Need help with exhaust question on 4.7L

[brewcity1]

Hi,

I'm a newbie, so please go easy on me.
If this has already been posted, forgive me. Just point me to the right thread.
I have a 2004 GC Limited 4.7L, and I am thinking about installing a new exhaust (cat back) on it. My question is this...do I, or should I, make any engine modifications before installing the new exhaust (like a COI)?
I read somewhere that you could get bad results from just installing a new cat back, and not opening up the engine. Is this true? Any help would really be appreicated. Any suggestions on the exhaust would help to!
Thanks!

[strizzy123]

kolak@aol.com

[sccaracer07]

X2

Originally Posted by strizzy123

kolak@aol.com

[scjeep4.7HO]

I have a Magnaflow on my jeep cat back.. I would just save a few pennies extra and get a CAI at the same time.

[brewcity1]

Thanks sc!
Is your Magnaflow really loud? I am looking for that nice V8 sound, but nothing to overbearing. What about inside the cabin with the windows rolled up?
Also, is there a CAI that is a better than others, or should I just go with the K&N? thanks for the help!

[scjeep4.7HO]

It's got a deep tone but not overbearing. I have a video of my jeep on hear where you can hear it from in the cabin.. CAI is a personl preference I think. K&N is roven but I have had good luck from others too.

[brewcity1]

Can you point me to that video, i would love to hear/see it.
thanks!

[strizzy123]

When I had my magnaflow, before it got ripped off, it was a nice deep mellow tone. Not loud and obnoxious, no "wooshing" sound, not raspy. It was also quite quiet at cruising speed, but decently loud when at WOT.
With that said, I actually like how my magnaflow resonator into straight pipe with turn down before the rear axle sounds MUCH better. Surprisingly ZERO drone in cabin and quiet on the highway.

[brewcity1]

thanks strizzy!
Any input about Borla?

[scjeep4.7HO]

http://videos.streetfire.net/video/4...2a007758df.htm

[buckod]

I used to work for Borla Performance and from that learned a lot...

You can't hurt your vehicle unless you end up doing something really wack like changing the pipe diameter dramatically (buy a cat back and your fine)....

Two schools of thought are; baffled exhaust (Flowmaster) increases back pressure, thats why they increase the pipe diameter... The second is free flow exhaust (Magnaflow, Borla, etc) reduces backpressure but keeps same pipe diameter as to not "loose" low end torque.
Note: more backpressure = more low end torque, less back pressure = less (loss) low end torque.

People think they gain performace with a cat back but in reality your just releasing existing "trapped" performance... It just depends where you want to feel it, low end or high end.

[buckod]

P.S unless you decide to keep your car forever don't buy Borla unless you like spending a lot of money or want to talk about how "cool" you are, Magnaflow should get you close to the same results with less cost...
I think IMOA Borla is over built (materials cost) = over priced...

I had a cat back on a '93 mustang GT and it sounded sick. Also a '91 Ford Exploder and It did nothing for me.

[Kolak]

Regardless of whether you choose a baffled muffler such as Magnaflow or a chambered muffler such as Flowmaster, the 4.7 V8 responds best, both in terms of low-end torque and power gains, to a 3" diameter exhaust.

It's critical to replace the main converter with a high flow unit. The stock converter is highly restrictive. The typical catback-only system thus leaves a huge bottleneck upstream of the muffler.

[scjeep4.7HO]

Good input on the Bottleneck of the main cat. I need to put a high flow cat in mine too.

[brewcity1]

Thanks for all the help people.
So, does what your saying mean that in addition to the cat back, I should also replace the catalytic converter with a high flow converter as well?

[RyanWJ]

Originally Posted by brewcity1

Thanks for all the help people.
So, does what your saying mean that in addition to the cat back, I should also replace the catalytic converter with a high flow converter as well?

Yes

I run a hi flow cat and magnaflow on mine, I use 2.5" instead of 3" but I am very happy with it

[Carter]

I have a Dynomax. Nice combo being baffled like a Flowmaster, and glass packed like a Magnaflow. Sounds great, no drone. I'll try and get a video/sound.

[brewcity1]

Thanks for the clarification. As you can tell, I have no idea about this stuff, so I was doing some research online, and came across this statement from http://www.kevinsoffroad.com/exhaust.html: "For some inexplicable reason, somewhere in the middle of the '04 model run, V8 model WJs no longer were built with a "classic" catalytic converter under the passenger floorboard (they use pre-cats only)."
How do I know if I have "classic" cat or a pre-cat? I looked under my Jeep, but I really don't know what I am looking for.
Can anyone help?

[Carter]

Look for bulges in the exhaust, about 6 in long. Those are cats. Two before the Y and then the main cat in the straight section.

[shelbyluvv]

No need to buy a cat back, period! The exhaust on a 4.7 WJ is already 2 1/2, mandrel bent stock. It flows really well. It's the muffler that sucks. Get a flowmaster 40 deltaflow, 3 heavy duty muffler clamps and a 2' long piece of 2 1/2" extension pipe from VatoZone.

Cut the stock muffler off and replace with your store bought exhaust. You will have less than $75 in the whole mod and it sounds great! It will droan at about 2500 RPM but you will get used to it.