Best fuel millage Cummins C/k 20

[601jack89]

High I'm Jack and new to the board and been looking around board.  My main question is about dropping a cummins in a c20 that I will latter convert into a k20.  I love by truck but a 350 sucks down gas, diesel on the other hand is pricier but goes a lot farther. I have a 92 cummins, that I am rebuild. I have looked into the nv4500 and a few others but for a manual nv is good except for 5th gear. I have 14 bolt rear end 10.5 ring gear and would like a transfer case I can shift to 2wd for work days.  So my question is what is the best set up for saving fuel but still having some fun when I feel like it?

[SomeTexan]

Should be a fun set up. Nv4500 from standard transmission and gear in Fort Worth. They have 5th gear figured out. Find a first gen np205 and the splined adapter, have one end turned to fit in the rear seal on the trans, and shortened 1/4 inch and you are good to go. Otherwise, second gen t-case and a ford front axle.

For that ve pump Cummins, I would recomend a quick spooling turbo, s300g is a good one, 366 governor spring, and an M&H #3 or 4 fuel pin and 4" exhaust. A set of 5x012 injectors wouldn't hurt either. Colt 1.5 cam and compound turbo's for real fun.

Gears depend on use, my 93 cummins has 3.54 gears and 33" tires. It does not lug or bog in 5th on the freeway, even towing, but gets 28mpg average. The ve pump trucks spool the turbo at low rpm and will make insane off idle torque, great for a low rpm cruise with good mpg. I think 35's, maybe 37's in a light truck, would give great mpg with 3.54 gears, but over that size you are looking at 4.10-4.56 gears for a street ride. More off road oriented, you would want lower gears.

[601jack89]

Thank you sir, and you get 28 wow that's nice and I am not looking to do a lot of off roading but I do plan to go mudding every now and then. As far as towing I have done and will do a lot.  Is this the best set up or have you seen better?

And by the way my 350 gets 8-12 mpg so 28 is way better the best I saw was 26 and 40 but the guy that had 40 was in and out of the Dino shop and it was not a cummins.

[Irish_Alley]

imo you have to do something with that c20 frame to hold the cummins. the c/k20 are the same frame as the c/k10s. there are a couple of us with cummins. idk if we have any on the road but i have one in my 84k30 but it has a 4l60 thats missing 3rd and 4th. working on piecing a 4l80e and 205 together. then start working on a crew cab. another user has a cummins in a crew, do a search for cummins and you swill see
http://forum.73-87chevytrucks.com/smforum/index.php?topic=25678.0

[SomeTexan]

Watch out for that 4l80. They take stupid power from gas engines, but Cummins engines kill them. I've heard different reasons why, but I'm not a trans guy. A friend killed a built one in a 90 d250 that was almost stock. His 47re has held up for years now.

[601jack89]

I have a c20 crew with 350 Muncie and it is fun. As far as the frame I plan to box it in although I have read in places were it says that it is not necessary . As far the link ya'll are talking about the man with the white  k20 and the red cummins who also posted that he got married near the end of his post. I have looked at . Although on that particular post it is mainly photos , not what he used. Based what I can tell he is well, if memory serves me correct but an nv4500 w/ an mp205 behind a compound turbo cummins.  And how high is best, I don't want to go too high.

[601jack89]

http://forum.73-87chevytrucks.com/smforum/index.php?topic=25678.0

Ok I saw the  the link and I have seen the thread before but it was just the pictures. I have not seen the description at the front maybe I skipped over it. Also he's say he did 40 over on his engine I thought you could only go up to 30 over safely or am I missing something?

[SomeTexan]

How high is best? Are you talking lift, gears or boost? Boost, shoot for the moon, these engines like it. Lift, I hate top heavy lifted trucks. I will trim fenders to fit massive rubber with minimal lift. Gears depend on tire size.

[SomeTexan]

40 over on a Cummins? I won't take them more that 10 over. More than that and they don't like boost so much. If you can clean one up by honing it, stick with that. The loss of cylinder wall strength isn't worth a few cubic inches.

[601jack89]

As far as lift what is best? I know lift affects fuel.

[SomeTexan]

How big of a tire do you want to run? Those trucks clear a lot of meat with not much lift. I ran 44's on my 79 with 4" lift and some fender trimming. 4-6" is the max I like to go on these trucks, but that's me. A 2.5" and 35's and you would probably be good.

[601jack89]

I was thinking 35 but you were getting 28 mpg on 44 that's good how did you figure that out before you put them on, and is there stuff I can do to figure my fuel millage before I get parts, all the way from ether tires up to the engine? As far as fuel and the tank did y'all put an electric pump on it with how much flow output?  The ones I have seen people drilled into the sending unit left (plugged) the old lines and put a brass fitting in the new whole.  I want a sending unit that is operational for the gauge and that will fit in that tank with all lines bing used I do not want to drop tanks to fix lines all the time and I do like the duel tank.

[SomeTexan]

28mpg was with 33's on my 93 Cummins. My old crawler/beater/ranch truck had 44's, but had a ramjet 502 in it. It was lucky to get 8mpg.

[601jack89]

 

[601jack89]

Should be a fun set up. Nv4500 from standard transmission and gear in Fort Worth. They have 5th gear figured out. Find a first gen np205 and the splined adapter, have one end turned to fit in the rear seal on the trans, and shortened 1/4 inch and you are good to go. Otherwise, second gen t-case and a ford front axle.

For that ve pump Cummins, I would recomend a quick spooling turbo, s300g is a good one, 366 governor spring, and an M&H #3 or 4 fuel pin and 4" exhaust. A set of 5x012 injectors wouldn't hurt either. Colt 1.5 cam and compound turbo's for real fun.

Gears depend on use, my 93 cummins has 3.54 gears and 33" tires. It does not lug or bog in 5th on the freeway, even towing, but gets 28mpg average. The ve pump trucks spool the turbo at low rpm and will make insane off idle torque, great for a low rpm cruise with good mpg. I think 35's, maybe 37's in a light truck, would give great mpg with 3.54 gears, but over that size you are looking at 4.10-4.56 gears for a street ride. More off road oriented, you would want lower gears.

I am sorry man but I need some clarification what years exactly for second gen ford axle and transfer, why ford, why  can I not us a dana 60, 44, or even something as low as a gm front end 10 bolt as long as I have the same gears in the front and the back?