NP833 tranny

[Stephen]

Speed is always the enemy, especially in a square.
I've thought about building a good milage daily out a square but it seems easier to have the latest beater car (TDI jetta right now) and fun square (all of them). I've been really tempted by gmt400 shortbed single cabs with the 4.3 and NV3500 and flirted with the idea of a cummins R2.8 swap. The most direct route is probably the 6.2L diesel like TRusty. My K5 was 6.2L powered in the beginning but was a mountain states version with 3.73s and 17-20 was typical. I knew a guy in college that had the 3.42 version and claimed 25 pretty believably. With some attention paid to air dams, ride height, tires and so on you might get a 3.08 geared version to go higher. But at some point you're pounding a square into a round hole.
to get back closer to the rails, I've maybe seen a NP833 but that's about it.

 

[79rustyk10]

I want one, but I don't think it would last for me, and should probably stick with the SM465.

Though I actually have been day dreaming of a very similar shortbox build, but with a 292, or a TPI 350.

 

[dyeager535]

I've been really tempted by gmt400 shortbed single cabs with the 4.3 and NV3500 and flirted with the idea of a cummins R2.8 swap.

Wow, that 2.8 only weighs 503lbs. About 50 more than the 250 I6. That, NV3500, 2wd square, I bet you'd turn in some impressive numbers if setup well.

 

[diesel4me]

A 292 six is a gas pig,but hard to beat for low end torque and durability--most of them are lucky to get 12 mpg....the "best" straight sixes for economy were the smaller ones,with shorter strokes---GM had them in 194,215 (Pontiac) ,230,250 and 292 cubic inch versions..none would likely get over 15 mpg in a C-10 square body though..too heavy and the ones less than 230 cubes would be struggling all the time..
A friend who had a '64 Tempest with a 215 six and a two speed automatic claimed to get over 20 mpg often..but he ditched that engine in favor of a 400 Pontiac ..

I knew a guy with a '75 C-10 who put a 229 V6 from a 78 Malibu in it along with whatever transmission the car had (A 2004R I think,it had overdrive and a "uni-bell" bell housing)..it got close to 20 mpg on highway trips,but overall he wasn't thrilled with the MPG in city driving,or it's power either..newer trucks with a 4.3 & EFI did better..
He bought the truck with no engine & trans and just used those because he had the 229 & Malibu trans lying around and he knew they worked good..

 

[thatK30guy]

Local kid texted me today asking if I was interested in buying an '84 K10 LWB from him for $350. It's a complete truck but the 6.2 is in the bed. It's an original diesel truck and says it's a crate motor but doesn't have proof. Truck has the 833, 208, 10 bolts with 3.73's. Gonna buy it but I'll be kicking myself since I live in town and have no place to park it while the city administrator is out issuing citations as he's trying to clean up the city. Oh boy this will be tempting and exciting.

 

[diesel4me]

I'd buy it if it were in my town!..just the transmission and rare T-case adapter & bell housing are worth much more than you can get the whole truck for..
Just tell the city administrator you have covid and start coughing,that'll keep him at bay.....

That truck sounds similar to the '85 K10 Suburban I got 10 years ago ,it has a 6.2,700R4 and a NP208 with 3:73's..former owner claimed he went over 1000 miles on a full tank with it more than once before having to fill up again,it has a 41 gallon tank..
I've never put it on the road,wish I had but life's events back when I got it prevented me from being able too..

 

[imiceman44]

I've seen one at a swap meet in CT for sale that someone adapted a straight 6 Perkins diesel from a farm tractor to the SM465 ..guy claimed it got over 20 mpg in city driving,but he didn't take it on the highway much because it had 4:56 gears..

I had a k5 with that straight 6 perkins with the sm465, 205, 3.08 gears and 35" tires.
I was getting 30 mpg but my top speed was about 62 mph.
When the fuel changed to low sulfur I lost about 5mpg. Still pretty good for a k5.
I am putting it in my crew cab and hoping I can get 20mpg since it is heavier, although I am also putting an nv4500 and 241. Gears will be 3.73 and 35" tires.
Hoping to reach 70 mph.

 

[diesel4me]

I also saw a 80's G-10 Chevy van for sale on craigslist a while back,that someone swapped in a Hercules straight six diesel in place of its original 250 straight six...ad said it got 30 mpg in "mixed driving".but its top speed was about 62 mph--I guess the governor kicks in at that speed...not a great commuting vehicle!..it was priced cheap at $1500 B/O...

Best diesel conversion I saw back in the day was a '73 C-30 3+3 crew cab truck a guy had ,that owned a mobile home dealership,he used the truck to tow mobile homes to MA from Indiana where the factory was..after he used up the 454 he put in it ,he bought an Isuzu box truck that had been hit from behind and took it's straight six Isuzu diesel & 5 speed transmission out of it and stuffed it in the crew cab..

He claimed it could get 20 mpg towing at 70 mph..truck had lots of power ,I rode in it once..he said everything fit nicely and the swap was not as difficult as he thought it would be to do..he said GM should have used that engine instead of the V8 Duramax..easier to work on,and didn't need to be worked on much!..