I will break down my comments by individual point to try and help as best I can.

1 - Never run less than 87 octane. The vehicle spec's 87( acceptable and 100% safe ) or 89( optimum ). Never run gas containing more than 10% ethanol blended in either. Running 85 octane can lead to piston damage that will not be covered under your warranty. Premium octane fuel( 91-93 )is a complete waste of your money unless you have a tuner program that calls for it or some serious engine mod's like a cam and NOS. Save your cash. Even tells you in the manual that premium provides no benefits and can even cause reduced performance.

I have had 2 5.7L Rams( 04 and 08 ). There has been zero difference between 87 and 89 in both of them. 87 has returned the same power( noticeable to driver )and MPG( hand calculated ). You can try 89 and see if it helps your MPG but reset the PCM and give it 3-4 tanks at least to see.

2 - IMO do not use a tuner. Your 08 Ram should have a Lifetime Powertrain Warranty. Using a tuner voids powertrain warranties( if the dealer finds out about it ). I know this will spark a lot of controversy but I am simply speaking as a former service writer who has dealt with this stuff a lot and also someone who has read and knows all about the Magnuson-Moss act. Despite what many will say and what the tuner mfg's say a tuner will have negative warranty coverage consequences on your powertrain. IMO any small MPG gains you might see( not everyone does )are not worth the risk of losing your LPTW coverage. If you disagree than go for it. Suoerchips and Diablo seem to have the best reported results and fewest problems with the 5.7L.

3 - OE 20" tire option is 275/60R-20 not 265/60R-20( is that a typo? ). Your gear ratio will be 3.92's. IMO this hurts your MPG significantly. I too have an 08 1500 BH with the 5.7L and 20's and my MPG, despite MDS, is significantly worse than my 04 1500 5.7L that came with the 17" wheel option and 3.55's and no MDS. Oh, both QC 4WD's as well.

It hurts the MPG IMO not due to the 20" wheel and tire combo weight( see below for more on that )but rather the increased surface area of the wider 20" tire( more rolling resistance )and the 3.92 gearing that comes with the 20" wheel option. More resistance from the wider tires and then higher RPM's with the lower gear ratio lead to an increase in fuel used. Around town a lower gear ratio like your 3.92's should actually help MPG a bit in these heavy trucks by getting them up to speed quicker and easier however. All other times they will hurt MPG.

My 04 with 265/70R-17's and 3.55's was much more fuel efficient than my 08 with 275/60R-20's and 3.92's overall. Pretty close and even slightly favoring the 08 all city but mixed and all highway the 04 was much, MUCH, better. Even with the 08 having MDS it gets worse MPG. IMO it is mainly the gear ratio but also the increased rolling resistance of the wider 20's.

4 - Believe it or not there is little if any weight saved by a swap to 17" tires. The OE 20's on your 08 are aluminum and don't weigh a ton. The chrome 17's are steel and are heavier. The OE 17 aluminum wheels are lighter though. In respect to the tires. 17" tires can weigh as much or even more than 20" tires due to more sidewall. This assumes of course you try and go with a tire that gives you the same approx overall diameter as the 20" setup to keep the speedo accurate.

The OE 275/60R-20 has an approx overall diameter of 32.99". The 3 most popular sizes in 17" I have seen used to replace the OE 20's on the Ram( without lifts )are...

265/70R-17 = 31.60"
275/70R-17 = 32.15"
285/70R-17 = 32.70"

If you pick a tire and look at the weights you can see dropping down to a 17" of the appropriate size saves you little to nothing or even adds weight. I will give you an example using a tire that is offered in all 4 sizes and is a popular tire being used on the Ram...

Firestone Destination AT:

275/60R-20 = 46lbs( P series only )
265/70R-17 = 40lbs( P series ) / 44lbs( LT series )
275/70R-17 = 47lbs( LT series only )
285/70R-17 = 44lbs( P series ) / 52lbs( LT series )

So to really save any weight you would need to go to an aluminum 17" wheel and then stay with a P series tire to replace those 20's. Even then I am going to guestimate your weight savings, in total for all 4 rims added up( + spare )at 100lbs +/-. Certainly will help some but not a huge weight saver. You will see benefits in ride quality( more sidewall = better ride )and less rolling resistance, plus the tires will be cheaper to buy/replace, but weight savings is not going to be a big factor.

