Re: what are you guys getting for mpg?
 

One thing to remember about MPG and vehicles of today is that those fuels are not as they were years ago, or, even 2, 3, 4 years ago. The main issue is the addition of Ethanol into the gasoline. Ethanol is grain alcohol, as E85 is. Depending on the percentage of Ethanol to gasoline, fuel mileage will get worse as the percentage of Ethanol goes up. It used to be that all grain enhanced fuels were 10 percent ethanol, and, mileage suffered to a percentage of that addition, but, just recently, the Ethanol percentage was upped by our lack luster government, from 10 to 15 percent, and that means fuel mileage goes down even more for it.

We must understand that alcohol fuels require richer fuel to air ratios, so, when we add Ethanol to gasoline, we effectively lean the fuel heat/light off burn-ability down, and that is like the older low octane fuels of the 1980's and 1990's, they required the throttle to be opened further to get the same power, and that meant more fuel usage for the amount of throttle opening. Add to this the leaner overall fuel to air mixtures built into the fuel systems of those vehicles, and mileage went south in one quick hurry.

Richening up the fuel curves for the Ethanol added fuels isn't the answer wither, all that does is make for more fuel usage. Very careful re-management of both injector duty cycles and creative ignition timing will help somewhat, but the return for the input doesn't bring the mileage all the way back. Very careful and sensible modifications to the fuel and ignition curves, modified exhaust systems and air inlet systems will help most of all, when all is done together, but individually, not much help. Also, "cooling off" engine operating temps only hurt mileage, as cooler inlet temps require more fuels, like a cold engine running on a carburetor needs a choke to operate when cold. Cooling off the engine temp cools the combustion chamber too much, and that demands richer mixtures, and loss of fuel mileage ensues.

Where I live in Northern Nevada, we just got 15 percent Ethanol doped up gasoline. We can tell the fuel mileages dropped considerably form that they were when we had only 10 percent Ethanol. My 1991 Buick park Avenue with 3.8 litre tuned port EFI V6 used to get 28 mpg on straight regular fuels, and when it went to 10 percent, mileage dropped to 21, and today, I filled up, calculated the mileage, with the new 15 percent, and it is now a whopping 16 mpg. I also daily ride a 1983 carburetted Honda GL650 V twin Silver Wing motorcycle that used to get 50 mpg with straight gas, with 10 percent, it dropped to 44 mpg, and now, with the 15 percent, down to 41/42 mpg.

Add to that the fuels are modified to make burn-ability "enhanced" for winter use and cold weather, vs summer fuels that have less volatility, and mileages are right dismal any more, even with the better EFI systems.

so, don't expect the mileage that is written on the window sticker, even if you drive with the proverbial "raw egg under your foot on the accelerator pedal", it just ain't gonna happen, because of government meddling and adverse additions to the fuels.

Re: what are you guys getting for mpg?
 

Yep, and the winter blends seem to be even worse...?

Re: what are you guys getting for mpg?
 

YES, they are, because of the 15 percent Ethanol blend now used, vs the 10 percent we used to have. Want to get really bad mileage, go to an E-85 vehicle. they get absolutely rotten fuel mileage after about 4,000 miles from brand new, from what I am led to believe from people that own them.

Re: what are you guys getting for mpg?
 

07 avalanche 5.3 4x4 flex with 104k miles. From the day I bought her brand new she never got over 15.5 mpg. I drive 40 city / 50 highway every day. Four weeks ago I decided to really watch my throttle input. No more WOT, nothing faster than 75, Easy acceleration! Mileage has gone up to 17.2! I am thinking of getting a bullydog gas tuner and maybe gain another 2-3 miles. I would be psyched if I could see 19-20!

Anybody running bullydog tuners? Anyone done any real fuel consumption comparisons?

