cat back exhaust on 02 avalanche

[modaddy04]

just bought an 02 avalanche (5.3) and was thinking about putting in a cat back exhaust. can someone explain the difference between the stock exhaust system and a cat back system? is there a significant increase in HP/Torque and MPG with a cat back? what other mods are suggested? i already put in a drop k&n air filter.

[sennister]

Originally Posted by modaddy04

just bought an 02 avalanche (5.3) and was thinking about putting in a cat back exhaust. can someone explain the difference between the stock exhaust system and a cat back system? is there a significant increase in HP/Torque and MPG with a cat back? what other mods are suggested? i already put in a drop k&n air filter.

Ahh the good old Cat back system debate. There are many Avalanche specific forums out there where this one is argued over and over. Some say Corsa is the only way to go, some say Borla and then there are the FlowMaster guys with their custom exhaust systems. The way I look at it the most expensive isn't always the best. Here is what I have....

I have a 03 Avalanche with the 5.3 also. I first did the K&N drop in filter as you have. So our trucks were pretty close to begin with. Back in January I got a FlowMaster Super 40 muffler from a guy I know. This is a single in dual out muffler that was on his truck for 250 miles. He had it on his truck but his wife made him take it off because it was too loud. He replaced it with a different one that wasn't so aggressive. I went to a custom exhaust installer that I got a lot of recommendations for (this is very important) and had him do the install. He replaced the exhaust from the Cats back to the tips and installed MagnaFlow Double walled Stainless Steel Tips. I chose to have my dual exhaust come out where the OEM exhaust does. When he was doing the install I mentioned to him that I was concerned about in cab drone at highway speed. I was fine with sound when accelerating but didn’t want to hear it when cruising at a constant speed like on the highway. The FlowMaster is about half the size as the OEM exhaust so he positioned it so that if it was too loud a resonator could be added to cancel out excess noise. The muffler I got for $40 and the install cost me another $322. That price included all tax and the MagnaFlow Tips which were a little over $100 of that price. So I got a custom cat back system for about $360. A Corsa system that I was looking at getting before jumping on this deal would have set me back $650-700 uninstalled. Granted I would have installed it myself but still. The $360 was installed and I didn’t have to deal with it. The key is finding a good installer. If you can’t find a shop that can do it and do it right then I would recommend going with a kit and spend the extra money.

Key points to keep in mind. With the 5.3 engine it is very important to maintain backpressure or you will loose a ton of performance. If you go with a single exhaust like OEM go no larger than 3”. If you go dual go no larger than 2.25” for the dual runs. These are inside diameter. Anything more and you will loose a ton of torque and HP.

My dual system is 2.75 for the single run from the Cats to the muffler input and 2.25 for the duals. My result is maybe about the same torque but a slight increase in HP. I don’t notice it right off the line but once rolling it has more power. Also when passing at highway speed I notice it. As for mileage I may have picked up .5mpg. You really don’t do this for mileage. You will never save enough gas to pay for the modification. The thing about it is if you like the sound as I do you will stomp on it more when coming off the line and make your mileage much worse. The biggest factor on gas mileage is the way you drive.

The one big thing that I can’t stress enough is finding a qualified installer. Some guys have gone to the big chain shops and had good experience others bad. I’m not going to name shops because it isn’t the shop it is the ability of the worker. This is really more of an art than anything else. I don’t think it can be taught.

[sennister]

Oh the one other thing that I left out of my post above is that I know with Corsa you get a lifetime nontransferable warranty. So if you buy a used Corsa exhaust you get no warranty. However many people with the Corsas like the fact that they don't have to worry about it and if something rusts through or they have some other problem with it they get the part replaced. Well my answer to this is fine. I'm really not worried about it. If the muffler bearings were to fail in my FlowMaster I will pay to get new muffler bearings. Do you understand my joke here? You see there are no moving parts to an exhaust. So really nothing to fail. If a pipe rusts through I would rather run to my local muffler guy and have them replace that part then have to take it appart myself and wait a week or two for a replacement part. Oh and for the price difference. Corsas are typically found for $700. Well I paid $360 so I could completely replace my exhaust 5 years from now and break about even. So the warranty doesn't mean much to me. I'm not sure what the Borlas cost but I hear they are closer to $1000. There is one guy with a Borla that was pissed about the cab noise and installed a resonator to calm it down.

I should also add that I am happy with my FM. I can hear it in the cab when the engine is under load in the 1800-2500 RPM range. By under load I mean while accelerating or going up a hill. If the engine is turning in the same RPM range but maintaining speed (i.e. going down the highway) it is no louder than OEM. My installer said I could add that resonator for $80 installed if it got to be too much for me. He stated that would clean up the cab noise in this RPM range when under load. I have not gone back.


Bottom line is that what ever you choose to do. Do not do it for saving gas. You will not ever save enough to pay for the modification. Do it for the sound. The sound is very personal. Meaning what I like could be very different than what you want. You can listen to all the clips you want on the internet (most manufacturers have some on thier site) but they all sound the same to me and most people out there. The best way to tell what you really want is to try and find someone in your area with an exhaust or two and go for a ride with them. Even if it isn't an Avalanche as long as it is the 5.3 it will give you an idea as to what it really sounds like.

[modaddy04]

Thanls for the tip.