Vortec 5300 Engine Mods

Chevy 5.3 Vortec Fuel Economy Improvement & MPG Mods

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and has been creating automotive content online since 2017. He has been the lead writer for Chevy Trucks and has transformed it from the old and outdated site it was into what it is today. Jake creates a ton of GM related content for the 8020 Media YouTube channel and specializes in Duramax and Vortec information but has a wealth of knowledge across all GM cars and engines. Jake believes the L5P is the best diesel on the market today.

Gas mileage is notoriously poor on all trucks, not just Chevy’s and not just the 5.3 Vortec. Every smart alec’s response to “how do I improve my trucks gas mileage?” is “buy a Prius”. But for a lot of us, we need a truck either for work or for hauling things around. A smaller and more fuel efficient car just isn’t an option.

The 5.3 Vortec ranges from 14-17mpg. However, there are a number of upgrades and modifications that can help add 3mpg. These mods are going to cost you around $1,200 but they will pay for themselves in just a few years with the added fuel savings.

5.3 Vortec Gas Mileage

Depending on the age of your engine, the factory mile per gallon specs ranged from 13-17mpg for city and 16-22mpg for highway driving. Obviously the newer engines are on the higher end of that range, and older are lower. Transmission also plays a part, with 6-speed autos performing better than 4-speeds.

Chevy 5.3 owners typically claim an average mpg in the range of 14-17mpg, depending on how much highway driving they do and how heavy on the gas they are. Certainly not great for people that do a ton of driving, but I guess it could be worse.

I’m not going to tell you “drive with a feather foot” or give you any useless overused advice. The general rule is that creating more horsepower equals lower gas mileage…but that’s not always the case. So, what mods can you use to increase the MPG on your 5.3 vortec?

Gas Mileage Mods for Chevy Vortec 5.3

  • Cold air intake upgrade
  • Cat-back exhaust
  • Engine tune
  • Wheels and tires
  • Tire pressure

While the last two might not be “mods” per say, they are two of the best (and free) ways to not unintentionally decrease MPG. Please read the bottom few paragraphs after I cover these as I’ll walk through a cost analysis for you to determine if it’s really worth.

An intake, exhaust, and tune will easily run you over $1,000 and you might not drive enough for the cost-benefit to really make sense.

1. Cold Air Intake – 1mpg

A cold air intake primarily serves two purposes: increasing the amount of air that flows into the engine and flowing colder air into the engine. By doing so, more horsepower is created. But, at the same time, the engine becomes more efficient and it can actually improve gas mileage.

Colder air is more dense, meaning it is more combustible. Colder intake air temps (IAT) means the engine can run leaner air-to-fuel (ARF) ratios which results in less fuel being required for the equivalent amount of air. Without getting into the technicalities, think of your AFR initially being 1:1 but now only needing to be 1:0.75 due to the colder air.

An upgraded cold air intake is going to cost you $200-300 and might gain you 1mpg. Manufacturers will probably claim 2-5mpg, but you’d be lucky to get over 1.0mpg in reality. The downside is, cold air intakes sound awesome, so it’s going to make you want to press the gas more frequently.

2. Cat-Back Exhaust Upgrade – 0.5mpg

In similar fashion with the cold air intake, a cat-back exhaust system can actually increase mpg’s while still increasing horsepower. Cat-back exhaust systems increase engine efficiency by creating a less restrictive exhaust system.

Speaking in engine generalities, less restriction equates to more efficiency which equates to better gas mileage. Sounds great right? Let’s get an exhaust system because it sounds cool and it’ll help me save money on gas! In theory, sure, but it’ll be a really long payback period.

With an exhaust system, you will probably get a 0.5mpg improvement. And similar to the intake, the added sound will definitely make you hit the gas more frequently. Overall, yes it does improve mpg, but no, it’s not worth it as an mpg mod alone.

3. Engine Tune – 2mpg

Engine tunes alter the engines ECU to change various factors such as engine timing and AFR’s. Tunes are mostly used to unleash horsepower and create more engine power. However, most tunes will come with multiple “maps” and all tunes that I’m aware of have an “economy” tune for improved gas mileage.

On this list, this is probably the only mod I would say “okay, maybe I’d spend money on this” for the sole sake of gas mileage. With a good tune, you can probably squeeze out a 2mpg improvement. But you still need to drive a lot to justify it. If you want to make more power from time to time for fun, but also want improved gas mileage for those long and frequent trips, a tune is great.

Outside of mpg efficiency, a tune is also probably the best bang for the buck mod on any Chevy truck.

4. Upgraded Wheels and Tires

This is more of a mod not to do. Big wheels and tires are cool, it’s the classic truck thing to do along with a nice lift kit. Unfortunately, it could be one of the worst gas mileage mods you could make…because it actually reduces mpg.

Bigger wheels and tires are heavier than the stock ones. Maybe each wheel and tire is only 10lbs heavier, or 40lbs across the whole truck. Doesn’t sound like a lot. However, the effect of rotational weight on power and gas efficiency is extremely greater than static weight. Meaning adding 40lbs to your wheels is not the equivalent to putting your 40lb dog in the front seat.

Rotational weight is about 5-6x greater than static weight. Additionally bigger and heavier wheels have higher roll resistance which means it takes more power to get them to start moving and to keep them moving.

Avoid heavy wheels and tires if you care about mpg! Reducing rotational weight is actually probably the best mpg mod.

