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aardvarcus 10-14-2016 10:54 AM

1994 Diesel Suburban Build
2 Attachment(s)
Hello all. I acquired a 1994 K2500 Diesel GMC Suburban to build up to eventually replace my 2005 Toyota Tacoma.

There were a lot of drivers into this decision. My basic requirement was low long term cost of ownership balancing cost, MPG, maintenance, insurance, etcetera. In addition the vehicle had to have room for my family and friends, able to tow and haul, and had to be 4x4. After significantly overanalyzing vehicle options (understatement) I decided a factory diesel 90s model GMT-400 Suburban was the right vehicle for what I need/want, realizing it will take some work to get it to the MPG I wish to hit.

I am very familiar with this GMT-400 platform having owned and worked on a 1991 K2500 LD truck, and several good parts from this truck will be swapped over (NV4500, NP241, etcetera). The suburban I got has 210k on the clock, but I plan on replacing the powertrain anyway and will eventually rebuild most of the major systems to end up with a like new vehicle. It functions now but I won’t be driving it until I get the powertrain rebuilt and have confidence it is reliable as I have no need for another vehicle until it can replace my Tacoma.

My short term goal is to hit 30 MPG consistently. My long term goal is to hit 40 MPG on most tanks. I think my current plan I will outline in a few posts below will get me at least to the first goal, the second goal will probably take lots of optimization of details beyond what is listed.

Please feel free to comment and offer suggestions, I post to get input and feedback.

aardvarcus 10-14-2016 10:55 AM

2 Attachment(s)
Powertrain: (Using best factory options, no exotic swaps.)

Surplus 2010 GEP Optimizer 6.5l diesel long block to replace the factory 1994 6.5l. No swap fitment, title, or emissions issues as this is stock for stock. Brackets off of the 1994 engine will be used to mate the 2010 engine to factory style suburban accessories. DB2 injection pump will be used.

Will use the new engine naturally aspirated not turbocharged. (After analyzing BSFC maps at comparative partial load throttle positions between turbocharged and naturally aspirated 6.5L engines I do not think I would see a significant efficiency gain turbocharging. WOT is another story, but this is not a WOT project.)

Electric Fan conversion. Will upgrade and use controller I built for the Tacoma, but use more powerful fans.

1994 GM NV4500 Transmission with the 6.34:1 first and 0.73:1 fifth gears. NP241 manual shift transfer case.

Eventually will swap the 4:10 gears in the 9.25 front and 10.5 rear differentials for 3.42 gears. (1800 RPM to 1500 RPM at 55 MPH with 32” tires)

aardvarcus 10-14-2016 10:56 AM

2 Attachment(s)
Aerodynamics: (After main powertrain has been completed)

Remove factory flares and steps.

Cargo area roof replaced with aluminum “sloping bedcover” style hatchback shell. Body sides will taper in to stepside tailgate. Should look like an Avalanche with an aeroshell.

Aluminum belly pan/skid plates and aluminum replacement bumpers. Bumpers will incorporate a non-destructive “crumple zone” with some give (for safety and durability reasons).

Appropriate grill blocking and engine airflow channeling.

Conveyor belt tire spats.

Probably other rearview mirrors.

Factory smooth wheelcovers.

aardvarcus 10-14-2016 10:57 AM

Other: (Done alongside previously listed projects.)

Reasonably low rolling resistance LT truck tires, either Michelin LTX or a mild all terrain from Cooper or BFG.

Significant weight loss, but only by removing unnecessary weight not stripping the truck bare. Like for like replacements with lighter options will be used heavily. (i.e. DD to GR starter, aluminum to replace steel wheels/skids/brackets/etcetera, swap plush interior panels for plain plastic work truck versions, etcetera.) Remove unneeded weight such as ashtrays, rear HVAC, brackets, etcetera.

Repaint suburban roof with white heat reflective/emissive paint. Add heat rejecting tint in legal levels to all windows.

Swap to work truck grill and use DOT approved sealed beam led headlights. Swap all bulbs for LED.

That is the plan thus far. I will update this thread as I make progress. Anyway, enough rambling from me. I am open to any thoughts or suggestions.

rmay635703 10-14-2016 12:57 PM

If your running mechanical, try to get smaller pre cups like a 80's c-code 6.2 and then up compression to 21:1 if na.

Time it for low rpm if you can get it as a 2 wheeler

Daox 10-14-2016 01:26 PM

Lots of plans, but the plans look good. Interesting build. :)

aardvarcus 10-14-2016 02:22 PM

The naturally aspirated optimizer that I got has the 20.2:1 compression ratio and the smaller “square” precups. I am not really sure how those compare in size to the single dot or older precups, but I do know they are smaller than the diamonds. Consensus seems to be that smaller precup openings is better for BSFC.

Four wheel drive is a requirement for me, but I would like to eventually change the cam to move my power down low, I prefer to lumber along.

Yes lots of plans. :D In my defense I have been planning this for quite a while and will slowly start to make progress. The biggest thing I want to get done is the powertrain rebuild to get it functioning, the other items will be stretched out over quite some time. I like to tinker in my (limited) spare time, so I can’t run out of projects.

oil pan 4 10-14-2016 04:12 PM

The problem with dot approved led head lights is it appears that a lot of the ones from China is they will put junk in a box and slap a "dot approved" sticker on it.
The real dot approved led head lights should run between $100 & $200 for each light..

cRiPpLe_rOoStEr 10-14-2016 06:57 PM

If I had the chance to get a barn-door Suburban, I'd probably not want to change its body. But anyway, with an old-school IDI Diesel you might be able to try vegetable oils as an alternate fuel.


Originally Posted by aardvarcus (Post 524752)
Will use the new engine naturally aspirated not turbocharged. (After analyzing BSFC maps at comparative partial load throttle positions between turbocharged and naturally aspirated 6.5L engines I do not think I would see a significant efficiency gain turbocharging. WOT is another story, but this is not a WOT project.)

Turbochargers have been used in Diesels not just for performance and efficiency, but more recently also for emissions compliance.

oldtamiyaphile 10-15-2016 12:32 AM


Originally Posted by aardvarcus (Post 524755)
Repaint suburban roof with white heat reflective/emissive paint.

'Heat reflective' paint is a bit of a myth. Gloss car paint has better emissivity. Just paint it gloss white or possibly do a chrome wrap.

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