How Many Miles Per Tank?

[Rich84]

Work gets in the way of spending the time it would take to learn how to do a custom tune myself..So I am using a piggyback chip that has the 89 prom in it. It was suposed to correct early tcc lockup problem that the earlier computers had, but mine still seems to go into lockup at about 38mph..Anyway, I did drive it without lockup for a while and I like it better with it.1800-1900 rpm @ 65mph is pretty cool.
Thanks for answering my questions, you guys know your stuff..

[Hoppedup85]

About 200 miles for mine to i got 35's and a Eldelbrock 600cfm haha.

[kwin]

Originally Posted by LUCKIN-FOU

My 82 BURBAN gets 24 MPG. It has the big 40 gal tank. 350/350 w/ gear vendors overdrive 3:42 in the rear. It rolls down the highway around 1200 rpm. Next is TPI

my 91 same setup bur with a 700r4 and tall gear gets 22-24 as well

[bnoon]

Originally Posted by Firebirdjones

Yep, playing with the TPS, TCC, vs speed settings will make it do exactly what you want.

Edit: Just realized in earlier post you run a TPI setup. I used to drive an 88 Iroc 350 TPI. I've since sold all the software to tune that thing but it's all still available through Moates.
It will take you more time to set things since you'll be removing/installing/flashing E-proms, but it's still do-able. If you don't want to spend money on the software you'll have to find a tuner willing to spend the time on it, and hopefully has the software to do it. Seems alot of tuners do OBDII stuff only nowadays.

There are chip relocator cables and jumper/piggyback cables to ease retunes so that you don't have to pull the chip every time to retune OBD-I vehicles just FYI. I had one of those attached to my Moates adapter in my TA and it worked wonderful. I located my chip up inside the glovebox wall and could swap out in seconds vs pulling the ECU every time.

EDIT: Just looked it up and it seems all of the ribbon cable 24 pin extensions are outdated. Most that want that capability these days are using live time emulators (that were just coming out at the time I used the cable extension idea).

[Firebirdjones]

Originally Posted by Rich84

Work gets in the way of spending the time it would take to learn how to do a custom tune myself..So I am using a piggyback chip that has the 89 prom in it. It was suposed to correct early tcc lockup problem that the earlier computers had, but mine still seems to go into lockup at about 38mph..Anyway, I did drive it without lockup for a while and I like it better with it.1800-1900 rpm @ 65mph is pretty cool.
Thanks for answering my questions, you guys know your stuff..

Interesting. I currently have my lockup occuring at 38 mph but that's at very light throttle applications. The 6.0 seems to have enough grunt that I can actually pick up speed easily without unlocking it. I was experimenting to see how low I can have the lockup while driving around town in 35 mph zones, if I push the limit just a tad it will lock and literally idle down the street with 3.73's and a 33" tire. When I ran 3.07 gears I had lockup at 43 mph and really couldn't use it at all around town in the lower limit areas. When I get more time to play with it I'll experiment more.
Just little tricks like this combined with other things is what allows me to get over 17 mpg around town in stop and go traffic.

[bnoon]

Originally Posted by Firebirdjones

Interesting. I currently have my lockup occuring at 38 mph but that's at very light throttle applications. The 6.0 seems to have enough grunt that I can actually pick up speed easily without unlocking it. I was experimenting to see how low I can have the lockup while driving around town in 35 mph zones, if I push the limit just a tad it will lock and literally idle down the street with 3.73's and a 33" tire. When I ran 3.07 gears I had lockup at 43 mph and really couldn't use it at all around town in the lower limit areas. When I get more time to play with it I'll experiment more.
Just little tricks like this combined with other things is what allows me to get over 17 mpg around town in stop and go traffic.

I did the same thing in my Silverado SS. It was AWD with a 3200 stall (Yank 3000ST restalled to 3200) and I got 18 or so around town running E85 (MPG drops a good 20% or so on this fuel). I was locking around 33 MPH and setting cruise control just about everywhere I could to keep it in lockup. I had the same issue as you with the stock taller tires 275/55/20 vs the shorter 295/45/20's and actually got the better MPG with the shorter tires and locked up vs taller and not locked. Sweet spot FTW!

