1987 c10 manual 4 spd.. factory trans?

[1976gmc20]

Originally Posted by TwoFiftyShifter

I've owned 3 SM465 equipped trucks. An 80 K10 with 2.73s, and 87 V20 with 3.42s and my current 84 K10 with 3.08s. The fuel economy seems to be just fine, maybe better than a TH350 even. The gears are gapped pretty fierce, though.

I've had two 4x4 Chevy pickups with the TH350, and they both got horrible gas mileage

I think the automatic sucks about 35% of your horsepower. The four speed pickups have been much snappier and better gas mileage.

[Bigstevex4]

My jimmy with throttle body 5.7 465 has 410s but it has 36 inch tires gets around 10mpg but its 8 feet high,

[1976gmc20]

Originally Posted by Bigstevex4

My jimmy with throttle body 5.7 465 has 410s but it has 36 inch tires gets around 10mpg but its 8 feet high,

It's pretty hard to get really good mileage from a Squarebody at interstate highway speeds

My aforementioned 1980 K10 (350/465) with the tall gearing got a solid 15mpg at 80mph, but around 18mpg at the then legal 55. That's with a carb

The TH350 automatic K20 and K10 were lucky to get 10mpg under any conditions, and would downshift on moderate Colorado hills. They were really good at converting gasoline into noise.

[Tom]

You guys worry about mileage too much. My 78 was originally a 385 with the sm465 and 3.73's. I got 10mpg everywhere I went. Then I bought a 79, put a vortec 350 converted to carb in with stock 3.07 rear gears and th350. It also got 10mpg in town. Then I put a built 200-4R in, and it still got 10mpg in town.

[1976gmc20]

Originally Posted by Tom

You guys worry about mileage too much. My 78 was originally a 385 with the sm465 and 3.73's. I got 10mpg everywhere I went. Then I bought a 79, put a vortec 350 converted to carb in with stock 3.07 rear gears and th350. It also got 10mpg in town. Then I put a built 200-4R in, and it still got 10mpg in town.

Worry ???

I get roughly half again the mileage out of a four speed manual versus the three speed automatic. Maybe only a margin of 5mpg but it's a lot of difference percentage wise (300 miles vs 200 miles for a tank).

The four speed automatic is a lot better on gas mileage than the old TH350.

Something's wrong if you're only getting 10mpg in a pickup with a manual. Maybe you're running it up too high before shifting...? I can shift my C-20 out of 2nd (don't normally use 1st) at around 8mph, and get into 3rd by 20.

[68post]

Originally Posted by 1976gmc20

Worry ???

I get roughly half again the mileage out of a four speed manual versus the three speed automatic. Maybe only a margin of 5mpg but it's a lot of difference percentage wise (300 miles vs 200 miles for a tank).

The four speed automatic is a lot better on gas mileage than the old TH350.

Something's wrong if you're only getting 10mpg in a pickup with a manual. Maybe you're running it up too high before shifting...? I can shift my C-20 out of 2nd (don't normally use 1st) at around 8mph, and get into 3rd by 20.

I think you're on to something, my 2000 3500HD diesel flatbed, (with an NV4500 trans,4.63 gears,19.5 rim/tall tires), was @10,200 lb with an empty bed center and got 10 mpg. Until I noticed an auto diesel one ton hit 4th gear at about thirty mph. I started short-shifting it and got 15 mpg twice in combined city 'n hiway (set cruise @ 55 or 60 only ,on a 50 mile hiway cruise home).

My last 4wd was a '83 5/4 K30 with 4.56 gears/SM465 and 33" tires and I could sneak a hair over 12 mpg out of it's hi-perf 350 on a hiway trip - with a load.
Everyone else that drove it on the interstate would push the clutch in and start to search for 5th gear - but I'd stop them asap !

There will be an '87 V1500/4.3/A833 for sale soon from my late friends estate , (more rusty than cherry). Those two 4wd's looked very similar - but couldn't have been more different !!

[1976gmc20]

Originally Posted by 68post

I think you're on to something, my 2000 3500HD diesel flatbed, (with an NV4500 trans,4.63 gears,19.5 rim/tall tires), was @10,200 lb with an empty bed center and got 10 mpg. Until I noticed an auto diesel one ton hit 4th gear at about thirty mph. I started short-shifting it and got 15 mpg twice in combined city 'n hiway (set cruise @ 55 or 60 only ,on a 50 mile hiway cruise home).

Yeah, these big tough American engines don't need a lot of RPM for normal driving.

I've had to yell at a few people that I let drive one of my trucks for revving them up like some sports car

[Tom]

Originally Posted by 1976gmc20

I get roughly half again the mileage out of a four speed manual versus the three speed automatic.

That's not normal. They have the same final drive ratio. By bypassing the compound low first gear your getting the same number of gears to accelerate threw. You should get about 10-15% better mileage, not 50%.

Something's wrong if you're only getting 10mpg in a pickup with a manual. Maybe you're running it up too high before shifting...? I can shift my C-20 out of 2nd (don't normally use 1st) at around 8mph, and get into 3rd by 20.

Apples to oranges. I had a medium to large size cam, RPM intake, holley 750DP, MSD iginition, headers with dual exhaust, 275/60/15 tires, 3.73's,385 stroker, vortec heads and 10:1 compression in the 78. Yes, the 79 with the vortec 350/200-4R got 15mpg on the freeway, but city mileage never changed. Besides all that, how is accelerating to final gear by 20mph at all fun?

[1976gmc20]

Originally Posted by Tom

That's not normal. They have the same final drive ratio. By bypassing the compound low first gear your getting the same number of gears to accelerate threw. You should get about 10-15% better mileage, not 50%.

The number of gears isn't the point.

I think the torque converter on the old TH350 just sucks out a lot of power, and as I remember the shift points were really high compared to the 4 speed overdrive automatic in our 1991 Suburban. Like I said, they were really good at converting gasoline to noise

Apples to oranges. I had a medium to large size cam, RPM intake, holley 750DP, MSD iginition, headers with dual exhaust, 275/60/15 tires, 3.73's,385 stroker, vortec heads and 10:1 compression in the 78. Yes, the 79 with the vortec 350/200-4R got 15mpg on the freeway, but city mileage never changed. Besides all that, how is accelerating to final gear by 20mph at all fun?

Fun ???

Well, my pickups have always been work pickups, and most of that ends up being on back roads. No big hurry just to get to 30 mph. Of course when towing a big load, you have to run them up a little faster in each gear before shifting, especially up hill.