Author Topic: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?  (Read 4570 times)

Offline Hillbillydrums

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As it sits, my k10 will never be a vehicle I can decently afford to just drive around and cruise places.
I've looked into ls swaps and that would be a boost in power and milage. But if I was to do a 4l60e or 4l80e, whats required for a t-case? Can I use my np 203 with an adapter? Or do I need a new tcase?   Do I need to get a drivers drop t case and axle or what?
And then what might be required to fit them all in the truck? I know motor mounts shouldn't be too hard. But what about the rest?
Thanks.
1972 C10 (Passed down since great granddad bought it new in '72)
1973 K5
1975 K10

Offline Irish_Alley

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #1 on: July 26, 2015, 08:26:42 PM »
you need to think about it all and plan it out. your 203 spline count will depend on the trans it has now th400 would be 32 a th350 would be 27 sm465 will be 10. then you have to think about a transmission and how it will be controlled via tcu cause the transmissions are electronically shifted. then you have to think about how to bolt the trans and transfer case together. gm bolted the 4l80e and 205 together in 1991 and 1991 only. the tcu will need an electric speed sensor from the transfer case you can get a 241 also from a 90+ square. theres many different options, then if you have to go with a drivers side drop you can put a ford front end under it.

engine is another thing with many options you can go ls swap or you can swap a diesel in it. either one will boost your mpgs and power. if i was going to go with a ls swap i would take the trans and pcm with the ls motor so you can keep everything together and keep the one computer and try to add a 241 transfer case.

if i wanted a lot of power i would think about a 4l80e or a built 4l60e
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Offline Jason S

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #2 on: July 27, 2015, 09:45:56 AM »
As it sits, my k10 will never be a vehicle I can decently afford to just drive around and cruise places.

Just throwin' out this idea...

Propane is inexpensive (compared to gasoline), high octane and the conversion onto a carbureted engine is relatively easy.
1973 GMC K2500, Super Custom, Camper Special, 350, TH350, NP203, 4.10's
1974 Chevrolet K10, Custom Deluxe, 350, SM465, NP203, 3.73's

"1) Peace through strength; 2) Trust but verify; 3) Beware of evil in the modern world"

Offline roundhouse

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #3 on: July 27, 2015, 11:53:10 AM »

As it sits, my k10 will never be a vehicle I can decently afford to just drive around and cruise places.

Just throwin' out this idea...

Propane is inexpensive (compared to gasoline), high octane and the conversion onto a carbureted engine is relatively easy.
you must be in Canada ?
If propane is cheaper than gasoline


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Offline Jason S

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #4 on: July 27, 2015, 12:12:43 PM »
you must be in Canada ?
If propane is cheaper than gasoline

Nope, Kansas.  The last fill up was in June, delivered to the house, with State & Federal Road Tax included was $1.98 per gallon.

Just after I had the trucks filled, another LP supplier advertised 99Ę per gallon.  With road taxes, it would've been around $1.35 per gallon...
1973 GMC K2500, Super Custom, Camper Special, 350, TH350, NP203, 4.10's
1974 Chevrolet K10, Custom Deluxe, 350, SM465, NP203, 3.73's

"1) Peace through strength; 2) Trust but verify; 3) Beware of evil in the modern world"

Offline Irish_Alley

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #5 on: July 27, 2015, 12:24:47 PM »
another thing to think about is the final cost of the swap. how much will you have to drive it to make up for the saved mpgs.
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline roundhouse

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #6 on: July 27, 2015, 01:06:11 PM »

you must be in Canada ?
If propane is cheaper than gasoline

Nope, Kansas.  The last fill up was in June, delivered to the house, with State & Federal Road Tax included was $1.98 per gallon.

Just after I had the trucks filled, another LP supplier advertised 99Ę per gallon.  With road taxes, it would've been around $1.35 per gallon...
seems like I paid about $3.50 to fill the 100 gal tank for my furnace last year