[Skunksmash]

Originally Posted by Firebirdjones

Actually it will drop your rpm quite a bit more than that. When you figure in the lockup converter that drops it down another 300 rpm easily, you are talking close to 2,000 rpm cruise speed with a shorter 28" tire.

3.73's are a perfect match with this setup. Drop the rpm too much in overdrive and you'll find the truck constantly kicking in and out every time you climb a slight grade, not only is that annoying, but it doesn't help fuel mileage.

My truck still has the stock 2:73's in it. So you're saying that even with 3:73's, I'll still be able to cruise at 75 MPH at a decent RPM? If so I'd love to be able to run 3.73's. What a boost that would be. I have a the stock 700R4 on my 87 so I'm not sure what the ratio is on that last overdrive gear. I guess you'd really need to know that to be able to tell me. As for tire size, I just wanna run stock or real close to it.

[Firebirdjones]

Originally Posted by Skunksmash

My truck still has the stock 2:73's in it. So you're saying that even with 3:73's, I'll still be able to cruise at 75 MPH at a decent RPM? If so I'd love to be able to run 3.73's. What a boost that would be. I have a the stock 700R4 on my 87 so I'm not sure what the ratio is on that last overdrive gear. I guess you'd really need to know that to be able to tell me. As for tire size, I just wanna run stock or real close to it.

Yes sir, but I guess "decent rpm" is somewhat different among everyone.

Probably best to use a calculator and decide what fits you best. Your 4th gear overdrive in the 700 is .70. That along with your prefered tire height, and the lockup converter, makes a 3.73 very streetable in my opinion.

You can go to Vexer.com and use their speed calculator, play with tire height and gearings and watch how it affects speed and rpm, it's an interactive screen that's pretty cool.

Hang on and I'll see if I can link it....

[Firebirdjones]

http://vexer.com/automotive-tools/speed-rpm-calculator

Here you go.

I plugged in your .70 overdrive with a 28" tire, converter locked up at 100% efficiency, and 3.73 gears and it says 2200 rpms for a 70 mph cruise speed. Of course it would be lower if you run say,,,a 30" tire...it drops to 2,000 rpms at the same speed.

Plug in some different stuff and move the slider around and see what you think.

[Edahall]

Originally Posted by bnoon

Agreed. I've found that the largest part of fuel economy isn't engine size, but friction. Since the crank/rods/cam/etc are all common between the 5.3/5.7/6.0/6.2 the friction differences are between the set are minimal. Makes me want to build a large bore 1.88 rod light weight looooooooooooong rod SBC with a very short stroke and every friction trick I can think of just to see how much MPG I can get with "old school" SBC tech.

Yes engine friction is part of the equation but addressing friction from wind resistance will probably gain more than just about anything else.

[Skunksmash]

Originally Posted by Firebirdjones

http://vexer.com/automotive-tools/speed-rpm-calculator

Here you go.

I plugged in your .70 overdrive with a 28" tire, converter locked up at 100% efficiency, and 3.73 gears and it says 2200 rpms for a 70 mph cruise speed. Of course it would be lower if you run say,,,a 30" tire...it drops to 2,000 rpms at the same speed.

Plug in some different stuff and move the slider around and see what you think.

That seems weird. That's a giant jump in gearing only to have it go up by about 200 RPM's.

[r8rz4l1f3]

before the debacle that I have now come across.. my 85 gmc carbed 5.7L got 12.4 mpg..thats daily driving... freeway.. city... everything...

[Your41Plague12]

In my 83 I get 6.24 MPG around town and about 12.3 MPG on the highway. This is a mild 355, a TH400, 4.10's, and 38x15.50 MT Baja Claws.

[Ziegelsteinfaust]

I just got my C20 a couple of weeks ago, and so far have gone from 10 mpg to 15+ mpg highway at 65 mph. Plus after the last of my initial round of mods I hope to sit at 17-18 mpg highway. City I think I am doing 12+ or so. I concern myself with highway mostly as that's where I drive 80% of the time, and 4.11 gears will keep the engine working to hard getting the truck moving.

