How Many Miles Per Tank?

[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

[foamypirate]

My TBI 305/700R4 gets about 12.6mpg around town, and about 18mpg on the highway. It's waaaay undergeared though, 3.08s out back with the 700R4 just kill this motor unless I'm doing 80+mph. In which case, aerodynamics kill any chance of good gas mileage. I really want to swap in 3.73s, I could probably get up to about 15mpg around town and 19mpg highway, by my educated guesstimates.

[gchemist]

Tune the carb with a vacuum gauge. Set idle vacuum to max.

I can get 18.5 MOG out of my 1406, 350 ZZ4, 700R4, 3.08 gears, 255/6R15 tires and tonneau cover. 13-15 MPG in the city. I've gotton as low as 9 MPG!! Yea, lead foot and burnouts add up!

[Firebirdjones]

Originally Posted by gchemist

Tune the carb with a vacuum gauge. Set idle vacuum to max.

That gets you close but it's even better to use a wideband to set anything on the carb. I've found when you set idle vacuum to max readings, the AFR is usually a bit rich around 12.8-13.5. I've always had to lean them slightly after using a vacuum gauge to get them to idle in the 14.5-14.7 range.

You'll pick up close to another mpg. That idle circuit also works in relation with your main jetting, so a leaner idle circuit will affect the whole curve slightly once the throttle blades are open passed the transfer slots.

With your overdrive, the 3.08 gears and that 27" tall tire, your light cruise rpms are probably low enough that you are running soley off the idle circuits at slower speeds, so you might be able to find more improvement than I initially mentioned.

[Edahall]

My diesel Surbarban has a 40 gallon tank and I can get close to 1000 miles on a tank of fuel. However, it costs me close to $160 to fill up that tank.

[cory d]

i got almost 200 miles on one 16 gallon tank with 2 dirtbikes in the bed and 3 people in the cab. also went over a mountain pass so i averaged about 12-13 mpg. 2.73 gears hurt me on the pass, i had to fly up it in second

[bnoon]

About 200-220 per tank at 13.5-14 gallons at fill-up depending on driving all interstate or not. 305/350 AT. I haven't calculated out the gear set yet, guessing mid 3's. Only modification from stock so far is a Summit Racing Stage 1 intake manifold. It has a recent tune up with a rebuilt stock carb.

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

What's the final drive on that Gear Vendors? 1200 RPM is just sick!

TPI tuning is fun for MPG's! You'll love it! Forcing lean cruise mode in my '86 Trans Am I had a 400 horse TPI 383 pulling 26 MPG averages on a good mix of in town and interstate driving. Makes me want to go junkyard budget TPI swap on my C10 to see how far I can push this brick per swallow.

[Skunksmash]

Originally Posted by Firebirdjones

Depends on your tire height. With a 1:1 final (no overdrive) and a 28" tire that's exactly 3,000 rpms. I generally cruise at 2800 which is 65 mph.

On a truck where you can easily fit a 30" tire or more, it makes the 3.73's very street friendly.

So with overdrive it would be about 2400. I think I could live with that. Might do 3:23's or 3:55's instead though.

[jimbonice]

I've got a 700r4 on my 4:10 geared dually. I don't know that it helped my economy enough to warrant putting it in, but it did drop the engine noise on the highway immensely and allowed me to cruise at 70 mph.
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[Rich84]

5.0 TPI with 3.73 and a 700r tranny and a 30" tire, getting around 22mpg. With very little highway cruising.
Stock '89 tune
Dual exhaust, no headers
Rv cam
Electric fan
No smog
So I think there is still room for improvement.

[Firebirdjones]

Originally Posted by Skunksmash

So with overdrive it would be about 2400. I think I could live with that. Might do 3:23's or 3:55's instead though.

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.

[bnoon]

Originally Posted by Firebirdjones

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.

While this is true, you can get adjustable vacuum switch to minimize the "in/out" lockup annoyance if you're carbed and if you're TBI/TPI you can adjust the lockup settings (via tune) vs throttle input as well as duty cycle and keep it locked going up those slight grades. As long as you build enough low end tq that is.

[Firebirdjones]

Originally Posted by bnoon

While this is true, you can get adjustable vacuum switch to minimize the "in/out" lockup annoyance if you're carbed and if you're TBI/TPI you can adjust the lockup settings (via tune) vs throttle input as well as duty cycle and keep it locked going up those slight grades. As long as you build enough low end tq that is.

