Does a 3" catback really make any difference over a 2.5"?

[MalcolmV8]

Kooks 1-7/8" x 3" and 3" off road X-pipe all Stainless Steel. With a JBA 3" full catback with JBA mufflers. I plan to one day swap out the 3" mufflers with Borla Stinger 3" Mufflers.

http://www.svtperformance.com/forums/showthread.php?813451-And-she-said-3-quot-was-small&highlight=

Oh shoot do you have that running yet? We have almost identical setup. I have those exact long tubes and x pipe from kooks. Now just looking for the cat back. I'll have to look at the JBA. Not a fan of those mufflers though. Was hoping for a straight through bullet style much like my borla stingers. The more free flowing and loud the better lol

 

[GodStang]

Oh shoot do you have that running yet? We have almost identical setup. I have those exact long tubes and x pipe from kooks. Now just looking for the cat back. I'll have to look at the JBA. Not a fan of those mufflers though. Was hoping for a straight through bullet style much like my borla stingers. The more free flowing and loud the better lol

Ya been running since 2012. I too think I prefer Borla Stingers. Sorry videos not Embedded.

https://www.youtube.com/watch?v=6drJrCHHDNo

https://www.youtube.com/watch?v=iWQ_Aafv35A

https://www.youtube.com/watch?v=v1o2PPeKn3k

 

[MalcolmV8]

Thanks for posting.

 

[MalcolmV8]

An update to finding a true full 3" exhaust system. It turns out the Bassani system, part # 4603R5, which does neck down to 2.5" for a stock X pipe is also available in a full 3" without the neck down. You just have to call when ordering and specify you want the full 3" flow tubes at the x pipe connection.
The mufflers are also a flow through design. Perfect and done!

 

[HuntFishCobra]

that's going to sound sick!

 

[MalcolmV8]

that's going to sound sick!

Hope so. I really wanted stingers in 3" but they don't make a kit. I called Borla and they do make a 3" version of the stinger muffler but it's $300 per muffler. So in addition to buying a different catback you'd have to pay $600 + shipping for the stinger mufflers and then custom fit them. I love my Borlas but not that much lol.

 

[WireMesh]

I'm not entirely sure either. The general consensus is that the headers and x pipe are of most importance... there after not as much... I don't really know how that is either. I have a few theories but I'll let someone who actually knows answer that.

A little input from looking around at exhaust data and an engineering background: exhaust gases are primarily nitrogen so for a decent estimate, they can modeled as an ideal gas. This allows the use of Charles' Law (assumes a constant pressure - atmospheric): V1/T1 = V2/T2.
I saw estimates of exhaust gas temperatures in the headers to be anywhere from 800-1600F and in the mufflers to be around 350F.
Plugging 1200F and 350F into the equation shows that a sample volume of 1ft^3 would shrink to a volume of 0.488ft^3 (Fahrenheit needs to be converted to Rankine to use Charles' Law)
While this is just based on estimates, it shows why a smaller pipe further downstream would not be a restriction since the gases are cooling off.

 

[HuntFishCobra]

wow I don't think any muffler is worth $300 per muffler holy crap. I really like my bassani too, and I'm excited to get my prochamber on there to really open things up too. I couldn't even hear myself driving over you and Brian and Craig and everyone else haha. Just gotta wait for that bonus check

 

[MalcolmV8]

Sweet

 

[Brandon03Cobra]

I run the 3" JBA that is necked down to 2.5" for the x-pipe. The sound is the best but I'm not sure about the header size to x pipe for my 2.9 whipple e85 setup. Eric Brooks tuned my car and told me 1 3/4 to 3" x to Catback was perfect for my setup. I am running ~21 psi.

 

[ctgreddy]

You're not going to gain more than 5whp with a 3inch over a good 2.5". Here's some comparisons from cars at my work which aren't cobra's and different power levels.

On a 2015 mustang, we put SW 1 3/4 primary/3" collector longtubes on, but that necked down to 2 1/4" stock size, then a 3" gibson which necked down to 2 1/4. That car with a jlt cai made 445whp. On another 2015 that got arh lt's with the same sizing but full 3", into a modified gibson catback so this one is full 3". With the same intake on the same dyno and in the same weather conditions it made 447whp.

Now on zl1's, they have a good free flowing catback from the factory. On our ooooold shop car we went from the factory 2.5" catback to a 3" corsa on a car that already made 700+whp. It made within 5whp of what it did before but it was a couple years after the initial pulls but on the same dyno.

Then you've got guys on here like Timspony who only picked up 2x whp by switching out stock ex manifolds to bassani midlengths and that was in the 7xx whp level. So how much of a restriction is a good 2.5" catback going to be if the ex manifolds aren't even a very big restriction?

