2008 Chevrolet Suburban 4x4. Need help calculating light mods.
 

So I am starting to commute about 60 miles per day which 50-55 of those miles are freeway. I am looking to get some feedback on the aero mods I am planning and which I should do first and help calculating the potential end result. I would like to get to 35mpg at 55mph which is more possible than you may think as this comes with the engine that can switch to v4 mode deactivating the other 4 cylinders.

100% stock I get about 25 mpg on the freeway but it gets in the 30's in v4 mode and I average 18.6 mpg combined city/hwy.

1. I removed the roof rack which moved my freeway mpg to about 26 mpg hwy at 55 mph. So +1 mpg.

I also noticed that the car was in v4 mode more often than before.

1. Lower air dam is 78” long and 4” tall making it 2.17 SQ FT
   
2. The side mirrors are each about 1 SQ FT so together they are 2 SQ FT
   
3. Roof rack is 6' x 2" which is about 1 SQ FT. (Done)

Now removing the front air dam is obviously going to expose the turbulent underside of the car and expose the tires so I have a 4" lowering kit in mind effectively putting it at the same height as before.

I also have a coroplast flat bottom planned and I will replace the side mirrors with rearview cameras and 3d print the housing designed like an airfoil.

Am I missing anything and what do you think the outcome will be?

https://ibb.co/9YG1d2K
https://ibb.co/88KcHt3

Sounds like the engine is already pretty efficient in four cylinder mode, and that it's the acceleration (v8 mode, or is it s v6?) that knocks down your fuel economy. It was similar in the Sienna minivan my family had - could easily get 30+ on the highway, but around town it was easy to get low 20s unless you were careful.

Coasting to stops and avoiding hard acceleration will probably yield you the greatest improvement in fuel economy.

That being said, one simple yet effective mod is to bump up the air pressure in your tires to sidewall max (usually 44 or 51 PSI).

Regarding the factory air dam, that is most likely there to improve the aerodynamics of your vehicle by directing air away from the aerodynamically dirty underside of your car.

Side mirrors may yield a small improvement, but make sure that it's legal in your area to remove them. Many areas require at least a driver's side mirror in addition to your rearview mirror, and most areas require two outside mirrors if rearward visibility is obstructed (i.e., window tint, luggage, towing, etc.). If you do delete your mirrors, I would highly recommend getting a panoramic rearview mirror, such as this one, and do some local driving to familarize yourself with driving without side mirrors - it can be daunting in a larger vehicle or one with major blind spots.

The 65+ efficiency mods link at the top of each page on here has several good ideas for improving fuel economy, from smooth wheel covers and underbody paneling, to more radical solutions such as wheel skirts, kammbacks, and boattails. It all depends on how radical you want to go, but always remember that 80%-90% of your fuel economy potential comes from , adjusting your own driving style (100+ hypermiling tips).

~ Happy hypermiling.

Yeah, Washington state requires the driver's outside mirror.

I do need to raise my tire pressure. I think I am only running 30 psi atm.

Indeed that is what I would imagine the air dam is for and the underbelly is the nastiest vehicular belly I have ever seen so I would only remove the dam after I completed the flat belly pan.

I was thinking about doing video camera side "mirrors" instead of just removing them as you are correct in that the blind spots are already horrible in this large of a vehicle.

Thanks for all the information!

Maybe I will just do a small outside mirror to stay legal and still do the video camera mod and just use the camera.

The big thing with this is I still want it to look presentable and look good so I am limited to cosmetically pleasing modifications.

Also, yes haha.

It is night and day. When in v4 mode it gets amazing gas mileage, for such a large vehicle, and has plenty of power to get around but when it drops into v8 mode, I can barely get over 20 mpg on the hwy going 55 mph.

I wish I could have a push button to turn it from v8 to v4 mode instead of it being an automatic thing. I would basically already be at my goal with no mods if I could have a push button v4 mode.

It is the 5.3L small block V8 matched to a 4 speed with a 5th gear OD that drops the RPM to about 1,300 rpm at 55 mph which I feel helps improve mpg a ton.

My Corvette was the same way with the 6 sp manual. in 6th and 55 mph it would be about 1,000 rpm and getting in the 30's with the 5.7L v8 and no v4 mode.

Thanks again!

Do yourself a favor: buy a small commuter car. Even if you can achieve 35 mpg in your suburban, do you really want to wear it out running down the highway all the time, quite possibly alone. 4X4's have far more and more expensive maintenance. Just replacing the tires once on that thing will get you a pretty good start on a really good economy car.

Don't remove the air dam.
Lower it and keep the air dam.

Also, keep an eye on your oil. The 5.3s like to burn oil when they are on 4-cyl mode

I doubt the fuel economy gauge is accurate in 4cylinder mode. I know my 5.7 Hemi with that feature was way off, as was the scan tool I had running with the Torque app. I also agree with the above, lower it but keep the air dam and still skin the bottom. Removing the air dam isn't going to decrease frontal aera one bit as everything else under there, like the rear axle, is just as low and the rear axle wont move an inch with a lowering kit.