, I am not sure the risk of broken bolts is worth swapping out a set of manifolds for 5 HP. Even changing an o2 sensor is a PITA, these engines are a tight fit. IMO, you would have to be changing heads for it to be worth it, because you have to remove them anyway then.

Spending the money on a tune would give you more HP, and save money on Band-Aids.

Al
 

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That may be true and I agree that stock manifolds will be more "sleeper" than any headers with the resulting change in sound, but there's no way that those stock log manifolds flow as good or better than even shorty headers that are designed to minimize blowback into the other cylinders. Now I can believe that the improvement can be so slight that who cares, why pay $$ for basically nothing beyond a more aggressive exhaust note, but log manifolds are the worst. Of course I can also believe that only shorty headers might be worse without improvements in the rest of the exhaust system but my car is aftermarket from the heads back. And for the record I have no annoying drone from the Flowmaster 40s out back (turndowns just past the lip of the bumper bottom).
Headers aren't designed to "minimize blowback", they are designed to create low pressure pulses in the exhaust stream that ideally make their way back up to the head just as the exhaust valve opens, in order to help suck the exhaust out of the engine. It is called scavenging. Fun fact; exhaust manifolds can be designed to do this too! The problem is that the shorter the tubes, the higher the rpm at which this scavenging effect takes place, so in the real world, the only headers that you will see this from is a set of long-tubes. Any shorties that give any performance increase is only from them flowing better than the manifolds they replaced, not from any scavenging effect. Now moving on to our platform, flow tests have confirmed that the JBA shorties, which are the only CARB approved header for our cars, flow no better than stock manifolds, and dyno tests have also confirmed no power improvement with them over stock manifolds. They are also notorious for cracking. There used to be a member here who ported the stock manifolds, and those ported manifolds were shown to flow significantly better than the stock ones or the JBAs, as well as showed a performance increase when you started getting close to the 300rwhp number or beyond. Properly designed headers will give you a significant power increase, but shorties are not properly designed headers. The fact of the matter is the JBAs for our cars are not a performance part, they are an engine dress-up part, just like a chrome air cleaner or painting your valve covers.
 

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Discussion Starter #26
hey nick (wild tuckey) what was the dimensions of the muffler you used? i searched ebay with the part number but different size mufflers came up
 

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It looks like the actual muffler is 14", the other measurement is including the total length with the pipes. Some have it as 20" while other have it a little over 21" overall. I have this one on mine.

Joe
 

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Ya, Los Angeles. People may ***** and moan about smog laws but I grew up here when there were smog alerts and days (not many, but there were some) where we kids were told to either not go to school at all or not have recess. Do you understand? So damn smoggy that running around for 10 minutes could screw up your whole day (that irritating cough that won't stop for hours as much as you try to hold it in). There were days when I could go outside and convince myself I lived in Kansas because I couldn't see any of the local mountains (I live in the San Fernando Valley so there are mountains viewable in every direction) through the haze. I will take the regulations over that garbage any day. And today, with smog regs, we have stock pony cars putting out 500, 600, 700+ HP. I'm not going to cry about a few cats on my exhaust. This is one of those instances where "the greater good" is actually true.
I grew up in the Inland Empire, specifically Ontario. Being surrounded by mountains, the smog just sits there and doesn't go anywhere until either the Santa Ana winds come in and blow it all away OR it rains and the smog gets washed away. From the house I grew up in, I had a direct shot of seeing Mt. Baldy. However, on the worst of the smog days, you couldn't even see the base of the mountain. It was bad. Now, I live out in the Pass Area (where the 60 and 10 FWY meet just west of Casino Morongo), and I'm at a much higher elevation where smog isn't as much of a big deal there. However, I work in San Bernardino so I gotta travel down the Yucaipa Grade into Redlands / San Bernardino you can see the thick layer of smog. It's grey and thick. Nasty stuff.

That may be true and I agree that stock manifolds will be more "sleeper" than any headers with the resulting change in sound, but there's no way that those stock log manifolds flow as good or better than even shorty headers that are designed to minimize blowback into the other cylinders. Now I can believe that the improvement can be so slight that who cares, why pay $$ for basically nothing beyond a more aggressive exhaust note, but log manifolds are the worst. Of course I can also believe that only shorty headers might be worse without improvements in the rest of the exhaust system but my car is aftermarket from the heads back. And for the record I have no annoying drone from the Flowmaster 40s out back (turndowns just past the lip of the bumper bottom).
Headers aren't designed to "minimize blowback", they are designed to create low pressure pulses in the exhaust stream that ideally make their way back up to the head just as the exhaust valve opens, in order to help suck the exhaust out of the engine. It is called scavenging. Fun fact; exhaust manifolds can be designed to do this too! The problem is that the shorter the tubes, the higher the rpm at which this scavenging effect takes place, so in the real world, the only headers that you will see this from is a set of long-tubes. Any shorties that give any performance increase is only from them flowing better than the manifolds they replaced, not from any scavenging effect. Now moving on to our platform, flow tests have confirmed that the JBA shorties, which are the only CARB approved header for our cars, flow no better than stock manifolds, and dyno tests have also confirmed no power improvement with them over stock manifolds. They are also notorious for cracking. There used to be a member here who ported the stock manifolds, and those ported manifolds were shown to flow significantly better than the stock ones or the JBAs, as well as showed a performance increase when you started getting close to the 300rwhp number or beyond. Properly designed headers will give you a significant power increase, but shorties are not properly designed headers. The fact of the matter is the JBAs for our cars are not a performance part, they are an engine dress-up part, just like a chrome air cleaner or painting your valve covers.
@MadMikeyL basically said it for me without me having to search for the answer, lol. Basically, getting my OEM manifolds ported is on the mod list for me. Probably when it's time to build an / the engine for my car is when I'll do this.


