SM465 X 2.5 gears

[DoubleDingo]

Go with 3.73 and enjoy some better mileage and still have the low end power. It won't be a race truck, but it will still be able to be used a truck. In my old 65 Mean Green, I found a 3.54 D60 from a 68 C20 Suburban and it was almost a direct swap. The track bar setup is different than the corporate HO52. Going from 4.57 to 3.54 was great, but going up steep grades the 350 bogged, so it was 2nd gear (sm420, the predecessor to the sm465) and going 45-50 at 3,000 rpms. It forced me to find the right tire size to get the happy medium, and LT245/74r16 was it, at 29-30 inches in diameter. 70 mph was 2,600 but the truck liked 3,000 and 80, for some reason that was the sweet spot for that engine. At 2,600 the old truck got 14-16 mpgs.

I don't understand how a manual transmission would overheat with 2.5**, but it would be a dog off the line, and using granny low as 1st would a pain in the arse.

 

[boltbrain]

I say go for it. We can all live vicariously thru the the OP's discovery. An LS for the heck of it and a 14 bolt with 2.50 gears! Subscribed.
Thanks, I’ve seen a couple YouTube vids on LS swaps which sure did motivate me, but one big reason I got this 79 was to have just one truck that was computer free ( well besides the ol dumper). I don’t suppose there’s any such thing as deleting a LS computer? I’m putting a NV4500 in a 92 right now just to get away from the computerized tranny ( 4L80E). Which is toast, due to the PO’s T case leak. That truck has a 350 too, with fuel injection of course, but I don’t know what rear end. The codes on the glovebox have one that’s G80 but that I think only indicates “ posi limited slip”. So I never could find the ratio. But I know 3:55 is fairly common so I’ll probably go with that regardless. I appreciate all the helpful comments and will have more to say in response. I sure do like the MS465 and the NP205

 

[boltbrain]

Go with 3.73 and enjoy some better mileage and still have the low end power. It won't be a race truck, but it will still be able to be used a truck. In my old 65 Mean Green, I found a 3.54 D60 from a 68 C20 Suburban and it was almost a direct swap. The track bar setup is different than the corporate HO52. Going from 4.57 to 3.54 was great, but going up steep grades the 350 bogged, so it was 2nd gear (sm420, the predecessor to the sm465) and going 45-50 at 3,000 rpms. It forced me to find the right tire size to get the happy medium, and LT245/74r16 was it, at 29-30 inches in diameter. 70 mph was 2,600 but the truck liked 3,000 and 80, for some reason that was the sweet spot for that engine. At 2,600 the old truck got 14-16 mpgs.

I don't understand how a manual transmission would overheat with 2.5**, but it would be a dog off the line, and using granny low as 1st would a pain in the arse.

Thanks, I forgot to say I like my 30” original tires, I forgot the numbers, so your experience with your 3:54 is very helpful. Maybe I’ll use 3:73. There aren’t many used 14 bolts with 3:73s I hear but I can put them in myself.

 

[boltbrain]

Tha

With a sm465 about the lowest I would ever venture is 3.55 and that would be no towing or very rare if ever. if I were using it as a work truck I would stick with no less than 3.73. If you really want to cruise and do not need the beef of a nv4500 you can check into a nv3500 but since those are terribly weak units you might also want to investigate a T5 swap.


Also, a bit of a curveball and probably much lesser known on a small block, but you might be able to check into an AR5 out of around a 2007 or 1st generation Colorado. I'm not sure how swap friendly they are on a Small block but they are slightly popular with the LS crowd as an alternative to a t56. They are far cheaper is what it boils down to. The setup I have is for an LS swap and includes an adapter plate between the AR5 and the mount for the hydraulic throwout bearing, on top of a 4l60E bellhousing, then it uses the clutch stuff for the vette LS motors, and a colorado hydraulic setup. I am sure that it is just a matter of measuring and either having the adapters made thicker or having them machined down some if needed, and it might be a case of contacting the guy who makes the adapter and some time to process.

I'm doing one right now going into my LS swapped 64 C10 Pre-runner build so kind of apples to oranges but while it is off I can get thickness dimensions. I just don't have a small block handy to check and test fit is all.

Sorry if I added mind fuel to the fire that will keep you awake at night, but I figured it's worth throwing the idea out there if you want options of gearing and cruising.

Thanks, I’ll write that down and file it, the NV4500s are getting hard to find, is that why you used the AR5? Or because they matched up?

 

[boltbrain]

I am not sure what exactly you are trying to accomplish with this theoretical gear swap. It doesn't matter what gear ratio you have or how low you drop the RPM, your fuel mileage will not improve to match that of a modern vehicle. You can gear it to turn only 1500 RPM at 55mph but the engine will be using just as much fuel as before but will require more throttle to get up to speed. The squareness of the Square Body doesn't slide through the air very efficiently. An LS Swap is about your best option if you want to get better fuel mileage. A modern fuel injection system would probably help you more than a gear swap.

I cannot imagine any benefit you expect to gain from a gear swap being worthwhile enough to remove your front driveshaft and thereby disable your 4wd capability.

Thanks, I should have explained: I’d remove the driveshaft so as not to forget and drive it with two different ratios. I do understand how it’s possible to go too high on ratio, but I’m also using mathematics to get the engine-to- wheel ratio. I multiply the transmission gear ratio by the tear end ratio. And then consider also engine torque and hp. Multiply say the .73 of a nv4500 fifth by the 3:54 diff and you get 2.58

 

[boltbrain]

Forgot to say, I’d just remove the driveshaft while I figured out whether I liked the results of the experiment

 

[wanderinthru]

Go with 3.73 and enjoy some better mileage and still have the low end power. It won't be a race truck, but it will still be able to be used a truck. In my old 65 Mean Green, I found a 3.54 D60 from a 68 C20 Suburban and it was almost a direct swap. The track bar setup is different than the corporate HO52. Going from 4.57 to 3.54 was great, but going up steep grades the 350 bogged, so it was 2nd gear (sm420, the predecessor to the sm465) and going 45-50 at 3,000 rpms. It forced me to find the right tire size to get the happy medium, and LT245/74r16 was it, at 29-30 inches in diameter. 70 mph was 2,600 but the truck liked 3,000 and 80, for some reason that was the sweet spot for that engine. At 2,600 the old truck got 14-16 mpgs.

I don't understand how a manual transmission would overheat with 2.5**, but it would be a dog off the line, and using granny low as 1st would a pain in the arse.

This all makes sense to me. Until the speedo broke my 84 K20, 350 (a little cammed up) 465 275/85/ 16 and 4:10 gears gets me around 14 mpg driving. It has pulled anything I've hooked to it with no problem.
Speedo has never worked in the same ish set up (different tires) 82 K 10, but seems fuel mileage is better. Nor can I get my mind around the trans heating deal. It's a gear box it does what it does. Higher gears means, less rotations, which means less friction, which means less heat?

For the po, nv 4500's, remans are all over the internet. 2000 to 2500 bucks with a core.