We just got back from a road trip to Prescott and Sedona. While out on road with the X, I had some pleasant discoveries; 1 The X loves to run 80+ mph, 2 The stock wheels are too narrow for BFG 285/75/16 tires. First a friend had set of American Racing 16x10 wheels he wanted clear out of his garage so he sold them to me for 100 bucks. I couldn't pass that up, so i took off the narrow(16x7?) stock wheels and mounted up my BFG's on the 16X10s. Wow what a difference? Besides the aggressive "poke" the X had a definite improvement in stability. I found myself rolling up to 75-80 on the freeway like no big deal. Now on our last road trip to DC I held the X to 75mph. I stayed below 80 because the engine was still new and didn't want to rev it over 3k. Some interstates have an 80mph speed limit, I was being passed constantly. On this last trip I found new territory for the 6.8. It loves 2700 to 3000 rpm, I'm running 4:30 gears. There's a long grade on I40 out of Needles California, I found myself running right along with all of the little SUV's and Crossovers (Audi,Explorer,Pilots,etc) in triple digit heat. I usually stay in the right lane, but not this time. I was running around people blasting up that grade. Now here's the best part, I got better gas mileage above 2500rpm than staying just below. I was getting 12mpg climbing that grade. I sure a lot of you guys and gals already know this. But it was a pleasant surprise for me. I see a lot of you running the larger tires on stock wheels, don't do it. The manager at Americas tire told they never should have mounted those tires on my stock wheels. Now I don't what would happen with say 7000lbs in tow, but I'm sure the X could easily handle it.

 

My v10 w/4.30 gears does not get better mileage at 80+, significantly less in fact

 

We’re these mpg observations calculated or based on the instant gauge?

good to know that the X is comfortable at those speeds as our primary use is for road trips (non towing) and the alternative platform we were looking at shines at those speeds (10sp Denali)

 

What was the hand calculated MPG for an entire tank at the higher speeds on all highway? For true comparative MPG numbers you have to do the hand calculation which may be a bit off from the Lie-O-Meter in the overhead.
72 MPH is about my max speed here in the East both towing the 12K TT and running unloaded, highway towing mileage depends a lot on the terrain with results between 8 and 9.5 MPG, unloaded with cruise control set to 65 MPH it gets 14.5 MPG.
My EX has 4.88 gears and true 35" (305/70R18) tires for an effective 4.39 ratio, Banks headers and Y pipe and all of the above results were while running the 5Star 89 Octane Performance tune. We will be doing another rare unloaded 900 mile round trip this weekend that is nearly all highway at between 65 and 70 MPH, most of our tow rig EXs miles are with the TT on the hitch.
My daily driver during the non salty months is a '94 Geo Metro XFi 3 cylinder 5 speed that I semi hypermile in, its last tank was its best so far by 2 MPG at 67 MPG. A new set of low rolling resistance tires and the recent hot weather helped raise the bar, my goal is to have a full tank at 70 MPG.

 

2001 7.3 4x4 - 238K miles OEM stock injectors
s300 turbine, Riff Raff compressor
S&B intake
Banks exhaust
Hydra with 40hp daily tune
285/75/17 Cooper Discoverer AT3 XLT

I just returned from a trip to Yellowstone. This is the third cross country trip in the Ex and it has performed flawlessly.

Hand calculated data via GPS
Jackson, WY to Aurora, CO - 555 miles
28.895 gallons
19.20mpg

cruise is set at about 68. I just dont see the oint in pushing an 8200# 20yo truck on the highway at 70-80mph.

max Eot 216 was on the long climb up from Laramie with a head wind
max Ect was 210

I Drive with a light foot. Easy acceleration to cruising speed. Try to keep rpms below 2500. The lie-o-meter was actually conservative here reading 18.7. At this mpg I should be able to hit 800 miles of range.

 

[QUOTE=Flyboy1100;19369797]My v10 w/4.30 gears does not get better mileage at 80+, significantly less in fact[/Quote
How many miles does your engine on it? What size tires are running? With my original engine the PCM was compensating as much as 20%(fuel trim) fuel enrichment, with new engine it's down to 7%(fuel trim) on both banks. Add a little rpm and the engine seems to be more comfortable. the engine has about 10K on it now.

 

I confess it was the gauge, however it may not be accurate, but I use as a point of reference.

 

I will see if I can construct a hand measure. I'm missing a fuel receipt for a fill up Lake Havasu. The round trip was 1236m, with I think about 100 gallons. I've got find the Havasu fill up. It's pretty much uphill from Needles to Williams/Flagstaff Az, and hot.

 

I agree the Denali and Tahoe are comfortable freeway flyers, but I'm not sure they are as hardy as the X/Superduty. When you get out on the road you see lots more of SD's towing and traveling. In the interest of full disclosure the front and suspension on my X is in a "new" condition. Steering gear(Redhead), ball joints, springs, shocks, track bars, steering stabilizer. If you haven't pulled the trigger on a used X, those are things to consider.

 

Before I did my suspension work, including the wider wheels I didn't care to drive the X much above 75. Caster was a big issue. With the front roll bar connected 75-80 is comfortable. Out on I-40 that's about the flow of traffic outside of Cali.

 

How much of a difference was the s300 turbine and RR wheel? I've towed our 8k camper from Denver to steamboat, now in Leadville and back to Denver tomorrow. I can't even get past 40mph from Morrison to Floyd hill. I did redo the front end with much better handling adding castor/camber adjustable bushings. Its no longer a white knuckle drive.

 

The turbo wheels make a difference. My goal is right lane @ 55 up Floyd hill.

 

Wait a minute, did I see 91MPH?

 

[QUOTE=bluovl;19370904]204k, 265/70r18 tires which makes an effective 4.15 gearing. Trims are similar to yours last i checked. It definitely has no problem cruising at 80+, but i see closer to 10mpg at that speed vs 11.5mpg @ 72 i normally cuise at. Also running 5* 87 performance tune

 

I'm running the K&N filter, but my plan is to reinstall the stock air filter. I wonder if that's making the difference? K&N dyno results show about a 10hp increase right in rpm range we are talking about.