That's interesting because I've been told that in California (and some other states) you can't change anything in terms of the cats, not only must you keep the same number of them but there are CARB approved cats with specific part numbers that must be there, so even getting 3 cats in the right places but using the "wrong" ones (flow better) is verboten. You can get CARB approved headers, you can get aftermarket CARB approved cats or cat systems (like the 441111 Magnaflow system I bought with much better tube bends for much better flow). After the cats, nobody cares.

I would actually be on board with wiping out that third cat, replacing it with an X-pipe and then adding 2 more cats after that if it's legal. For-real true dual exhaust. But it's my understanding that I can't. Now that is something that bothers me in this anti-pollution world, that the specific parts are more important than results. I think that if you buy approved cats you should be able to mount them however and wherever so long as the car blows below the max on the various poisonous gasses. But apparently they don't care about that, only about what parts they've been paid off to accept. Nothing's perfect.
Well, I'm just stating what my smog guy said. He's a by the book guy too. Though, I have the suspicion that since I've been going to him for all my cars for the last few years that I've built a rapport with him that he'll let a few things slide; for example, having a 4-CAT setup instead of a 3-CAT setup that these cars have from factory. He told me that so long as all the CATs are CA legal, he'll pass the car during the visual inspection. Being a 4-CAT setup, I'd imagine that the car will have leaner emissions for the sniffer part of the smog test and won't cause any red flags to come up.
 

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Headers aren't designed to "minimize blowback", they are designed to create low pressure pulses in the exhaust stream that ideally make their way back up to the head just as the exhaust valve opens, in order to help suck the exhaust out of the engine. It is called scavenging. Fun fact; exhaust manifolds can be designed to do this too! The problem is that the shorter the tubes, the higher the rpm at which this scavenging effect takes place, so in the real world, the only headers that you will see this from is a set of long-tubes. Any shorties that give any performance increase is only from them flowing better than the manifolds they replaced, not from any scavenging effect. Now moving on to our platform, flow tests have confirmed that the JBA shorties, which are the only CARB approved header for our cars, flow no better than stock manifolds, and dyno tests have also confirmed no power improvement with them over stock manifolds. They are also notorious for cracking. There used to be a member here who ported the stock manifolds, and those ported manifolds were shown to flow significantly better than the stock ones or the JBAs, as well as showed a performance increase when you started getting close to the 300rwhp number or beyond. Properly designed headers will give you a significant power increase, but shorties are not properly designed headers. The fact of the matter is the JBAs for our cars are not a performance part, they are an engine dress-up part, just like a chrome air cleaner or painting your valve covers.
I understand that "blowback" is in no way a technical term but I was using it in terms of an episode of "Wheeler Dealers". I know, not scientific or a show run by exhaust flow experts. But he (Ant) was comparing a stock manifold off an old English car(?) and how if you blow compressed air down one of the tubes a lot of it blows back up the other tubes into the exhaust ports (he had a paper towel covering the other head port openings and it immediately blew away). He then compared to a shorty header (not a lot of room in the engine bay for a nice set of long-tube headers) that he was welding up for the engine with the same test and the compressed air was actually sucking the paper towel down into the ports (stayed put even upside down). Which I agree is the point of not long-tube headers, flow improvements. Long-tube headers will be much more effective (scavenging) but even those 3/4 length Kooks headers (which I would have chosen) aren't legal here.

My headers haven't cracked and part of what I was originally getting at was that the simple act of adding those JBA headers changed the exhaust note of my car significantly, which is what much of this discussion has been about (mostly which mufflers to add to true dual pipes to get the right sound). My advice is that if you plan to add performance mufflers and headers, do the headers first and see what it sounds like then. You will probably find that you don't need the most aggressive mufflers to get the sound you want and you can worry more about flow and back pressure since the sound is already like halfway where you want it. I'm not in the mood to deal with getting my stock manifolds ported for marginal gains, I prefer the marginal gains from the shorty headers along with the improved sound out the tail pipes and in the engine bay since that was my goal (more of an overall muscle car sound vs. a loud muffler sound).

I'd be curious to see dyno tests of full stock exhaust sytem for the Thunderbird 4.6 vs. single changes (full-length headers, shorty headers, aftermarket mufflers, Magnaflow cat system, dual exhaust pipes after the 3rd cat) vs. multiple changes (headers + dual pipes, etc.) to the system and then also with a 300+ HP engine (I know, easy to ask when I'm not the one doing it, that's like 20+ swaps). I'm also curious about flow numbers for stock Thunderbird exhaust manifolds vs. stock Mustang 4.6 manifolds.
 

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I'd bet if you search here hard enough, you can find all that data.

You might have to piece it together from multiple posts, but every mod that can be performed to these cars has been done, and dyno tuned, at one time or another.

JL and KDanner had the best NA performance, IIRC.
 

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Im another happy trubendz customer as well. Although they did send my exhaust with signature required and it got sent back and I had to pay for shipping again it was otherwise pretty smooth.

I bought their dual 3" pipes for my 02 harley truck. It wraps the axle perfectly.
 

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Im another happy trubendz customer as well. Although they did send my exhaust with signature required and it got sent back and I had to pay for shipping again it was otherwise pretty smooth.

I bought their dual 3" pipes for my 02 harley truck. It wraps the axle perfectly.
That sux you had to pay; my ups guy drops my stuff in the garage, and sends me a text to LMK it's there. :)

I give him presents every year at xmas, tho. :)

The mail lady hates me over the Wheels I got 10 years ago tho, lol.
 

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I also did the true bendz. But cut it up a little. Added vband clamps at all the connections. dual in dual out mid mount muffler and kooks headers all stainless 2.5 inch
 

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