 

[MalcolmV8]

You're not going to gain more than 5whp with a 3inch over a good 2.5". Here's some comparisons from cars at my work which aren't cobra's and different power levels.

On a 2015 mustang, we put SW 1 3/4 primary/3" collector longtubes on, but that necked down to 2 1/4" stock size, then a 3" gibson which necked down to 2 1/4. That car with a jlt cai made 445whp. On another 2015 that got arh lt's with the same sizing but full 3", into a modified gibson catback so this one is full 3". With the same intake on the same dyno and in the same weather conditions it made 447whp.

I agree with you there but those cars are at such low power levels I wouldn't expect much difference either. I'm talking the 700 to 1000 whp range.

 

[whitedevil95]

Then you've got guys on here like Timspony who only picked up 2x whp by switching out stock ex manifolds to bassani midlengths and that was in the 7xx whp level. So how much of a restriction is a good 2.5" catback going to be if the ex manifolds aren't even a very big restriction?

This is the main reason why my manifolds are staying on for a long time. Too many guys making big power spend 1k on long tubes and more for the matching mid pipe then gain 10-20rwhp for $1500bucks.

 

[MalcolmV8]

This is the main reason why my manifolds are staying on for a long time. Too many guys making big power spend 1k on long tubes and more for the matching mid pipe then gain 10-20rwhp for $1500bucks.

But where's the data? That's what I as trying to find. No one seems to have any real first hand experience. Not saying you're wrong, just trying to find the data that supports/validates it.

 

[whitedevil95]

But where's the data? That's what I as trying to find. No one seems to have any real first hand experience. Not saying you're wrong, just trying to find the data that supports/validates it.

Good question. I just recall seeing a few threads over the years where guys were expecting a big boost from their new exhaust but found it wasnt so.

 

[choate]

Hope so. I really wanted stingers in 3" but they don't make a kit. I called Borla and they do make a 3" version of the stinger muffler but it's $300 per muffler. So in addition to buying a different catback you'd have to pay $600 + shipping for the stinger mufflers and then custom fit them. I love my Borlas but not that much lol.

Just a thought but can you buy the ones that are 2.5" and have a shop weld them on? I would think the inside is the same on both but it doesn't seem like it's worth an extra $175 per muffler just to get a little area of 3" instead of 2.5". Usually a shop can expand the pipe too. I know when I got my resonators removed on my 5.0 the pipe was 2.75'' and they installed 3" resonator delete pipe with no problem. Might have to pay $60-$80 for a muffler weld in but that's a lot better than $300 for the 3" mufflers. Btw all the exhaust clips I've listed to of 03-04 cobras with stingers sound good but there is one with a bassani 3" catback with stingers that trumps them all. Not sure if he has the 3" stinger mufflers or not. Just sounds a lot more wicked. Too bad Borla doesn't offer a 3" version of the SS cat back with stingers.

 

[MalcolmV8]

Probably could have had something custom welded up but this is long done purchased and installed on the car.

 

[choate]

What did you end up with? I was just searching for 3" catbacks and this came up and didn't think this was all that old.....Whoops yeah it was lol. 3/11/2015 not 3/11/2016. :Insert Tombstone emoji here:

 

[MalcolmV8]

Lol no worries, searching the threads is a great resource and been able to ask the people in those threads questions is even more valuable IMO.
I ended up using the 3" kooks X and a Bassani 3" cat back. It was a simple 100% bolt in solution. I also like how the Bassani tips have removable resonators you can slide in and out and it makes a big difference in how loud and obnoxious the exhaust note is. Easy enough to remove when going out cruising with your buddies and easy enough to slip back in when cruising around town.

Cons, the Bassani mufflers are not 100% straight through mufflers like I wanted. I called Bassani to confirm before purchase and they assured me they were so I was kind of pissed when I got them especially after paying $800 some for it. They are close though, the air gets slit by a center divider and flows down to separate tunnels and then joints back up to exit.
Another con is those mufflers are freaking huge. I had to put wrench between the mufflers and between the passenger's muffler and the body to keep them from touching while tightening down the clamps.
I also can't remove the drive shaft anymore without pulling the mufflers or at least loosening up almost everything and twisting, fighting them out the way and turning them up sideways. This is going to be true of any large muffler though.

Overall I like the Bassani cat back and could always swap out some bullet mufflers from Summit Racing or something but the exhaust is so freaking loud already I've held out doing that just yet.

 

[Gamer2Cars]

I also went full 3" kooks/Bassani and have the same complaints. My mufflers can't sit flat they are more at an angle so they don't hit each other. I like the same stuff Malcolm mentioned too. Here are a few pics of the inside of the Bassani mufflers.

I am around 600RWHP running about 19lbs and I definitely feel the car is more torque-y and more responsive.