Also thinking of new injectors and plugs since they are original!
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Re: what are you guys getting for mpg?
 

dont get the bullydog tuner. i bought one from summit and enjoyed it, but when i went to set the parking break, it broke off the little switch for the plug that goes into the obd-2 port. also, i had my truck tuned in person by blackbear performance. first, i would highly recommend them. second, when he was tuning my truck, justin told me the bullydog had retarded my timing a rediculous amount. i have also seen aproximatly 2 mpg increase with the bb tune

Re: what are you guys getting for mpg?
 

Skip the regular tuners and get a custom tune, their more expensive and if you live out in the hills like I do I have to drive 3 + hours to find one, but if I had a truck like this I would do that.

Re: what are you guys getting for mpg?
 

Wow, guys. Those numbers seem low. I keep a fuel and maintenance log. I calculate by hand in addition to checking the DIC. I average 15.6 m.p.g. around town and will get 20-20.3 on purely Interstate driving.

My truck is an ext. cab. 4x2 with the 4.8/3.23/4-spd. drivetrain. It is a 2008 LS 1/2-ton Silverado. I love it!

I will admit that I do get the best m.p.g. between 60-70 m.p.h. and don't get caught in much stop and go driving. Plus, things are pretty flat around the Tidewater area here.

Re: what are you guys getting for mpg?
 

I second the flex fuel vehicles sucking gas. My wife's tahoe gets no better than 14-15 mpg and with E-85 in it, we've seen less.

Re: what are you guys getting for mpg?
 

Have an 09 CCSB 5.3 Flex 4x4 w/3.42 gears. Took a 600 mile trip to Chicago and back running 75-80 and averaged 18.9 for the trip on summer gas - no ethanol. I also had the tires aired up within 2-3 Lbs of max preassure for that trip as well.

Day to Day running e10 get ~15 in the winter and 16.5-17 in the summer. Thats probably 60% highway. Yet to try E85 see how bad it is. This is my wifes daily driver.

Day to day driving has been really consistant over the past 40k. Overall I'm pretty impressed for something that can tow 10k by the book. Now would I put more then 7k behind there- nope and that only occasionally.

Re: what are you guys getting for mpg?
 

In my '10 crewcab half ton 4X4 3.73, auto, I'm getting around 14 - but that's "around town", including dirt roads/in and out of 4 wheel drive. I would be curious to see what the mieage would be in my '67 if you fitted it with an equally efficient drive train - in other words, I wonder how much the aerodynamics really effect the fuel mileage at these lower mpg levels.

Re: what are you guys getting for mpg?
 

My 2010 Silverado ext cab 5.3 4x4 with 3.42's averaged 18 mpg at 75 mph on a 600 mile trip. In town which is 60/40 highway driving I average 15. I do not drive with a light foot because of hills and traffic. The truck has 5000 miles so she is hardly broken in.

I seem to get over 20 mpg at 60-65 but have yet to take the highway on a long trip.

Re: what are you guys getting for mpg?
 

The whole mileage game is linked to air/fuel ratios, and engine performance packages.

That said, with a cruise air/fuel ratio of say, 14.5:1, 60 mph would use LESS air/fuel flow than 75 mph. Any engine that uses less air to run, such as those with smaller displacements and air flow passages in the head, such as Honda, will get better mileage than other engines that are larger and have larger air flow passages, such as the old 153 Nova inline 4 cylinder.

One deviation to this rule is carburetor vs EFI systems. A carburetor relies on air flow past set orifii to pull the fuel into the engine, and that fuel is in the form of somewhat large rain droplets. EFI, on the other hand, uses pressure technology, which injects a more precise volume of fuel, doesn't rely on vacuum as the carb does, and the fuel is injected as a very fine "London fog" of a vapor.

So, smaller displacement, lower total air flow, more finite handing of the fuel/air mixture and fuel in a vapor form, over a giant rain drop = better volumetric efficiency, better mileage.

Re: what are you guys getting for mpg?
 

