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What kind of gas mileage are y'all getting with your ADs with a T-5?
I just got back from an 1800 mile round trip from Virginia to Illinois and burned 100 gallons. 18 MPG.
My 1950 3100 has a '53 full pressure 235 with a YF2100, an '83 T-5 with .73 overdrive 5th gear, a 2001 Nissan Xterra limited slip rear axle with 4.64 gears and 30.5'" high 215-85R16 radial tires.
I drove the whole way there and back doing between 60 and 70 MPH. I did not enjoy the 70 MPH much because the aerodynamics of these trucks makes them a bit waffly much over 65.
I have gone over every moving part on this truck, adjusting or replacing worn parts. It is like a new 1950 truck really.
I can drive it with no hands on straightaways. It likes to go straight down the road with no slop anywhere.
I was pleasantly surprised with 18 MPG with the 4.64 rear ratio, but with the .73 overdrive and the taller 30.5" tires, I guess that dials everything in.

On our recent trip to the AD Nationals in Indiana we averaged 14.8. The '53 has a 235 with a Rochester B, T5 with a 3.73 rear.

We did a lot of climbing on I-40 and I-75. We were running 65- 70.

With OD there is such a thing as "too tall", in which the engine RPM is so low that you are already on your power circuit.
IMHO the engine RPM at your favorite cruising speed is the beginning of your torque curve, but still on the primary circuits (PV not open, etc.).

Tell me about too tall… my 46 with fresh 235 came to me with a T5 and a Curry rear with a 3.0 ratio.
I never have used 5th as 1 to 1 4th is the perfect highway gear for 55-65 mph
While I’m actually ok to this setup now, I am in the process of calc-ing/sourcing a new final drive, mostly because reverse is SO TALL ( which no-one seems to discuss). I can’t back the truck up without riding the clutch the whole time, and living on a hill that is often. 1st gear is slightly tall but that works because you don’t ride the clutch like trying to keep it slow in reverse. I always liked the granny gear in my dually work trucks for just that reason.
With my D-back tires at 29” tall I am now looking for a 3.8 diff (a F*** 8” is what fits this Curry housing).

Chuck

Couple of years ago I checked mileage for the weekend of an out of town car show trip (with all the scientific [in]accuracy that comes with listening for the sound of the gas in the filler neck to change pitch to avoid it puking out the top when filling up, and multiple top-offs instead of one big fill-up).

'50 3100, stock 216, Carter YF 964S, 0.76 5th, 3.90 rear, 28.66" tall rear tire. I figured 12.-something mpg (maybe 12.8?) for a weekend of running 65-75 on the highway. The vacuum gauge is down to 5" when running highway speed in 5th with the 216. 70 mph is around 2500 rpm with my setup.

Stock was 58 at 2800. Now 2800 gets me to 80.



Carl, do you even use first gear with a 4.64 rear?

Carl, I'd say 18 mpg with your setup is impressive. The 30.5 inch tires probably help a lot. Try driving at 55 for the sake of curiosity. Air drag (in a very simplistic explanation) generally follows a quadratic formula...meaning the square of the increase x 2 equals the increased drag amount. Or if you increased speed from 30 to 60 (2 times) your drag would increase by 4 times. The coefficient of drag of the AD truck is bad, by the way. Worse than you would expect. Years ago I calculated that each 5 miles per hour over 50 mph (an arbitrary number) will mean you are paying apx. 25 cents extra per gallon of gas. We have a Subaru Forester. I once drove 175 miles at 57 miles per hour and got 40 mpg. It is not a hybrid, just a plain 4 cylinder engine with the CV transmission.

Jon,
I could do a 55 MPH test if I could find a road which I wouldn't get run off the road or run into.
Besides that, I am a Climate Change activist.
If I get 20 MPG at 55 MPH, then I would be violating my oath of preventing the next Ice Age by neglecting to do my part by adding extra C02 into the atmosphere...

My 250 gets it's best mileage around 2400 rpm, that gets me to 65 mph with a 3.08 gear and 28 tires, no lock-up or overdrive. Vacuum stays above 10 if on level road, and little wind. A head wind will knock off 1 to 2 mpg. Last trip out it got 20.5 mpg, truck weighs 3450lbs full of fuel and two on board.

Best thing for fuel mileage is an Air Fuel ratio gauge, I picked up 6 to 7 mph by tuning the W-1 carbs, mostly leaning them out at cruise rpm. On level road at 65mph, it runs about 15.2 - 16.0:1 a/f ratio depending on temp, wind, and which fuel station I was at.
With a A/F gauge, you will know right away if its geared right and jetted right.

Something else I did was make a cardboard throttle position gauge taped to the dash. I had a moveable needle with a spring on it pulling back to zero, the other end had a string tied to the throttle pedal under the dash. I marked idle, and full throttle, split the rest evenly with a few dashes. I found 95% of my driving used the first 20% of the throttle, this then told me where I needed to change the metering rods. W-1 Carters use mechanical means to richen the mixture with three step metering rods. Since I have dual Carters, a .030" change in height of the two metering rods, will change the A/F ratio about 1 point. It takes a dial indicator mounted on a plate on each carburetor to set them accurately. A 1/32 of a turn of the idle screws changes the idle a/f ratio 1 point, sometimes it hard to tell if I turn them, I have to look at the gauge to know.

