Another fuel economy check with my '65 one ton

[66Submarine]

I had to drive all the way across Atlanta to Conyers to pick up some parts last Friday for my Impala project, so I thought it would be a good time to do another fuel mileage check. Combined with my driving the next day, the total distance was about 190 miles. 50 of those were on I-20 going 65 (when traffic didn't prevent it), and the rest were on minor highways/surface streets going 55-60 for the most part.

Anyway, even under less than perfect conditions, I still got just a touch less than 15MPG. I'm actually pretty happy with that, considering what it is.

1965 C30 stepside pickup with 245/75R16 front and 235/85R16 rear tires (mud tires), '71 250 six with points and parts store rebuild Monojet carb, SM420 4 speed trans, and 4.10 rear gears. Not too bad IMO...

[chevota]

Not too bad at all! I'm between 13 and 14 mpg most of the time. 65 c20 with 283 and th400.

[TJ's Chevy]

Not bad at all bud! Yer probably doin waaay better then my ol 292 is! lol!

[streetrodchev]

Not bad at all.

I haven't checked mine in years, but was in the 12 to 13 mpg range with my '66 K20 which has a 350, SM420, 4.56 gears and the tires were 17-40/ 16.5 (big mud tires).

[Todd W. White]

I get 16 mpg in town consistently, and 18.5-20 on the highway traveling 60 miles per hour. My engine is a 283 bored out to .060"-over (now a 292), a Holley 4360 Economaster 4-barrel Carb, SM 420 transmission, and a 3.08 rear end.

[66Submarine]

Originally Posted by Todd W. White

I get 16 mpg in town consistently, and 18.5-20 on the highway traveling 60 miles per hour. My engine is a 283 bored out to .060"-over (now a 292), a Holley 4360 Economaster 4-barrel Carb, SM 420 transmission, and a 3.08 rear end.

This is a 1 ton work truck that really isn't set up for maximum fuel economy at all. It's nearly 1,000lbs heavier than your truck is, it turns 2,900@65, has heavy (retreaded) mud tires on the back, parachute mirrors on both sides, is several inches higher in the air than a 1/2 ton, etc...it's going to suck a little more fuel keeping up with traffic.

My father gets about the same mileage you get with his 350/car 4 speed/3.07 1/2 ton, and my worn out 250/3 speed/3.73 1/2 ton got about the same as that when he drove it for a few months (17-20, avg about 18).

[64chevycrewcab]

I like what you did with the hub caps.

[awbrown]

I had a 65 one ton dually with a ramp on it and a 6 cyl , 4.10 gears .. One day I checked it and it too got 15 miles per gallon .. I could not believe it ...

[TwoFiftyShifter]

That's good. I had a 57 with a 235 3spd, 3.90 gears. Short bed half ton. Got 13-15MPG always, but that truck was much lighter and better geared than yours.

[Dans66Chevy]

My Dad and Mom drove a 1966 Chevy Caprice cross country a few years ago. 327/PG and 3.08 gears. It got 19-21 mpg. I thought it was really good.

[cg285]

64 c30 panel, 292 fact a/c, sm420, 4.10 w/ranger od. 600+ hwy miles 8.75-9.4
(although towing 3k# enclosed trailer) no data empty

[66Submarine]

Originally Posted by cg285

64 c30 panel, 292 fact a/c, sm420, 4.10 w/ranger od. 600+ hwy miles 8.75-9.4
(although towing 3k# enclosed trailer) no data empty

Ouch! How fast were you going? Hopefully it'll get a lot better without the trailer.

I'm interested in seeing what kind of mileage I'm going to be able to pull out of the 454 I'm putting in...

[cg285]

60mph. some hills. on flat land 10 mpg once. speedo 3mph fast so mileage slightly lwr than shown

[cg285]

Originally Posted by cg285

64 c30 panel, 292 fact a/c, sm420, 4.10 w/ranger od. 600+ hwy miles 8.75-9.4
(although towing 3k# enclosed trailer) no data empty

no trailer - hwy - just shy of 12mpg

[66Submarine]

Originally Posted by cg285

no trailer - hwy - just shy of 12mpg

I would have guessed better than that. Are you going to do any tuning to try to get it better?

[joedoh]

The amount of truthful people in this thread is astounding. I salute you all.

I bought an 82 2wd blazer with a warm 350, I really liked that truck and got 8-9mpg. I got a 99 suburban the same week that got 18, it wasnt hard to pick which one to drive.. haha

[66Submarine]

Originally Posted by cg285

60mph. some hills. on flat land 10 mpg once. speedo 3mph fast so mileage slightly lwr than shown

Have you checked the odometer itself? My speedo reads a lot faster than it should based on the actual odometer correction.

I'll also note that I actually determined I have 4.57 gears in the truck a while after I posted this; the tach reads about 5% slow and the pace car speedo read fast. What I thought was 2,900RPM @ 65MPH was/is actually about 3,050RPM @ 62MPH...I've apparently spent a pretty good bit of time cruising above 3,000RPM.

[Jeff La]

Originally Posted by joedoh

.. I got a 99 suburban the same week that got 18,

I had a 99 suburban and coudn't believe the gas mileage it got. Wish I had never gotten rid of it.

[66Submarine]

I mean stuff like working with the timing curve and carb jetting when I say "tuning". I don't know, <12MPG on the highway while driving pretty slow with an overdrive trans just seems low to me.