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Offline fitz

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #7 on: July 27, 2015, 02:19:41 PM »
another thing to think about is the final cost of the swap. how much will you have to drive it to make up for the saved mpgs.
  Irish nailed it.
  I think allot of people do improvements to their trucks to improve the mpg's, no realizing how far they will have to drive the vehicle to break even.
  I think its safe to say that an LS swap with a 4L80 could reach $5k by the time its all said & done. I pulled that number out of the air, but by the time you do the fuel system, motor mounts, exhaust, etc, I think $5k is a good guess.
  Let's do some quick calcs.
  Say you drive your truck 10,000 miles a year.  Your K10 probably gets about 10 mpg. At $3 a gallon for gas you would spend $3,000 a year in gas.  If your LS / 4l80 increases your mpg's to 15 mpg's (a 50% increase) your now looking at $2,000 a year in fuel. At this rate it would  take you 5 years to make back your $5,000 investment.
  Don't get me wrong, I like seeing cool motors swapped into our trucks. Just make sure that you do your homework if you are on a budget.
  Don't laugh, but have you considered a 6.2 diesel?  Like most of us, I never gave these a second thought until I bought a M1028 (Military K30) a few years ago and became a huge fan.
  These K30's get about 15 mpg's running 4.56 gears. The M1009 (Military k5 Blazers) get 20-23 mpg's running 3.08 gears.  These aren't powerhouses like today's Cummins, Duramax, or Powerstrokes, but they get great mileage.
  You can pick up a rot box truck with a strong running 6.2 for dirt cheap (I've paid $500 for some). 
  A 6.2 should be able to get 20 mpg's in your K10. 

Offline Irish_Alley

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #8 on: July 27, 2015, 03:02:48 PM »
i just swapped a cummins in my 91 crew cab. paid 4k for the 84 k30 that had a cummins and adapter plate. if i bough it all separate i would of paid 2.5k for the motor prob .9-1k for the gm adapter plate and starter. made a rear drive shaft and the 84 had the right motor mounts. so lets say it cost 4k to do the swap, i was getting 10 mpgs with the 350 tbi one fill up it was about 17. so i gained 7 mpgs on 4k then you have to account for the higher price for diesel did find one gas station where its only $0.10 more than grade 87
lets say i travel everyday to work in my truck 60/day 300/week 1200/month 14400/year
so  (gas) 14400 miles / 10 mpg X $2.60 per gal = $3744/year
(Diesel) 14400 miles / 17 mpg x 2.80 per gal = $2372/year
so i saved 1372 / year so in a little under 3 years it will pay itself off

BUT then i have to keep my foot out of it to save mpg and the power increase is fun
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline fitz

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #9 on: July 27, 2015, 04:38:32 PM »
  Irish,
  I was thinking of your trucks as I was typing my last post.
  Your 84 K30  was a great deal for $4k with a Cummins in it.  Do you think the guy you got it from got his moneys worth out of the conversion?  I'm guessing  he had more than $4k in it, maybe even doubl that. That truck was a great buy. I know you still have plans for the 84, but we all know what that Dank 60 is worth..
  It seems to me that allot of engine conversations are sold off as unfinished projects or a soon as they are completed. Im guessing this is because the credit card bills are pilling up as the project spirals out of cotrol.
  Your 91 crew cab had a geat head start because you got a great deal on the  84 .
  Although the 6.2  can't compete with the Cummins, it does have a cheaper buy in price.
  I was just thinking that the 6.2 was a cheap way to get 20 +/- mpg's.  It should be a fairly easy swap using parts off a parts truck.
  If  the budget allows, I'm sure the Cummins is allot more fun to drive. 

Hillbilly, sorry I got sidetracked on my 6.2 rant.  Hopefully some of the members who have completed LS swaps will post some replies.
« Last Edit: July 27, 2015, 04:52:59 PM by fitz »

Offline Irish_Alley

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #10 on: July 27, 2015, 07:18:17 PM »
lol yeah the 6.2 is going to be a cheaper and better mpgs. a good option if funds are low. and one thing i think is people get tired of working on their projects and sell them off half way through or right after like you said. the 84 i got from a kid (dont even think he was 20) he just got a dirtymax but he got the 84 off another guy with the cummins in it he didnt know all the details but it was done back in the 80s or early 90s. i might have been able to get it cheaper but his listing on craigs list said 4.5k and i knew others would be on it fast. he was stedy getting calls and he honored my call and its a good thing cause it was like a 2 hr trip.

 the crew i only paid for 1800 so that was a good deal by itself, the 84 my buddy wanted me to give it to him.. as much as i would love to give away one of my trucks i still have 1.5k in it due to the axles and scrap price. im a nice guy but i cant just give that away to a friend lol, but i might be giving it to my brother along with a 350 sm465/205 combo.
If you canít tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Jason S

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #11 on: July 27, 2015, 10:18:37 PM »
  Don't get me wrong, I like seeing cool motors swapped into our trucks. Just make sure that you do your homework if you are on a budget.

