How did you do it?? MPG bragging rights!!

[Hal Steward]

Starting new -- old thread keep it simple preferably 4x4 full size don't care what motor just details ie 69 B1200 4x4 400 Pontiac headers rhoades lifters 3S auto 410 gears 35 12.50 50 to 60 mph,,watching Vacuum gauge like a hawk over mountain and back solid 15 mpg Please list gear ratio,, motor and modifications,, tire size and anything else that plaid a roll in MPG 4x4 full size v8 preferably Another side ? what was your mpg gain from carb to FI ???

 

[RobertC]

With 35 dia tires;

How ACCURATE is your speedometer / odometer?

 

[Erik VanRenselaar]

The 50-60 mph max speed is the secret. I routinely get 14-15 mpg with my Scout if I keep it slow (relatively) on the highway.

 

[RobertC]

Erik,

Yes, I realize that 50 - 60 mph is the "secret".... Many, many years ago, I sometimes got 14 mpg in my T/A on long freeway runs at 55 - 60mph (in od).

Lately, I can get 12 mpg (if no headwinds) running 65 - 75 (in od) -- and I know my speedo / odo is not accurate. I ran 70 (on my speedo) on I10 east of El Paso -- my friend was running 77 on his cruise control -- I got 11 - 12 mpg -- based on my odometer (which I think may be 5% - 10% "slow").

 

[Hal Steward]

With 35 dia tires;

How ACCURATE is your speedometer / odometer?

I used registered distance and ran with someone prior to test and relied on tac to get mph

 

[Socrates]

"THE Secret"

Simple. A vacuum gauge. Use a vacuum gauge to tune your carb and your timing for the most vacuum possible under all conditions. Then mount that gauge in the cab and make sure you modulate your driving to maintain the highest vacuum possible.

I rarely see this mentioned when folks strive for mileage, yet it is the best measure of efficiency that our old rigs have. I'm pulling a solid 20" with my 345, which is stellar. My 428 Pontiac race engine is lucky to pull double digits unless I'm rolling with Rhoads or solid lifters. Hmm, now I'm curious, does Rhoads make a lifter for the IH engine? They are good for a solid 2-4" alone and work great on low compression engines...again, it all boils down to vacuum as the "secret" for economy/efficiency, me thinks...

That said, the aerodynamics of a brick are a huge issue here, along with the weight. You'll never get great mileage out of a Scout. Going from 15-18mpg to 20mpg is a HUGE step, despite what some may claim. It seems small by the numbers, but actually going to the 20mpg range in a brick at highway speeds takes far more technology then was available 40yrs ago to accomplish. In fact, it takes the very best tech available to day, as few trucks and SUV break 20mpg. When people claim "it gets 18 or xx mpg and going up to 20mpg should be easy" all I can do is ...

 

[ihslave]

"THE Secret"

Simple. A vacuum gauge. Use a vacuum gauge to tune your carb and your timing for the most vacuum possible under all conditions. Then mount that gauge in the cab and make sure you modulate your driving to maintain the highest vacuum possible.

Agreed. Pops did this on his 65 F250 when I was a wee lad... we had a 12' camper on back, and pulled a trailer made from SEWER PIPE that weighed a ton, with a dune buggy on it. That was back in... '81-'83, when he was complaining about the price of $1.15 for gas.

I seem to recall that after one trip, the mileage went from 10mpg to 13mpg!!! Which, when putting all that together, was pretty impressive.

Haven't heard of the use of a vacuum gauge in years! But this post brought it all back...

scott

 

[xyz12383318]

27 Mpg!

1978 Traveler
NV4500
NP205 t-case
Cummins 4BT motor

Currently back under the knife for paint. Pretty tough to beat that little 4 cylinder diesel. Back when I had my SD33T Scout I broke into the low to mid 20's regularly.

 

[ihslave]

People tend to call BS on my mileage claims, but when I had the 304 in my ScoutII, I got 20mpg pretty regularly, providing it was a 50 mile+ trip, highway driving.