I think there is something to be said in the difference in weight of wheel and tire combos also.I even experienced a slight loss in mpg's going from factory 17's to factory 20's.I also had a set of 20x10 kmc's with 305/50's for about 3 years on my 07,and they were definitely the worst.I thought they would be better with the taller tire.My truck is 2wd with the 5.3 and 3.73 gear.Averaged 13.5 with the kmc's,15.2 with factory 20's,and 16 with the 17's.

Re: what are you guys getting for mpg?
 

I would say that for the most part the difference would not be the rolling weight, but the diameter of the tire. The amount of power that is needed to roll a 32" tire is more than what would be needed to roll a 28" or 29" tire. My new truck had factory 32" tires and now I have 30.4" tires on it. It did make a difference to the acceleration, not to mention the wheel well clearance.

Re: what are you guys getting for mpg?
 

1970 c20 custom camper 350 8:1 compression, slightly more aggressive cam, 3 speed 4.56 rear 235/85R16 tires

I only measured it once, but I also was leaking gas out of the gas cap so I don't know how accurate it is. It was all highway, mostly around 65, but a few times I found myself doing 75 and a few times I took it up over 90. I got about 12mpg.

A/F ratios are very important, so I plan to install a set of A/F ratio gauges one day to get it tuned in as precise as a carb from the 70's can be tuned. Another big factor that problems almost all cars is fuel atomization. Liquid fuel does not burn, only atomized fuel. There are alot of crazy ideas out there like putting a screen below your carb or tapping the intake ports to help swirl the A/F mixture better.

Re: what are you guys getting for mpg?
 

With those MPG numbers, they may as well have nixed the 5.3 with DOD and gone for the old 5.7 or 6.0 mill with more horsepower and torque. At the end of the day, it's a two and a half ton brick designed to do work; cutting power for tenths of an MPG isn't worth it, and while there are cost savings to be had, the truck has to be driven tens of thousands of miles over the course of many years to see worthwhile savings from going with a 5.3 over a 5.7 or 6.0.

Re: what are you guys getting for mpg?
 

I can say that the 5.3 that I now have is stronger and has more roadability than the 91 that I sold, when I bought the 2011. The computer tune may have something to do with that. It is a strong engine and the acceleration is much better. The gain in gas mileage from the 91 is not so noticeable, but the performance is.

Re: what are you guys getting for mpg?
 

I surmise that we can thank federal regulation for the DOD's, AFM's and other do-nothing addons. Enjoy it while you can though, 54.5 mpg by 2025!

Re: what are you guys getting for mpg?
 

My DIC is reading an overall average of 11.5mpg's...
2008 6.0, 4 speed trans (4L70E), 3.73 gears, 4x4, 5'9" bed, extended cab, 20" aluminum rims, 35x12.50 Toyo's, Cat-back Magna Flow exhaust 1 into 2 duals out the back, some air intake like K&N, and a Hypertech programmer, 85k miles.

I didn't do any of this stuff, I bought it like this in Jan with just under 76k on it. I haven't did the mpg's on paper, but roughly from fillup to fillup it's about right (fillup with about 20 gallons, went about 220 miles, etc)

The Hypertech re-adjusts for the tire size and corrects the speedometer... I think I'm gonna plug it in and see what it says about the program it's running...

Re: what are you guys getting for mpg?
 

my 2011 rclb with the 5.3 and 6 speed and 3.42 averages 15.5-16 has 20k on it. it's an oil field truck and 70 percent of my driving is dirt road under 40 mph. my 08 with the v6 and 3.73's averaged 14 the entire 175000 miles i had it.

Re: what are you guys getting for mpg?
 

My 2010 Silverado 4.3V6 with 3.23 gears gets 18.5mpg mixed between rush hour traffic and highway, I ain't complaining.

