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Hot Rod Avalanches: Cats or No Cats?

igotzzoom

SM 2017
SM 2016
Full Member
Joined
May 30, 2016
Messages
90
Location
Orange County, CA
Hi Guys, I'm in the early planning stages of an engine & drivetrain build on my '04 1500. I know some of you on here have some pretty fast & powerful Avys. Unfortunately (at least from a performance and tax standpoint) I live in California. So that ties my hands pretty significantly for mods I can do on a streetable, smoggable truck. My question for you guys with high-performance engines is if you're running cats, or no cats? I just want to know if cats are a total death sentence for performance, of if you can make it clean and mean. I know there are several CARB-legal blowers, which might be my best bet. Thanks in advance.
 
I can only imagine that California would fail you without cats on a street vehicle. From what I have read the modern cats are relatively free flowing if in good shape or you could use some freer flowing aftermarket cats and not set off your O2 sensors or fail an inspection. I have read where some have had issues passing inspection in some areas with long tube headers but most shorty headers pass.
I also assume that anything is possible if you want to spend the time and money to get the performance but you will have an uphill battle since the AV isn't the best starting point for a high performance vehicle. It is too heavy and has the aerodynamics of a brick.
If it was me I would be happy with just adding a Magnuson Supercharger kit ,maybe cam and shorty headers with a cat back performance exhaust like Corsa Sport. It may not give you maximum HP but will give you usable torque at usable street rpm range. Installing all that may put a strain on your transmission and rear end but assume you are planning to beef those areas up too.
Then when you increase acceleration and top speed you may stress the suspension and limits to the brakes so you may end up wanting to beef up those areas too. Many members have upgraded the first generation brakes to the second generation brakes and there are threads discussing the change.
Good luck with your mods.
http://www.magnusonproducts.com/p-67-chevrolet-gmc-suv-48l-53l-60l-2004-2006-radix-retro-magnuson-supercharger.aspx

Overall I would talk to a professional speed shop in California and follow their recommendations since they have probably done many conversions and will know what works and what will pass California inspections. It will cut out headaches for you by trying to reinvent the wheel and Frankenstein  a collection of parts together. Just because you have the best of each part mentioned it doesn't mean all parts were tested to work together...........
 
Thanks Vaeagleav. Yeah, it's definitely more of an uphill battle here in CA. But I think it's doable. I'm definitely leaning toward the Maggie. I think I'm going to start with a fresh engine. The current LM7 has about 164,000 miles on it. I'm afraid throwing a blower on it might not be the best idea at this point. I think I may try and find a new or reman LQ4 or LQ9 short block, and maybe throw a cam and some CARB-legal AFR heads on it. I know I'm going to have to do some downstream beefing up of the trans and possibly the rear end.

Regarding ultimate performance... Obviously, starting with a nearly three-ton truck isn't the best starting point for a hot rod. Mainly, I'm looking for something that has plenty of torque, is responsive around town and on the freeway, that can tow about a 5-6,000-lb travel trailer easily. I want something that's surprisingly fast for its size, but I'm not in a contest to run a 12-second quarter, or put down 700 hp on the dyno. I'd like to put down 450-500 to the wheels, which I think is achievable.
 
With only 164k miles, it's not worth the effort of rebuilding.  Do a compression check, but I'm sure you'll find the engine tight.  When you tear it down, you will find very little wear.  I've helped a friend who's swapped several of these into older cars, tear them down for inspection.  Many of the donor vehicles (trucks) had similar mileage or even more (over 200k), and it's amazing the shape they're in!  Now we just do a compression check to make sure one cylinder isn't fried.  Modern fuel injection systems, close factory tolerances, and overdrive  keep the wear and tear down compared to the olden days.

Save you're money on the engine rebuild, and use it to build the hell out of that transmission.  That's going to be your weak link once you add a blower, cam, headers, and catback.  Find a good tuner to make the most of that combination.
 
Yeah. It runs really good. It just threw a code the other day for the rear knock sensor, which I have ordered, and will probably replace in the next few weeks. I'm hoping it'll improve fuel economy and responsiveness a little. But idles smooth, and runs like a champ, all things considered. Think I might do a compression check to see if strapping a blower to the existing engine is a viable option. Thanks.
 
I put a blower on my truck's original 5.3 at around 240K miles after having run aftermarket cams in the engine since about 100K miles.  After a couple of years it developed a slight miss on cylinder 7 that no amount of swapping wires, plugs, coils or injectors could make go away so at 289K miles replaced that motor with a 460 hp crate 6.0.

One of these days I'll get around to putting the blower on the 6.0!  >:D
 
I agree with the dynatech. I have them on my 02 camaro SS. Better with high flow cats than straight pipe. Can swap out with a few bolts. Dynatech high flow cats cut down gas smell and did not lose any noticeable power.

Will be looking at there long tube for 04 avalanche.
 
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