[Micmac]

I think all this is good stuff. I have the 230 inline 6 in my '63, drove about 130 miles today in the Blue Ridge in Virginia and NC and used 5 gallons. Only reason I know that is I live 4 miles from Independence, VA and gas is 35 cents a gallon there than here in NC. All I saw out riding today was a "56 Furd PU.

[rcwirka]

Thats real good for the sm420 and 4.10 rear.Can't help but think it has a lot to do with the 250.I had a 1970 250 nova 6 in my 64 C10 that got nearly 20mpg.That has the 3.07 gears.Believe or not I rebuilt and put the original 230 in this truck and recently on a trip to NH for a truck show in Barrington I clocked 22mpg.These trucks are just great.

[LuckyLightning]

I finally got my '62 out on the road today. Up until now, I'd just been driving around the neighborhood about 3 times over the last 2 months to identify issues. Looks like I fixed 'em all and finally got to take 'er out for a spin.

My truck is a C20:

• Rear axle is either 4.56 or 5.14 according to the owner's manual, and factory assembly manual identifies it only as 4.56.
• Transmission is a "4 on the floor" (factory assembly manual identifies it as a Warner Gear 4-speed).
• Tires are 265/75/R16.

1st gear is like a granny gear or something: super low. I don't even use it. I use 2nd to get off the line, and 3rd will take me to about 30mph and it's ready to go into 4th. Problem is, 4th will only take me to 40mph with high RPMs. I installed a 3rd party tach I found at a salvage yard. Readings are always a little high, but at 40mph it reads around 3,000 to 4,000 RPMs. I know the truck is intentionally geared low (as a 3/4 ton), but that seems ridiculous.

66submarine, since you have the same gearing in your rear axle, are you not getting the same experience? I would think not, since you talk about getting up to 65mph. Is it your transmission that makes a difference for you? We both have a 4 speed, although mine is a Warner and yours a Muncie.

Scratching my head, not sure what else I should be looking at.

[66Submarine]

Originally Posted by LuckyLightning

I finally got my '62 out on the road today. Up until now, I'd just been driving around the neighborhood about 3 times over the last 2 months to identify issues. Looks like I fixed 'em all and finally got to take 'er out for a spin.

My truck is a C20:

• Rear axle is either 4.56 or 5.14 according to the owner's manual, and factory assembly manual identifies it only as 4.56.
• Transmission is a "4 on the floor" (factory assembly manual identifies it as a Warner Gear 4-speed).
• Tires are 265/75/R16.

1st gear is like a granny gear or something: super low. I don't even use it. I use 2nd to get off the line, and 3rd will take me to about 30mph and it's ready to go into 4th. Problem is, 4th will only take me to 40mph with high RPMs. I installed a 3rd party tach I found at a salvage yard. Readings are always a little high, but at 40mph it reads around 3,000 to 4,000 RPMs. I know the truck is intentionally geared low (as a 3/4 ton), but that seems ridiculous.

66submarine, since you have the same gearing in your rear axle, are you not getting the same experience? I would think not, since you talk about getting up to 65mph. Is it your transmission that makes a difference for you? We both have a 4 speed, although mine is a Warner and yours a Muncie.

Scratching my head, not sure what else I should be looking at.

Yeah, I don't really consider first a road gear.

'62 would have also used the SM420 like I have (not sure why it's mentioned as that in the assembly book?). At any rate, all the old stuff without overdrive is 1:1 in high "gear" (it actually is just locking the input shaft to the output shaft and letting the gears freewheel).

If you are showing 3,000RPM+ at 40MPH the tach is wrong or the clutch is slipping; you should be going 60 @ about 3,000 with 4.57's, and even if you have 5.14's it should be less than 3,400.

'65 Chevrolet C30 towing at 60MPH - YouTube

In that clip I am going a little over 60MPH.

[factorystock]

Originally Posted by LuckyLightning

Scratching my head, not sure what else I should be looking at.

Rear axle ratio on '62 C 20 was 4.57, there were no other optional ratios in '62. Engine condition is also a factor in MPG. A worn 235 will not get the same mileage as a healthy 235 or a worn 250 will not get the same mileage as a healthy 250. A speedo is not accurate once the original diameter tires are removed. The formula for RPM: RPM= MPH x axle ratio x 336 divide by tire diameter. Example typical C20 at 60 mph ( a top speed which I would be comfortable with: 60 mph x 4.57 axle x 336 constant divided by 32" tire diameter = 2879 rpms . With a 4.11 pumpkin change 2583 rpms.

[66Submarine]

Originally Posted by factorystock

Rear axle ratio on '62 C 20 was 4.57, there were no other optional ratios in '62. Engine condition is also a factor in MPG. A worn 235 will not get the same mileage as a healthy 235 or a worn 250 will not get the same mileage as a healthy 250. A speedo is not accurate once the original diameter tires are removed. The formula for RPM: RPM= MPH x axle ratio x 336 divide by tire diameter. Example typical C20 at 60 mph ( a top speed which I would be comfortable with: 60 mph x 4.57 axle x 336 constant divided by 32" tire diameter = 2879 rpms . With a 4.11 pumpkin change 2583 rpms.

A 32" tire is also not actually 32" for the purpose of figuring speed (etc.); you need to use the loaded radius/revs per mile.

My 32" tires take 650 revolutions (or so) to go a mile, which would make them 31" if you were using diameter to figure speed. Using 32" gets you 630 revs per mile.