Having the idle and run mixtures at or above 14.7:1 ratio will increase your mileage more than you think. Mine ran good and was getting 14 mpg on the road, once leaned out and adjust right, it jumped to over 20, and that's at 65-70 mph!

Aside from losing some power with such a lean mixture, don't you risk engine damage (melted spark plugs, pre-ignition, etc?

No power loose, fact it gots more power since leaning it out. Very seldom does it run steady at those numbers, even the slightest amount of throttle changes the ratio. With 8.0:1 compression, there is no pre-ignition. If you ever get to use a scanner tool with live data to watch, everything runs on the lean side at some point, the computer is always changing the fuel ratio, same as my throttle does, rich/lean. 14.7:1 is a perfect air to fuel ratio, mid 15 is not that far from it. Most cars and trucks like these we play with are in the 12:1 area or worse. If you can smell fuel at the back, its way to rich. My stock Monojet with factory settings was in the low 12 range.

What makes mine run better is the dual carburetors spaced apart so cylinders 123 run off one and 456 run off the other carb on one open manifold. Single carb intakes run lean on the out cylinders and rich on the two inner ones, there's no way around it. Mine evens out the flow, so all cylinders are relatively even.

Full throttle mine will be in the high 12:1, letting off down a long hill, the gauge will hit the lean peg a set till you give it throttle. Around town ( 35 mph ) right at 14 or tad higher.

I need to type up a very belated trip report. Did the STL “Hotrod Hundred” in mid September. Longest drive by a big margin I’ve ever done in my 51.

With a Carter YF 2100s, 235, SM420 and 3:38 gears….averaged between 14-15 mpg over 380 miles. All but 100 of those miles would have been interstate at 65-72 mph.

The middle fill up of the day would have been roughly half two lane at 50-55 and interstate at 65-70. That tank was 18ish mpg. I was pretty blown away by that.

18 is pretty darn good for the age of the truck. They are terrible when it comes to aerodynamics, if we could drive 55 all day, the mileage would jump pretty good.
I was on the interstate all day Sunday, posted 70 mph, most were driving 80, even in my '03 Tacoma I was nervous driving 75.

The ratio of two lane to interstate on that 18 mpg tank was roughly 50/50.

My hunch is that the two lane mpg would have been bumping 20 had it been measured alone.

I'd be curious to see more T-5 (or other manual overdrive) accounts for comparison with the original post.


Also, surely I'm not the only one with a 216/T-5 combo..?

I assume a T-5 is a 5 speed of some kind?

I have a 216 with 3 spd and get around 12-14mph city/highway combined

Yes, T5 is a manual 5 speed (5th is OD) used in a bunch of makes/ models in the 80s and 90s. The most popular version for our trucks is the S10 tranny as it locates the shifter in such a way to be compatible with a bench seat. But many variants can be used and there are several different ways to do the swap.

If you web search “Lugnutz T5” you will find Lugnutz’s site and enough reading/videos on the subject to keep you busy for a very long time.

I bought my T5 from Lugnutz when he had one out of (as I recall) a 1989 Astro Van. It has the gear chain which starts at 4.03 for first and ends with .86 which is very good for the 3.07 rear end. It allows one to use the first 3 gears almost in almost the exact same ratio chain as the OEM gear chain of the AD truck (meaning I can haul 1000 pounds in the bed without trouble and it feels just like the old AD). At 4th I get a 25% reduction in rpm from 3rd and in fifth you are at the same overall ratio as if you had a 3 speed with overdrive (a 14% drop from fourth). As long as you're not dealing with too many hills and/or headwinds, it will work well for you. And if all things are in harmony (no notably tall hills and still wind to slight tail wind) you will get around 20 mpg. That's not a promise but if you drive slower (50-55mph) you could see that number fairly routinely. Again, wind and speed are the two main determinants. The way mine is set up at 60 mph my engine is right on 2000 rpm.

His site was a big help in planning my swap.

If the moderators feel the need to remove this post, as the vehicle is off-topic, please do so; but the example fits well with the topic of this thread.

In 1975, I was bitten by the "buy American" bug. Before that, I bought what I could find, liked, and could afford.

In 1972, I special-ordered a Toyota Corolla, with a factory 5-speed from my best friend, who was co-owner in a Toyota dealership.

As I planned to enter the car in rally events, I spent some time with the physics books and the slide rule doing some research.

Once the car arrived, modified the car with a different carburetor (duh), factory headers, a recurved distributor, American Racing wheels, and Michelin tires. The tire diameter thus the size, was determined by the aforementioned calculations.

As it was necessary for success in rallies, we calibrated both the speedometer and odometer, so we knew the accuracy of various test results.

Once the engine was sufficiently broken-in, mileage tests acquired 39.3 MPG at 70 MPH (Missouri speed limit).

In 1973, the Federal speed limit changed to a maximum of 55 MPH. We had an "interstate highway" trip planned a couple of weeks later, and was really looking forward to seeing if I could break 40 MPG !