You can only go so far with it before you get diminishing returns though. trying to run too low of a gear with the setup and then adjusting to keep the converter locked as much as possible via adjustments doesn't do any good if the car/truck is loosing speed on the grades. Then you end up matting the throttle to get it to unlock, just to gain 4-5 mph.

Low speed torque as you mentioned is the key to make this work but in trucks it's much more difficult. I've played with this scenario on my LQ4 6.0 and 4L60E swapped into my 72 blazer. This thing makes good grunt down low (snaps pinion gears off the rear ), but it still didn't like trying to lug a big heavy truck up some of the grades around here, especially cruising below 70 mph. Playing with the tune trying to find that happy spot took about 300 miles of driving but it still wasn't optimum in my opinion. It just didn't like the 3.07 gears unless I was on completely flat ground (hard to find around here) So I switched to 3.73's and went backwards on the TCC settings. Much happier. Now I'm not matting the throttle to get the darn torque converter to release when I want to pass.

Just my opinion, but you are better off gearing the truck properly along with the tire size you run, rather than try to bandaid it with hard to release TCC settings.

[Rich84]

Is the converter supposed to lock as soon as the tranny goes into 4th gear??
Is it supposed to be able to come out of lock up without coming out of 4th gear?
When going up a grade, I do not feel it come out of lockup, it simply downshifts to 3rd.
Conversly, I can feel it go from 4th to lockup when running thru the gears.

[bnoon]

Oh tcc settings are not a bandaid, they can be very helpful. There is definitely a sweet spot and it can take some time to find it, that is for sure. I had my 2003 Silverado SS LQ9 AWD pulling 22 MPG averages on E85 with the stock 4:10's and 295/40/20's with light weight Centerline Rapid wheels. Other MPG helping mods were self made 4" intake and OBX stainless long tube headers.

On that truck, I had lock up set to 33 MPH at low throttle and pretty much left the "in/out" throttle settings stock, but on my 86 Trans Am I had better luck with 45 MPH lockup and harder throttle required to knock out the lockup due to the much taller final drive and better aero. Different combos and different driving styles will always require different tunes. I was just explaining options.

[Firebirdjones]

Originally Posted by Rich84

Is the converter supposed to lock as soon as the tranny goes into 4th gear??
Is it supposed to be able to come out of lock up without coming out of 4th gear?
When going up a grade, I do not feel it come out of lockup, it simply downshifts to 3rd.
Conversly, I can feel it go from 4th to lockup when running thru the gears.

1) Not really, it's all related to throttle angle. If you run the adjustable vacuum switch on the older 700's, the adjustment isn't really finess. You would have to also get inside the transmission governor to get 4th and lockup to work together. Most times what you find when at medium throttle and going up through the gears, by the time you get ready for 4th and you reach the speed you desire and start backing off the throttle, it will tend to shift to 4th and go immediately to lockup. Not unusual, but sometimes when you want a little more speed you end up unlocking the converter again. This back and forth gets annoying for some.
If you run computer controlled 4L60E it's much easier to go in and change the trans tables, shift speeds vs throttle angle and TCC lockup to minimize this occurance. You can taylor the shift tables to your exact driving style, which is nice with just a few key strokes.

2) Yes it is supposed to come out of lockup without coming out of 4th gear. This however is the issue with a TCC table (or switch) that is set to a point to keep the torque converter locked with more throttle position. The draw back is that when you do want the converter to unlock, you have to give it so much throttle angle that it knocks the trans back to 3rd (or even 2nd in extreme settings). Much harder to get these settings correct with the adjustable vacuum switch. On mine I've set the tables to unlock the converter while staying in 4th (took alot of drive time and alot of miles). I can climb mountain grades by slight throttle movement to unlock the converter, stay in 4th gear and maintain 65-70 mph in 4th which keeps rpms to a minimum at the same time.

It's all just a matter of fine tuning and adjustments that suit your particular truck. These things are heavy and shaped like bricks, so it definately takes more fine tuning to get it right.

[bnoon]

Originally Posted by Rich84

Is the converter supposed to lock as soon as the tranny goes into 4th gear??
Is it supposed to be able to come out of lock up without coming out of 4th gear?
When going up a grade, I do not feel it come out of lockup, it simply downshifts to 3rd.
Conversly, I can feel it go from 4th to lockup when running thru the gears.

