Mileage After Gear Swap

lbilich · January 18, 2011

Hello everyone I am new to this forum.

I have a 06 Silverado with a 5.3, i have k&n cold air, throttle body spacer, long tubes, glasspack, and a tune.

My question to everyone is that i used to acheive 16.5/21 mpg (city / hwy) with 265/70/17 tires and 3.23 gears, now with a 6" lift, 33's, and 3.73's im getting 11.5/14 mpg.

does this sound normal or a bit too low?

pwall · January 18, 2011

From the various posts I've read, sounds normal to me.

Welcome btw!

January 18, 2011

That's the reason I'll be leaving my truck stock... I get 21 mpg in a perfect case scenario on the highway ....

I used to have a K5 blazer with 33's and a lift, 8 mpg got old very fast for a Daily driver. I'll never go that route again.

stlavsa · January 18, 2011

That's the reason I'll be leaving my truck stock... I get 21 mpg in a perfect case scenario on the highway ....

I used to have a K5 blazer with 33's and a lift, 8 mpg got old very fast for a Daily driver. I'll never go that route again.

Thats about right even though you changed the gearing you still have the much heavier tires (with E-range load rating probably). That kills it, Some people also have posted about losing MPG just by installing a leveling kit so it might be the change in stance too that has a slightly negative effect.

Stevens03 · January 18, 2011

Sounds low to me.

I had an 03 5.3 with 4.10 gears and BFG 315's that got consistently 13-19mpg without fail. I guess the next question would be are your gears and tires programmed into the custom tune? If either is off, your mileage would report wrong. I'd also loose the throttle body space. The only thing it's good for is a whistle or a paper weight.

And Welcome to the site.

matt3 · January 18, 2011

You probably would have been better off putting 4:10's in. Your mileage sounds about right for your mods though.

dewfpo · January 18, 2011

Make sure your odometer is recalibrated to the new tire size so your mpg calculations are correct. Never use the DIC. I have found every one I have ever owned to be overly optimistic.

The 6" lift creates much more drag under the vehicle which will hurt mpg. That's why new Silverados have the chin spoiler on it to direct airflow around the vehicle and limit the amount going under it.

If you want a lifted vehicle with larger tires your going to pay for it every time the tires roll.

DEWFPO

Mckenzie · January 19, 2011

yep sounds just like my truck. I have got 33's and some other stuff weighing my truck down and i get around 10-11 in going short drives, and about 14 on the interstate with the cruise set on 65-67...oh and i've got 3.73 gears

lbilich · January 19, 2011

Thanks for the replies

GrapeSoda, what were you getting before tires and gears?

brad519 · January 19, 2011

A little different set up here but with 35" ATZ's and 4.88 gears along with a BlackBear Performance Tune I'm getting 11.7 city. No highway figures cause I seldom do straight highway. The best I ever got with the same tires and gears was 13.1 city using 93 octane with a Diablo 87 octane tune.

Mckenzie · January 19, 2011

Thanks for the replies
GrapeSoda, what were you getting before tires and gears?

To be honest, i never really checked before the tires, but im guessing it was somewhere in the neighborhood of 13'ish in the city and maybe in the 16's on the interstate.

Just filled my truck all the way up, and i did the figuring and i got 14.778 MPG with pretty much all interstate driving with cruise on 67, now keep in mind that is with a 10% mix of ethanol.

I'll try another long distance trip on pure gas and see what i get.

lbilich · January 20, 2011

I hear ya, thanks.

Does anyone think that if i were to switch back to a 3.23 or maybe a 3.43 with the same tires my mpg would go back up?

I know it'd be slow as a turtle but if it'd do better id consider it

nickvrebel · January 21, 2011

just FYI:

*the throttle body spacer is doing nothing for your VORTEC engine. Look up the orgins of how the Vortec name came about.

*you would see an improvement by reinstalling the factory y-pipe with cats. A stock 5.3L has plenty of breathing room through the stock high-flow catalytic converters. Long tubes are only necessary on engines running a higher duration camshaft, improved flowing heads and spinning over 5500 rpms. Instead you are only losing low end torque with your current configuration.

*as others have stated, with 33's and a 4 speed transmission you would get better mileage around town running 4.10's, especially with the low end torque loss from your exhaust configuration.

dlewis1111 · January 22, 2011

Hello everyone I am new to this forum.
I have a 06 Silverado with a 5.3, i have k&n cold air, throttle body spacer, long tubes, glasspack, and a tune.

My question to everyone is that i used to acheive 16.5/21 mpg (city / hwy) with 265/70/17 tires and 3.23 gears, now with a 6" lift, 33's, and 3.73's im getting 11.5/14 mpg.

does this sound normal or a bit too low?

Welcome to the site! I would recommend first taking that throttle body spacer and junking it. Also, mentioning it again will get you taunted pretty heavily on here by some. The glasspack muffler is not doing you any favors in the power / economy department either. Did you get your truck reprogrammed when you did those modifications? Use a GPS and check to see how accurate your speedometer is.

cliobogger · January 22, 2011

I hear ya, thanks.
Does anyone think that if i were to switch back to a 3.23 or maybe a 3.43 with the same tires my mpg would go back up?

I know it'd be slow as a turtle but if it'd do better id consider it

your tranny will hate you.