BTW if you really want better gas mileage you would have to run leaner fuel ratios (that the engine would allow), but you can't pass emissions. I'd have to disagree with carbs getting worse fuel mileage than FI due to them generating a larger dropplet. If tuned right ideally, a carb could achieve the same fuel mileage, but with EFI it is much easier to tailor an ideal fuel curve than a carb and you can get feedback from O2 sensor.

Re: what are you guys getting for mpg?
 

05, 2500HD 6.0 4.10 gears, last 7.5 hour road trip at speeds of 75-85 I actually got 12.5 mpg! I have never babied the truck and it has 175K miles. The best I got ever was 16 hwy doing 65 the entire way on a very flat road witht he cruise set. When I replace it I plan on a custom tune.

Re: what are you guys getting for mpg?
 

i bought a 2011 gmc sierra, rcsb, 2wd, 5.3 AFM Flex Fuel,6 sp, 3.42, all stock and im gettin 22mpg averaging 50mph (back roads). This is no lie, i barely believe it myself. I havent driven it on the highway much, ive had it for two months and just rolled over 1500 miles.

Re: what are you guys getting for mpg?
 

I just hit 10000 miles on my 11 crew 4x4 I had fast motorsports tune it with 600 miles on it and I average 17.2 mpg back and forth to work hwy/city mix on the 3 hr trip to my parents house I will get about 21
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Re: what are you guys getting for mpg?
 

+1

truck with rims lager then 17" will get lower MPG, my 07 suburban with the stock 17's on the Hwy gets 18.5mpg running 70/75mph with my 22" rims same speeds same trip (Chicago to Cleveland) only get 16mpg, mix city/hwy avg 12.5mpg but i have a heavy foot and any time i'm on the e-way i'm driving over 80mph

now I have a programer that I put in economy when taking a trip and can get 17.5mpg with my 22" wheels but it really kills the performance of the suburban and makes it feel like a V6

as for the AFM its a joke only time it gos in to v4 is down hill or when i lift my foot off the go peddle to stop

Re: what are you guys getting for mpg?
 

It is not the fact that the rims are larger in diameter. It is the taller tire and the affect that it has on the RPMS and the power needed to make it move. If you go 20" rims, but the tire is approximately the same diameter,then the RPMS will be the same and the MPG will be the same. I am getting decent mileage with my 265/50/20 tires on my new truck, just because it works well with my gear ratio. Plan your change and align gears and tires effectively.

Re: what are you guys getting for mpg?
 

your right its the WEIGHT difference pick up a stock 17" wheel then a 22" wheel you'll see what i'm talking about I've had a few set of rims (8 and counting) on my suburban and most was the same over all tire height so the speedometer would ready correctly but the weight of the bigger or even just a different wheel that weights more in the same size is what kills mpg

my stock tire size is 265/70/17= 31.7 Overall Diameter

my aftermarket wheels have 305/40/22= 31.6 Overall Diameter but weight a lot more then the stock rim/tire combo so mpg suffers

the more they weight the more power it takes to turn them even if they are the same size

if you typed your current tire size correctly you should be getting better MPG that size 265/50/20 is a 30.6 Overall Diameter witch is smaller then the stock 20 inch size that is 275/55/20 and that is a 31.8 Overall Diameter tire

Re: what are you guys getting for mpg?
 

Remember the wheel and tire are rolling weight and so with that in mind, there is only a small portion of it that is actully suspended and adding weight to the vehicle. It is not the weight that you are dealing with as much as it is the circumference that you have to get the wheel to turn effectively to make it work. Turning a small gear is easier than turning a larger gear with the same output ratio from the tranny. That is why drag racers go for the different lower gears for different length tracks

You are right, my tire diameter is smaller than the monsters that were on the truck when it was stock. That smaller diameter along with my 3.42 gearing makes the application of torque to the ground much easier, since the smaller diameter essentially changes the gear ratio to a lower gear.

