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  1. #1

    Default 09 5.3l Flex: CAI/Exhaust/Tune Q's

    I've read the existing threads on these topics, just figured I'd post again to see if there was more updated info! Hopefully this isn't too much for one thread, sorry if so...

    Q 1. CAI - Cheapest, best, most efficient CAI set up for my engine?
    - And are separate parts, tubes, couplers, etc... available for the 09's yet?

    Q 2. Exhaust - Do exhaust notes change much on the V8/V4 fuel management switch?
    - Is is worth perf. gain wise to buy a single in/out catback system, or just go full dual?
    - How much does the noise level go up with LT headers?

    Q 3. Tune - Does the V8/V4 fuel mgmt switch really help mpg, or should I get it tuned out?
    - Is it best to get a custom tune or pre-done ex. hypertech, etc...?

    Reasons for: I love performance and have a heavy foot so that would be main reasoning for performance upgrades. Money is really an issue but I'm not interested in wasting it on dumb parts and false claims. Also I drive A LOT for work so any MPG tips would be greatly appreciated!

    Thank you to all that respond, I love getting yalls feedback!
    09 Silverado LTZ
    Crew cab 4x2 5.3L Flex

    Current mods:

    Black billet bowties
    Bolt over Billet Grill
    Spectre Drop-in filter
    EZ bed cover
    2 JBL 12" Subs
    Custom sub box
    2 JBL 600w amps

    Upcoming mods:
    CGS intake
    Aero Exhaust
    Black Bear Custom Tune
    Black 22"s
    Spray-in Liner

  2. #2


    Answer to question 1: There are a lot of people that believe heavily on CAIs. I, however, do not. I'm an engineering major at Texas A&M and in my thermodynamics class one semester, we actually worked out the physics behind CAIs for a project. The results were that the performance increase you get from a CAI comes soley from the fact that you are using a higher flow filter. The enclosed box that comes stock on these trucks is very effective at blocking out the heat from around the engine. So when people install open box CAIs, they are actually hurting their performance because they are actually sucking in hot air from around the engine. Which actually winds up hurting performance because the hotter air is less dense and does not hold as much oxygen as cooler air. The only types of CAIs that really do improve performance significantly is one that uses forced air. For example, a CAI that has a tube or pipe that runs to the front of the truck will help out. With this type of CAI, you are forcing air into the intake as well as using the coldest air that you can get without using an intercooler or something. Other than that, you are better off buying a good drop in filter (K&N, AFE, etc.) for about $60 and taking the other $200 that you save from not buying a full CAI set up, and spending it on your exhaust system. (BTW, something I'm currently working on is designing some sort of system to connect to the stock air box and force air from the holes in my air dam. I'll post something about it with results when I'm done.)

    Answer to question 2: Exhaust is much more in depth that most people think. With a 5.3L, I would think that you would be best off with a single in/out system, but using 2.5in or 3in pipe. A lot of people say that you need to get the exhaust out as fast as you can. And while this is true to some point, if you start getting the exhaust out to fast, you loose too much back pressure, and then you will notice less torque. The stock exhaust for sure creates too much back pressure, that's for sure! And it also does not flow very well. You want to find a nice balance of flow and back pressure to increase both HP and torque. If you go with true dual, I definitely wouldn't go with any pipes bigger than 2.5in. With the 5.3L, it's kinda right on that border line of which is better: dual or not. Something you might think about doing is doing if you dual it out is maxing sure you use an x-pipe (or the not as efficient, H-pipe) to help balance out the flow of your engine. This will definitely help increase HP, plus, having the crossover will help keep a little more back pressure than having straight out true duals.

    Answer to question 3: I have not driven one of the new chevy's with the active fuel management. I did, however, own a Dodge Ram with the active fuel management. If you drive a fair amount of highway miles, then it definitely helps! When my active fuel management system was engaged on with that dodge, I was getting around 17 to 18MPG. When I was in the city driving around and it was using all 8 cylinders all the time, I was getting around 14 to 15MPG. So, in my opinion, I really liked it. I actually miss having it on my truck now. About 50% of my driving is highway miles, so it definitely helped me out a lot.

    2004 Silverado 2500 "Judas"
    Crew Cab and Short Bed
    6.0L Vortec
    Diablo Predator
    True Dual Exhaust: Hooker MaxFlow Mufflers and X-Pipe
    Drop-In K&N Air Filter
    Alpine Stereo System: iDA-x303 Deck, SPS-600 Front and Rear Speakers, KTP-445 Amplifier

    Future Upgrades Include:
    Cosmetic/Other: Spray-In Bed Liner, HID head lights, Leveling Kit
    Performance: Underdrive Pulleys

  3. #3


    Btw, as far as tuning out the V8/V4 fuel management, you can easily do it with a handheld programer. I think just about all of them give you the option to do that for those trucks.