No, the trans can shift into 4th without being locked. The TCC settings have a throttle input, minimum speed, max load, and a delay setting that must be met before lockup occurs.

Coming out of lockup vs downshifting to 3rd will depend on the throttle input vs the load calculated by the MAF/MAP vs RPM vs speed. You should be able to get lockup to kick off on level ground or slight grades by slowly pushing the gas pedal down little by little, then as you push farther it will pop down to 3rd/2nd/1st as required. In your scenario, the grade you're going up is either too much throttle input, too much load, too little RPM, or combination of all to just go to 4th unlocked. In a custom tune, you can lock the converter in any gear at just about any speed or throttle input.

[Firebirdjones]

Originally Posted by bnoon

Oh tcc settings are not a bandaid, they can be very helpful. There is definitely a sweet spot and it can take some time to find it, that is for sure. I had my 2003 Silverado SS LQ9 AWD pulling 22 MPG averages on E85 with the stock 4:10's and 295/40/20's with light weight Centerline Rapid wheels. Other MPG helping mods were self made 4" intake and OBX stainless long tube headers.

On that truck, I had lock up set to 33 MPH at low throttle and pretty much left the "in/out" throttle settings stock, but on my 86 Trans Am I had better luck with 45 MPH lockup and harder throttle required to knock out the lockup due to the much taller final drive and better aero. Different combos and different driving styles will always require different tunes. I was just explaining options.

I completely understand, didn't mean to make it sound like a bad idea. I've been playing with it for a while and there are some definate benefits.
I've gotten my 72 4x4 blazer to regularly get 22 mpg as well with the 6.0/4L60E running 33" tires and now a 3.73 gear. No headers on mine but I do run a custom 4" intake and currently running an SD tune (no MAF). Not too shabby for a boxy truck that sticks up in the air.
I found alot of gains in MPG with the trans tables and TCC stuff. I also think there is more to be had when I get more time to play with it.

[bnoon]

Dang, beat me to it. Oh well. That's what I get for starting to type then taking a pee break, LOL!

[bnoon]

Oh yeah, SD tune can use the command fuel to really pull some MPG's if you're running catless. MAF makes for better idle/low speed control though with custom cams. I say "better" because it's easier, not that it can't be done. Custom tunes = fun times!

[Firebirdjones]

Originally Posted by bnoon

Dang, beat me to it. Oh well. That's what I get for starting to type then taking a pee break, LOL!

That's okay, the way I explain it sounds too complicated, your version is much shorter and to the point

I'm better if you just bring the truck over, we hook up the laptop and go driving until your happy.

[Firebirdjones]

Originally Posted by bnoon

Oh yeah, SD tune can use the command fuel to really pull some MPG's if you're running catless. MAF makes for better idle/low speed control though with custom cams. I say "better" because it's easier, not that it can't be done. Custom tunes = fun times!

I'm a fan of the SD tunes, run one in my wifes SS camaro that knocks down 30 mpg.

I still have some tuning to do on my blazer but I'm happy with the mpg returns so far. Alot of people keep telling me the 6.0's are gas hogs It's just a 364, they can be nearly as economical as the 5.3's with a good tune

[Rich84]

Originally Posted by bnoon

Coming out of lockup vs downshifting to 3rd will depend on the throttle input vs the load calculated by the MAF/MAP vs RPM vs speed. You should be able to get lockup to kick off on level ground or slight grades by slowly pushing the gas pedal down little by little, then as you push farther it will pop down to 3rd/2nd/1st as required. In your scenario, the grade you're going up is either too much throttle input, too much load, too little RPM, or combination of all to just go to 4th unlocked. In a custom tune, you can lock the converter in any gear at just about any speed or throttle input.

So, I would need to reprogram the computer to get it out of lockup and stay in 4th since the truck is much heavier then the Camaro and the different tires/rear gears..

[bnoon]

Originally Posted by Firebirdjones

Alot of people keep telling me the 6.0's are gas hogs It's just a 364, they can be nearly as economical as the 5.3's with a good tune

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.

[Firebirdjones]

Originally Posted by Rich84

So, I would need to reprogram the computer to get it out of lockup and stay in 4th since the truck is much heavier then the Camaro and the different tires/rear gears..

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.