5 - IMO don't waste your time and $$$ trying to build a CAI. Even the ones produced by companies that invest time into R&D to ensure you actually do see an improvment in air flow and power( a real crap shoot if you build your own )don't give a lot of real useable power. A CAI won't hurt, and might give you a + 0.5 - 1 MPG highway gain, but it isn't going to return huge results.

Many people actually lose MPG because they like the increased noise when getting on the throttle so you need to be easy with the accelerator to see any gains. Around town a CAI is just not going to give you any MPG gains. Pretty much the same applies to exhaust. It will help a little but you need to stay out of the throttle which many have trouble with due to wanting to hear the noise.

A CAI and/or exhaust upgrade help a little but it is not a ton. If you aren't careful they can cost you MPG while you play.

6 - Things that can actually help your MPG...

1 - Synthetic fluids all around( reduces friction and improves drivetrain performance + better product )
2 - Make sure tires are properly inflated
3 - Tonneau cover on the bed
4 - Remove all excess weight from the truck( i.e. junk you keep in it you don't really need )
5 - Accelerate easy from a stop( remember you are not at the drag strip )
6 - SLOW DOWN on the highway( 60-65 in CC not 75-85+ )

 

lmao... But seriously, I head nitrogen in the tires can help

 

NHHemi...thanks for the thorough response. I just might have to leave the CAI alone then...I will have to try the 87-89 w/<10% ethanol and see how she does.

Thanks!

The tires are 265/60/20 for sure..probably just what the guy before me put on

 

1. Drive slower, accelerate slower and coast to stop lights.

2. Keep your tires inflated.

3. The tuner for my '07 4.7L picked me up about 1.5 to 2 mpg but I would avoid it if I had the life time warranty.

 

The only thing I've done to my truck that had any effect on city MPG was the electric fan. It's not a ton but, 1 to 1.5 depending on conditions.

 

Nitrogen will not help directly, but can help indirectly. Nitrogen molecules will not contract like Oxygen molecules will in the cold, so during cold weather, the pressure in your tires will remain higher, netting better fuel economy.

Regularly checking the PSI in your tires (especially in cold weather) will achieve the same thing.

 

ya...I do check those things regularly and have changed my driving conditions from my early 20's...LOL... I'll track it more and see if I can squeeze some more out of it w/filter.

 

As for the warranty...everything that I'm reading both online at dodge.com and in the owner's manual says that it is non-transferrable and only covers the original owner. Can anyone shed some light on that, my grandfather transferred his but both the site and owner's manual says different! I'd gladly pay the $150 if I'm covered.

 

The "Lifetime Powertrain Warranty" year vehicles are non-transferable. If your grandfather has an '08 and has warranty then it's not factory but rather 3rd party. Many times people get a warranty from a dealership on a used vehicle and don't realize that the dealer is using 3rd party underwriters...

 

The base Lifetime PTW that came with you and your Grandfather's 08's is non transferable. It is for the original owner of the vehicle only. I did not know you weren't the original owner of your truck or I would not have mentioned it in my 1st response.

Chrysler has many levels of warranty that you can buy and add that can be transferred however and it can be taken all the way to lifetime under their maxcare plan. Aftermarket warranties can be transferred usually as well. I am assuming here that is the case with your Grandfather if he had some kind of lifetime warranty transferrred to him. The base LPTW that came with his truck is not transferable.

However, with that said, I have heard of it being done in very rare instances when problems have arisen with a lemon like truck still under the 3/36( that does transfer )as a peace offering to the 2nd owner similar to what GM did with free PTW warrranty extensions for people with piston slap( well, their engines not them ) but 99.999999% of the time it can't be done.