2nd Gen Cummins build

MT6bt

Rock hound
Hello all! I have decided to start a thread to chronicle the build, and hopefully several lengthy expeditions over the coming several years. I have chosen the engine for the trade to be the bulletproof 12 valve cummins.
I acquired the truck from a good friend of mine who bought it from an old timer who obviously took very good care of it. It currently has 170k. Basically stock except some minor upgrades to make the engine more efficient.
-KDP tabbed
-4" exhaust(currently has a 3.5" downpipe, which I need to fix soon)
-DDP Fuel plate
-S&B cold air intake
-upgraded torque converter
-ancient Banks EGT, Trans, Boost gauges
-285/75/18E range

I plan on maximizing fuel economy with my setup. This will be one of the biggest factors for me because I want to see just how efficient this engine can be. Currently averaging about 18-21 when traveling at speeds between 65-75. I have no problem going slower than that to achieve more MPGs, but the issue is the 3.55 gears with 35" tires. I can actually drive in D/D at 53mph, while maintaining the sweet spot rpm(1750 for the 12 valve, I've read.) and get numbers around 25 mpg.
I believe this gearing is one of the main things that have to go. I was thinking of pairing some F/G rated tires (around 33-35" tall) with a 3.73/4.10 gear ratio. Again, My objective is maximum fuel economy and with that, RPMs must be around 1750@ 60-65.
0710131648[1].jpg

Above is my current setup. I am debating between going minimalist, and engineering my own setup in the back of the camper shell, or going with another truck camper.
I had and lived in a northern lite 10-2000 12" basement model for about a year. It was a beast of a truck camper. Much too big for any serious offroading applications although the amenities were impressive. I lived fairly comfortably in the mountains at 8500 feet for over 4 months, through the dead of winter. Temperatures hit -20F several nights, and had a couple days when my truck wouldn't start. Fortunately the Northern lite was fairly well insulated!
Unfortunately fuel economy was greatly affected by such a large setup. Averaged about 14-16 mpg with this truck camper. Not bad considering how huge the thing was.
0420130922a[1].jpg
 

blakeape

Adventurer
As an owner of a 97 12 valve I say very nice truck! Your mileage numbers seem pretty impressive so far. I am running E rated 37's with 4:10 gears and very happy with the combo. I though about going the 19.5 rim route but don't want to deal with the less than stellar unloaded ride quality and inability to air down. If you want to stick with 35's I think you'd do well staying with your 3.55 gears 4.10's might be a little deep. Mine is a 5spd and I'm not super familiar with the auto's but I know a handful I guys hear in the Flathead valley with 5spd, 3.55's and 35's who are very happy towing and daily driving and really like my 37's and 4.10's except when it is time to buy tires $$$$. Maybe do a free spin kit on the front and to free up an MPG or 2.

Oh yeah I run a 4 inch exhaust with a 3" or 3.5" down-pipe with a Pacbrake exhaust brake, tow a lot and have no EGT issues.
 

MT6bt

Rock hound
Yes the 19.5 tires would certainly have a rougher ride, however, I plan on using them exclusively for use during hauling/expedition circumstances. My current tires are Toyo A/Ts and they seem to wear very quickly. I like the concept of the tall skinny tire, but it seems the majority of E rated and lower tires' tread compound is too soft. Would a wider tire help reduce tread wear? Hmm...

The manual hub is certainly on the list. Even if the MPG increase is minimal, it will put less wear and tear on my front end.

Also debating on a water/methanol kit. I have heard these can also increase fuel economy between 1-3 mpg, while reducing EGTs greatly.

It's interesting you have no problem with your EGTs. I have had to back off many times going up mountain passes-even when my RPMs are around 2000-2300. Perhaps my ancient gauges need upgrading because EGTs will spike to 1350 before I immediately back off the throttle. It may have to do with my upgraded compressor housing and the 3.5" downpipe. Too much restriction! I haven't seen more than 30psi as well...

The auto on this truck is a P.I.A. It wouldn't be so bad if you could lock it into a gear when ascending instead of gear hunting and upshifting when completely unnecessary! I wish it was a manual but I had to compromise.
 

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