Ditto, Fitz.  One definitely don't want to go broke trying to save money. Also wanting to give Hillbillydrums some additional food for thought...

Price point for parts, plus your time for labor/installation should be a definite factor on any swap, along with the price of fuel and how the truck is used.

Adding some more data and putting some numbers to fluctuating fuel prices on a 1973 K2500:

Converting to LP with used parts that I rebuilt along with new hoses and tank fittings cost me around $500 and a weekend's time in 2012/13.  I don't often tow with mine, so keeping the current drivetrain combination and minimal time/labor while saving money on fuel was the goal.

At that time (and where I was located in 2012/13) non-ethanol 87 was $3.50/gallon and LP was $1.70/gallon.
$3.50 Gasoline at 10 mpg = $0.35/mile x 8,000 miles = $2,800/year
$1.70 LP at 9 mpg= $0.19/mile x 8,000 miles = $1,511/year
The conversion paid for itself in the first year with a total of $1,300/year saving ($800 after parts) at those particular fuel prices.  Getting a Gasoline Gallon Equivalent of 18 mpg (i.e., a Honda Civic) in mostly town driving didn't hurt either. 

As it stands today,
$2.60 Gasoline at 10 mpg = $0.26/mile x 8,000 miles = $2,080/year
$1.98 LP at 9 mpg = 0.22/mile x 8,000 miles = $1,760/year
Not as significant as a year or two ago, but still a $320/year saving over gasoline (at current prices) without any other upgrades or swaps and less to operate daily than my 2005 Chevy 2500 4x4 with an LS 6.0l.

I completely understand it's not for everyone, but it works extremely well for me. Enough so that both trucks are now on LPG; so I'm off the LP rant now.



« Last Edit: July 27, 2015, 10:24:24 PM by Jason S »
1973 GMC K2500, Super Custom, Camper Special, 350, TH350, NP203, 4.10's
1974 Chevrolet K10, Custom Deluxe, 350, SM465, NP203, 3.73's

"1) Peace through strength; 2) Trust but verify; 3) Beware of evil in the modern world"

Offline Displaced_Txn

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #12 on: July 30, 2015, 08:40:05 PM »
5k is actually really low for some swaps. I could have almost eclipsed that in mine with a 4l70e, 700 purchase price great build from a well known and proven company 2500 plus fluids, new lines etc, So i pulled it and am now going nv4500. Plus it depends if you get a turnkey 5.3 like i did or get one from somwhere else and modify the harness etc on your own, and as far as t-case you will need a np241c as it will match the output of a newer transmission and still have the vss to to send a signal to the ecm for shifting etc. or could get a drive shaft or  yoke mounted one but those can get damaged easily. and sorry for the jumbled response trying to type this on my phone at work.

Offline Hillbillydrums

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #13 on: September 15, 2015, 03:24:02 PM »
So far, I plan on finding a junkyard 5.3, and swapping that in for now. That will be loads more power than i make now, and a bit better mpgs.  My buddy and his dad ls swap every. From square bodys to my friend's long traveled baja bug. They cut and mod wiring harnesses and have a programmer for the computers.     On the occasional 50% off days at the junkyard, i can get a motor and harness for $450, and then My buddy goes there and gets some framerail mounted fuel pumps from certain fords or Mercedes for $20 instead of the new $250 ones for the swaps. I can weld my own exhaust, so that is free. And looks like motor mounts and flywheel adapters is about $150 new. so I feel like with extra wires and the small stuff i might need, and some beers for my friends, I could pull off a motor swap for under $1k.

Trannys would be great, but maybe not just yet.
1972 C10 (Passed down since great granddad bought it new in '72)
1973 K5
1975 K10

Offline roundhouse

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Re: Motor+trans+transfer case swap for 1975 k10. Performance and Mpgs?
« Reply #14 on: September 15, 2015, 11:07:47 PM »
We're looking at a motor swap
LS looks like the way to go
Figure it's gonna cost $700 for the engine with harness and computer
$250 for flywheel and clutch
$200 motor mounts
$400 for AC brackets and compressor
$250-200 for computer reflash and tune
$200 for exhaust


Thought about a 6.2 diesel but all that noise for 85 HP ...
Meh.  I dunno


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