Re: what are you guys getting for mpg?
 

if that was true why is it that with my 22" rims witch is just a touch smaller Overall Diameter then my stock 17" rims I loose 2.5mpg??

driving the same trip cruise set at the same speeds??? I run from Chicago IL. to Cleavland OH. on business a lot I have made the run many times on my stock rims and on my big rims with my stock rims I get about 65 mile more to a tank

Sorry for the hijack, every one

Re: what are you guys getting for mpg?
 

Well my 07 nnbs cc 2wd did wicked this past weekend. Driving flat with cruise set I got 26mpg at 145k or 90mph in 4 cyl mode. Kickin it to V8 I was getting atleast 22mpg at that speed.

Re: what are you guys getting for mpg?
 

What is your gear ratio, tranny type, and what are the two different tire sizes that you are running? If you put your engine at a point where it is now running at an RPM that is just out of the band on the opposite end, it works the other way.

Re: what are you guys getting for mpg?
 

It's probably resulting from a higher rotating mass from the 22" wheels. It takes more power to turn a heavier tire than a lighter one. Either that or a smaller OD is causing the motor to turn more rpms at 65 which can also cause a dip in mpg depending on how much of a difference in OD.

Re: what are you guys getting for mpg?
 

07 yukon 5.3 auto 3.42's with 305/45-22 seems to get 12.5-14.5 city, hwy or combined.

Re: what are you guys getting for mpg?
 

Even with identical overall tire diameters, heavier rims (ie, higher mass) will absolutely hurt fuel economy, along with acceleration and braking. Look up Newton's law of motion if you're having trouble wrapping your head around it.

Re: what are you guys getting for mpg?
 

Last weekend I took a trip to Canton, OH (with a pitstop at Summit Racing in Tallmadge). It was about a 3 hour drive from where I live in western NY. My 2wd RCSB with the 4.3 averaged 19.6mpg with the cruise set at 73mph. That's the best Ive seen on the highway. I usually average 13/14 mpg around town and 17/18 on the highway.

Re: what are you guys getting for mpg?
 

I get 15.5 in a 2010 ccsb z71 5.3 6 speed 3.08 gears, straight pipe exhaust and 10 ply mudgrips.

My mom has an 07 Tahoe that she escorts with and gets about 20 following oversize loads.

My 70 gets roughly 10 and my 4x4 gets 8
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Re: what are you guys getting for mpg?
 

I have been getting 18.6 daily going back and forth to work, with the 5.3 in my 2011 GMC, in the cold weather. It has not been that cold around Kansas, this year, but the mornings at 4 AM are usually around the high 20s. This is with the cruise on and the bed cover open. I have found that the colder weather, below 45 degrees hits the mileage harder on this truck.

Re: what are you guys getting for mpg?
 

Well, I've had my truck a little over a year now,and I am cosistantly getting 15.5mpg.
I'll take that over the 13.5 at the breakin point. hahaha.

but its sooooooooooooooooooo nice. still LOVE IT!

Re: what are you guys getting for mpg?
 

My guess is that your mileage could be associated with the 4X4 in your truck and the fact that you drive in the city a lot. My 2011 gets average at 18.5 (mixed driving) and if I keep the speeds at 70 or less, the mileage climbs above 20. I have even been playing with my trips to work and if I stay out of cruise and work the gas pedal to stay in V4 mode, the mileage goes to 2. It can be done, but I would not like the truck very much if I had to do it all of the time. The items that I did to the engine air intake, exhaust and tune were done to enhance my performance.

Remember, I am running a 3.42 gear and 265/50/20 tires on this truck. The whole thing is in what the RPMs run and the efforts that is involved in making the engine work the best at an optimum speed.

Re: what are you guys getting for mpg?
 

yeh, i have the 3.08 gears with 275/55-20 tires. if i was to have ordered it,id had got 3.42.,but i took the one they had on the lot that had everything else i wanted. overall, after a year of ownership, I have no regrets trading the 2010 camaro in for it.