Screaming down the highway

['94IDITurbo7.3]

driving to and from the fall idi rally a month ago i averaged 70-80mph and drove it quite aggressively while at the rally and i averaged 15.5mpg.......2wd, 4.10, and E4.

 

[lindstromjd]

With the Auto and the 4.10's I feel like im screaming down the highway, At 60MPH im at 2k RPM

I have 265/75 tires on the truck

My question is what can I do to help get my RPM's down?

... that's not screaming. 2k RPM's is not even anywhere close to it. Screaming would be a C6 with 4.10's at 70 MPH.

 

[rob93]

I have the same truck as you basically, but 315/75/16 tires. (35" tall) Im at pretty much the same rpm as you. I wouldn't regear if I were you unless the truck spends most of its time empty on the highway. The 4.10s really help off the line towing.

 

[pedro_8149]

i have an e4od and 4:10's and i turn 1400 at 60mph haha take that, ok fine i cant be like that im running 38s on my truck haha. and in the winter i run 2200 at 60mph and there stock 235 85 16

 

[rockbender]

Thanks for the MPG info, fellas. I was just curious if perhaps a C6 might be more efficient if running higher RPM's due to less TC slip? Also, I can't seem to get over the anomaly of IDIDieselJohn getting 16 mpg + out of his 4.10 C6 van turning 2600+ down the highway so I thought maybe there was some other piece of the puzzle that I had not put together yet.

I must be in the 2100 range at 60 MPH give or take. I typically don't drive much faster, but I might try a trip at a little faster speed just out of curiosity to see how much it affects my economy. Spinning 2300-2400 should bump up the boost on the turbo a little bit. I do know that I'd love to have the ability to cruise at highway speeds at a lower rpm just from a noise standpoint - bumping along at 1700-1800 would be really nice.

 

[Greg5OH]

i cruise right at 60 mph, turning 1850 rpm. SOmetimes even a litle slower, 1800 rpm...falling asleep behind the wheel lol. mpg is good though (18 or so)

 

[tbirdfiend281]

I have no idea what my RPM is, but whatever it is, the max speed is met at 82mph. I can cruise at 75-80mph all day long, and return usually about 13mpg. I need to raise that top speed big time to bring my mileage up a bit. I think I may want to try and track down a 3.55 gear rear. I am pretty sure I have 4.10s right now. I do have some 285/75r16s coming in soon, that should help a lot with raising my top speed.

 

[jayro88]

Also, I can't seem to get over the anomaly of IDIDieselJohn getting 16 mpg + out of his 4.10 C6 van turning 2600+ down the highway so I thought maybe there was some other piece of the puzzle that I had not put together yet.

I am working on figuring out the puzzle too. I think with the vans the aero (or lack of) plays a big roll. With IDIDieselJohn's new ClubWagon he got 16mpg with the CC set around 70mph and 20-21mpg with the CC set between 60-65mph. While RPM's probably play a role I think wind drag is bigger for ours. His C6/4.10 van usually cruises at 50-55mph (if I remember correctly). He also doesn't have any of the running boards etc and I would be curious about the weight of it vs mine since it is a cargo van. Another thing to look at is the terrain that you are driving. I noticed that this weekend on a 220 mile road trip. It was to an area that I usually don't drive. There were a lot less long hills etc. My EGT's were substantially lower with the CC set the same speed......meaning it was taking less fuel to maintain. When I got back to the hwy I usually drive on my EGT's went back up and I notice that it is rolling hills constantly......nothing steep, just long low inclines. I am thiking of trying to figure out how to reduce my CC throttle input so it will allow some MPH loss going up the hills and then recover it on the other side.

With your turbo do you have enough torque to drop to 3.55 gears?

Sorry for the hijack.

 

[dizdak]

If i keep my truck i want to swap up to 4.10s, maybe even 4.56s... want to run a 35" tire, but also want that gear so i can get up to speed a little easier when hauling my gooseneck and play truck which combined is roughly about 9500lbs... my 5 spd when hauling at 60mph i usually keep it in 4th gear and pull at about 2100 rpm... if i jump into 5th with that speed and weight it drops to about 1800rpm and seems like its lugging a little too much.. don't know mpg, don't really drive it enough to be concerned..

 

[junk]

Diz Dak I'm in the same boat as you. When I pull heavy I run 4th. I like the 3.55's for running empty, but with a heavy load they suck.

 

[tbirdfiend281]

Heaviest load mine would see would be my zj, with trailer she should be right about 6k. 3.55s are what I want, unless these 35s work out really well for me.

 

[HS108]

I use my truck to pull my TJ, im not pulling super heavy loads with it.

I would love to have a GV unit, but the price is just too high for me to see the savings as I dont drive my truck every day

I will prob step up to 285's next time I get tires, and that will help some.

I think running 3.73s would put me right in the range I want to be, but again how long before I see the bennys of that.

I think my best bet will be to try and source and run WMO, that way who cares how many MPG when your paying cents on the gallon

 

[rockbender]

I am working on figuring out the puzzle too.
With your turbo do you have enough torque to drop to 3.55 gears?

Sorry for the hijack.

I probably could pull 3.55's, but the 4.10's are probably more appropriate for 33" tires (effectively about a 3.73 ratio compared to a stockish 30" tire) and an average weight of 8000-8500 pounds. Bottom line is that I would go for a E4OD tranny swap before changing out gears in both the front and rear axles. Ironically, the previous owner ran 35" tires and actually regeared to 4.10's because he used the van to tow his travel trailer all the time. It would have been nice to have had the original gears (probably 3.55), but I've at least got the piece of mind that my R&P's are nearly new front and rear. I might go to 35" tires next time around too, though it makes a mighty tight fit in the garage!

 

[tbirdfiend281]

I think 3.55s are the best thing. Cheapest way to o/d would be a zf swap, but I dont really want a stick shift truck. If I had o/d I would keep my 4.10s There is a guy 80 miles from here on the forum selling a 3.55 gear, so maybe I will go down and get them. I also want to go to a dually sometime in the life of the truck, so maybe I will hold off for a while, and just run the 285s on the rear. That puts the top speed right about 92-94mph for me, witch means cruising at 60-70 the revs are not to bad.