  4. #4
    Jr. Engineer 09Z71BLKBST's Avatar
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    Nov 2009
    Grand Forks AFB, North Dakota
    Blog Entries



    Ques. 1: I have the Volant CAI that is enclosed and i love it i notice about 1/2 mpg and good bit of horsepower gain.

    Ques. 2: I also have a Flowmaster series 40 exhaust, have noticed a good bit of power gain with this, an it was my first mod. It definitely helped and sounds way better... ;)

    Ques. 3: As far as tuning goes i just added a diablosport tuner and just used the diblo tune. I have noticed a VAST improvement with horsepower and also a jump from around 12/13 to now 19/20 mpg when driving around the AFB @ 30 mph.

    I hope this helps some, and once again i am no expert but i love those three mods and my truck is a ton faster and i get better HP as well!
    2009 Silverado Z71 LT/5.3/Flowmaster 40 Series/Volant/Diablosport
    2006 Trailblazer 4X4 LS

    Past Rides:
    2001 GMC SIERRA 4x4 - Totaled
    99 Chevy Silverado 2x4 traded in

  5. #5


    Thanks for the info guys! Ya I've heard that CAI's aren't really worth the $, unless its a fully closed box similar to stock like a Volant. I think i'll just get a drop in for now! But I'm looking at a CORSA exhaust on the highend, and CGS on the low end and Magnaflow in between, just not sure how much I wanna spend. I've been looking single in single out 2.5-3".... I am def gonna get a programmer but I have no clue which one to get, I've got to start researching!

  6. #6


    I don't have much experience with other programmers other than the Diablo that I have. I have had really good experience with the Diablo though. It's been really user friendly, you can customize all the parameters you want. I think the newer models have 5 tune slots: one for stock tune, one for the DiabloSport Tune, one for 87 Octane Tune, and then two slots for your own custom tunes. Also, for what it's worth, I think that the general consensus on this site is that Diablo is preferred.

  7. #7


    c m chance....kudos....great reply
    2002 Chevy Suburban 5.3 L59 Flex Fuel

  8. #8

    Default great questions

    great post! thanks for the great answers and opinions... That is why i spend so much time here!!!

    Urban Tactical Design
    2008 Silverado Z71 Crew Cab
    -Custom Grill Insert
    -Nerf Bars Steps
    -Leer Canopy with Thule Racks 100XL
    -285 65 18's
    -Incubus"Recoil" Wheels18x9
    -Tuff Country 2 inch Level Lift
    -Weather Tech Molded Mud Guards
    -Thule MOAB Basket (painted)
    -Reverse Lights mounted rear of steps (55w)
    -Garmin GPS (Portable)
    -Flo-Pro Exhaust 40 series
    Winter Set
    265 70 17's on stock z71 wheels painted xtreme liner black

  9. #9


    I'm taking the advice I just bought a drop in filter today instead of doing the full intake... I'm still shopping exhaust, there are too many damn choices and price ranges I can't make up my mind what brand of 2.5" single in/single out to go with... any good salesmen on here to sway me towards a product???

  10. #10


    Quote Originally Posted by 1morepart View Post
    c m chance....kudos....great reply
    Thanks! Just trying to be as much help as I can.

    Quote Originally Posted by PIKE33
    I'm taking the advice I just bought a drop in filter today instead of doing the full intake... I'm still shopping exhaust, there are too many damn choices and price ranges I can't make up my mind what brand of 2.5" single in/single out to go with... any good salesmen on here to sway me towards a product???
    Here's a chart that you might like to check out.

    I've only used magnaflow before and I have been very impressed with their mufflers. Great sound and pretty good performance. On my truck, the exhaust that I'm about to do, I'm actually going to be installing Hooker Maximum Flow mufflers due to the data that I found on that chart that I gave you the link to above. It's got a good bit of info on it.

    Also, I just crunched a few numbers on your truck. Those 5.3L engines are rated at 285-295 HP. So I went with the higher of the two. Rule of thumb is, for every horsepower, you need 2.2CFM of exhaust flow. So that means you should have about 649CFM of exhaust flow at the minimum. Now having more wont hurt too much, you just don't get too much more performance increase going over. But, if you do go to far over, then you start loosing too much back pressure and hurt torque. Anywho, with this in mind, 2.5" straight pipe flows about 521CFM I believe. So, if you went with 3" pipe all the way through, you would be doing pretty great on flow! Or, option two could be a dual in/dual out exhaust with 2.5" pipe. That would give you plenty of flow necessary as far as the pipes are concerned. Then your limiting factor would be the muffler. Just find a muffler that you feel is the most high flow and that go from there. Another link that might help you out with that decision is this:

    Also, keep in mind, it doesn't say, but I think all the mufflers on this flow test page are more than likely all single in/single out mufflers. So with a DI/DO, it will have more flow than is listed here.

    Hopefully these links help ya out at deciding what brand you'd like to go with.

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