Imagine my chagrin when I found the engine would NOT function smoothly at 55 MPH in 5th gear !!!!!

I now had to run highway speeds in FOURTH gear to keep the engine RPMs in the power curve (see post 3 in this thread by panic).

I learned a lot FOLLOWING this exercise about fuel economy.

At the time I was still working on my first degree, and had an excellent relationship with some of the physics professors (I minored in physics). It was a real life problem they could sink their teeth into. In a nutshell, any fuel economy benefit of an overdrive may be acquired with some math, some physics, and tailoring the transmission high gear ratio, rear differential ratio and tire diameter to the vehicle dynamic resistance curve (air resistance) in conjunction with the engine efficiency curve.

The real benefit of a four speed or better, a five speed, is improved applied torque (driveability) over the useful speed range of the vehicle.

I have since proved this several times on various vehicles.

Of course, shifting more than twice (I once had a sports car with 7 speeds) impresses some of your passengers

Jon

Back in 2017 we visited Luckenbach TX, a 1300 mile round trip from our place in Arkansas. Drove our 1951 3600, with a flatbed, original engine (stock 50,000 mile 216) in good condition and with the original Rochester carburetor. It has a S10, T5 transmission with .72 5th gear and original 4.57 rear gears (on that trip). We averaged 16 to 20 mpg. Mileage was really affected by hills and wind. Head wind BAD...tail wind very good for mileage. Speed was usually in a 50 to 65mph window. Did see 72 one time in Dallas traffic for a short spell and that was it, all she had.

RonR

Jon, I think my 216 is in the same boat as your Corolla, as far as economy goes. I can see the difference on the vac gauge at, say, 50mph in 4th vs 5th.

I'm running the T-5 for the increased top speed first and foremost, and the synchros second (think lots of lights, stop signs, and stop & go traffic). Any potential fuel economy from the overdrive was wishful thinking, though the numbers the 235 guys are showing here aren't bad, and I look forward to seeing how my 57 235 does whenever it's finally swapped into my '50.

Hey RonR,
What is your tire height on your 3600?
Your other features mirror mine pretty closely.

Carl, tires are Mastercraft Courser HXT 215/85R16s, new they were 30.3" diameter, I suspect in '17 that would have been correct, today with 20k miles on em perhaps less.

Great results on your NOS truck by the way!

RonR

Ron,
I was looking for a 3.73 rear axle when I changed over to the T-5, but couldn't find one, so I got a real nice 4.64 limited slip one from the Pick n Pull for a hundred bucks. It's a Japanese clone of a Dana and fits the truck perfectly. Correct width and Chevy 6 lug bolt pattern.
The 215/85R16s that I went with really dialed everything in in all 5 gears.
Now all I need to do is pull a stump and see if I can drag it down the road doing 65 MPH and still get 18 MPG.

I just finished a 4,000 mi trip to the 4-Corners area visiting Indian ruins. The engine is a 261. Typical road speed is 60-65 and down to maybe 35-38 on a 6% upgrade, about as fast as a typical PNW log truck. We're carrying a 11 ft. Avion Camper and last Cat Scale ticket showed 9350 lbs. It averages 10 MPG. Eleven between SLC and the Oregon line with a tail wind; 8.7 across the Blue Mtns, of Oregon.

In overdrive at 60mph I'm turning 2500RPM and 2-5 in. Vacuum depending on altitude. I put a pyrometer on it this trip and the Exh. temp runs 1200-1350. 265/75x16 rear tires and 4.57:1 axle with the brownie 1.24:1 under 1:1 direct and 0.87 overdrive. I don't expect I'll ever see mileage in the teens but you never know what more twiddling with carbs might bring.

Years ago I changed the power valve spring so it starts to open at about 5 in. HG instead of 12 in, figuring I'd get better mileage. Now, with an exhaust temperature gauge I think that's wrong and I should go back to stock settings because the exhaust temperature begins to rise alarmingly once the power valve shuts at 5 in. Hg. I don't have an A/F gauge and I can see the utility of that but the Pyrometer came to me free so I put it on.

The previous engine, a 235 ran about 200,000 miles before it burnt a piston when the thermostat stuck near the Salton Sea (minus 200ft. elevation). Same load, carburation & cam, a bit lower compression, 8.2 rather than 9:1 That it ran that long tells me my tune isn't too far off but there's always room for improvement.

Wow Tommy, I wouldn't have expected egt's that warm. I always put the pyrometer probe just ahead of the turbo on the little 6BT Cummins and 1200F is where I start backing out of the fuel. Obviously you know your rig and it's really dialed in. Reading your exploits makes me want to dig my 261 out of the shop corner and put it to work in the '51. Someday!

RonR

Better get on it! My '60 is way more fun with a 261!

Moparguy: remember that gas engines run hotter than diesels. How much hotter is the question. I know that aircraft engine jockies spoke of 1300 degrees as a limit on 14 cyl radials but they have sodium cooled valves and valve rotators. I used to work on gas truck engines so equipped but they didn't have pyrometers so I don't know what the temps were. I do remember that sodium valves were very expensive!