12.6 mpg today

[1998454]

I drove 340 miles today, all interstate at 70 mph, cruise set. Empty truck with just passengers and it got 12.6mpg....Sets a rich code sometimes after the injector swap. Truck has 4L80, 4.10 gear and is a srw ecsb. Would a tune help fuel mileage? Currently just has a hypertech program.

[Outlawz2004]

Yes, a custom tune will give better results than a hypertech, both in power and fuel economy. I dont know if I should be answering this question though, after all it is the big block section and I dont own one.LOL Just a little FYI, I never could get better than 13 mpg with my 98 k2500 ecsb with 4l80/350/4:10/14bolt with street tires. With mud tires it wouldnt do better than 11mpg.LOL

[1998454]

I've heard of some claims of 14-15 on here. Hopefully they will post their setup. It has to be too rich, the entire trip was in OD with the converter locked at 2,400 rpm. even on hills the engine is in no strain at all.

[454cid]

12.6mpg is what I used to get most often when I was driving the highway 100 miles per day for work. Unless maybe you're in the south, you're running winter gas.

I've got a RCLB so I'd think out trucks don't weigh much different....... and we're geared the same.

[1998454]

Maybe that's as good as it gets then. I cleared the codes and it reset the rich code twice on the trip, and the rear o2's, but they aren't in the pipes anymore. The plugs are white like it's lean, but the tailpipes are black. Is winter gas worse for gas mileage?
12.6mpg is what I used to get most often when I was driving the highway 100 miles per day for work. Unless maybe you're in the south, you're running winter gas.

I've got a RCLB so I'd think out trucks don't weigh much different....... and we're geared the same.

[454cid]

Maybe that's as good as it gets then. I cleared the codes and it reset the rich code twice on the trip, and the rear o2's, but they aren't in the pipes anymore. The plugs are white like it's lean, but the tailpipes are black. Is winter gas worse for gas mileage?

I'd sometimes get higher, but 12.6 was normal on the highway.

Winter gas typically does lower mileage.

If your tailpipes are black you've got something going on...... plus you're getting a rich code.

[Miles B]

I'd be aiming for a little higher. In the limited driving I got to do in my truck, I'd do 70mph on cruise, highway, 454 4L80 ECLB DRW 4.56:1 and get in the mid 12s. I'd have thought your truck should get a bit better than mine. Summer gas might fix you up though.

[454cid]

I'd be aiming for a little higher. In the limited driving I got to do in my truck, I'd do 70mph on cruise, highway, 454 4L80 ECLB DRW 4.56:1 and get in the mid 12s. I'd have thought your truck should get a bit better than mine. Summer gas might fix you up though.

How is that possible with 4:56's?

[Miles B]

No idea. Every other vehicle I've had, spinning higher RPM = lower mileage.

[N0DIH]

Mine's nothing special, but cruise rpms are in the low 2000's, around 2100-2200 rpm at 75. So that helps I am sure some. 4.56's and the 225's would raise rpms as well as add parasitic losses like the driveshaft just plain spinning faster (rotating mass).

I do run synthetic or semi-synthetic (Rotella T 5W40 or 10W30), but I don't think that really makes a diff to mpg.

Tune will help, adds some more timing to the map at cruise. And if you have the towing improvement program, that hurts too, it doesn't engage TCC lockup till higher rpm (61 in 4.10's and 66-67 with 3.73's).

I am getting somewhat better city mpg now, but only due to an extreme lock up TCC at low rpm so I can cruise at 1100 rpm in 4th TCC locked at 35-40 mph. I like it, but it isn't the best on driveability, I wouldn't ever think about towing with it like that. Just something I worked up to help the short trips my wife does when she drives it (now not as often). The TCC engagement at low rpms is akin to a stick and engage the clutch too fast. But once engage it feels great.

[N0DIH]

I can dig up someone that might be able to tune for you, just not sure where he is in relation to you.

[454cid]

Mine's nothing special, but cruise rpms are in the low 2000's, around 2100-2200 rpm at 75. So that helps I am sure some. 4.56's and the 225's would raise rpms as well as add parasitic losses like the driveshaft just plain spinning faster (rotating mass).

Given the small diameter of the driveshaft, and steady speed on the highway, I don't think that would make much difference.

[N0DIH]

Huge, no, but it is spinning along awfully fast and it still has a fair amount of weight. But it all ads up.


Given the small diameter of the driveshaft, and steady speed on the highway, I don't think that would make much difference.

[Quyonmob]

I've heard of some claims of 14-15 on here. Hopefully they will post their setup. It has to be too rich, the entire trip was in OD with the converter locked at 2,400 rpm. even on hills the engine is in no strain at all.

I bet you would have got 14-15mpg @60mph bringing that rpm closer to 2K or under.

And yes, winter is worse for gas mileage. I go from 20mpg to 17 or less in the winter.

[1998454]

Ok, thanks. I know i need a tune, but i keep planning other changes. I think I am going to get a tune after the upper intake spacers go on. From there i will call it good for a while.
I can dig up someone that might be able to tune for you, just not sure where he is in relation to you.

[1998454]

It probably would. Problem is where i live, all the 55mph 2 lane roads have steep hills and lots of turns and aren't too good for gas mileage. I can't force myself to drive 60 in a 70 though. lol. My next trip will be with the tune back to stock just to see where that puts mileage.
I bet you would have got 14-15mpg @60mph bringing that rpm closer to 2K or under.

And yes, winter is worse for gas mileage. I go from 20mpg to 17 or less in the winter.

[99burban2500]

I average 9-11 in the city and 12-14 highway/mixed. The best I ever saw was 16.4 mpg on a long road trip @ 65 mph (no hills).

[DieselPower]

I bet you would have got 14-15mpg @60mph bringing that rpm closer to 2K or under.
+1
You've (1998454) got the aerodynamics of a brick and you are pushing it pretty quickly. You've got the power to do it, but that takes fuel - and there goes your mileage. How do you drive? If you just nail the throttle and go, that's going to kill your economy as well. You'll want to drive like your own testicles are between your foot and the gas pedal. And that 2400 rpm is stomping them into the pedal. Try cutting that speed down to 60 and see what an improvement that makes.

DieselPower magazine did a write up on a 1 ton dually a while back that was aerodynamically "enhanced" and driven gently enough to return 31 mpg. Now - diesel fuel has more energy to it and a compression ignition engine is more efficient naturally, but that's still a significant improvement over "normal". The aerodynamics and the driving style apply directly to what you are trying to accomplish.