5. Tire Pressure

Maintain high tire pressure to see the best fuel efficiency. This isn’t necessarily going to improve gas mileage, but it will certainly help you not reduce gas mileage. The US Department of Energy claims that every 1psi of tire pressure drop below the factory pressure can result in a loss of 0.6% of fuel efficiency.

The thought process is that higher tire pressure create a smaller contact patch with the road which means less roll resistance. Just think about how hard it is to peddle a bike with a flat tire vs one with fully inflated tires.

Are MPG Mods Worth it on the Vortec 5.3?

In my opinion, the only two main things worth it are: not adding weight to your wheels and keeping your tires properly inflated. In most cases small increases to mpg are nice little perks for intakes, tunes, and exhaust systems. If you want to use the mpg stuff to make you feel better (or make your wife feel better) about spending a bunch of money on mods, then great.

Here is a bit of a cost breakdown/analysis on the cost of mods and mpg. I’d assume with a tune, intake, and exhaust you maybe average 3mpg better overall.

Avg. MPG1518
$ / Gallon$2.50$2.50
Miles Driven20,00020,000
Cost of Gas$3,333$2,778
Savings $556
Cost of Mods $1,200
Payback Period 2.2 years

Obviously, this assumes only 20,000 miles driven per year and I know a lot of you folks might put 50k+ miles on your trucks per year. However, the 3mpg increase assumption is probably generous. But all-in-all, a 2.2 year payback period is probably unfavorable.

Ultimately, I’d recommend going with a budget-friendly intake and tuner which will run you closer to about $500 and still get you close to the 3mpg gains. Exhaust systems just aren’t worth the cost.

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  1. So basically, the GM engineers have done pretty much all they could to give a good balance of mileage and power.

    1. The engineers at Garbage Motors are all electric vehicle pushin whackjobs.. Unfortunately, my Dad passed and left me 3 vehicles: a 74 Ford Bronco that’s a badass rig, a 99 Ford F350 7.3L Powerstroke 4dr LongBox 4×4 that’s nothin but a torque monster, and my Mom’s 2007 Trailblazer LS piece of sh*t. I mean, it was the owner of the Chevy dealerships wife’s car, so it has literally every option including the 3.73 posi front and back gearing and 5.3 V8 6spd Auto..:.I’m selling it by next spring, after the compounding issues that the 85 Stepside and 94 Z-71 gave me for years, I’ll never own another Garbage Motors product again…,.#FORD

  2. Is it true that to get the best gas mileage you should be going around 50-55 mph. If not then what constant speed will get you the best gas mileage?

  3. This chevrolets are gas addicts massive motors with poor performance, in Europe is possible to do the same with 1/3 of the motor

  4. I am so blessed! My 99 2wd 3 door Silverado with 280 000 miles and slipping transmission ( 5.3) gets 19 city and 21 hwy every time, and recently pulling a single axle 12 ft trailer full of stuff – 23 mpg!
    God is so amazing!
    I know exact mpg because of my OBDI and a car scanner app. I would like a newer, nice looking truck, but I’m afraid I would be upgrading to a downgrade.

      1. We have a 2002 Suburban 1500 and it’s logged about 220,000 miles with virtually zero maintenance in the 20 years we’ve owned it. Oil changes, batteries, and tires are probably the only thing that’s ever been done to it.

  5. Do you have any information regarding fuel mileage for the 5.3 LS out of a 2007 Tahoe?
    I have the engine in a ’94 K1500 Blazer with a Tremec TR6060 6 speed manual. The ECM and engine wiring is from BP Performance and was set up as a 2010 Camaro manual transmission.
    Getting pretty crappy mpg; expected mid-high teens.
    Thanks for any feedback.

  6. I’m going from a 96 Dodge 12 valve Cummins beast to an 05 GMC Sierra 5.3. I expect mileage to be similar, but fuel costs will be much lower.

    1. I hear you. Went from a F250 6.7 Leaker to a Trail Boss 5.3. Same milage but cheaper fuel. Oh – and no death wobble and extremely high maintenance costs! It’s my first Chevy and I’m in my 40’s. Goodbye Ford.

  7. My 2002 Chevy Silverado 1500 Z71 LS off road with tow package and the 5.3 vortec engine is better on gas than the last 6 cylinder car I had which was a 2002 Oldsmobile intrigue with a 3.5 in it. Most reliable vehicle with the over 215,000 miles on it and I am just now putting a new rear end in it and new wheel bearings and leaf springs just so I can keep driving it and haul with it like I do because I am convinced that I could not find a better truck than this. Even if I could afford to buy a brand new truck it would not be able to take all that this ole girl has and she is a little bit of a badass in the speed department also just saying what a well rounded machine… Always have been a GM lover and I had a couple fabulous ford’s but nothing in comparison to this lovely truck..

  8. I once had a used car dealership as a sideline. Bought, I think a 2003, Buick park ave with 3800 engine. It was a pretty car, but couldn’t sell it My daughter and wife started driving it and we couldn’t believe it got 41 -44 MPG and had lots more power then the super charged Buick motor. I had no experience with chips then and I couldn’t figure out what had been done to the engine. Selling it at about 130K miles was only one of my mistakes. Often thought why can’t they make all cars like that?? I have tried chips supposed to increase power and milage and all they do is keep cars from shutting down at stop lites.

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