As per the original post, How I Did It: 304, 2bbl carb, 31" tires, 3.07 axles, no OD, MSD 6A, 65mph on the dot.

And I was always told I couldn't offroad with that configuration, but it pulled sand hills VERY nicely.

 

[Erik VanRenselaar]

"THE Secret"

Simple. A vacuum gauge. ...Then mount that gauge in the cab and make sure you modulate your driving to maintain the highest vacuum possible...

Any of you remember that quite a few cars from the mid '70s to early '80s had vacuum gauges or idiot lights that were labeled *economy gauge* or something similar? Most of the gauges had a green, yellow, and red zone. Red=low manifold vacuum, green=high.

Maybe these things will be making a comeback?

 

[steve bridge]

My '77 Scout has a 345, auto, 3.52 gears, 235/75 tires. If I am day-dreaming, it seems to gravitate to 62.5 mph. It has always got, and still gets 15 mpg at that speed. It seems to drop about 1 mpg for every 5 mph over that speed.


With the rat rod thing going, I have been thinking I can put my K1 panel on the road with a 196, auto, and 3.08 gears. Weight is a key issue along with aerodynamics for mileage and I am thinking the panel can be very light. No need to do bodywork with the current fad and all of the doors work well, so...

 

[Hal Steward]

People tend to call BS on my mileage claims, but when I had the 304 in my ScoutII, I got 20mpg pretty regularly, providing it was a 50 mile+ trip, highway driving.

As per the original post, How I Did It: 304, 2bbl carb, 31" tires, 3.07 axles, no OD, MSD 6A, 65mph on the dot.

And I was always told I couldn't offroad with that configuration, but it pulled sand hills VERY nicely.

Did you have headers --dual ex any port work on heads ?????

 

[ihslave]

Did you have headers --dual ex any port work on heads ?????

That particular engine had nothing special about it... except that it had about 5k miles on it after being rebuilt when I started charting mileage.

I ran an MSD ignition, that I think supposedly would drop the multiple sparking above 3k rpm... but with my gear ratio, cruising at 65 put me at approx 2600rpm, so maybe the multiple spark was helping? I also went and bought a new 350cfm Holley... and spent some time tuning it.

Started with a factory 'wishbone' pipe single exhaust (and manifolds) into a Dynomaxx muffler that I was talked into by a 'pro'... the resonance was enough to go mad. Dumped the Dynomaxx for a 'stock' truck muffler of some sort. Much, much quieter, no detectable difference in mileage.

Later went to dual exhaust; still using factory manifolds, now had two of the cheap truck muffler, no crossover pipe. Was quieter still, and felt like it was working less hard to do the same job, but still, no difference in mileage.

That 20mpg figure came from driving between San Diego and Los Angeles twice a week for a year and a half. I used the same route every time. The mileage was 98 miles from start to stop. I came to that mileage by watching the Odometer, and comparing it to road mileage markers. Cross-reference by online mapping programs. I was usually able to fill up with the same pumps almost every time.

Mileage would drop considerably if I got caught in stop-and-go traffic. To be fair, I always felt the plugs looked just a tad lean, but when I would pull a trailer or do trail stuff, they would look just a bit darker, so I may have been on the bleeding edge of needing a main jet change?

scott

 

[truck mechanic]

72 Scout, 258 six,gm hei dizzy, 4 spd , 33s and 307s. I can get just over 17 mpg at 70 mph. I am going to 373s so we will see what hapens to the mpg.
Paul

 

[Ben Perkins]

My 72 w/ 345, auto and 3.73 gears went from 10 to 15 when I went from 2 to 4 barrel. I have been tempted to try the 2 barrel on the 4 barrel manifold and see what that would do. I suspect the manifold flows much better than the 2 barrel. But I am happy with it at the 15 which is good as everything in Northern Idaho is up down or around.