The previous owner had dual exhaust installed, and it has 9.5x16.5 tires, and the 14 bolt came with 4.11 gears.

I curved and added a HEI distributer, and tuned the Q-jet to the most I can with out a rebuild. I plan to add headers, new exhaust because the old one is shot, and dual electric fans to get the last of the drag off the motor.

My next big mod is to drop in a T200R4 which will sit my rpm at 2200 rpm at 70 mph. I am choosing this trans because its practically a direct replacement for T350 with only new holes needing to be drilled. No drive shaft mods like a T700R4, and its just as strong with a close ratio.

My current 9.5x16.5 tires are some sort of HT tread so I will get 255/60 or 70/17's with highway tread on probably H2 rims.

After all the mods I am hoping for 20mpg highway.

[Mustard72]

87 K20 with a 6.2 diesel, TH400, 4.11 gears, stock height tires (31" or so), pulling gooseneck horse trailer (combined truck/trailer weight of about 12,500#). I'm getting 11-13 mpg. I just got the truck a little while ago and couldn't believe these figures when I calculated it out. It's about the same as my 72 C20 gets empty...with a fresh tune... Maybe it's the 80 psi in the tires...

[meatwagon83]

i get about 140 to a tank, my engine is tired and my cam is too big!

[izzy_Britton]

86 short bed, 305/700r4: I get an average of 300 miles to a tank, as little as 190 and as many as 360 depending upon my driving style for that week. so I average about 20 MPG.

btw, this is considerably better fuel economy than my old truck, a 97 ford ranger with 4.0 and A/T. it was averaging about 9MPG

I have everything to do a tune-up but have not had the time. Hoping i can get to that tune-up this coming weekend. I hope it is a 3 day weekend so i have enough time to get done all the things i want to get done.

-Izzy

[Edahall]

Originally Posted by Mustard72

87 K20 with a 6.2 diesel, TH400, 4.11 gears, stock height tires (31" or so), pulling gooseneck horse trailer (combined truck/trailer weight of about 12,500#). I'm getting 11-13 mpg. I just got the truck a little while ago and couldn't believe these figures when I calculated it out. It's about the same as my 72 C20 gets empty...with a fresh tune... Maybe it's the 80 psi in the tires...

Yup, these 6.2 diesels are not very powerful but really do well in the fuel economy department.

[jon75]

Originally Posted by Firebirdjones

I get 22 mpg with the 6.0 LQ4 (LS engine basically) swapped into my 72 4x4 blazer, 4L60 and 3.73's on 33" tires, and no cylinder deactivation (that's cheating ). Alot of people told me mileage wasn't going to be it's strong suit either, but it holds it's own against any new V8 SUV. A 6.0 is just 364 cubes, it's not a big engine by any means.

There is so much more to mileage than the engine choice. It's really best to concentrate on the little things before spending money changing the total package. So many things that rob power and MPG. Tires, wheels, the weight of the tires and wheels, tread patterns, the tune, the weight of the vehicle, driveshaft, engine driven fans, oil viscosity, gas quality, correct gear choices, transmission choices. You can go on and on, and find at least 2-3 mpg if you are willing to spend the time and money on simple things first.

If I can get 14 mpg out of my 79 1 ton with a 502/400 turbo and 3.73's then anyone can at least do it with a 350. I'm expecting to pick up another 2-3 mpg with the gearvendor install.

I find your claims of 22mpg interesting with a 6.0 in a blazer, especially with the setup you are running. I worked for GM for a number of years and was there when the LQ engines were released. They have never been efficient engines, they are made for torque. But if that claim IS true, please write GM and let them know how you did it!

I do agree that there is a lot more to MPG than the engine so I was glad to hear you say that.

And I have a 350 in my truck. Without changing the front and rear gears to a 2.89 or something, there's no way I will achieve the economy you are claiming in your truck with the 502 (I have 4.11 gears and an SM465 tranny). Maybe one thing you are missing in your list is load % on the engine while cruising.

I'm really not trying to start anything, but if you could clarify how in the heck you did achieve these numbers, please enlighten us! Share the wealth man!