 

[Socrates]

Ben,

It's not the intake: the IH intakes are both ok pieces that flow plenty for the heads they are mated with and have equiviocal runner lengths and runner angles, plenum volumes, etc (I have a 2bbl and a spreadbore that I've compared). It's the carb that likely is to thank for your mpg increase. IF you went from a sloppy fuel gushing big bore Holley 2bbl to a Q-jet or T-quad, or even a small primary carter or the likes it's expected to pick up big mpg, at least so long as you keep your foot out of the secondaries...

 

[Dave Meyers]

Erik, in high school, a friend of mine had an aftermarket fuel economy gauge as mentioned above. It had the red, yellow and green zones. Of course, it was a glorified vacuum gauge.

IHSlave, my previous SII had a 727, 3.07 gears and 33" tires, and could pull anything and offroad and climb hills very well in high range. When in low range it had a slight advantage, though. Its Dana 300 provided a bit lower ratio than the Dana 20 would have. Milage wasn't great, and it lacked highway power and off the line acceleration.

 

[Hal Steward]

Erik, in high school, a friend of mine had an aftermarket fuel economy gauge as mentioned above. It had the red, yellow and green zones. Of course, it was a glorified vacuum gauge.

IHSlave, my previous SII had a 727, 3.07 gears and 33" tires, and could pull anything and offroad and climb hills very well in high range. When in low range it had a slight advantage, though. Its Dana 300 provided a bit lower ratio than the Dana 20 would have. Milage wasn't great, and it lacked highway power and off the line acceleration.

Thanks for posting up guys!!! Any FI 345 or 392 out there with anything MPG.. I may stay 345 or back to 400 Pontiac that motor was a H*** of a truck motor and I have a few more after market options.. But I don't have one anymore and the cost of motor bell and tranny to say nothing of more work to install I may stay 345.. Since I'm a engine machinist the work would be the same on any motor... It is of my Basic opinion that a major MPG build vs performance is cam selection and yes I'm shooting for MPG I would love to stay IH This motor will end up in my other post 120 to 1200 to 1300 ---- all B series it is coming along as well as wallet will allow 120 is down to frame- running gear 4 in lift 1/2 way done aprox 2 year project KEEP your post coming thanks again

 

[Erik VanRenselaar]

I should say one thing: going from 31" tires and a 2.5" lift, to 33" tires and a 4" lift (the axle gear change from 3.54 to 3.73 kept the rpm/road speed relationship the same), lost me about 1 mpg. Probably due to the greater body height and increased tire weight.

If I ever get this TBI EFI thing together, I'd like to see a 1-2 mpg improvement over the current carb.

 

[Hal Steward]

"THE Secret"

Simple. A vacuum gauge. Use a vacuum gauge to tune your carb and your timing for the most vacuum possible under all conditions. Then mount that gauge in the cab and make sure you modulate your driving to maintain the highest vacuum possible.

I rarely see this mentioned when folks strive for mileage, yet it is the best measure of efficiency that our old rigs have. I'm pulling a solid 20" with my 345, which is stellar. My 428 Pontiac race engine is lucky to pull double digits unless I'm rolling with Rhoads or solid lifters. Hmm, now I'm curious, does Rhoads make a lifter for the IH engine? They are good for a solid 2-4" alone and work great on low compression engines...again, it all boils down to vacuum as the "secret" for economy/efficiency, me thinks...

That said, the aerodynamics of a brick are a huge issue here, along with the weight. You'll never get great mileage out of a Scout. Going from 15-18mpg to 20mpg is a HUGE step, despite what some may claim. It seems small by the numbers, but actually going to the 20mpg range in a brick at highway speeds takes far more technology then was available 40yrs ago to accomplish. In fact, it takes the very best tech available to day, as few trucks and SUV break 20mpg. When people claim "it gets 18 or xx mpg and going up to 20mpg should be easy" all I can do is ...

Socrates I found # for Rhoads lifters 520-229-9375 I didn't know forsure if IH would interchange with any others but I could send new ones to them and they would do their work for $ 100 and it used to be $100 would buy a lot of gas no LOL